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Optimization of nitrogen and potassium nutrition to improve yield and yield parameters of irrigated almond (Prunus dulcis (Mill.) D. A. webb)
Scientia Horticulturae 228 (2018) 204–212
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Optimization of nitrogen and potassium nutrition to improve yield and yield parameters of irrigated almond (Prunus dulcis (Mill.) D. A. webb)
MARK
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Saiful Muhammada, , Blake L. Sandenb, Sebastian Saac, Bruce D. Lampinena, David R. Smartd, Kenneth A. Shackela, Theodore M. DeJonga, Patrick H. Browna a
Department of Plant Sciences, University of California Davis, One Shields Avenue, Davis, CA 95616, USA Kern County Cooperative Extension, University of California, 1031 South Mount Vernon Avenue, Bakersfield, CA 93307, USA c Escuela de Agronomía, Pontificia Universidad Católica de Valparaíso, Casilla 4D, Quillota, Chile d Department of Viticulture and Enology, University of California, One Shields Avenue, Davis, CA 95616, USA b
A R T I C L E I N F O
A B S T R A C T
Keywords: Nitrogen Potassium Yield Leaf nitrogen Yield parameters Prunus dulcis Almond
An experiment was conducted to evaluate the effect of nitrogen (N) and potassium (K) fertilization rates and fertilizer sources on almond yield and yield related parameters- fruit and kernel weight, number of fruits per tree, crackout percentage and leaf nutrient status by individually monitoring 768 trees. The experiment was carried out between 2008 and 2012 with four rates (140, 224, 309 and 392 kg N ha−1) and two sources (UAN and CAN) of N and three rates (112, 224 and 336 kg K ha−1) and sources (SOP + KTS, SOP and KCl) of K. Nitrogen fertilizer rate had a significant effect on yield in the second through the fourth year of the experiment. Tree yield was maximized at 18.5 kg and 23.7 kg kernel per tree in 2010 and 2011 season respectively when July leaf N was in the range 2.4–2.5% corresponding to an N application rate of 309 kg N ha−1 and there was no increment in yield above 2.5% leaf N. Source of N had no significant effect on yield response. Potassium fertilization rate had no significant effect on yield while K sources had significant effect in 2010 only. Increasing N application resulted in lighter fruit, and kernel weight decreased with increasing N application under moderate yield conditions, and increased under high yield conditions. Yield increase with increasing N application was due to an increase in number of fruits and increased crackout percentage. Leaf K above 1% did not increase yield and there was no consistent effect of K supply and K source on yield parameters. There was a strong relationship between total yield and number of fruits per tree, which increased with increasing N application. Crackout percentage was also positively correlated to kernel yield. Nitrogen and potassium fertilization rate should be based on expected yield and tree N and K status. For a well productive mature orchard, N application of 309 kg ha−1 with either UAN or CAN can meet crop N needs. K fertilization should consider K contribution from soil. Under condition of 100–150 mg kg−1 soil exchangeable potassium, K application of 112 kg ha−1 with any K fertilizer source can satisfy crop K demand.
1. Introduction Efficient fertilization practices are important to maximize crop yield while optimizing environmental stewardship. Excessive use of nitrogen (N) increases crop production costs and low recovery of N by the crop can contribute to nitrate contamination of groundwater (Drake et al., 2002). On the other hand inadequate fertilizer application can compromise crop yield and thus may not be economically sustainable. For consistent high yields, application of right rate of fertilizer at the right time is important so that any deficiency may not appear and that fertilizer is not wasted. In a long term experiment in almond, Muhammad et al. (2015) found that 68 kg of N and 75 kg potassium (K) is removed
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in fruit per metric ton of kernel yield. 67–76% of the total N and 45–61% of the total K accumulated in the almond fruit by 86 days after full bloom (Muhammad et al., 2015). The use of suitable N source is important in the context of environmental problems. Schellenberg et al. (2012) reported significantly high nitrous oxide losses from Urea Ammonium Nitrate compared to Calcium Ammonium Nitrate in almond orchards although the total N2O losses were lower compared to other cropping system. Nitrogen and potassium are the nutrients required in largest amounts by an almond crop. Nitrogen deficiency reduces photosynthesis and plant growth and in severe N deficiency fruit drop may occur and nut quality is affected by reducing protein content. Nitrogen
Corresponding author. E-mail address: [email protected] (S. Muhammad).
http://dx.doi.org/10.1016/j.scienta.2017.10.024 Received 23 March 2017; Received in revised form 29 September 2017; Accepted 13 October 2017 0304-4238/ © 2017 Published by Elsevier B.V.
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Table 1 Soil analysis of the experimental site in 2008 at the beginning of the experiment. Depth (cm)
pH
EC (ds m−1)
HCO3 (meq L−1)
NO3-N (mg kg−1)
X-K (mg kg−1)
OM (%)
0–46 47–90
7.8 7.9
1.3 2.2
2.7 1.8
2 1.5
138 89
0.88 0.8
almond yield, b) to determine the effect of potassium rate and source on almond yield, and c) to determine the effect of N and K fertilization rate and sources on fruit weight, kernel weight, number of fruits and crackout percentage.
fertilization in excess of tree demand is poorly utilized by the plant and may be lost to leaching or result in excessive vegetative growth and will increase susceptibility to diseases such as almond hull rot (Saa et al., 2016). Over-fertilization with N fertilizers is a leading cause of contamination of ground water with nitrate and the deterioration of drinking water quality (Weinbaum et al., 1992). Potassium deficiency reduces photosynthesis and carbohydrate transport and accelerates premature leaf senescence and premature leaf abscission. Leaf potassium concentration less than 0.5–0.6% also limits leaf CO2 exchange rates and reduces leaf carbon fixation by imposing biochemical limitations on photosynthesis (Basile et al., 2003). Brown et al. (2000) found that K deficiency in one year reduced numbers of flowers and fruits in the subsequent year(s) and reported that yield from treatments not receiving K fertilizer was significantly lower than fertilized trees in the 3rd year of the experiment. Research on N and K fertilization effects on yield and yield components is limited in almond. In research published in an Almond Board of California (ABC) annual report, Weinbaum et al. (1994) reported results from a N fertilization trial in almond conducted at two locations in California with differential N applications of 0 kg, 140 kg, 280 kg and 560 kg ha−1 respectively. Yield was only different after the third year and between control and 280 kg ha−1 N application; both sites had high nitrate in the irrigation water (33 ppm and 44 ppm nitrate in site 1 and 2 respectively) that likely affected the results of the experiment. Other research in almond focused on rate and time of N application (Weinbaum et al., 1984a,b; Weinbaum et al., 1987) but no results of yield and related parameters was reported. Meyer et al. (2001) did not find yield differences between N sources of urea, calcium nitrate (CAN), urea-ammonium nitrate solution (UAN32) and urea-sulfuric acid though they reported significantly lower leaf N for calcium nitrate in some years. Applications of 139 kg, 278 kg, and 556 kg ha−1 K2O increased yield compared to the control but there was no additional benefit of K application over 139 kg ha−1 (Meyer, 1999). Mono potassium phosphate (MKP, KH2PO4) produced significantly higher yields than potassium sulfate (K2SO4), MKP/potassium chloride (KCl). The explanation for these results was not provided. Almond yield is influenced by the number of fruits and kernel weight (Lampinen et al., 2011) but fruit number is the most important yield determinant (Reidel et al., 2001). Weinbaum et al. (1980) attributed an increase in yield to an increase in the number of flowers with soil application of urea. In pistachio (Gunes et al., 2010), apple (Neilsen et al., 2009) and citrus (Koo, 1988), N application increased yield but the individual fruit weight decreased. In walnut, yield increase from increased N application has been attributed to an increase in kernel weight and kernel percentage (Gray and Garrett, 1998). Brown et al. (2000) reported no significant differences in kernel and fruit weight between control treatments (no K) and trees receiving different rates of potassium fertilizer, while Reidel et al. (2004) reported no significant differences in kernel and fruit weight between 0 and 960 kg ha−1 K application. Hence, the influence of K fertilizers on almond yields remains unresolved and reports may indicate it may be site specific. There is no published data on the effect of N supply and source on yield and fruit and kernel weight, number of fruits and crackout percentage in almond, while the effects of K sources on these yield parameters have not been reported. The objectives of the experiments included: a) to determine the effect of N fertilization rate and sources on
2. Materials and methods 2.1. Experimental site The experiment was carried out at Belridge, Kern County California (35.5° N 119.6° E) from 2008 to 2012 in a commercial almond orchard. In 2008, a nine year old almond orchard planted to 50% Nonpareil and 50% Monterey was selected. Both varieties were grafted on Nemaguard peach rootstock with a planting density of 214 trees per ha. The soil type was Panoche and Kimberlina very fine sandy loam (Loamy, mixed, superactive, calcareous, thermic Typic Torriorthents) with EC of 1.3 ds m−1 and pH 7.8 in the top 46 cm and EC 2.2 ds m−1 and pH 7.8 in 47–91 cm depth and organic matter of less than 1% with good drainage and aeration (Table 1). 2.2. Fertilizer treatments The experiment was established as a randomized complete block design. Four rates of nitrogen 140 kg, 224 kg, 309 kg and 392 kg ha−1 N were applied with two N fertilizer sources − Urea Ammonium Nitrate 32 (UAN 32) and Calcium Ammonium Nitrate 17 (CAN 17) as detailed in Table 2. Nitrogen was applied in four fertigation events as 20%, 30%, 30% and 20% of the total in mid-February, early April, mid-June and postharvest respectively. At this location flowering typically occurred in late February and harvest occurred in mid-August. All the nitrogen treatments received 90 kg ha−1 P as phosphoric acid (52% P2O5) and 224 kg ha−1 K applied as 60% sulfate of potash [SOP, (50% K2O)] in winter and 40% potassium thiosulphate [KTS, (25% K2O)] fertigated four times as for nitrogen. Potassium rate treatments included 112 kg, 224 kg and 336 kg ha−1 K, applied as 60% SOP (Table 2) in granular form in winter and the remaining 40% as KTS fertigated four times during the season as described for N. All K rate treatments received 309 kg ha−1 N as UAN 32 and 90 kg ha−1 P. In addition, three sources of K were contrasted; either 100% SOP, SOP + KTS at a ratio of 60:40 or 100% potassium chloride (KCl), applied at 224 kg ha−1 as K. All K source treatments received 309 kg ha−1 N as UAN 32 and 90 kg ha−1 P. SOP was applied in 60 cm wide strips in January and incorporated by winter rains followed by irrigation. KTS and KCl were applied in irrigation water during four fertigation cycles as described for N. Fifteen trees of Nonpareil in a row and their immediate neighbor trees in rows of Monterey were treated as one experimental unit with a plot size of 0.211 ha. Data were collected from six trees of Nonpareil in the middle row. Each treatment was replicated five/six times each under fan jet (micro-sprinkler) and drip irrigation. Irrigation treatments were applied in two separate blocks and there was no replication. Control valves were installed at the riser to regulate fertilizer application. Fertilizers were applied using a fertilizer injection pump, (Hypro Roller pump, Model 7560XL-R, New Brighton, MN USA). Fertilizer concentration was controlled by a digital turbine flow meter (model TM075-N, Great Plains Industries, Inc. North Wichita, KS USA). Orchard were irrigated at 100% ETc as determined from two custom surface renewal instruments in towers installed onsite (see Shapland 205
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Table 2 Detail of fertilizer treatments. Treatments
N Source
N amount (kg ha−1)
K Source
N rate and source
UAN32 UAN32 UAN32 UAN32 CAN17 CAN17 CAN17 CAN17 UAN32 UAN32 UAN32 UAN32 UAN32 UAN32
140 224 309 392 140 224 309 392 309 309 309 309 309 309
60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 100% SOP 100% KCl
K rate
K source
K amount (kg ha−1) KTS KTS KTS KTS KTS KTS KTS KTS KTS KTS KTS KTS
224 224 224 224 224 224 224 224 112 224 336 224 224 224
UAN 32 = Urea Ammonium Nitrate 32% N, CAN 17 = Calcium Ammonium Nitrate 17% N, SOP = Sulfate of Potash, KTS = Potassium Thiosulfate, KCl = Potassium Chloride.
the periphery of each individual data tree. Samples were oven dried at 60 °C for 5 days. After drying the numbers of fruits in each sample were counted and weight recorded. Kernels were separated from the fruits and their weight was recorded.
et al., 2012). Soil moisture was monitored via neutron probe (Model 503DR, ICT International Armidale Australia) in 40 bore holes established to 2 m and distributed uniformly throughout the orchard. Periodic measurements of stem water potential were obtained using a pressure chamber (Model 3005HGPL Soil Moisture Inc. Santa Barbara, CA USA).
2.3.5. Number of fruits per tree Number of fruits per tree was calculated by dividing the individual tree yield and average fruit weight as:
2.3. Data collection
Number offruits per tree =
2.3.1. Yield Trees were shaken individually using a commercial shaker after 100% hull split and nuts from each data tree were kept separated and allowed to dry on the orchard floor for a week. After one week nuts were picked up using a commercial harvester and individual tree yield was recorded using a scale mounted gondola. The nuts from the nine non data trees were pooled to get plot scale yield data. Periodic samples were collected from the harvester to determine the weight of nonharvest debris and nut moisture content. Two kg fruit samples from two trees in each replicate were collected, dried, hulled, and cracked, to estimate kernel weight. Final yield was adjusted for moisture content and kernel yield was calculated using the data for moisture loss and crackout percentage from the 2 kg samples.
2.3.6. Photosynthetically active radiation Photosynthetically active radiation (PAR) interception was measured with a mobile platform light bar (Lampinen et al., 2012). 2.4. Statistical data analysis Statistical data analyzed was performed using JMP statistical software version 10, SAS institute Inc. USA. 3. Results
2.3.2. Leaf samples Leaf samples from all individual data trees were collected at 10% hull split. Leaves were washed and dried at 60 °C for five days and ground to pass 0.4 mm screen using Wiley Mini-Mill (Thomas Scientific). Samples were analyzed for N and K concentration at Agriculture and Natural Resource Laboratory (ANL) University of California Davis. N was determined through combustion (AOAC, 2006) and K was determined through nitric acid digestion (Meyer and Keliher, 1992; Sah and Miller, 1992).
All treatments under micro-sprinkler and drip irrigation produced similar results so we are reporting the results for treatments under micro-sprinkler irrigation only. 3.1. Effect of nitrogen supply on tissue N and kernel yield After establishment of treatment effect, N concentrations in leaves were positively correlated with N supply and yield (Fig. 1). N applications 140 and 224 kg ha−1 resulted in lower leaf N and lower yield. In 2010 and 2011, yield was maximum when tissue N concentrations ranged from 2.4 to 2.5% which was achieved by application of 309 kg ha−1 N. Kernel yield under differential N rate treatments is shown in Table 3. In the first year of the experiment (2008) there was no significant effect of increasing N application on kernel yield, however, there was a trend of yield increase with increasing N application. In 2009, 2010 and 2011 significant differences in kernel yield (p < 0.05) were observed. Minimum kernel yield was observed for 140 kg ha−1 N and maximum yield was achieved with N applications of 309 kg ha−1 N and above. Overall orchard productivity declined in 2012, probably due to alternate bearing habit as a consequence of high yield in 2011, but also from high hull rot incidence and possibly other reasons that have not been determined. There were no significant effects of N rates on yield in 2012. Cumulative kernel yield was highest for N rate
2.3.3. Crackout percentage A day before harvest, 2 kg clean fruit samples were collected from two trees in each replicated treatment unit. The samples were then dried in forced air driers at 45 °C for a week, cleaned and final weight was recorded. Kernels from these samples were separated using a small almond huller (Jessee Equipment Manufacturing Chico, California) at the Pomology Headquarters University of California Davis. Crackout percentage was determined as:
Crack out percentage =
Yield (kg )*1000 Average fruit weight (g )
Kernel weight (kg ) *100 Fruit weight (kg )
2.3.4. Fruit and kernel weight A day before shaking the trees, 30 fruit samples were collected from 206
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Fig. 1. Relationship between yield (kg ha−1) and July leaf nitrogen concentration (% dry weight) for Nonpareil almond in 2010 and 2011. Each point is mean of six individual trees.
3.2. Effect of potassium fertilization rate and source on kernel yield
Table 3 Kernel yield (kg ha−1) of Nonpareil almond with different rates of N as UAN 32. Letters indicate significant difference in yield within the same year at < 0.05 level of significance using student t-test. Year
2008 2009 2010 2011 2012 Cumulative yield
Leaf potassium concentrations increased with application of K fertilizer. K concentrations were low in 2008 when the experiment was started and increased from 2009 to 2011. In 2008, majority of the trees were K deficient according to the standard critical value of 1.4% but no yield response to increased leaf K concentrations were observed (Fig. 2). Potassium fertilizer application rates did not influence kernel yield (data not shown). The effect of K fertilizer sources was inconsistent. Potassium fertilizer sources had a significant differential effect on yield only in 2010 under fan jet irrigation (p < 0.05) where SOP + KTS produced maximum yield (Table 4).
Nitrogen rate (kg ha−1) 140
224
309
392
3437 3154 b 2639 c 4335 b 903 14,468 c
3689 3434 ab 3231 b 4496 b 885 15,735 b
3657 3603 a 3932 a 5018 a 990 17,200 a
3870 3701 a 3670 a 4956 a 1089 17,286 a
3.3. Effect of nitrogen fertilization on yield components of nonpareil
309 kg ha−1 and above whereas N rate 140 kg ha−1 produced lowest cumulative kernel yield. The effect of N source on the yield was not significant.
3.3.1. Effect on fruit weight Following the establishment of N treatments in 2008, increasing N rates resulted in decreased individual fruit weight in all subsequent years (Fig. 3). Significant effects of N application rate on fruit weight were observed in 2009, 2010 and 2011 where maximum fruit weight was recorded at lower N application rates (140 kg ha−1 and 224 kg ha−1 N). Minimum fruit weight was observed for 392 kg ha−1 207
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Fig. 2. Relationship between yield (kg ha−1) and July leaf potassium concentration (% dry weight) for Nonpareil almond from 2008 to 2011. Each point is mean of six individual trees.
resulted in lowest crackout percentage while all other N rates produced similar results.
Table 4 Kernel yield of Nonpareil almond (kg ha−1) with different potassium sources. Letters indicate significant difference in yield within the same year at < 0.05 level of significance using student t-test. Year
2008 2009 2010 2011 2012 Cumulative yield 2008–2012
3.4. Effect of nitrogen sources and potassium fertilizer rate and sources on yield parameters of nonpareil
Potassium Source @ 224 kg ha−1 SOP + KTS
SOP
KCl
3739 3621 3859 a 5009 1003 17,231
3673 3745 3779 a 4886 832 16,915
3654 3828 3232 b 4870 814 16,398
There was no consistent effect of N fertilizer source and K fertilizer rate and source on fruit and kernel weight, number of fruits per tree or crackout percentage. 3.5. Effect of N on intercepted photosynthetically active radiation (PAR) Effect of N application on intercepted PAR was recorded in 2011 and 2012 (Table 5). N application increased intercepted PAR. In 2012, lowest PAR interception (80%) was recorded for 140 kg ha−1 and maximum PAR interception (90%) was recorded for 392 kg ha−1 N rate.
in 2009, 2010 and 2011. 3.3.2. Effect on kernel weight The response of kernel weight to N supply is shown in Fig. 4. There were no consistent trends in kernel weight in any year. In 2010 N application of 224 kg ha−1 produced the heaviest kernel while 392 kg ha−1 N produced lighter kernels. Increasing N application produced heavier kernels in 2011.
4. Discussions 4.1. Effect of nitrogen rate and sources on yield and yield components Increasing N application rate increased kernel yield of Nonpareil almond following the first year of the experiment. In the first year of variable N rate applications, the lack of tree response likely reflects the use of stored nutrients in perennial tree parts, the amount of which then changed in subsequent experimental years in response to N application rates (Muhammad et al., 2015). Unlike annual species, perennial plants have significant amounts of stored N and other nutrients (Millard and Grelet, 2010; Millard and Neilsen, 1989; Millard and Proe, 1993; Millard and Thomson, 1989; Muhammad et al., 2015; Tagliavini et al., 1999) that are remobilized to support early spring growth. Following the first year of the experiment, the yield of the 140 kg ha−1 N treatment declined likely as a result of N export in the crop exceeding N fertilizer application. Nitrogen exported in harvested fruit in the
3.3.3. Effect on number of fruits per tree Nitrogen supply increased the number of fruits per tree. Following experiment establishment in 2008, the 140 kg ha−1 N rate produced the minimum number of fruits while the maximum number of fruits was produced under 309 kg ha−1 N rate and above (Fig. 5). 3.3.4. Effect on crackout percentage Effect of N rate on crackout percentage was not consistent and was only significant in 2009 and 2010 (Fig. 6). In 2009 N rate 392 kg ha−1 resulted in maximum crackout percentage whereas N rate 140, 224 and 309 kg ha−1 produced similar results. In 2010, N rate 140 kg ha−1 208
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Fig. 3. Mean individual fruit weight of Nonpareil with differential N supply with UAN 32. Each bar shows mean and standard error. Means not connected by same letter indicate significant difference in mean fruit weight within the same year at < 0.05 level of significance using student’s t-test.
140 kg ha−1 N treatment was 189 and 164 kg ha−1 in 2008 and 2009 respectively (Muhammad et al., 2015). The decline in fruit number and leaf N observed in the low N treatments (140 and 224 kg ha−1) indicated that tree growth was reduced from 2008 onward and final tree size in 2012 was significantly lower. Increasing N application increased shoot growth as evidenced from an increase in photosynthetically active radiation (PAR) intercepted by the tree canopy with increasing N application (Table 5) that presumably increased spur population. Increasing N supply generally increased tree growth and kernel yield, however there was no significant increase in kernel yield beyond the 309 kg ha−1 N treatment. There was a strong relationship between tree N status (as indicated by leaf N in July) and yield. Yield increased as leaf N concentrations increased but there was no additional significant benefit of increasing leaf N over 2.5%. In previous experiments (Brown and Uriu, 1996), July leaf N concentration below 2% has been considered deficient and 2.2-2.5% N has been recommended as critical value. We found July leaf N concentrations 2.3-2.5% sufficient and N below 2.2% is deficient (Fig. 1). The increase in kernel yield with increasing N application was a
result of an increase in the number of fruits per tree although crackout percentage also increased in high N trees. Almond yield can be influenced by the number of fruits and individual kernel weight (Lampinen et al., 2011) but fruit number has been reported to be the most important yield determinant (Reidel et al., 2001). Number of fruits per tree increased with increasing N application rate in this experiment (Fig. 5). In a number of tree crops an increase in yield has been attributed to an increase in the number of fruits such as in apple (Neilsen et al., 2009; Wargo et al., 2003) and citrus (Koo, 1988). Increasing N application increased yield but the individual fruit weight decreased. A similar effect of decreasing fruit weight with increasing yield was reported in pistachio (Gunes et al., 2010), apple (Neilsen et al., 2009) and citrus (Koo, 1988). In other tree species, fruit weight increased as a result of an increase in N supply including pear (Raese, 1997) and peach (Rader et al., 1985; Saenz et al., 1997). Decrease in fruit size with a constant or increased kernel weight resulted in a higher crackout percentage as N application increased (Fig. 6). Similar findings were reported for black walnut by Gray and Garrett (1998) where N supply increased kernel weight and kernel percentage. Fig. 4. Mean individual kernel weight of Nonpareil with differential N supply with UAN 32. Each bar shows mean and standard error. Letters indicate significant difference in mean kernel weight within the same year at < 0.05 level of significance using student’s t-test.
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Fig. 5. Number of fruits per tree of Nonpareil with differential N supply with UAN 32. Each bar shows mean and standard error. Means not connected by same letters indicate significant difference in number of fruits per tree within the same year at < 0.05 level of significance using student’s t-test.
In 2012 kernel yield dropped as a consequence of disease and the stress apparently caused as a result of the high yields in 2011 and perhaps other unknown factors. Almond is a partially alternate bearing species and high yield in one year can affect the number of flowering spurs the next year (Heerema et al., 2008; Tombesi et al., 2011). Therefore, very high yield in one year can reduce the number of fruiting spurs the next year resulting in an ‘alternate bearing’ behavior. This can be further exacerbated if new shoot growth and replacement spur production is inhibited by environmental factors. The low yield in 2012 may be a consequence of the very high yield in 2011. Fruit load affects nutritional status (Reidel et al., 2004) and carbohydrate balance of many fruit species (Jackson and Palmer, 1977; Rosecrance et al., 1998; Spann et al., 2008) that may in turn affect spur survival. Leaf nutrient analysis in 2011 show sufficient N and K in leaf tissue for the 309 kg and 392 kg ha−1 N rates compared to standards, however, N was deficient in the 140 kg and 224 kg ha−1 N rates (Figs. 1 and 2). The low yield of the 309 kg and 392 kg ha−1 in 2012 was clearly not an effect of nutrient deficiency as tree vegetative growth was not affected as indicated by increased in canopy growth (Table 5); however, we did not determine carbohydrate status of the trees during
Table 5 Mean percent Photosynthetically Active Radiation (PAR) intercepted by the orchard in 2011 and 2012 as affected by nitrogen application. Letters indicate significant difference in PAR interception within the same date at < 0.05 level of significance. Date
6/28/2011 6/13/2012
Mean Percent PAR N 140 kg ha−1
N 224 kg ha−1
N 309 kg ha−1
N 392 kg ha−1
78 c 80 c
81 b 84 bc
83 ab 87 ab
84 a 90 a
dormancy. In almond, spurs are semi-autonomous regarding carbohydrate demand (Heerema et al., 2008) suggesting that the survival of the spur is dependent on the presence of fruit and the carbohydrate supply of the spur leaves and that greater demand of fruit can result in carbohydrate limitation of the developing flower buds. In Nonpareil flower initiation occurs after hull split (Lamp et al., 2001) when fruits are still on trees, hence flower bud development may compete for Fig. 6. Crackout percentage of Nonpareil almond for N rates with UAN 32. Each bar shows mean and standard error. Means not connected by same letter indicate significant difference in crackout percentage within the same year at < 0.05 level of significance using student’s t-test.
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Acknowledgements
carbohydrates when a heavy fruit load is present. The carbohydrate dependency of the flower buds is also evident from the fact that spurs with high nonstructural carbohydrate content during dormancy produced more flower buds per spur (Heerema et al., 2008; Polito et al., 2002). The high yield in 2011 may have reduced spur survival and the development of the flower buds as a result of carbohydrate deficiency for the flower initiations. In addition to changes in fruit load, the incidence of hull rot in the moderate to high N rate treatments contributed to loss of some spurs and shoots (Saa et al., 2016) however there could be other unknown factors that limited yield for all N rates.
We would like to thank California Department of Food and Agriculture, Almond Board of California and Yara Fertilizer Company for funding this research. This project was supported by the USDA National Institute of Food and Agriculture, Hatch project number# CAD-PLS-2000-OG. We also like to thank Paramount Farming Company for material as well as providing human resources for the experiment. References AOAC, 2006. AOAC Official Method 972. 43. Microchemical Determination of Carbon, Hydrogen, and Nitrogen, Automated Method, 18th ed. AOAC International, Gaithersburg, MD. Basile, B., Reidel, E.J., Weinbaum, S.A., DeJong, T.M., 2003. Leaf potassium concentration, CO2 exchange and light interception in almond trees (Prunus dulcis (Mill) D.A. Webb). Sci. Hort. 98, 185–194. Brown, P.H., Uriu, K., 1996. Nutrition deficiencies and toxicities: diagnosing and correcting imbalances. In: In: Micke, W.C. (Ed.), Almond Production Manual 3364. University of California, Division of Agriculture and Natural Resources Publication, pp. 179–188. Brown, P.H., Weinbaum, S.A., DeJong, T.M., 2000. Reassessment of Potassium Critical Values. In Years of Discovery (1972–2003). Almond Board of California. Drake, S.R., Raese, J.T., Smith, T.J., 2002. Time of nitrogen application and its influence on ‘golden delicious' apple yield and fruit quality. J. Plant Nutr. 25, 143–157. Gray, D., Garrett, H.E.G., 1998. Nitrogen fertilization and aspects of fruit yield in a Missouri black walnut alley cropping practice. Agrofor. Syst. 44, 333–344. Gunes, N.T., Okay, Y., Koksal, A.I., Koroglu, M., 2010. The effect of nitrogen and phosphorus fertilization on yield, some fruit characteristics, hormone concentrations, and alternate bearing in pistachio. Turk. J. Agric. For. 34, 33–43. Heerema, R.J., Weinbaum, S.A., Pernice, F., Dejong, T.M., 2008. Spur survival and return bloom in almond Prunus dulcis (Mill.) DA Webb varied with spur fruit load, specific leaf weight, and leaf area. J. Horticul. Sci. Biotechnol. 83, 274–281. Jackson, J.E., Palmer, J.W., 1977. Effects of shade on growth and cropping of apple-trees .2: Effects on components of yield. J. Horticul. Sci. 52, 253–266. Koo, R.C.J., 1988. Fertilization and irrigation effects of fruit quality. In: Ferguson, J.J., Wardowski, W.F. (Eds.), Factors Affecting Fruit Quality— Citrus Short Course, pp. 35–42 (Gainesville, FL). Lamp, B.M., Connell, J.H., Duncan, R.A., Viveros, M., Polito, V.S., 2001. Almond flower development: floral initiation and organogenesis. J. Am. Soc. Hortic. Sci. 126, 689–696. Lampinen, B.D., Tombesi, S., Metcalf, S.G., DeJong, T.M., 2011. Spur behaviour in almond trees: relationships between previous year spur leaf area, fruit bearing and mortality. Tree Physiol. 31, 700–706. Lampinen, B.D., Udompetaikul, V., Browne, G.T., Metcalf, S.G., Stewart, W.L., Contador, L., Negron, C., Upadhyaya, S.K., 2012. A mobile platform for measuring canopy photosynthetically active radiation interception in orchard systems. HortTechnology 22, 237–244. Meyer, G.A., Keliher, P.N., 1992. An Overview of Analysis by Inductively Coupled Plasma-Atomic Emission Spectrometry. In: Inductively Coupled Plasmas in Analytical Atomic Spectrometry. VCH Publishers, New York, NY. Meyer, R.D., Edstrom, J.P., Schulbach, H., Deng, J., 2001. Almond yields and leaf analyses as influenced by nitrogen source and acidification remediation treatments through drip irrigation. Hortscience 36, 450. Meyer, R.D., 1999. In: Potassium Fertilizer Regimes on Almond. 27th Annual Almond Industry Conference Proceedings Almond Board of California, Modesto. pp. 111–119. Millard, P., Grelet, G.-A., 2010. Nitrogen storage and remobilization by trees: ecophysiological relevance in a changing world. Tree Physiol. 30, 1083–1095. Millard, P., Neilsen, G.H., 1989. The influence of nitrogen supply on the uptake and remobilization of stored N for the seasonal growth of apple-trees. Ann. Bot. 63, 301–309. Millard, P., Proe, M.F., 1993. Nitrogen uptake: partitioning and internal cycling in Picea sitchensis (Bong) Carr. as influenced by nitrogen supply. New Phytologist 125, 113–119. Millard, P., Thomson, C.M., 1989. The effect of the autumn senescence of leaves on the internal cycling of nitrogen for the spring growth of apple trees. J. Exp. Bot. 40, 1285–1289. Muhammad, S., Sanden, B.L., Lampinen, B.D., Saa, S., Siddiqui, M.I., Smart, D.R., Olivos, A., Shackel, K.A., Dejong, T.M., Brown, P.H., 2015. Seasonal changes in nutrient content and concentrations in a mature deciduous tree species: studies in almond (Prunus dulcis (Mill.) D. A. Webb). Eur. J. Agron. 65, 52–68. Neilsen, G.H., Neilsen, D., Herbert, L., 2009. Nitrogen fertigation concentration and timing of application affect nitrogen nutrition, yield, firmness, and color of apples grown at high density. Hortscience 44, 1425–1431. Polito, V.S., Pinney, K., Heerema, R., Weinbaum, S.A., 2002. Flower differentiation and spur leaf area in almond. J. Hortic. Sci. Biotechnol. 77, 474–478. Rader, J.S., Walser, R.H., Williams, C.F., Davis, T.D., 1985. Organic and conventional peach Prunus-persica production and economics. Biol. Agricul. Horticul. 2, 215–222. Raese, J.T., 1997. Cold tolerance, yield, and fruit quality of ‘d'Anjou' pears influenced by nitrogen fertilizer rates and time of application. J. Plant Nutr 20, 1007–1025. Reidel, J.E., Brown, H.P., Duncan, A.R., Weinbaum, A.S., 2001. Almond productivity as related to tissue potassium. Better Crops 85, 21–23.
4.2. Effect of potassium rate on kernel yield Potassium rate treatments did not show any significant impact on kernel yield in Nonpareil suggesting that potassium requirement of Nonpareil almond was fulfilled with the 112 kg ha−1 application rate along with soil K supply from parent material and mineralization. Meyer (1999) reported an increase in almond kernel yield of Nonpareil for K rate treatments compared to control and recommended 1 lb (0.453 kg) K2O per tree. In almond a yield response to K application was observed in two years when compared to the unfertilized control (Reidel et al., 2001). In the experiments conducted here, no zero kg ha−1 K control was used and hence it can only be concluded that 112 kg ha−1 K application was sufficient to meet the demand of Nonpareil when added to the native K supply from soil. The critical K value for almond for July leaf sampling has been suggested as 1.4% on a dry weight basis (Meyer, 1999; Reidel et al., 2004). In our studies we did not observe a yield response to tissue K levels even when they fell below 1% (Fig. 2). This suggests that critical value for K in almond may actually be less than 1.4%. Trees from the 112 kg ha−1 K treatment would eventually be expected to show K deficiency over the long-term since the K export in fruits is substantially higher than the K applied as fertilizer (Muhammad et al., 2015). Ultimately soil K reserves would decline to below critical levels. The low yield of Nonpareil under KCl as the K source in 2010 (Table 4) was only observed in a single year. Leaf chloride analysis showed similar chloride concentration for all K sources, likely as a result of the high background Cl in the irrigation water which contributes in excess of 1000 kg ha−1 Cl per year in this location (data not shown). Meyer (1999) observed high yield for mono-potassium phosphate (MKP) compared to potassium sulfate under sprinkler irrigation but K sources had no effect on yield under double line drip irrigation. Interestingly Meyer reported similar leaf K concentrations for all K sources. K sources had no significant effect on the yield and leaf K concentration. In other crops K fertilizer sources did not show an effect on yield. In Pistachio, Zeng et al. (2001) could not find a significant effect of K source on leaf K and nut yield. Similarly, Szewczuk et al. (2011) could not find differences in apple yield with different K sources. The non-significant effect of N and K sources on yield and yield parameters suggests that N and K from all sources were equally available for uptake. These results confirm those of Meyer et al. (2001) who did not find significant differences in yield for N sources UAN 32 and CAN 17 and Meyer (1999) reported non-significant differences between K sources MKP/KCl and SOP. The lack of an N or K source effect may be a consequence of the excellent soils, growing conditions, split application fertigation practices and excellent irrigation conditions of this experimental orchard. 5. Conclusions Increasing nitrogen application rates increased leaf N and kernel yield through an increase in number of fruits and crackout percentage. Leaf N of 2.4-2.5% produced the maximum yield and yield did not improve when leaf N exceeded 2.5%. Leaf K above 1% did not increase yield. 211
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affects winter storage and spring remobilisation of nitrogen in nectarine (Prunus persica var. nectarina) trees. Plant Soil 211, 149–153. Tombesi, S., Lampinen, B.D., Metcalf, S., DeJong, T.M., 2011. Relationships between spur- and orchard-level fruit bearing in almond (Prunus dulcis). Tree Physiol. 31, 1413–1421. Wargo, J.M., Merwin, I.A., Watkins, C.B., 2003. Fruit size, yield, and market value of ‘GoldRush' apple are affected by amount, timing and method of nitrogen fertilization. Horttechnology 13, 153–161. Weinbaum, S.A., Uriu, K., Micke, W.C., Meith, H.C., 1980. Nitrogen fertilization increases yield without enhancing blossom receptivity in almond Prunus amygdalus cultivar nonpareil. Hortscience 15, 78–79. Weinbaum, S.A., Klein, I., Broadbent, F.E., Micke, W.C., Muraoka, T.T., 1984a. Effects of time of nitrogen application and soil texture on the availability of isotopically labeled fertilizer nitrogen to reproductive and vegetative tissue of mature almond trees Prunus dulcis. J. Am. Soc. Hortic. Sci. 109, 339–343. Weinbaum, S.A., Klein, I., Broadbent, F.E., Micke, W.C., Muraoka, T.T., 1984b. Use of isotopic nitrogen to demonstrate dependence of mature almond Prunus dulcis cultivar nonpareil trees on annual uptake of soil nitrogen. J. Plant Nutr. 7, 975–990. Weinbaum, S.A., Klein, I., Muraoka, T.T., 1987. Use of nitrogen isotopes and a lighttextured soil to assess annual contributions of nitrogen from soil and storage pools in mature almond trees. J. Am. Soc. Hortic. Sci. 112, 526–529. Weinbaum, S.A., Johnson, R.S., DeJong, T.M., 1992. Causes and consequences of overfertilization in orchards. Hort. Technol. 2, 112–121. Weinbaum, A.S., Goldhamer, D., Asai, W., Niederholzer, F., 1994. In: Optimization of fertilizer N usage in almond orchards. 22th Annual Almond Industry Conference Proceedings Almond Board of California, Modesto. pp. 46–49. Zeng, Q.P., Brown, P.H., Holtz, B.A., 2001. Potassium fertilization affects soil K, leaf K concentration, and nut yield and quality of mature pistachio trees. Hortscience 36, 85–89.
Reidel, J.E., Brown, P.H., Duncan, R.A., Heerema, R.J., Weinbaum, S.A., 2004. Sensitivity of yield determinants to potassium deficiency in ‘Nonpareil' almond (Prunus dulcis (Mill.) DA Webb). J. Horticul. Sci. Biotechnol. 79, 906–910. Rosecrance, R.C., Weinbaum, S.A., Brown, P.H., 1998. Alternate bearing affects nitrogen, phosphorus, potassium and starch storage pools in mature pistachio trees. Ann. Bot. 82, 463–470. Saa, S., Peach-Fine, E., Brown, P.H., Michailides, T.J., Castro, S., Bostock, R., Laca, E., 2016. Nitrogen increases hull rot and interferes with the hull split phenology in almond (Prunus dulcis). Sci. Hort. 199, 41–48. Saenz, J.L., DeJong, T.M., Weinbaum, S.A., 1997. Nitrogen stimulated increases in peach yields are associated with extended fruit development period and increased fruit sink capacity. J. Am. Soc. Hortic. Sci. 122, 772–777. Sah, R.N., Miller, R.O., 1992. Spontaneous reaction for acid dissolution of biological tissues in closed vessels. Anal. Chem. 64, 230–233. Schellenberg, D.L., Alsina, M.M., Muhammad, S., Stockert, C.M., Wolff, M.W., Sanden, B.L., Brown, P.H., Smart, D.R., 2012. Yield-scaled global warming potential from N2O emissions and CH4 oxidation for almond (Prunus dulcis) irrigated with nitrogen fertilizers on arid land. Agricul. Ecosys. Environ. 155, 7–15. Shapland, T.M., Snyder, R.L., Smart, D.R., Williams, L.E., 2012. Estimation of actual evapotranspiration in winegrape vineyards located on hillside terrain using surface renewal analysis. Irrigation Sci. 30, 471–484. Spann, T.M., Beede, R.H., Dejong, T.M., 2008. Seasonal carbohydrate storage and mobilization in bearing and non-bearing pistachio (Pistacia vera) trees. Tree Physiol. 28, 207–213. Szewczuk, A., Komosa, A., Gudarowska, E., 2011. Effect of soil potassium levels and different potassium fertilizers on yield, macroelement and chloride nutrion status of apple trees in full fruition period. Acta Scientiarum Polonorum-Hortorum Cultus 10, 83–94. Tagliavini, M., Millard, P., Quartieri, M., Marangoni, B., 1999. Timing of nitrogen uptake
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Optimization of nitrogen and potassium nutrition to improve yield and yield parameters of irrigated almond (Prunus dulcis (Mill.) D. A. webb)
MARK
⁎
Saiful Muhammada, , Blake L. Sandenb, Sebastian Saac, Bruce D. Lampinena, David R. Smartd, Kenneth A. Shackela, Theodore M. DeJonga, Patrick H. Browna a
Department of Plant Sciences, University of California Davis, One Shields Avenue, Davis, CA 95616, USA Kern County Cooperative Extension, University of California, 1031 South Mount Vernon Avenue, Bakersfield, CA 93307, USA c Escuela de Agronomía, Pontificia Universidad Católica de Valparaíso, Casilla 4D, Quillota, Chile d Department of Viticulture and Enology, University of California, One Shields Avenue, Davis, CA 95616, USA b
A R T I C L E I N F O
A B S T R A C T
Keywords: Nitrogen Potassium Yield Leaf nitrogen Yield parameters Prunus dulcis Almond
An experiment was conducted to evaluate the effect of nitrogen (N) and potassium (K) fertilization rates and fertilizer sources on almond yield and yield related parameters- fruit and kernel weight, number of fruits per tree, crackout percentage and leaf nutrient status by individually monitoring 768 trees. The experiment was carried out between 2008 and 2012 with four rates (140, 224, 309 and 392 kg N ha−1) and two sources (UAN and CAN) of N and three rates (112, 224 and 336 kg K ha−1) and sources (SOP + KTS, SOP and KCl) of K. Nitrogen fertilizer rate had a significant effect on yield in the second through the fourth year of the experiment. Tree yield was maximized at 18.5 kg and 23.7 kg kernel per tree in 2010 and 2011 season respectively when July leaf N was in the range 2.4–2.5% corresponding to an N application rate of 309 kg N ha−1 and there was no increment in yield above 2.5% leaf N. Source of N had no significant effect on yield response. Potassium fertilization rate had no significant effect on yield while K sources had significant effect in 2010 only. Increasing N application resulted in lighter fruit, and kernel weight decreased with increasing N application under moderate yield conditions, and increased under high yield conditions. Yield increase with increasing N application was due to an increase in number of fruits and increased crackout percentage. Leaf K above 1% did not increase yield and there was no consistent effect of K supply and K source on yield parameters. There was a strong relationship between total yield and number of fruits per tree, which increased with increasing N application. Crackout percentage was also positively correlated to kernel yield. Nitrogen and potassium fertilization rate should be based on expected yield and tree N and K status. For a well productive mature orchard, N application of 309 kg ha−1 with either UAN or CAN can meet crop N needs. K fertilization should consider K contribution from soil. Under condition of 100–150 mg kg−1 soil exchangeable potassium, K application of 112 kg ha−1 with any K fertilizer source can satisfy crop K demand.
1. Introduction Efficient fertilization practices are important to maximize crop yield while optimizing environmental stewardship. Excessive use of nitrogen (N) increases crop production costs and low recovery of N by the crop can contribute to nitrate contamination of groundwater (Drake et al., 2002). On the other hand inadequate fertilizer application can compromise crop yield and thus may not be economically sustainable. For consistent high yields, application of right rate of fertilizer at the right time is important so that any deficiency may not appear and that fertilizer is not wasted. In a long term experiment in almond, Muhammad et al. (2015) found that 68 kg of N and 75 kg potassium (K) is removed
⁎
in fruit per metric ton of kernel yield. 67–76% of the total N and 45–61% of the total K accumulated in the almond fruit by 86 days after full bloom (Muhammad et al., 2015). The use of suitable N source is important in the context of environmental problems. Schellenberg et al. (2012) reported significantly high nitrous oxide losses from Urea Ammonium Nitrate compared to Calcium Ammonium Nitrate in almond orchards although the total N2O losses were lower compared to other cropping system. Nitrogen and potassium are the nutrients required in largest amounts by an almond crop. Nitrogen deficiency reduces photosynthesis and plant growth and in severe N deficiency fruit drop may occur and nut quality is affected by reducing protein content. Nitrogen
Corresponding author. E-mail address: [email protected] (S. Muhammad).
http://dx.doi.org/10.1016/j.scienta.2017.10.024 Received 23 March 2017; Received in revised form 29 September 2017; Accepted 13 October 2017 0304-4238/ © 2017 Published by Elsevier B.V.
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Table 1 Soil analysis of the experimental site in 2008 at the beginning of the experiment. Depth (cm)
pH
EC (ds m−1)
HCO3 (meq L−1)
NO3-N (mg kg−1)
X-K (mg kg−1)
OM (%)
0–46 47–90
7.8 7.9
1.3 2.2
2.7 1.8
2 1.5
138 89
0.88 0.8
almond yield, b) to determine the effect of potassium rate and source on almond yield, and c) to determine the effect of N and K fertilization rate and sources on fruit weight, kernel weight, number of fruits and crackout percentage.
fertilization in excess of tree demand is poorly utilized by the plant and may be lost to leaching or result in excessive vegetative growth and will increase susceptibility to diseases such as almond hull rot (Saa et al., 2016). Over-fertilization with N fertilizers is a leading cause of contamination of ground water with nitrate and the deterioration of drinking water quality (Weinbaum et al., 1992). Potassium deficiency reduces photosynthesis and carbohydrate transport and accelerates premature leaf senescence and premature leaf abscission. Leaf potassium concentration less than 0.5–0.6% also limits leaf CO2 exchange rates and reduces leaf carbon fixation by imposing biochemical limitations on photosynthesis (Basile et al., 2003). Brown et al. (2000) found that K deficiency in one year reduced numbers of flowers and fruits in the subsequent year(s) and reported that yield from treatments not receiving K fertilizer was significantly lower than fertilized trees in the 3rd year of the experiment. Research on N and K fertilization effects on yield and yield components is limited in almond. In research published in an Almond Board of California (ABC) annual report, Weinbaum et al. (1994) reported results from a N fertilization trial in almond conducted at two locations in California with differential N applications of 0 kg, 140 kg, 280 kg and 560 kg ha−1 respectively. Yield was only different after the third year and between control and 280 kg ha−1 N application; both sites had high nitrate in the irrigation water (33 ppm and 44 ppm nitrate in site 1 and 2 respectively) that likely affected the results of the experiment. Other research in almond focused on rate and time of N application (Weinbaum et al., 1984a,b; Weinbaum et al., 1987) but no results of yield and related parameters was reported. Meyer et al. (2001) did not find yield differences between N sources of urea, calcium nitrate (CAN), urea-ammonium nitrate solution (UAN32) and urea-sulfuric acid though they reported significantly lower leaf N for calcium nitrate in some years. Applications of 139 kg, 278 kg, and 556 kg ha−1 K2O increased yield compared to the control but there was no additional benefit of K application over 139 kg ha−1 (Meyer, 1999). Mono potassium phosphate (MKP, KH2PO4) produced significantly higher yields than potassium sulfate (K2SO4), MKP/potassium chloride (KCl). The explanation for these results was not provided. Almond yield is influenced by the number of fruits and kernel weight (Lampinen et al., 2011) but fruit number is the most important yield determinant (Reidel et al., 2001). Weinbaum et al. (1980) attributed an increase in yield to an increase in the number of flowers with soil application of urea. In pistachio (Gunes et al., 2010), apple (Neilsen et al., 2009) and citrus (Koo, 1988), N application increased yield but the individual fruit weight decreased. In walnut, yield increase from increased N application has been attributed to an increase in kernel weight and kernel percentage (Gray and Garrett, 1998). Brown et al. (2000) reported no significant differences in kernel and fruit weight between control treatments (no K) and trees receiving different rates of potassium fertilizer, while Reidel et al. (2004) reported no significant differences in kernel and fruit weight between 0 and 960 kg ha−1 K application. Hence, the influence of K fertilizers on almond yields remains unresolved and reports may indicate it may be site specific. There is no published data on the effect of N supply and source on yield and fruit and kernel weight, number of fruits and crackout percentage in almond, while the effects of K sources on these yield parameters have not been reported. The objectives of the experiments included: a) to determine the effect of N fertilization rate and sources on
2. Materials and methods 2.1. Experimental site The experiment was carried out at Belridge, Kern County California (35.5° N 119.6° E) from 2008 to 2012 in a commercial almond orchard. In 2008, a nine year old almond orchard planted to 50% Nonpareil and 50% Monterey was selected. Both varieties were grafted on Nemaguard peach rootstock with a planting density of 214 trees per ha. The soil type was Panoche and Kimberlina very fine sandy loam (Loamy, mixed, superactive, calcareous, thermic Typic Torriorthents) with EC of 1.3 ds m−1 and pH 7.8 in the top 46 cm and EC 2.2 ds m−1 and pH 7.8 in 47–91 cm depth and organic matter of less than 1% with good drainage and aeration (Table 1). 2.2. Fertilizer treatments The experiment was established as a randomized complete block design. Four rates of nitrogen 140 kg, 224 kg, 309 kg and 392 kg ha−1 N were applied with two N fertilizer sources − Urea Ammonium Nitrate 32 (UAN 32) and Calcium Ammonium Nitrate 17 (CAN 17) as detailed in Table 2. Nitrogen was applied in four fertigation events as 20%, 30%, 30% and 20% of the total in mid-February, early April, mid-June and postharvest respectively. At this location flowering typically occurred in late February and harvest occurred in mid-August. All the nitrogen treatments received 90 kg ha−1 P as phosphoric acid (52% P2O5) and 224 kg ha−1 K applied as 60% sulfate of potash [SOP, (50% K2O)] in winter and 40% potassium thiosulphate [KTS, (25% K2O)] fertigated four times as for nitrogen. Potassium rate treatments included 112 kg, 224 kg and 336 kg ha−1 K, applied as 60% SOP (Table 2) in granular form in winter and the remaining 40% as KTS fertigated four times during the season as described for N. All K rate treatments received 309 kg ha−1 N as UAN 32 and 90 kg ha−1 P. In addition, three sources of K were contrasted; either 100% SOP, SOP + KTS at a ratio of 60:40 or 100% potassium chloride (KCl), applied at 224 kg ha−1 as K. All K source treatments received 309 kg ha−1 N as UAN 32 and 90 kg ha−1 P. SOP was applied in 60 cm wide strips in January and incorporated by winter rains followed by irrigation. KTS and KCl were applied in irrigation water during four fertigation cycles as described for N. Fifteen trees of Nonpareil in a row and their immediate neighbor trees in rows of Monterey were treated as one experimental unit with a plot size of 0.211 ha. Data were collected from six trees of Nonpareil in the middle row. Each treatment was replicated five/six times each under fan jet (micro-sprinkler) and drip irrigation. Irrigation treatments were applied in two separate blocks and there was no replication. Control valves were installed at the riser to regulate fertilizer application. Fertilizers were applied using a fertilizer injection pump, (Hypro Roller pump, Model 7560XL-R, New Brighton, MN USA). Fertilizer concentration was controlled by a digital turbine flow meter (model TM075-N, Great Plains Industries, Inc. North Wichita, KS USA). Orchard were irrigated at 100% ETc as determined from two custom surface renewal instruments in towers installed onsite (see Shapland 205
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Table 2 Detail of fertilizer treatments. Treatments
N Source
N amount (kg ha−1)
K Source
N rate and source
UAN32 UAN32 UAN32 UAN32 CAN17 CAN17 CAN17 CAN17 UAN32 UAN32 UAN32 UAN32 UAN32 UAN32
140 224 309 392 140 224 309 392 309 309 309 309 309 309
60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 60% SOP/40% 100% SOP 100% KCl
K rate
K source
K amount (kg ha−1) KTS KTS KTS KTS KTS KTS KTS KTS KTS KTS KTS KTS
224 224 224 224 224 224 224 224 112 224 336 224 224 224
UAN 32 = Urea Ammonium Nitrate 32% N, CAN 17 = Calcium Ammonium Nitrate 17% N, SOP = Sulfate of Potash, KTS = Potassium Thiosulfate, KCl = Potassium Chloride.
the periphery of each individual data tree. Samples were oven dried at 60 °C for 5 days. After drying the numbers of fruits in each sample were counted and weight recorded. Kernels were separated from the fruits and their weight was recorded.
et al., 2012). Soil moisture was monitored via neutron probe (Model 503DR, ICT International Armidale Australia) in 40 bore holes established to 2 m and distributed uniformly throughout the orchard. Periodic measurements of stem water potential were obtained using a pressure chamber (Model 3005HGPL Soil Moisture Inc. Santa Barbara, CA USA).
2.3.5. Number of fruits per tree Number of fruits per tree was calculated by dividing the individual tree yield and average fruit weight as:
2.3. Data collection
Number offruits per tree =
2.3.1. Yield Trees were shaken individually using a commercial shaker after 100% hull split and nuts from each data tree were kept separated and allowed to dry on the orchard floor for a week. After one week nuts were picked up using a commercial harvester and individual tree yield was recorded using a scale mounted gondola. The nuts from the nine non data trees were pooled to get plot scale yield data. Periodic samples were collected from the harvester to determine the weight of nonharvest debris and nut moisture content. Two kg fruit samples from two trees in each replicate were collected, dried, hulled, and cracked, to estimate kernel weight. Final yield was adjusted for moisture content and kernel yield was calculated using the data for moisture loss and crackout percentage from the 2 kg samples.
2.3.6. Photosynthetically active radiation Photosynthetically active radiation (PAR) interception was measured with a mobile platform light bar (Lampinen et al., 2012). 2.4. Statistical data analysis Statistical data analyzed was performed using JMP statistical software version 10, SAS institute Inc. USA. 3. Results
2.3.2. Leaf samples Leaf samples from all individual data trees were collected at 10% hull split. Leaves were washed and dried at 60 °C for five days and ground to pass 0.4 mm screen using Wiley Mini-Mill (Thomas Scientific). Samples were analyzed for N and K concentration at Agriculture and Natural Resource Laboratory (ANL) University of California Davis. N was determined through combustion (AOAC, 2006) and K was determined through nitric acid digestion (Meyer and Keliher, 1992; Sah and Miller, 1992).
All treatments under micro-sprinkler and drip irrigation produced similar results so we are reporting the results for treatments under micro-sprinkler irrigation only. 3.1. Effect of nitrogen supply on tissue N and kernel yield After establishment of treatment effect, N concentrations in leaves were positively correlated with N supply and yield (Fig. 1). N applications 140 and 224 kg ha−1 resulted in lower leaf N and lower yield. In 2010 and 2011, yield was maximum when tissue N concentrations ranged from 2.4 to 2.5% which was achieved by application of 309 kg ha−1 N. Kernel yield under differential N rate treatments is shown in Table 3. In the first year of the experiment (2008) there was no significant effect of increasing N application on kernel yield, however, there was a trend of yield increase with increasing N application. In 2009, 2010 and 2011 significant differences in kernel yield (p < 0.05) were observed. Minimum kernel yield was observed for 140 kg ha−1 N and maximum yield was achieved with N applications of 309 kg ha−1 N and above. Overall orchard productivity declined in 2012, probably due to alternate bearing habit as a consequence of high yield in 2011, but also from high hull rot incidence and possibly other reasons that have not been determined. There were no significant effects of N rates on yield in 2012. Cumulative kernel yield was highest for N rate
2.3.3. Crackout percentage A day before harvest, 2 kg clean fruit samples were collected from two trees in each replicated treatment unit. The samples were then dried in forced air driers at 45 °C for a week, cleaned and final weight was recorded. Kernels from these samples were separated using a small almond huller (Jessee Equipment Manufacturing Chico, California) at the Pomology Headquarters University of California Davis. Crackout percentage was determined as:
Crack out percentage =
Yield (kg )*1000 Average fruit weight (g )
Kernel weight (kg ) *100 Fruit weight (kg )
2.3.4. Fruit and kernel weight A day before shaking the trees, 30 fruit samples were collected from 206
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Fig. 1. Relationship between yield (kg ha−1) and July leaf nitrogen concentration (% dry weight) for Nonpareil almond in 2010 and 2011. Each point is mean of six individual trees.
3.2. Effect of potassium fertilization rate and source on kernel yield
Table 3 Kernel yield (kg ha−1) of Nonpareil almond with different rates of N as UAN 32. Letters indicate significant difference in yield within the same year at < 0.05 level of significance using student t-test. Year
2008 2009 2010 2011 2012 Cumulative yield
Leaf potassium concentrations increased with application of K fertilizer. K concentrations were low in 2008 when the experiment was started and increased from 2009 to 2011. In 2008, majority of the trees were K deficient according to the standard critical value of 1.4% but no yield response to increased leaf K concentrations were observed (Fig. 2). Potassium fertilizer application rates did not influence kernel yield (data not shown). The effect of K fertilizer sources was inconsistent. Potassium fertilizer sources had a significant differential effect on yield only in 2010 under fan jet irrigation (p < 0.05) where SOP + KTS produced maximum yield (Table 4).
Nitrogen rate (kg ha−1) 140
224
309
392
3437 3154 b 2639 c 4335 b 903 14,468 c
3689 3434 ab 3231 b 4496 b 885 15,735 b
3657 3603 a 3932 a 5018 a 990 17,200 a
3870 3701 a 3670 a 4956 a 1089 17,286 a
3.3. Effect of nitrogen fertilization on yield components of nonpareil
309 kg ha−1 and above whereas N rate 140 kg ha−1 produced lowest cumulative kernel yield. The effect of N source on the yield was not significant.
3.3.1. Effect on fruit weight Following the establishment of N treatments in 2008, increasing N rates resulted in decreased individual fruit weight in all subsequent years (Fig. 3). Significant effects of N application rate on fruit weight were observed in 2009, 2010 and 2011 where maximum fruit weight was recorded at lower N application rates (140 kg ha−1 and 224 kg ha−1 N). Minimum fruit weight was observed for 392 kg ha−1 207
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Fig. 2. Relationship between yield (kg ha−1) and July leaf potassium concentration (% dry weight) for Nonpareil almond from 2008 to 2011. Each point is mean of six individual trees.
resulted in lowest crackout percentage while all other N rates produced similar results.
Table 4 Kernel yield of Nonpareil almond (kg ha−1) with different potassium sources. Letters indicate significant difference in yield within the same year at < 0.05 level of significance using student t-test. Year
2008 2009 2010 2011 2012 Cumulative yield 2008–2012
3.4. Effect of nitrogen sources and potassium fertilizer rate and sources on yield parameters of nonpareil
Potassium Source @ 224 kg ha−1 SOP + KTS
SOP
KCl
3739 3621 3859 a 5009 1003 17,231
3673 3745 3779 a 4886 832 16,915
3654 3828 3232 b 4870 814 16,398
There was no consistent effect of N fertilizer source and K fertilizer rate and source on fruit and kernel weight, number of fruits per tree or crackout percentage. 3.5. Effect of N on intercepted photosynthetically active radiation (PAR) Effect of N application on intercepted PAR was recorded in 2011 and 2012 (Table 5). N application increased intercepted PAR. In 2012, lowest PAR interception (80%) was recorded for 140 kg ha−1 and maximum PAR interception (90%) was recorded for 392 kg ha−1 N rate.
in 2009, 2010 and 2011. 3.3.2. Effect on kernel weight The response of kernel weight to N supply is shown in Fig. 4. There were no consistent trends in kernel weight in any year. In 2010 N application of 224 kg ha−1 produced the heaviest kernel while 392 kg ha−1 N produced lighter kernels. Increasing N application produced heavier kernels in 2011.
4. Discussions 4.1. Effect of nitrogen rate and sources on yield and yield components Increasing N application rate increased kernel yield of Nonpareil almond following the first year of the experiment. In the first year of variable N rate applications, the lack of tree response likely reflects the use of stored nutrients in perennial tree parts, the amount of which then changed in subsequent experimental years in response to N application rates (Muhammad et al., 2015). Unlike annual species, perennial plants have significant amounts of stored N and other nutrients (Millard and Grelet, 2010; Millard and Neilsen, 1989; Millard and Proe, 1993; Millard and Thomson, 1989; Muhammad et al., 2015; Tagliavini et al., 1999) that are remobilized to support early spring growth. Following the first year of the experiment, the yield of the 140 kg ha−1 N treatment declined likely as a result of N export in the crop exceeding N fertilizer application. Nitrogen exported in harvested fruit in the
3.3.3. Effect on number of fruits per tree Nitrogen supply increased the number of fruits per tree. Following experiment establishment in 2008, the 140 kg ha−1 N rate produced the minimum number of fruits while the maximum number of fruits was produced under 309 kg ha−1 N rate and above (Fig. 5). 3.3.4. Effect on crackout percentage Effect of N rate on crackout percentage was not consistent and was only significant in 2009 and 2010 (Fig. 6). In 2009 N rate 392 kg ha−1 resulted in maximum crackout percentage whereas N rate 140, 224 and 309 kg ha−1 produced similar results. In 2010, N rate 140 kg ha−1 208
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Fig. 3. Mean individual fruit weight of Nonpareil with differential N supply with UAN 32. Each bar shows mean and standard error. Means not connected by same letter indicate significant difference in mean fruit weight within the same year at < 0.05 level of significance using student’s t-test.
140 kg ha−1 N treatment was 189 and 164 kg ha−1 in 2008 and 2009 respectively (Muhammad et al., 2015). The decline in fruit number and leaf N observed in the low N treatments (140 and 224 kg ha−1) indicated that tree growth was reduced from 2008 onward and final tree size in 2012 was significantly lower. Increasing N application increased shoot growth as evidenced from an increase in photosynthetically active radiation (PAR) intercepted by the tree canopy with increasing N application (Table 5) that presumably increased spur population. Increasing N supply generally increased tree growth and kernel yield, however there was no significant increase in kernel yield beyond the 309 kg ha−1 N treatment. There was a strong relationship between tree N status (as indicated by leaf N in July) and yield. Yield increased as leaf N concentrations increased but there was no additional significant benefit of increasing leaf N over 2.5%. In previous experiments (Brown and Uriu, 1996), July leaf N concentration below 2% has been considered deficient and 2.2-2.5% N has been recommended as critical value. We found July leaf N concentrations 2.3-2.5% sufficient and N below 2.2% is deficient (Fig. 1). The increase in kernel yield with increasing N application was a
result of an increase in the number of fruits per tree although crackout percentage also increased in high N trees. Almond yield can be influenced by the number of fruits and individual kernel weight (Lampinen et al., 2011) but fruit number has been reported to be the most important yield determinant (Reidel et al., 2001). Number of fruits per tree increased with increasing N application rate in this experiment (Fig. 5). In a number of tree crops an increase in yield has been attributed to an increase in the number of fruits such as in apple (Neilsen et al., 2009; Wargo et al., 2003) and citrus (Koo, 1988). Increasing N application increased yield but the individual fruit weight decreased. A similar effect of decreasing fruit weight with increasing yield was reported in pistachio (Gunes et al., 2010), apple (Neilsen et al., 2009) and citrus (Koo, 1988). In other tree species, fruit weight increased as a result of an increase in N supply including pear (Raese, 1997) and peach (Rader et al., 1985; Saenz et al., 1997). Decrease in fruit size with a constant or increased kernel weight resulted in a higher crackout percentage as N application increased (Fig. 6). Similar findings were reported for black walnut by Gray and Garrett (1998) where N supply increased kernel weight and kernel percentage. Fig. 4. Mean individual kernel weight of Nonpareil with differential N supply with UAN 32. Each bar shows mean and standard error. Letters indicate significant difference in mean kernel weight within the same year at < 0.05 level of significance using student’s t-test.
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Fig. 5. Number of fruits per tree of Nonpareil with differential N supply with UAN 32. Each bar shows mean and standard error. Means not connected by same letters indicate significant difference in number of fruits per tree within the same year at < 0.05 level of significance using student’s t-test.
In 2012 kernel yield dropped as a consequence of disease and the stress apparently caused as a result of the high yields in 2011 and perhaps other unknown factors. Almond is a partially alternate bearing species and high yield in one year can affect the number of flowering spurs the next year (Heerema et al., 2008; Tombesi et al., 2011). Therefore, very high yield in one year can reduce the number of fruiting spurs the next year resulting in an ‘alternate bearing’ behavior. This can be further exacerbated if new shoot growth and replacement spur production is inhibited by environmental factors. The low yield in 2012 may be a consequence of the very high yield in 2011. Fruit load affects nutritional status (Reidel et al., 2004) and carbohydrate balance of many fruit species (Jackson and Palmer, 1977; Rosecrance et al., 1998; Spann et al., 2008) that may in turn affect spur survival. Leaf nutrient analysis in 2011 show sufficient N and K in leaf tissue for the 309 kg and 392 kg ha−1 N rates compared to standards, however, N was deficient in the 140 kg and 224 kg ha−1 N rates (Figs. 1 and 2). The low yield of the 309 kg and 392 kg ha−1 in 2012 was clearly not an effect of nutrient deficiency as tree vegetative growth was not affected as indicated by increased in canopy growth (Table 5); however, we did not determine carbohydrate status of the trees during
Table 5 Mean percent Photosynthetically Active Radiation (PAR) intercepted by the orchard in 2011 and 2012 as affected by nitrogen application. Letters indicate significant difference in PAR interception within the same date at < 0.05 level of significance. Date
6/28/2011 6/13/2012
Mean Percent PAR N 140 kg ha−1
N 224 kg ha−1
N 309 kg ha−1
N 392 kg ha−1
78 c 80 c
81 b 84 bc
83 ab 87 ab
84 a 90 a
dormancy. In almond, spurs are semi-autonomous regarding carbohydrate demand (Heerema et al., 2008) suggesting that the survival of the spur is dependent on the presence of fruit and the carbohydrate supply of the spur leaves and that greater demand of fruit can result in carbohydrate limitation of the developing flower buds. In Nonpareil flower initiation occurs after hull split (Lamp et al., 2001) when fruits are still on trees, hence flower bud development may compete for Fig. 6. Crackout percentage of Nonpareil almond for N rates with UAN 32. Each bar shows mean and standard error. Means not connected by same letter indicate significant difference in crackout percentage within the same year at < 0.05 level of significance using student’s t-test.
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Acknowledgements
carbohydrates when a heavy fruit load is present. The carbohydrate dependency of the flower buds is also evident from the fact that spurs with high nonstructural carbohydrate content during dormancy produced more flower buds per spur (Heerema et al., 2008; Polito et al., 2002). The high yield in 2011 may have reduced spur survival and the development of the flower buds as a result of carbohydrate deficiency for the flower initiations. In addition to changes in fruit load, the incidence of hull rot in the moderate to high N rate treatments contributed to loss of some spurs and shoots (Saa et al., 2016) however there could be other unknown factors that limited yield for all N rates.
We would like to thank California Department of Food and Agriculture, Almond Board of California and Yara Fertilizer Company for funding this research. This project was supported by the USDA National Institute of Food and Agriculture, Hatch project number# CAD-PLS-2000-OG. We also like to thank Paramount Farming Company for material as well as providing human resources for the experiment. References AOAC, 2006. AOAC Official Method 972. 43. Microchemical Determination of Carbon, Hydrogen, and Nitrogen, Automated Method, 18th ed. AOAC International, Gaithersburg, MD. Basile, B., Reidel, E.J., Weinbaum, S.A., DeJong, T.M., 2003. Leaf potassium concentration, CO2 exchange and light interception in almond trees (Prunus dulcis (Mill) D.A. Webb). Sci. Hort. 98, 185–194. Brown, P.H., Uriu, K., 1996. Nutrition deficiencies and toxicities: diagnosing and correcting imbalances. In: In: Micke, W.C. (Ed.), Almond Production Manual 3364. University of California, Division of Agriculture and Natural Resources Publication, pp. 179–188. Brown, P.H., Weinbaum, S.A., DeJong, T.M., 2000. Reassessment of Potassium Critical Values. In Years of Discovery (1972–2003). Almond Board of California. Drake, S.R., Raese, J.T., Smith, T.J., 2002. Time of nitrogen application and its influence on ‘golden delicious' apple yield and fruit quality. J. Plant Nutr. 25, 143–157. Gray, D., Garrett, H.E.G., 1998. Nitrogen fertilization and aspects of fruit yield in a Missouri black walnut alley cropping practice. Agrofor. Syst. 44, 333–344. Gunes, N.T., Okay, Y., Koksal, A.I., Koroglu, M., 2010. The effect of nitrogen and phosphorus fertilization on yield, some fruit characteristics, hormone concentrations, and alternate bearing in pistachio. Turk. J. Agric. For. 34, 33–43. Heerema, R.J., Weinbaum, S.A., Pernice, F., Dejong, T.M., 2008. Spur survival and return bloom in almond Prunus dulcis (Mill.) DA Webb varied with spur fruit load, specific leaf weight, and leaf area. J. Horticul. Sci. Biotechnol. 83, 274–281. Jackson, J.E., Palmer, J.W., 1977. Effects of shade on growth and cropping of apple-trees .2: Effects on components of yield. J. Horticul. Sci. 52, 253–266. Koo, R.C.J., 1988. Fertilization and irrigation effects of fruit quality. In: Ferguson, J.J., Wardowski, W.F. (Eds.), Factors Affecting Fruit Quality— Citrus Short Course, pp. 35–42 (Gainesville, FL). Lamp, B.M., Connell, J.H., Duncan, R.A., Viveros, M., Polito, V.S., 2001. Almond flower development: floral initiation and organogenesis. J. Am. Soc. Hortic. Sci. 126, 689–696. Lampinen, B.D., Tombesi, S., Metcalf, S.G., DeJong, T.M., 2011. Spur behaviour in almond trees: relationships between previous year spur leaf area, fruit bearing and mortality. Tree Physiol. 31, 700–706. Lampinen, B.D., Udompetaikul, V., Browne, G.T., Metcalf, S.G., Stewart, W.L., Contador, L., Negron, C., Upadhyaya, S.K., 2012. A mobile platform for measuring canopy photosynthetically active radiation interception in orchard systems. HortTechnology 22, 237–244. Meyer, G.A., Keliher, P.N., 1992. An Overview of Analysis by Inductively Coupled Plasma-Atomic Emission Spectrometry. In: Inductively Coupled Plasmas in Analytical Atomic Spectrometry. VCH Publishers, New York, NY. Meyer, R.D., Edstrom, J.P., Schulbach, H., Deng, J., 2001. Almond yields and leaf analyses as influenced by nitrogen source and acidification remediation treatments through drip irrigation. Hortscience 36, 450. Meyer, R.D., 1999. In: Potassium Fertilizer Regimes on Almond. 27th Annual Almond Industry Conference Proceedings Almond Board of California, Modesto. pp. 111–119. Millard, P., Grelet, G.-A., 2010. Nitrogen storage and remobilization by trees: ecophysiological relevance in a changing world. Tree Physiol. 30, 1083–1095. Millard, P., Neilsen, G.H., 1989. The influence of nitrogen supply on the uptake and remobilization of stored N for the seasonal growth of apple-trees. Ann. Bot. 63, 301–309. Millard, P., Proe, M.F., 1993. Nitrogen uptake: partitioning and internal cycling in Picea sitchensis (Bong) Carr. as influenced by nitrogen supply. New Phytologist 125, 113–119. Millard, P., Thomson, C.M., 1989. The effect of the autumn senescence of leaves on the internal cycling of nitrogen for the spring growth of apple trees. J. Exp. Bot. 40, 1285–1289. Muhammad, S., Sanden, B.L., Lampinen, B.D., Saa, S., Siddiqui, M.I., Smart, D.R., Olivos, A., Shackel, K.A., Dejong, T.M., Brown, P.H., 2015. Seasonal changes in nutrient content and concentrations in a mature deciduous tree species: studies in almond (Prunus dulcis (Mill.) D. A. Webb). Eur. J. Agron. 65, 52–68. Neilsen, G.H., Neilsen, D., Herbert, L., 2009. Nitrogen fertigation concentration and timing of application affect nitrogen nutrition, yield, firmness, and color of apples grown at high density. Hortscience 44, 1425–1431. Polito, V.S., Pinney, K., Heerema, R., Weinbaum, S.A., 2002. Flower differentiation and spur leaf area in almond. J. Hortic. Sci. Biotechnol. 77, 474–478. Rader, J.S., Walser, R.H., Williams, C.F., Davis, T.D., 1985. Organic and conventional peach Prunus-persica production and economics. Biol. Agricul. Horticul. 2, 215–222. Raese, J.T., 1997. Cold tolerance, yield, and fruit quality of ‘d'Anjou' pears influenced by nitrogen fertilizer rates and time of application. J. Plant Nutr 20, 1007–1025. Reidel, J.E., Brown, H.P., Duncan, A.R., Weinbaum, A.S., 2001. Almond productivity as related to tissue potassium. Better Crops 85, 21–23.
4.2. Effect of potassium rate on kernel yield Potassium rate treatments did not show any significant impact on kernel yield in Nonpareil suggesting that potassium requirement of Nonpareil almond was fulfilled with the 112 kg ha−1 application rate along with soil K supply from parent material and mineralization. Meyer (1999) reported an increase in almond kernel yield of Nonpareil for K rate treatments compared to control and recommended 1 lb (0.453 kg) K2O per tree. In almond a yield response to K application was observed in two years when compared to the unfertilized control (Reidel et al., 2001). In the experiments conducted here, no zero kg ha−1 K control was used and hence it can only be concluded that 112 kg ha−1 K application was sufficient to meet the demand of Nonpareil when added to the native K supply from soil. The critical K value for almond for July leaf sampling has been suggested as 1.4% on a dry weight basis (Meyer, 1999; Reidel et al., 2004). In our studies we did not observe a yield response to tissue K levels even when they fell below 1% (Fig. 2). This suggests that critical value for K in almond may actually be less than 1.4%. Trees from the 112 kg ha−1 K treatment would eventually be expected to show K deficiency over the long-term since the K export in fruits is substantially higher than the K applied as fertilizer (Muhammad et al., 2015). Ultimately soil K reserves would decline to below critical levels. The low yield of Nonpareil under KCl as the K source in 2010 (Table 4) was only observed in a single year. Leaf chloride analysis showed similar chloride concentration for all K sources, likely as a result of the high background Cl in the irrigation water which contributes in excess of 1000 kg ha−1 Cl per year in this location (data not shown). Meyer (1999) observed high yield for mono-potassium phosphate (MKP) compared to potassium sulfate under sprinkler irrigation but K sources had no effect on yield under double line drip irrigation. Interestingly Meyer reported similar leaf K concentrations for all K sources. K sources had no significant effect on the yield and leaf K concentration. In other crops K fertilizer sources did not show an effect on yield. In Pistachio, Zeng et al. (2001) could not find a significant effect of K source on leaf K and nut yield. Similarly, Szewczuk et al. (2011) could not find differences in apple yield with different K sources. The non-significant effect of N and K sources on yield and yield parameters suggests that N and K from all sources were equally available for uptake. These results confirm those of Meyer et al. (2001) who did not find significant differences in yield for N sources UAN 32 and CAN 17 and Meyer (1999) reported non-significant differences between K sources MKP/KCl and SOP. The lack of an N or K source effect may be a consequence of the excellent soils, growing conditions, split application fertigation practices and excellent irrigation conditions of this experimental orchard. 5. Conclusions Increasing nitrogen application rates increased leaf N and kernel yield through an increase in number of fruits and crackout percentage. Leaf N of 2.4-2.5% produced the maximum yield and yield did not improve when leaf N exceeded 2.5%. Leaf K above 1% did not increase yield. 211
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affects winter storage and spring remobilisation of nitrogen in nectarine (Prunus persica var. nectarina) trees. Plant Soil 211, 149–153. Tombesi, S., Lampinen, B.D., Metcalf, S., DeJong, T.M., 2011. Relationships between spur- and orchard-level fruit bearing in almond (Prunus dulcis). Tree Physiol. 31, 1413–1421. Wargo, J.M., Merwin, I.A., Watkins, C.B., 2003. Fruit size, yield, and market value of ‘GoldRush' apple are affected by amount, timing and method of nitrogen fertilization. Horttechnology 13, 153–161. Weinbaum, S.A., Uriu, K., Micke, W.C., Meith, H.C., 1980. Nitrogen fertilization increases yield without enhancing blossom receptivity in almond Prunus amygdalus cultivar nonpareil. Hortscience 15, 78–79. Weinbaum, S.A., Klein, I., Broadbent, F.E., Micke, W.C., Muraoka, T.T., 1984a. Effects of time of nitrogen application and soil texture on the availability of isotopically labeled fertilizer nitrogen to reproductive and vegetative tissue of mature almond trees Prunus dulcis. J. Am. Soc. Hortic. Sci. 109, 339–343. Weinbaum, S.A., Klein, I., Broadbent, F.E., Micke, W.C., Muraoka, T.T., 1984b. Use of isotopic nitrogen to demonstrate dependence of mature almond Prunus dulcis cultivar nonpareil trees on annual uptake of soil nitrogen. J. Plant Nutr. 7, 975–990. Weinbaum, S.A., Klein, I., Muraoka, T.T., 1987. Use of nitrogen isotopes and a lighttextured soil to assess annual contributions of nitrogen from soil and storage pools in mature almond trees. J. Am. Soc. Hortic. Sci. 112, 526–529. Weinbaum, S.A., Johnson, R.S., DeJong, T.M., 1992. Causes and consequences of overfertilization in orchards. Hort. Technol. 2, 112–121. Weinbaum, A.S., Goldhamer, D., Asai, W., Niederholzer, F., 1994. In: Optimization of fertilizer N usage in almond orchards. 22th Annual Almond Industry Conference Proceedings Almond Board of California, Modesto. pp. 46–49. Zeng, Q.P., Brown, P.H., Holtz, B.A., 2001. Potassium fertilization affects soil K, leaf K concentration, and nut yield and quality of mature pistachio trees. Hortscience 36, 85–89.
Reidel, J.E., Brown, P.H., Duncan, R.A., Heerema, R.J., Weinbaum, S.A., 2004. Sensitivity of yield determinants to potassium deficiency in ‘Nonpareil' almond (Prunus dulcis (Mill.) DA Webb). J. Horticul. Sci. Biotechnol. 79, 906–910. Rosecrance, R.C., Weinbaum, S.A., Brown, P.H., 1998. Alternate bearing affects nitrogen, phosphorus, potassium and starch storage pools in mature pistachio trees. Ann. Bot. 82, 463–470. Saa, S., Peach-Fine, E., Brown, P.H., Michailides, T.J., Castro, S., Bostock, R., Laca, E., 2016. Nitrogen increases hull rot and interferes with the hull split phenology in almond (Prunus dulcis). Sci. Hort. 199, 41–48. Saenz, J.L., DeJong, T.M., Weinbaum, S.A., 1997. Nitrogen stimulated increases in peach yields are associated with extended fruit development period and increased fruit sink capacity. J. Am. Soc. Hortic. Sci. 122, 772–777. Sah, R.N., Miller, R.O., 1992. Spontaneous reaction for acid dissolution of biological tissues in closed vessels. Anal. Chem. 64, 230–233. Schellenberg, D.L., Alsina, M.M., Muhammad, S., Stockert, C.M., Wolff, M.W., Sanden, B.L., Brown, P.H., Smart, D.R., 2012. Yield-scaled global warming potential from N2O emissions and CH4 oxidation for almond (Prunus dulcis) irrigated with nitrogen fertilizers on arid land. Agricul. Ecosys. Environ. 155, 7–15. Shapland, T.M., Snyder, R.L., Smart, D.R., Williams, L.E., 2012. Estimation of actual evapotranspiration in winegrape vineyards located on hillside terrain using surface renewal analysis. Irrigation Sci. 30, 471–484. Spann, T.M., Beede, R.H., Dejong, T.M., 2008. Seasonal carbohydrate storage and mobilization in bearing and non-bearing pistachio (Pistacia vera) trees. Tree Physiol. 28, 207–213. Szewczuk, A., Komosa, A., Gudarowska, E., 2011. Effect of soil potassium levels and different potassium fertilizers on yield, macroelement and chloride nutrion status of apple trees in full fruition period. Acta Scientiarum Polonorum-Hortorum Cultus 10, 83–94. Tagliavini, M., Millard, P., Quartieri, M., Marangoni, B., 1999. Timing of nitrogen uptake
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