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Potato uptake and recovery of nitrogen 15N-enriched ammonium nitrate
Geoderma 105 Ž2002. 167–177 www.elsevier.comrlocatergeoderma
Potato uptake and recovery of nitrogen 15 N-enriched ammonium nitrate F.-X. Maidl ) , H. Brunner, E. Sticksel Technical UniÕersity of Munich, D-85350 Freising-Weihenstephan, Germany
Abstract Tuber yield and nitrogen uptake in potatoes were recorded during 1996 and 1997 in Southern Bavaria. Recovery of applied fertilizer nitrogen was measured by using 15 N Ž15 NH 415 NO 3 .. Nitrogen fertilizer was brought out either broadcast or in the ridge; 150 kg N hay1 were applied either at planting or in split doses of 50 kg N hay1 Žat planting, emergence and at 20-cm plant height.. Due to unfavorable conditions, tuber yield and fertilizer N recovery were lower in 1996 as compared with 1997. Fertilizer N recovery in plant biomass Žtuber and foliage. ranged from 35.9% to 68.5% at growth stage EC 79; the main fraction was allocated to tubers. Placement of fertilizer N in the ridge had a positive effect on N recovery, when the total N amount was applied at planting. In broadcast application, fertilizer N recovery was higher when the fertilizer doses were split, as compared with a single broadcast application at planting. When fertilizer N was applied in split doses, the effect of N placement became negligibly small. Fertilizer N recovery in soil ranged from 19.5% to 24.6%, and total recovery ranged from 60.1% to 88.0%. Rainfall between planting and plant emergence, and conditions restricting plant development in early developmental stages were related with unaccounted fertilizer N losses. Therefore, the positive effects of split N applications or fertilizer placement are most likely to occur under unfavorable growing conditions. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Potato; Nitrogen fertilizer; Labeled fertilizer; Yield; Nitrogen uptake; Nitrogen efficiency
1. Introduction The risk of nitrogen ŽN. losses in potato fields is relatively high Ž Neeteson, 1995., due to crop specific effects, i.e. long-lasting early developmental stage with a low N uptake, low amount and density of roots especially between the )
Corresponding author. Fax: q49-8161-714511. E-mail address: [email protected] ŽF.-X. Maidl..
0016-7061r02r$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 1 6 - 7 0 6 1 Ž 0 1 . 0 0 1 0 2 - 1
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ridges, and low total N uptake at harvest Ž Burton, 1989; Himken, 1995; Maidl, 1995; Schmidtke et al., 1999.. In addition to N losses via leaching, investigations conducted by the FAM Research Network on Agroecosystems have revealed that gaseous losses may also have a significant impact on potatoes. In particular, compacted zones between the ridges are susceptible to nitrous oxide emissions ŽRuser et al., 1998.. The most promising approach to minimize N losses is to improve the utilization of applied fertilizer nitrogen. Westermann and Sojka Ž 1996. emphasize the advantages of fertilizer placement in the ridge. MacKerron et al. Ž 1993. and Walther et al. Ž 1996. recommend low start N dressings, in order to take into account the release of soil borne N when calculating total N amount. Maidl Ž1995. emphasizes the importance of a well developed root system in row crops to prevent N losses. The goal of the present study was to examine the impact of N fertilizer timing and placement on N utilization in potatoes. Field trials were performed on soils representative for potato crop regions in Southern Bavaria. Fertilizer N performance was examined by using double tagged 15 N enriched NH 4 NO 3. 2. Material and methods 2.1. Trial sites Two-year field trials were conducted at the Research Station Scheyern in Southern Bavaria. A detailed description of the Research Station Scheyern and the FAM Research Network on Agroecosystems is given in the introduction of this special issue. In 1996, the soil was a fine-loamy Dystric Eutrochrept and root growth was limited by underlying gravel material in 60-cm depth. In 1997, the trial plots had a higher sand content and no layers in the profile restricted root growth. Total N in topsoil was 0.15% and 0.11% in 1996 and in 1997, respectively. The average plant-available water storage capacity was estimated at approximately 100 mm, with a total water storage capacity of 160 mm in 1996. In 1997, these values were 70 and 100 mm, respectively. At planting, the y1 Ž NOy 0–60 cm, 1996. and 104 kg N hay1 3 N content in soil was 54 kg N ha Ž0–90 cm, 1997. . 2.2. Layout and management of the trials Potato planting took place at April 21, 1996 and April 25, 1997. The planting density was 4.5 tubers my2 Žcv. ‘Agria’. and the distance between ridges was 0.75 m. Plant protection during the vegetation period was applied as necessary. The description of growth stages ŽEC. followed the scheme of Meier Ž 1997. . The experimental layout was a completely randomized block design with four replications. Micro-plot size was 3 m2. The plots were bordered by iron plates to
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a depth of 45 cm to prevent lateral interactions, thus covering the main rooting zone. The total amount of fertilizer N utilized was 150 kg N hay1, applied either broadcast or in the ridge, and applied either as a single dose Ž 150 kg N hay1 . at planting or split into three doses of 50 kg N hay1 each. When applied in split doses, the third application was broadcast since foliage hindered application in the ridge. The timing of fertilizer application is shown in Table 1. The amount of labeled nitrogen Ž15 NH 415 NO 3 , 99% purity; NIRDIMT, Cluj, Napoca, Romania. used was 1 g N my2 , whereby the compound was dissolved and applied with a watering can. Additional 30-m2 plots were treated identically. N content in tubers and foliage were comparable on micro- and normal plots but border effects on tuber yield occurred on micro-plots. Therefore, tuber yield was determined on normal plots. 2.3. 15N-isotope measurements Total fresh weight of tubers was measured at EC 65 Ž treatments N1, N2. and EC 79. A small amount was taken from each sample, chopped, dried at 60 8C and pulverized in a Vibratory Disc Mill RS 100 ŽRetsch, Germany. . 15 N was measured with a mass spectrometer ŽANCA-MS, Europe Scientific 20-20, UK. , following the analytical and mathematical procedures of Heuwinkel Ž 1999. . The percentage fertilizer N uptake was derived from the hand harvested tubers and foliage on micro-plots and the fertilizer N uptake Ž kg N hay1 . was determined from the tuber yield obtained on normal plots. Potato foliage was harvested in EC 31, EC 65 Ž treatments N1, N2. and in EC 79. Tubers were analyzed as previously described. Soil samples were collected in EC 31, EC 65 Ž treatments N1, N2. and in EC 79. In order to consider fertilizer placement effects, samples were defined as
Table 1 Amount Žkg N hay1 ., timing and placement of fertilizer N and timing of labeled N application Treatment N1 N2 N3 N4 N5 N6 N7 N8
Placement broadcast ridge broadcast
ridge
Timing Planting
Emergence
Plant height 20 cm
150 Žlabeled. 150 Žlabeled. 50 Žlabeled. 50 50 50 Žlabeled. 50 50
– – 50 50 Žlabeled. 50 50 50 Žlabeled. 50
– – 50 50 50 Žlabeled. 50 50 50 Žlabeled.
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being Ain the ridgeB and Abetween the ridgeB. Eight replications were done with a Purckhauer auger, at sampling depths of 60 cm in 1996 and 80 cm for 1997, ¨ respectively. The soil samples were divided into 20-cm sections, and 15 N content was estimated by setting the bulk density to 1.3 g cmy3 for the upper 20 cm of the ridge, and 1.5 g cmy3 for the remainder. 2.4. Weather and plant growth In May 1996, the total rainfall was 122.5 mm and thus in the range of soil water storage capacity ŽTable 2.. The interval between 15 N application at planting and the onset of the rainy period was 10 days and plants had not yet emerged. Actual evapotranspiration and amount of seepage water was calculated according to the method of Riess Ž1993. . Total seepage water in May 1996 was 63 mm. Meteorological as well as plant data indicated that nitrate leaching losses were likely to occur during this time. In both years, 1996 and 1997, leaching occurred in July Ž 1996: 85 mm, 1997: 131 mm. Ž Table 2. , coinciding with a phase of vigorous plant growth so that the risk of nitrate leaching was small. The findings shown in Table 2 indicate that the impact of nitrate leaching in 1996 was more pronounced than in 1997. 2.5. Statistical analysis Data analysis was carried out using the statistical package SPSS Ž SPSS, 1993.. The comparison of means was conducted with the two-tailed Student’s t-test.
Table 2 Monthly precipitation Ž P ., mean air temperature ŽT ., actual evapotranspiration ŽEact., amount of seepage water ŽSW. during the growing period 1996 and 1997, and long-term average ŽÝ sum; B mean. P 1996 Žmm. P 1997 Žmm. Long-term average T 1996 Ž8C. T 1997 Ž8C. Long-term average Eact 1996 Žmm. Eact 1997 Žmm. SW 1996 Žmm. SW 1997 Žmm.
April
May
June
July
August
September
20.1 43.3 55.8 7.6 5.4 7.2 25 15 0 3
122.5 29.5 88.7 11.9 12.8 11.9 32 48 63 1
73.1 102.2 105.0 16.2 15.4 15.0 78 61 1 23
142.1 201.1 98.7 15.3 16.1 16.7 84 81 85 131
117.0 118.3 95.1 15.8 17.8 16.1 76 77 6 30
51.9 17.0 65.7 10.1 12.9 12.9 34 48 22 0
Ý 526.7 Ý 511.4 Ý 509.0 B 12.8 B 13.4 B 13.3 Ý 329 Ý 330 Ý 177 Ý 188
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3. Results 3.1. Fertilizer N recoÕery in potato foliage in EC 31 and EC 65 At EC 31, foliage dry matter production and N uptake in foliage differed markedly between 1996 and 1997, thus reflecting the adverse growing conditions during early developmental stages in 1996 Ž Table 3. . In 1996, observed N uptake in EC 31 was 24 kg N hay1 for broadcast application and 29 kg N hay1 for ridge application, both values being below the site specific NOy 3 N content at planting. N placement had a significant effect on N recovery. Application in the ridge led to a sharp increase of fertilizer N recovery, which was statistically significant Ž p - 0.05. at EC 31 and at EC 65 Ž 1996.. The fertilizer N recovery at EC 31 was 8.3% and 14.2% for broadcast and ridge application, respectively. Thus, the total uptake of fertilizer N was negligibly small. The distribution of labeled N in the soil profile at this sampling date showed no evidence of displacement within the root zone Ždata not shown. . In 1997, no differences in fertilizer N recovery as a function of N placement were observed ŽTable 3.. As for 1996, N uptake in EC 31 was below soil NOy 3 N content at planting. Taken together, the results indicate that N placement in the ridge had a positive effect on foliage dry matter production and N uptake in foliage during early developmental stages, which was more pronounced at EC 65 than EC 31. Annual effects were more pronounced than fertilizer treatment effects. 3.2. Fertilizer N recoÕery in potato foliage at EC 92 Fertilizer N recovery in foliage at final harvest was low, ranging from 6.1% to 8.4% Ž Table 4.. Although the effect of fertilizer treatment was negligibly Table 3 Potato foliage dry matter production, N uptake in foliage and fertilizer N recovery, as affected by N placement during early developmental stages Ž p: probability. Year
Treatment Žkg N hay1 .
Foliage dry matter production Ždt hay1 .
N uptake foliage Žkg N hay1 .
15
N recovery Ž%. p Ž%.
Sampling date: EC 31 1996 150 b a 150 r a 1997 150 b 150 r
4.7 4.8 12.0 12.8
24 29 64 69
8.3 14.2 14.6 14.1
0.01
Sampling date: EC 65 1996 150 b 150 r 1997 150 b 150 r
17.5 20.2 32.9 39.3
73 103 178 226
22.2 47.4 52.0 48.5
0.051
a
b: N application broadcast, r: N application in the ridge.
0.76
0.38
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Table 4 Potato foliage dry matter production, N uptake in foliage and fertilizer N recovery at EC 92, as affected by fertilizer placement and timing Year
Treatment Žkg N hay1 .
Foliage dry matter production Ždt hay1 .
N uptake foliage Žkg N hay1 .
15
1996
150 b a 150 r a 3=50 b 3=50 r 150 b 150 r 3=50 b 3=50 r
23.8 22.3 26.0 23.6 23.5 31.2 27.9 22.0
37 40 43 40 40 54 46 34
6.1 6.9 6.9 7.6 6.5 7.3 8.4 8.0
1997
a
N recovery Ž%.
b: N application broadcast, r: N application in the ridge.
small, a tendency for split application and application in the ridge to result in increased N recovery was noted. Treatments had only minor and inconsistent effects on foliage dry matter production and N uptake. Total N uptake in potato foliage at final harvest was low Ž 34–54 kg N hay1 . and the contribution of fertilizer N recovery in foliage to overall N recovery was hence of minor importance. This result was expected since most aboveground biomass had died off at final harvest, thus compensating for fertilizer-induced differences in dry matter production and fertilizer N uptake. 3.3. Fertilizer N recoÕery in tubers at EC 92 In 1996, tuber fresh weight ranged from 519 to 571 t hay1 Ž Table 5. , and was approximately 100 t hay1 lower than in 1997 Ž Table 5. . N uptake in tubers was Table 5 Tuber yield Žfresh weight., N uptake in tubers and fertilizer N recovery, as affected by N placement and timing at EC 92 Year
Treatment Žkg N hay1 .
Tuber yield Žfresh weight. Ždt hay1 .
N uptake tubers Žkg N hay1 .
15
1996
150 b a 150 r a 3=50 b 3=50 r 150 b a 150 r a 3=50 b 3=50 r
542 571 566 519 660 619 684 647
110 128 125 116 182 171 208 191
29.8 40.4 36.2 37.7 49.9 59.0 58.4 60.6
1997
a
b: N application broadcast, r: N application in the ridge.
N recovery Ž%.
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below fertilizer N supply in 1996, whereas N uptake exceeded N supply during the second trial season Ž1997.. Further, no consistent effects of timing and placement of fertilizer N on tuber yield and N uptake were observed. Clearly, the applied N amount Ž 150 kg N hay1 . was in a magnitude which masked these effects. Fertilizer N recovery was also strongly influenced by seasonal variations. Subsequent to low yielding conditions in 1996, 15 N recovery ranged from 29.8% to 40.4%, compared to higher recovery Ž 49.9–60.6%. obtained in 1997 Ž Table 5.. However, fertilizer N recovery was always below average if applied broadcast at planting Ž 1996: 29.8%; 1997: 49.9%. Ž Table 5. . Broadcast fertilizer application, carried out as three separate doses, led to considerable increases in 15 N recovery Ž1996: 36.2%; 1997: 58.4%. . If application was done in the ridge, the effect of timing was negligibly small and inconsistent. In summary, these data demonstrate that split fertilizer doses applied irrespective of placement, as well as single application in the ridge at planting were more effective than a single broadcast fertilizer application. Though a low fertilizer N recovery was recorded when the fertilizer was brought out as a single broadcast application at planting, tuber yield and N uptake were not negatively affected. Therefore, one may conclude that high fertilizer N uptake was not associated with high tuber yield.
Table 6 15 N recovery Ž%. in potato tubers, foliage and soil and total 15 N losses at EC 92, as affected by N placement and timing of labeled N ) application Placement of N application 1996 Broadcast
In the ridge
1997 Broadcast
In the ridge
)
Timing of N application
Tuber
Foliage
Soil in ridge
Soil between ridge
N losses
1st application labeled 2nd application labeled 3rd application labeled 1st application labeled 2nd application labeled 3rd application labeled
25.5 a 39.8 b 43.7 b 33.9 35.6 43.7
4.7 a 7.8 b 8.1 b 6.5 7.0 9.2
14.7 14.7 14.4 14.6 16.5 13.9
9.9 10.8 9.3 8.3 9.1 10.5
45.2 26.9 24.5 36.7 31.8 22.7
1st application labeled 2nd application labeled 3rd application labeled 1st application labeled 2nd application labeled 3rd application labeled
57.6 ab 52.1 a 65.6 b 61.4 61.6 58.7
8.4 9.0 7.8 7.8 8.8 7.2
12.9 12.1 9.4 12.3 10.8 9.7
8.7 9.1 9.4 8.1 8.3 9.2
12.4 17.7 7.8 10.4 10.5 15.2
Different letters indicate a significant difference at P - 0.05.
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3.4. Effects of split N dose application timing on N recoÕery in tubers, foliage and soil at EC 92 In order to study the effect of fertilizer placement and timing in detail,15 N recovery was determined in relation to the timing of split N doses. The most striking result was that in the first trial season; fertilizer N recovery in tubers and foliage increased when fertilizer was applied later in development Ž Table 6. . In 1996, the start N broadcast application resulted in N recovery of 25.5% in tubers. N application at emergence and at 20-cm plant height resulted in recovery of 39.8% and 43.7%, respectively Ž Table 6. . This tendency was also noted for fertilizer N recovery in potato foliage. N application in the ridge led to a higher 15 N recovery in tubers Ž 33.9%. derived from the first split dose as compared with broadcast application. Application at emergence and at 20-cm plant height resulted in a 15 N recovery of 35.6% and 43.7%, respectively. The low recovery of planting-applied fertilizer was most likely due to N immobilization during early growth stages Ž Table 2. . Disregarding these adverse growing conditions, placement of fertilizer N had a positive effect on 15 N recovery. In 1997, the effect of timing and placement of split doses had no consistent effect on 15 N recovery in tubers and foliage ŽTable 6. . Furthermore, fertilizer recovery in soil during both years remained almost unaffected by placement and timing of split doses.
4. Discussion Tuber yield and N uptake in potatoes was strongly influenced by seasonal effects. In 1996, yield potential was reduced due to a rainy period, which occurred during early growth stages and which induced severe damage by waterlogging. This is confirmed by the 1996 data of foliage dry matter production and foliage N uptake, revealing a substantial delay in early growth stages, as compared with results obtained in 1997 ŽTable 3. . The adverse effects of weather conditions on yield potential could not be compensated by treatment with N fertilizer. Although growing conditions were more favorable in the subsequent trial season, fertilizer treatments also failed to show consistent effects on tuber yield. Similarly, Neeteson et al. Ž 1989. and Walther Ž 1990. have demonstrated that, for potato production, site and seasonal effects on tuber yield and N uptake are more pronounced than N supply via fertilizer. Although soil NOy 3 N content in spring and tuber yield were relatively high in the second trial year Ž1997. as compared with the first Ž 1996. , 15 N recovery was higher in the second trial year Ž Tables 5 and 6. . These data provide strong evidence that high soil NOy 3 N content does not suppress the fertilizer N uptake of potatoes, and one may conclude that favorable growing conditions in 1997, which enhanced tuber growth, had a positive effect on fertilizer N recovery.
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In both trial years, placement of fertilizer increased foliage dry matter production and N uptake during early developmental stages Ž Table 3. , a temporary positive effect that could not be maintained until final harvest. This was not an unusual finding, since the above ground biomass had died off and was subject to decomposition processes Ž Table 4. . Regarding tuber yield and tuber N uptake, N availability during ripening was apparently sufficient to compensate for fertilizer-induced variation in plant growth in early growth stages. Therefore we can conclude that effects of fertilizer placement and timing were masked to a great extend by N uptake during late growth Ž Joern and Vitosh, 1995. . While total N uptake levels were comparable between treatments, fertilizer recovery in treatment N1 Ž150 kg N hay1 broadcast at planting. was below average, thus indicating an above average uptake of N released from soil ŽTable 5. . Under low-yield conditions Žtrial year 1996. , 15 N recovery was lower as compared with 15 N recovery under favorable conditions in 1997 Ž Table 5. , and may be attributed to leaching losses occurring in May 1996 Ž Table 2. . The possibility that leaching losses reduced fertilizer recovery in 1996 is confirmed by lower 15 N recovery level of nitrogen applied at planting, as compared with later N application ŽTable 6.. In addition, N recovery in 1996 subsequent to application at planting was lower with broadcast than with ridge application ŽTable 5 and 6. , indicating that in adverse growing conditions, placement of fertilizer reduced N losses. These results are in agreement with those of Benkenstein et al. Ž 1991. . Irrespective of year-specific level of 15 N recovery, N fertilizer placement had a positive effect when a single application was carried out at planting. Application in the ridge at planting resulted in increased 15 N recovery Žapproximately 10%., as compared with broadcast application at planting ŽTable 5. . When split fertilizer doses were applied, placement failed to have positive effects on average 15 N recovery or tuber yield Ž Table 5. . In addition, these results indicate that a large amount of fertilizer applied broadcast at planting increases the risk of unproductive fertilizer losses. These conclusions are support for the results of Roberts et al. Ž 1991. and Walther Ž 1995. . Summarized, it may be concluded that N fertilizer applied at planting plays a minor role on tuber yield formation. Tuber yield reached comparable levels whether planting-applied N was 150 or 50 kg N hay1 ŽTable 5. . The NOy 3 N content in soil and the release of soil borne N was clearly sufficient to meet the plant demands during early developmental stages. Comparable results have been found maize ŽSticksel et al., 1994.. Especially in late sown crops, where adequate soil temperature and soil moisture promote the release of soil borne N, low starter fertilizer dressings may be applied without adversely affecting the yield. These findings confirm that fertilizer recommendations should be based on soil nitrate values or tissue N content, taken shortly before the phase of vigorous growth and concomitant increases in plant N demand Ž Nitsch and Varis, 1991; Walther, 1995; MacKerron et al., 1993; Walther et al., 1996. .
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These data allow us to develop a design of a fertilizer strategy aimed at maximizing fertilizer uptake in potatoes. In order to make use of soil nitrate content at planting and N released during early developmental stages, fertilization should begin with a moderate dressing. Application in the ridge reduces further the risk of unproductive N losses via leaching or denitrification during this stage. A second application should take place when potato plants reach 10–20-cm height. It is at this stage that N demand sharply rises and supplemental fertilization is necessary. Fertilizer placement for the second application is of minor importance.
Acknowledgements The scientific activities of the FAM Research Network on Agroecosystems are financially supported by the German Federal Ministry of Education and Research ŽBMBF 0339370.. Overhead costs of the Research Station Scheyern are funded by the Bavarian State Ministry for Science, Research and the Arts.
References Benkenstein, H., Schenk, R., Kruger, W., 1991. Ertragsbildung, N-Aufnahme und Ausnutzung ¨ von 15 N-markiertem Ammoniumsulfat durch Kartoffeln unter Berucksichtigung von ¨ Fahrspurverdichtungen und Dungerplazierung. Arch. Acker-Pflanzenbau Bodenkund. 35 Ž6., ¨ 435–441. Burton, W.G., 1989. The Potato. Longman Scientific and Technical, Harlow, England. Heuwinkel, H., 1999. N2-Fixierung von Kornerleguminosen: Aussagekraft und Weiterentwicklung ¨ vorhandener Messmethoden am Beispiel Lupinus albus L. PhD thesis, TU Munchen¨ Weihenstephan, Germany. Himken, M., 1995. Einfluß plazierter N-Dungung zu Mais und Kartoffeln auf die N-Effizienz und ¨ das Sproß-und Wurzelwachstum. PhD thesis, University Hannover, Germany. Joern, B.C., Vitosh, M.L., 1995. Influence of applied nitrogen on potato: Part II. Recovery and partitioning of applied nitrogen. Am. Potato J. 72, 73–84. MacKerron, D.K.L., Young, M.W., Davies, H.V., 1993. A method to optimize N—application in relation to soil supply of N, and yield of potato. Plant Soil 154, 139–144. ¨ Maidl, F.-X., 1995. Uberlegungen zu einer gezielteren Stickstoffdungung. Kartoffelbau 46, 56–58. ¨ Meier, U., 1997. Growth stages of mono- and dicotyledonous plants. Federal Biological Research Centre of Agriculture and Forestry. Blackwell, Berlin. Neeteson, J.J., 1995. Nitrogen management for intensively grown arable crops and field vegetables. In: Bacon, P.E. ŽEd.., Nitrogen Fertilization in the Environment. Marcel Dekker, NY, pp. 295–325. Neeteson, J.J., Greenwood, D.J., Draycott, A., 1989. Model calculations of nitrate leaching during the growth period of potatoes. Neth. J. Agric. Sci. 37, 237–256. Nitsch, A., Varis, E., 1991. Nitrate estimates using the Nitrachek test for precise N-fertilization during plant growth and after harvest, for quality testing of potato tubers. Potato Res. 34 Ž2., 95–105.
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Riess, F., 1993. Untersuchungen zur Nitratauswaschung nach mineralischer und organischer Dungung von Ackerland und Grunland mittels der Saugkerzenmethode. PhD thesis, TU ¨ ¨ Munchen-Weihenstephan, Germany. ¨ Roberts, S., Cheng, H.H., Farrow, F.O., 1991. Potato uptake and recovery of nitrogen-15 enriched ammonium nitrate from periodic applications. Agron. J. 83, 378–381. Ruser, R., Flessa, H., Schilling, R., Steindl, H., Beese, F., 1998. Soil compaction and fertilization effects on nitrous oxide and methane fluxes in potato fields. Soil Sci. Soc. Am. J. 62, 1587–1595. Schmidtke, K., Rauber, R., Stubbe, B., Homburg, M., Heckemeier, K., 1999. Wurzelwachstum von Kartoffeln. Kartoffelbau 50 Ž1r2., 13–15. SPSS, 1993. SPSS for Windows: User’s Guide, Release 6.0. SPSS, Chicago, USA. Sticksel, E., Maidl, F.-X., Fischbeck, G., 1994. Reduzierung des Nitrataustrags unter Silomais auf Boden hoher N-Austragsgefahrdung durch angepaßte Dungungstrategien. Agrobiol. Res. 47, ¨ ¨ ¨ 324–334. Walther, U., 1990. Ertrag und Qualitat des Nmin-Gehaltes des ¨ von Kartoffeln in Abhangigkeit ¨ Bodens sowie des Zeitpunktes und der Hohe Landw. Schweiz 3 Ž6., ¨ der Stickstoffdungung. ¨ 323–330. Walther, U., 1995. Stickstoffentzug und N-Ausnutzung einiger Kulturen. Agrarforschung 2 Ž11–12., 508–511. Walther, U., Schubiger, F.X., Jaggli, F., 1996. N-Aufnahme durch Kartoffeln und Nmin-Gehalte ¨ des Bodens. Agrarforschung 3 Ž2., 61–64. Westermann, D.T., Sojka, R.E., 1996. Tillage and nitrogen placement effects on nutrient uptake by potato. Soil Sci. Soc. Am. J. 60, 1448–1453.
Potato uptake and recovery of nitrogen 15 N-enriched ammonium nitrate F.-X. Maidl ) , H. Brunner, E. Sticksel Technical UniÕersity of Munich, D-85350 Freising-Weihenstephan, Germany
Abstract Tuber yield and nitrogen uptake in potatoes were recorded during 1996 and 1997 in Southern Bavaria. Recovery of applied fertilizer nitrogen was measured by using 15 N Ž15 NH 415 NO 3 .. Nitrogen fertilizer was brought out either broadcast or in the ridge; 150 kg N hay1 were applied either at planting or in split doses of 50 kg N hay1 Žat planting, emergence and at 20-cm plant height.. Due to unfavorable conditions, tuber yield and fertilizer N recovery were lower in 1996 as compared with 1997. Fertilizer N recovery in plant biomass Žtuber and foliage. ranged from 35.9% to 68.5% at growth stage EC 79; the main fraction was allocated to tubers. Placement of fertilizer N in the ridge had a positive effect on N recovery, when the total N amount was applied at planting. In broadcast application, fertilizer N recovery was higher when the fertilizer doses were split, as compared with a single broadcast application at planting. When fertilizer N was applied in split doses, the effect of N placement became negligibly small. Fertilizer N recovery in soil ranged from 19.5% to 24.6%, and total recovery ranged from 60.1% to 88.0%. Rainfall between planting and plant emergence, and conditions restricting plant development in early developmental stages were related with unaccounted fertilizer N losses. Therefore, the positive effects of split N applications or fertilizer placement are most likely to occur under unfavorable growing conditions. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Potato; Nitrogen fertilizer; Labeled fertilizer; Yield; Nitrogen uptake; Nitrogen efficiency
1. Introduction The risk of nitrogen ŽN. losses in potato fields is relatively high Ž Neeteson, 1995., due to crop specific effects, i.e. long-lasting early developmental stage with a low N uptake, low amount and density of roots especially between the )
Corresponding author. Fax: q49-8161-714511. E-mail address: [email protected] ŽF.-X. Maidl..
0016-7061r02r$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 1 6 - 7 0 6 1 Ž 0 1 . 0 0 1 0 2 - 1
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ridges, and low total N uptake at harvest Ž Burton, 1989; Himken, 1995; Maidl, 1995; Schmidtke et al., 1999.. In addition to N losses via leaching, investigations conducted by the FAM Research Network on Agroecosystems have revealed that gaseous losses may also have a significant impact on potatoes. In particular, compacted zones between the ridges are susceptible to nitrous oxide emissions ŽRuser et al., 1998.. The most promising approach to minimize N losses is to improve the utilization of applied fertilizer nitrogen. Westermann and Sojka Ž 1996. emphasize the advantages of fertilizer placement in the ridge. MacKerron et al. Ž 1993. and Walther et al. Ž 1996. recommend low start N dressings, in order to take into account the release of soil borne N when calculating total N amount. Maidl Ž1995. emphasizes the importance of a well developed root system in row crops to prevent N losses. The goal of the present study was to examine the impact of N fertilizer timing and placement on N utilization in potatoes. Field trials were performed on soils representative for potato crop regions in Southern Bavaria. Fertilizer N performance was examined by using double tagged 15 N enriched NH 4 NO 3. 2. Material and methods 2.1. Trial sites Two-year field trials were conducted at the Research Station Scheyern in Southern Bavaria. A detailed description of the Research Station Scheyern and the FAM Research Network on Agroecosystems is given in the introduction of this special issue. In 1996, the soil was a fine-loamy Dystric Eutrochrept and root growth was limited by underlying gravel material in 60-cm depth. In 1997, the trial plots had a higher sand content and no layers in the profile restricted root growth. Total N in topsoil was 0.15% and 0.11% in 1996 and in 1997, respectively. The average plant-available water storage capacity was estimated at approximately 100 mm, with a total water storage capacity of 160 mm in 1996. In 1997, these values were 70 and 100 mm, respectively. At planting, the y1 Ž NOy 0–60 cm, 1996. and 104 kg N hay1 3 N content in soil was 54 kg N ha Ž0–90 cm, 1997. . 2.2. Layout and management of the trials Potato planting took place at April 21, 1996 and April 25, 1997. The planting density was 4.5 tubers my2 Žcv. ‘Agria’. and the distance between ridges was 0.75 m. Plant protection during the vegetation period was applied as necessary. The description of growth stages ŽEC. followed the scheme of Meier Ž 1997. . The experimental layout was a completely randomized block design with four replications. Micro-plot size was 3 m2. The plots were bordered by iron plates to
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a depth of 45 cm to prevent lateral interactions, thus covering the main rooting zone. The total amount of fertilizer N utilized was 150 kg N hay1, applied either broadcast or in the ridge, and applied either as a single dose Ž 150 kg N hay1 . at planting or split into three doses of 50 kg N hay1 each. When applied in split doses, the third application was broadcast since foliage hindered application in the ridge. The timing of fertilizer application is shown in Table 1. The amount of labeled nitrogen Ž15 NH 415 NO 3 , 99% purity; NIRDIMT, Cluj, Napoca, Romania. used was 1 g N my2 , whereby the compound was dissolved and applied with a watering can. Additional 30-m2 plots were treated identically. N content in tubers and foliage were comparable on micro- and normal plots but border effects on tuber yield occurred on micro-plots. Therefore, tuber yield was determined on normal plots. 2.3. 15N-isotope measurements Total fresh weight of tubers was measured at EC 65 Ž treatments N1, N2. and EC 79. A small amount was taken from each sample, chopped, dried at 60 8C and pulverized in a Vibratory Disc Mill RS 100 ŽRetsch, Germany. . 15 N was measured with a mass spectrometer ŽANCA-MS, Europe Scientific 20-20, UK. , following the analytical and mathematical procedures of Heuwinkel Ž 1999. . The percentage fertilizer N uptake was derived from the hand harvested tubers and foliage on micro-plots and the fertilizer N uptake Ž kg N hay1 . was determined from the tuber yield obtained on normal plots. Potato foliage was harvested in EC 31, EC 65 Ž treatments N1, N2. and in EC 79. Tubers were analyzed as previously described. Soil samples were collected in EC 31, EC 65 Ž treatments N1, N2. and in EC 79. In order to consider fertilizer placement effects, samples were defined as
Table 1 Amount Žkg N hay1 ., timing and placement of fertilizer N and timing of labeled N application Treatment N1 N2 N3 N4 N5 N6 N7 N8
Placement broadcast ridge broadcast
ridge
Timing Planting
Emergence
Plant height 20 cm
150 Žlabeled. 150 Žlabeled. 50 Žlabeled. 50 50 50 Žlabeled. 50 50
– – 50 50 Žlabeled. 50 50 50 Žlabeled. 50
– – 50 50 50 Žlabeled. 50 50 50 Žlabeled.
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being Ain the ridgeB and Abetween the ridgeB. Eight replications were done with a Purckhauer auger, at sampling depths of 60 cm in 1996 and 80 cm for 1997, ¨ respectively. The soil samples were divided into 20-cm sections, and 15 N content was estimated by setting the bulk density to 1.3 g cmy3 for the upper 20 cm of the ridge, and 1.5 g cmy3 for the remainder. 2.4. Weather and plant growth In May 1996, the total rainfall was 122.5 mm and thus in the range of soil water storage capacity ŽTable 2.. The interval between 15 N application at planting and the onset of the rainy period was 10 days and plants had not yet emerged. Actual evapotranspiration and amount of seepage water was calculated according to the method of Riess Ž1993. . Total seepage water in May 1996 was 63 mm. Meteorological as well as plant data indicated that nitrate leaching losses were likely to occur during this time. In both years, 1996 and 1997, leaching occurred in July Ž 1996: 85 mm, 1997: 131 mm. Ž Table 2. , coinciding with a phase of vigorous plant growth so that the risk of nitrate leaching was small. The findings shown in Table 2 indicate that the impact of nitrate leaching in 1996 was more pronounced than in 1997. 2.5. Statistical analysis Data analysis was carried out using the statistical package SPSS Ž SPSS, 1993.. The comparison of means was conducted with the two-tailed Student’s t-test.
Table 2 Monthly precipitation Ž P ., mean air temperature ŽT ., actual evapotranspiration ŽEact., amount of seepage water ŽSW. during the growing period 1996 and 1997, and long-term average ŽÝ sum; B mean. P 1996 Žmm. P 1997 Žmm. Long-term average T 1996 Ž8C. T 1997 Ž8C. Long-term average Eact 1996 Žmm. Eact 1997 Žmm. SW 1996 Žmm. SW 1997 Žmm.
April
May
June
July
August
September
20.1 43.3 55.8 7.6 5.4 7.2 25 15 0 3
122.5 29.5 88.7 11.9 12.8 11.9 32 48 63 1
73.1 102.2 105.0 16.2 15.4 15.0 78 61 1 23
142.1 201.1 98.7 15.3 16.1 16.7 84 81 85 131
117.0 118.3 95.1 15.8 17.8 16.1 76 77 6 30
51.9 17.0 65.7 10.1 12.9 12.9 34 48 22 0
Ý 526.7 Ý 511.4 Ý 509.0 B 12.8 B 13.4 B 13.3 Ý 329 Ý 330 Ý 177 Ý 188
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3. Results 3.1. Fertilizer N recoÕery in potato foliage in EC 31 and EC 65 At EC 31, foliage dry matter production and N uptake in foliage differed markedly between 1996 and 1997, thus reflecting the adverse growing conditions during early developmental stages in 1996 Ž Table 3. . In 1996, observed N uptake in EC 31 was 24 kg N hay1 for broadcast application and 29 kg N hay1 for ridge application, both values being below the site specific NOy 3 N content at planting. N placement had a significant effect on N recovery. Application in the ridge led to a sharp increase of fertilizer N recovery, which was statistically significant Ž p - 0.05. at EC 31 and at EC 65 Ž 1996.. The fertilizer N recovery at EC 31 was 8.3% and 14.2% for broadcast and ridge application, respectively. Thus, the total uptake of fertilizer N was negligibly small. The distribution of labeled N in the soil profile at this sampling date showed no evidence of displacement within the root zone Ždata not shown. . In 1997, no differences in fertilizer N recovery as a function of N placement were observed ŽTable 3.. As for 1996, N uptake in EC 31 was below soil NOy 3 N content at planting. Taken together, the results indicate that N placement in the ridge had a positive effect on foliage dry matter production and N uptake in foliage during early developmental stages, which was more pronounced at EC 65 than EC 31. Annual effects were more pronounced than fertilizer treatment effects. 3.2. Fertilizer N recoÕery in potato foliage at EC 92 Fertilizer N recovery in foliage at final harvest was low, ranging from 6.1% to 8.4% Ž Table 4.. Although the effect of fertilizer treatment was negligibly Table 3 Potato foliage dry matter production, N uptake in foliage and fertilizer N recovery, as affected by N placement during early developmental stages Ž p: probability. Year
Treatment Žkg N hay1 .
Foliage dry matter production Ždt hay1 .
N uptake foliage Žkg N hay1 .
15
N recovery Ž%. p Ž%.
Sampling date: EC 31 1996 150 b a 150 r a 1997 150 b 150 r
4.7 4.8 12.0 12.8
24 29 64 69
8.3 14.2 14.6 14.1
0.01
Sampling date: EC 65 1996 150 b 150 r 1997 150 b 150 r
17.5 20.2 32.9 39.3
73 103 178 226
22.2 47.4 52.0 48.5
0.051
a
b: N application broadcast, r: N application in the ridge.
0.76
0.38
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Table 4 Potato foliage dry matter production, N uptake in foliage and fertilizer N recovery at EC 92, as affected by fertilizer placement and timing Year
Treatment Žkg N hay1 .
Foliage dry matter production Ždt hay1 .
N uptake foliage Žkg N hay1 .
15
1996
150 b a 150 r a 3=50 b 3=50 r 150 b 150 r 3=50 b 3=50 r
23.8 22.3 26.0 23.6 23.5 31.2 27.9 22.0
37 40 43 40 40 54 46 34
6.1 6.9 6.9 7.6 6.5 7.3 8.4 8.0
1997
a
N recovery Ž%.
b: N application broadcast, r: N application in the ridge.
small, a tendency for split application and application in the ridge to result in increased N recovery was noted. Treatments had only minor and inconsistent effects on foliage dry matter production and N uptake. Total N uptake in potato foliage at final harvest was low Ž 34–54 kg N hay1 . and the contribution of fertilizer N recovery in foliage to overall N recovery was hence of minor importance. This result was expected since most aboveground biomass had died off at final harvest, thus compensating for fertilizer-induced differences in dry matter production and fertilizer N uptake. 3.3. Fertilizer N recoÕery in tubers at EC 92 In 1996, tuber fresh weight ranged from 519 to 571 t hay1 Ž Table 5. , and was approximately 100 t hay1 lower than in 1997 Ž Table 5. . N uptake in tubers was Table 5 Tuber yield Žfresh weight., N uptake in tubers and fertilizer N recovery, as affected by N placement and timing at EC 92 Year
Treatment Žkg N hay1 .
Tuber yield Žfresh weight. Ždt hay1 .
N uptake tubers Žkg N hay1 .
15
1996
150 b a 150 r a 3=50 b 3=50 r 150 b a 150 r a 3=50 b 3=50 r
542 571 566 519 660 619 684 647
110 128 125 116 182 171 208 191
29.8 40.4 36.2 37.7 49.9 59.0 58.4 60.6
1997
a
b: N application broadcast, r: N application in the ridge.
N recovery Ž%.
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below fertilizer N supply in 1996, whereas N uptake exceeded N supply during the second trial season Ž1997.. Further, no consistent effects of timing and placement of fertilizer N on tuber yield and N uptake were observed. Clearly, the applied N amount Ž 150 kg N hay1 . was in a magnitude which masked these effects. Fertilizer N recovery was also strongly influenced by seasonal variations. Subsequent to low yielding conditions in 1996, 15 N recovery ranged from 29.8% to 40.4%, compared to higher recovery Ž 49.9–60.6%. obtained in 1997 Ž Table 5.. However, fertilizer N recovery was always below average if applied broadcast at planting Ž 1996: 29.8%; 1997: 49.9%. Ž Table 5. . Broadcast fertilizer application, carried out as three separate doses, led to considerable increases in 15 N recovery Ž1996: 36.2%; 1997: 58.4%. . If application was done in the ridge, the effect of timing was negligibly small and inconsistent. In summary, these data demonstrate that split fertilizer doses applied irrespective of placement, as well as single application in the ridge at planting were more effective than a single broadcast fertilizer application. Though a low fertilizer N recovery was recorded when the fertilizer was brought out as a single broadcast application at planting, tuber yield and N uptake were not negatively affected. Therefore, one may conclude that high fertilizer N uptake was not associated with high tuber yield.
Table 6 15 N recovery Ž%. in potato tubers, foliage and soil and total 15 N losses at EC 92, as affected by N placement and timing of labeled N ) application Placement of N application 1996 Broadcast
In the ridge
1997 Broadcast
In the ridge
)
Timing of N application
Tuber
Foliage
Soil in ridge
Soil between ridge
N losses
1st application labeled 2nd application labeled 3rd application labeled 1st application labeled 2nd application labeled 3rd application labeled
25.5 a 39.8 b 43.7 b 33.9 35.6 43.7
4.7 a 7.8 b 8.1 b 6.5 7.0 9.2
14.7 14.7 14.4 14.6 16.5 13.9
9.9 10.8 9.3 8.3 9.1 10.5
45.2 26.9 24.5 36.7 31.8 22.7
1st application labeled 2nd application labeled 3rd application labeled 1st application labeled 2nd application labeled 3rd application labeled
57.6 ab 52.1 a 65.6 b 61.4 61.6 58.7
8.4 9.0 7.8 7.8 8.8 7.2
12.9 12.1 9.4 12.3 10.8 9.7
8.7 9.1 9.4 8.1 8.3 9.2
12.4 17.7 7.8 10.4 10.5 15.2
Different letters indicate a significant difference at P - 0.05.
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3.4. Effects of split N dose application timing on N recoÕery in tubers, foliage and soil at EC 92 In order to study the effect of fertilizer placement and timing in detail,15 N recovery was determined in relation to the timing of split N doses. The most striking result was that in the first trial season; fertilizer N recovery in tubers and foliage increased when fertilizer was applied later in development Ž Table 6. . In 1996, the start N broadcast application resulted in N recovery of 25.5% in tubers. N application at emergence and at 20-cm plant height resulted in recovery of 39.8% and 43.7%, respectively Ž Table 6. . This tendency was also noted for fertilizer N recovery in potato foliage. N application in the ridge led to a higher 15 N recovery in tubers Ž 33.9%. derived from the first split dose as compared with broadcast application. Application at emergence and at 20-cm plant height resulted in a 15 N recovery of 35.6% and 43.7%, respectively. The low recovery of planting-applied fertilizer was most likely due to N immobilization during early growth stages Ž Table 2. . Disregarding these adverse growing conditions, placement of fertilizer N had a positive effect on 15 N recovery. In 1997, the effect of timing and placement of split doses had no consistent effect on 15 N recovery in tubers and foliage ŽTable 6. . Furthermore, fertilizer recovery in soil during both years remained almost unaffected by placement and timing of split doses.
4. Discussion Tuber yield and N uptake in potatoes was strongly influenced by seasonal effects. In 1996, yield potential was reduced due to a rainy period, which occurred during early growth stages and which induced severe damage by waterlogging. This is confirmed by the 1996 data of foliage dry matter production and foliage N uptake, revealing a substantial delay in early growth stages, as compared with results obtained in 1997 ŽTable 3. . The adverse effects of weather conditions on yield potential could not be compensated by treatment with N fertilizer. Although growing conditions were more favorable in the subsequent trial season, fertilizer treatments also failed to show consistent effects on tuber yield. Similarly, Neeteson et al. Ž 1989. and Walther Ž 1990. have demonstrated that, for potato production, site and seasonal effects on tuber yield and N uptake are more pronounced than N supply via fertilizer. Although soil NOy 3 N content in spring and tuber yield were relatively high in the second trial year Ž1997. as compared with the first Ž 1996. , 15 N recovery was higher in the second trial year Ž Tables 5 and 6. . These data provide strong evidence that high soil NOy 3 N content does not suppress the fertilizer N uptake of potatoes, and one may conclude that favorable growing conditions in 1997, which enhanced tuber growth, had a positive effect on fertilizer N recovery.
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In both trial years, placement of fertilizer increased foliage dry matter production and N uptake during early developmental stages Ž Table 3. , a temporary positive effect that could not be maintained until final harvest. This was not an unusual finding, since the above ground biomass had died off and was subject to decomposition processes Ž Table 4. . Regarding tuber yield and tuber N uptake, N availability during ripening was apparently sufficient to compensate for fertilizer-induced variation in plant growth in early growth stages. Therefore we can conclude that effects of fertilizer placement and timing were masked to a great extend by N uptake during late growth Ž Joern and Vitosh, 1995. . While total N uptake levels were comparable between treatments, fertilizer recovery in treatment N1 Ž150 kg N hay1 broadcast at planting. was below average, thus indicating an above average uptake of N released from soil ŽTable 5. . Under low-yield conditions Žtrial year 1996. , 15 N recovery was lower as compared with 15 N recovery under favorable conditions in 1997 Ž Table 5. , and may be attributed to leaching losses occurring in May 1996 Ž Table 2. . The possibility that leaching losses reduced fertilizer recovery in 1996 is confirmed by lower 15 N recovery level of nitrogen applied at planting, as compared with later N application ŽTable 6.. In addition, N recovery in 1996 subsequent to application at planting was lower with broadcast than with ridge application ŽTable 5 and 6. , indicating that in adverse growing conditions, placement of fertilizer reduced N losses. These results are in agreement with those of Benkenstein et al. Ž 1991. . Irrespective of year-specific level of 15 N recovery, N fertilizer placement had a positive effect when a single application was carried out at planting. Application in the ridge at planting resulted in increased 15 N recovery Žapproximately 10%., as compared with broadcast application at planting ŽTable 5. . When split fertilizer doses were applied, placement failed to have positive effects on average 15 N recovery or tuber yield Ž Table 5. . In addition, these results indicate that a large amount of fertilizer applied broadcast at planting increases the risk of unproductive fertilizer losses. These conclusions are support for the results of Roberts et al. Ž 1991. and Walther Ž 1995. . Summarized, it may be concluded that N fertilizer applied at planting plays a minor role on tuber yield formation. Tuber yield reached comparable levels whether planting-applied N was 150 or 50 kg N hay1 ŽTable 5. . The NOy 3 N content in soil and the release of soil borne N was clearly sufficient to meet the plant demands during early developmental stages. Comparable results have been found maize ŽSticksel et al., 1994.. Especially in late sown crops, where adequate soil temperature and soil moisture promote the release of soil borne N, low starter fertilizer dressings may be applied without adversely affecting the yield. These findings confirm that fertilizer recommendations should be based on soil nitrate values or tissue N content, taken shortly before the phase of vigorous growth and concomitant increases in plant N demand Ž Nitsch and Varis, 1991; Walther, 1995; MacKerron et al., 1993; Walther et al., 1996. .
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These data allow us to develop a design of a fertilizer strategy aimed at maximizing fertilizer uptake in potatoes. In order to make use of soil nitrate content at planting and N released during early developmental stages, fertilization should begin with a moderate dressing. Application in the ridge reduces further the risk of unproductive N losses via leaching or denitrification during this stage. A second application should take place when potato plants reach 10–20-cm height. It is at this stage that N demand sharply rises and supplemental fertilization is necessary. Fertilizer placement for the second application is of minor importance.
Acknowledgements The scientific activities of the FAM Research Network on Agroecosystems are financially supported by the German Federal Ministry of Education and Research ŽBMBF 0339370.. Overhead costs of the Research Station Scheyern are funded by the Bavarian State Ministry for Science, Research and the Arts.
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