Effects of drip irrigation regimes and basin irrigation on Nagpur mandarin agronomical and physiological performance

Agricultural Water Management 104 (2012) 79–88

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Effects of drip irrigation regimes and basin irrigation on Nagpur mandarin agronomical and physiological performance P. Panigrahi ∗ , A.K. Srivastava, A.D. Huchche National Research Centre for Citrus, P.O. Shankar Nagar, Nagpur 440 010, Maharastra, India

a r t i c l e

i n f o

Article history: Received 25 August 2011 Accepted 27 November 2011 Available online 21 December 2011 Keywords: Citrus Water management Soil chemical changes Leaf nutrient composition Leaf physiology Yield parameters

a b s t r a c t The scarcity of irrigation water is one of the major causes of low productivity and decline of citrus orchards. The present study was planned with a hypothesis that the drip irrigation (DI) could save a substantial amount of water over surface irrigation, besides improving the yield of citrus plants. The experiment was conducted for 3 seasons during 2006–2009, with ‘Nagpur’ mandarin (Citrus reticulata Blanco) plants budded on rough lemon (Citrus Jambhiri Lush) rootstock in central India. The effects of DI and basin irrigation (BI) on soil chemical properties and crop responses were studied. DI was scheduled everyother-day at 40%, 60%, 80% and 100% of the alternate day cumulative evaporation (Ecp ) measured in Class-A evaporation pan. DI except irrigation at 40% Ecp proved superior to BI, producing more growth and fruit yield of plants. The higher plant growth was recorded with higher regime of DI. The maximum fruit yield in DI at 80% Ecp , using 29% less irrigation water resulted in 111% improvement in irrigation water productivity under this treatment over BI. The heavier fruits, with lower acidity and higher total soluble solids, were harvested in DI at 80% Ecp compared with BI. The significant variation of soil water content at 0–0.2 m depth under DI indicated the confinement of effective root zone of the plants in top 0.2 m soil. The maximum rate of net-photosynthesis, stomatal conductance and transpiration in leafs was recorded in DI at 100% Ecp . However, the plants under DI at 80% Ecp exhibited the highest leaf water use efficiency. The maximum salinity build-up with highest decrease in pH was observed in 0–0.2 m soil under DI, whereas the salinity development was prominent in 0.4–0.6 m soil with an increase in pH under BI. The gain in available macronutrients (N, P and K) and loss of micronutrients (Fe, Mn, Cu and Zn) in soil followed the similar trend of EC. The leaf nutrient (N, P, K, Fe, Mn, Cu and Zn) analysis revealed that DI produced significantly (P < 0.05) higher concentration of macronutrients in leafs than that with basinirrigated plants. However, the effect of irrigation on micronutrients in leafs was statistically insignificant. Overall, these results reveal that the application of optimum quantity of water through DI (80% Ecp ) could impose desirable water stress on ‘Nagpur’ mandarin plants, improving their yield and fruit quality, without producing the higher vegetative growth. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Availability of irrigation water is the major constraint to crop production in many parts of the world. The advent of drip irrigation (DI) is a significant technological improvement in irrigation system, which helps to combat water scarcity in agriculture. In recent years, the adoption of DI gains momentum owing to its positive impact on water saving, productivity and quality of produces in many crops. Citrus, a high water requiring evergreen perennial fruit crop, is grown in tropical and sub-tropical regions of the world. The suboptimum soil water in root zone of the plant during any stage of

∗ Corresponding author. Tel.: +91 712 2500813; fax: +91 712 2500813. E-mail addresses: [email protected], pra73 [email protected] (P. Panigrahi). 0378-3774/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2011.11.018

its growth drastically reduces the fruit yield (Davies and Albrigo, 1994). Irrigation is practiced in all most all citrus groves of the world to avoid water stress in cropping season. Efficient use of irrigation water is a prerequisite for successful cultivation of citrus in water scarcity areas. Basin is the most common method of irrigation used in perennial fruit crops including citrus, though the use of DI has been increased in recent years (Fereres et al., 2003). The role of DI in improving plant growth and fruit yield along with water economy is well recognized in different citrus cultivars grown in various regions of the world (Germanà et al., 1992). Irrigation scheduling is vital for improving the efficiency of DI system, as excessive or sub-optimum water supply has detrimental effects on yield and fruit quality of citrus (Davies and Albrigo, 1994). Various methods have been proposed for DI scheduling of citrus based on soil, environmental and plant physiological parameters. Chartzoulakis et al. (1999) reported

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that ‘Bonanza’ orange growth and fruit yield did not differ in −0.01 and −0.05 MPa soil water potential treatments, but were significantly reduced at −1.5 MPa soil water potential. Irrigation based on pan coefficient that varied from 0.6 to 1.2 by 0.2 increments did not show any significant result in relation to yield performance of ‘Washington navel’ orange (Kanber et al., 1996). Abu-Awwad (2001) compared the lemon tree performance under different irrigation regimes: 0.0%, 25%, 50%, 75%, 100% and 150% Class-A pan evaporation, and reported that irrigation at 100% evaporation produced the maximum plant growth and highest fruit yield. Velez et al. (2007), measuring maximum daily trunk shrinkage (MDS), concluded that maintaining MDS ratio (MDS value of any treatment relative to MDS of fully irrigated plant) at 125% was useful for deficit irrigation scheduling of ‘Clementina de Nules’ orange plant. GarcíaTejero et al. (2010) demonstrated that irrigation at 0.5, 0.65, 0.75 and 1.0 water stress index (ratio of actual volume of water supply to estimated crop evapotranspiration) did not impact significantly on tree yield, but rather affected the fruit qualities of ‘Salustiana’ orange. ‘Nagpur’ mandarin (Citrus reticulata Blanco), a commercially important citrus cultivar, is grown in around 0.2 million hectares of central India (Singh and Srivastava, 2004). Irrigation is practiced in post rainy season (November–June) for higher productivity of the crop. The soil type in citrus orchards of central India is predominantly cracking black clay soils (Vertisols), with 35–60% clay content (Srivastava et al., 2000). The crop is basically irrigated by basin and/or furrow method using ground water in this region. For last few years, the ground water level has declined alarmingly, creating water shortage in citrus orchards. On the other hand, the area under citrus production is increasing exponentially due to the higher economic return from this crop compared with other crops (Gangwar et al., 1997). Farmers are more concerned with increasing yield of ‘Nagpur’ mandarin using less water, which could be achieved through adoption of efficient irrigation system like drip irrigation in this crop. The nutritional status of plant is one of the important indicators of its health and productivity. Nitrogen is associated with proper growth, flower initiation, and fruit drop, development and quality of citrus plants (Davies and Albrigo, 1994). Phosphorous is essential for better root development and proper functioning of cell energy systems, whereas potassium plays a major role in regulating ionic balances in the cell and for developing adequate fruit size and regulating peel thickness (Davies and Albrigo, 1994). Micronutrients such as iron, manganese, copper and zinc are greatly necessary for proper enzyme functioning and are present in small quantities in the citrus plant (Singh and Sharma, 2000). Deficiency in any one of the essential nutrients prevents the metabolic activity resulting in reduced vegetative growth and less yield and may ultimately be responsible for complete decline of the plants. The availability of required nutrients in soil plays a major role in nutrients uptake by plants. However, the soil chemical properties (pH, EC, etc.) and crop management practices including irrigation plays an important role in governing the nutrients availability to plants (Amberger, 2006). Srivastava et al. (1999) reported that the sub-optimum level of available N, P and micronutrients (Fe, Mn, Cu, and Zn) in soils with high pH (>7.5), coupled with the higher loss of nutrients from effective root zone of plants through leaching under surface irrigation causes low nutrients acquisition by mandarin plants in central India. Leaf nutrients analysis is an effective tool for monitoring the nutritional status of citrus plant (Tucker et al., 1995). The plant water status regulates many physiological processes including leaf physiology, which affects crop productivity in citrus (Gomes et al., 2004). Information on leaf physiological parameters (net-photosynthesis, stomatal conductance and transpiration) in response to irrigation offers a better understanding of plant–water relationship and its effect on crop performance under water deficit

condition (Vu and Yelenosky, 1988). Moreover, this information could be used for optimizing irrigation scheduling in citrus. The studies on nutrients uptake, leaf physiological parameters, plant growth and fruit yield response of mandarin cultivars of citrus to drip irrigation in clay soils are very limited worldwide. With this background, research was carried out to develop the optimal irrigation schedule in relation to vegetative growth, yield and leaf nutrient composition of ‘Nagpur’ mandarin, by comparative evaluation of pan evaporation-based DI with conventional basin irrigation method under a hot sub-humid tropical climate of central India. 2. Materials and methods 2.1. Experimental site The field experiment was conducted at the Research Farm of National Research Centre for Citrus, Nagpur (latitude 21◦ 08 45 N, longitude 79◦ 02 15 E, 340 m above mean sea level), Maharashtra state, India. The citrus plant used in the study was ‘Nagpur’ mandarin (C. reticulata Blanco) budded on rough lemon (Citrus jambhiri Lush) rootstock. The experiment was started with 5-yearold plant and continued for three consecutive years (2006–2007, 2007–2008 and 2008–2009) with the same plantation. The plant spacing was 6 m × 6 m. At the beginning of experiment, the average height, canopy spread diameter, stock girth diameter and scion girth diameter of the plants were 2.7 m, 2.2 m, 90 mm and 84 mm, respectively. The texture of experimental soil was clay. Basic soil physical properties of different horizons are presented in Table 1. The soil was alkaline in nature. The cation exchange capacity of the soil was 42.8 cmol(p+ ) kg−1 . The important chemical properties of different soil layers are presented in Table 2. The irrigation water was free from salinity (EC, 0.74 dS m−1 ) and alkalinity (pH 7.1). The mean concentrations of Ca2+ , Mg2+ , Na+ , K+ , SO4 −2 , HCO3 − , and Cl− in irrigation water during irrigation seasons were 1.4, 1.1, 1.2, 0.4, 0.6, 0.7, 3.0, and 1.2 mequiv. l−1 , respectively. The water level in the wells situated at 30–50 m distance from the experimental plot was 12–13 m deep from ground surface. The weather data were collected at the meteorological observatory of the Research Centre present at about 500 m away from the experimental site. The climate is characterized as sub-humid tropical, with hot and dry summers. Mean air temperature varies from 14.1 ◦ C in winter to 35.7 ◦ C in summer. However, the maximum daily temperature in summer seldom rises up to 45 ◦ C. The mean daily evaporation loss measured in USWB (United State Weather Bureau) Class-A pan ranges from 2.4 mm in December to as high as 13.2 mm in May. The mean annual rainfall of 810 mm is concentrated mostly (>90% of total rainfall) during July to October. However, in the experimental years, the mean annual rainfall and rainfall during irrigation season (November–June) were 796 mm and 15 mm, respectively. Mean monthly meteorological parameters during the experimental years are presented in Fig. 1. 2.2. Treatments and layout Five irrigation treatments applied to ‘Nagpur’ mandarin plants were DI at 40% alternate day cumulative Class-A pan evaporation data (40% Ecp ), DI at 60% Ecp , DI at 80% Ecp , DI at 100% Ecp and basin irrigation (BI). DI was scheduled every other day. A circular basin of radius 0.8 m, keeping the plant at the centre was made for basin irrigation. The peripheral ridge height of the basin was 0.3 m. The watering period was from early November to end of June in each year of the experiment. Area of the experimental block was 6480 m2 (72 m × 90 m), accommodating 180 mandarin plants in 15 rows. Each row contained 12 plants. The experimental design was

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Table 1 Physical properties of soil (0–0.9 m) at the experimental site. Soil depth (m)

0–0.2 0.2–0.4 0.4–0.6 0.6–0.9

Particle size distribution

BD (Mg m−3 )

Soil moisture characteristics

Sand (%)

Silt (%)

Clay (%)

Texture class

FC (%, v/v)

PWP (%, v/v)

32.3 31.0 34.7 32.0

24.7 22.5 23.4 25.4

43.0 46.5 41.9 42.6

Clay Clay Clay Clay

29.3 30.1 28.8 29.3

18.5 19.2 18.6 18.5

1.18 1.17 1.21 1.18

FC: field capacity (at −1500 kPa); PWP: permanent wilting point (−33 kPa); v/v: volume basis; BD: bulk density (dry weight basis). Table 2 Chemical properties of soil (0–0.9 m) at the experimental site. Soil depth (m)

0–0.2 0.2–0.4 0.4–0.6 0.6–0.9

EC (dS m−1 )

pH

0.84 0.72 0.64 0.66

7.8 7.5 7.3 7.4

Available macronutrients (mg kg−1 soil)

Available micronutrients (mg kg−1 soil)

N

P

K

Fe

Mn

Cu

Zn

115.0 98.3 45.5 32.4

10.0 4.5 2.1 0.8

144.0 102.8 67.5 32.4

18.2 11.1 5.2 1.6

9.4 3.2 1.1 0.7

1.1 0.6 0.2 0.1

0.7 0.4 0.2 0.1

randomized complete block, with four replicates per treatment. The entire block was divided into 4 equal size plots (18.0 m × 90.0 m) and each plot was again divided into 5 sub-plots (18.0 m × 18.0 m). Nine plants in three adjacent rows (3 plants in each row) in each sub-plot were taken as a replicated unit. Three plants present in the central line of each replicated plot were considered for data recording, so-called experimental plants. 2.3. Irrigation scheduling and crop management practices DI was imposed through two on-line 4 l h−1 pressure compensated emitters per plant, placed at 0.6 m away from plant stem. The water quantities applied under DI treatments were estimated using the following formula (Germanà et al., 1992):



Vid = 

D2 4



× Kp × Kc ×

E − R  cp e Ei

(1)

where Vid is the irrigation volume applied in each irrigation (l plant−1 ), D the mean plant canopy spread diameter measured in north–south and east–west directions (m), Kp the pan factor (0.7), Kc the crop coefficient (0.7) as suggested by Allen et al. (1998), Ecp the cumulative Class-A pan evaporation depth for two consecutive days (mm), Re the effective rainfall depth for corresponding 2 days (mm) and Ei the irrigation efficiency of drip system (90%). The total rainfall depth during the irrigation seasons was considered as effective rainfall, as drainage (surface runoff + deep percolation) induced

by each rainfall event was negligible within the experimental plots (Panigrahi et al., 2009). For BI, water was applied at 50% depletion of available soil water in 0–0.3 m soil layer. Irrigation water quantity required for BI was computed using the formula:

 Vib = (FC − RSM) × d × 

D2 4

 × 103

(2)

where Vid is the volume of irrigation water (l), FC the field capacity of soil (%, volume basis), RSM the required soil water content at 50% depletion of available soil water (24.2%, volume basis), d the depth of effective root zone (0.3 m) of 5- to 7-year-old ‘Nagpur’ mandarin plants as observed by Autkar et al. (1988) and D the mean plant canopy spread diameter measured in north–south and east–west directions (m). Irrigation was applied to each basin through flexible hosepipe. The volume of mean daily water applied per plant in various months of the study years under both drip and basin irrigation methods are presented in Table 3. The quantity of water applied per plant increased with increase in plant canopy spread diameter from 2006–2007 to 2008–2009. The water supply to each irrigation treatment was regulated by adjusting the operating hours with the help of water meters and gate valves provided at the inlet end of sub-mains. The recommended dose of fertilizers (600 g N as both urea and urea-phosphate, 200 g P2 O5 as urea-phosphate and 100 g K2 O as muriate of potash per plant) was uniformly applied in

Fig. 1. Mean meteorological parameters during the experimental years (2006–2009).

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Table 3 Water applied (l plant−1 day−1 ) for ‘Nagpur’ mandarin plants in different months under various irrigation treatments during 2006–2009. Year

Treatment

Months November

December

January

February

March

April

May

June

2006–2007

DI at 40% Ecp DI at 60% Ecp DI at 80% Ecp DI at 100% Ecp BI

4.9 7.4 9.9 12.4 13.6

4.4 6.6 8.8 11.0 12.0

6.9 10.3 13.8 17.2 18.7

7.5 11.3 15.0 18.8 20.7

11.4 17.2 23.0 28.6 32.7

15.9 23.8 31.8 39.7 44.5

17.3 26.0 34.7 43.4 53.1

18.9 28.3 37.8 47.2 56.8

2007–2008

DI at 40% Ecp DI at 60% Ecp DI at 80% Ecp DI at 100% Ecp BI

6.7 10.0 13.3 16.7 18.4

5.6 8.3 11.1 13.9 15.6

9.7 14.5 19.3 24.2 26.1

10.5 15.8 21.1 26.4 28.8

15.9 23.9 31.8 39.8 44.2

20.6 30.9 41.2 51.5 57.3

22.4 33.7 44.9 56.2 68.7

24.2 36.4 48.5 60.6 70.4

2008–2009

DI at 40% Ecp DI at 60% Ecp DI at 80% Ecp DI at 100% Ecp BI

7.9 11.8 15.7 19.6 21.8

6.5 9.8 13.0 16.3 17.9

12.2 18.4 24.5 30.6 34.2

13.4 20.0 26.7 33.4 36.8

18.9 28.4 37.9 47.3 52.8

25.9 38.8 51.8 64.7 70.1

28.2 42.4 56.5 70.6 76.8

28.7 43.1 57.4 71.8 80.1

DI: drip irrigation; BI: basin irrigation, Ecp : Class-A pan evaporation for two consecutive days.

all treatments (Srivastava and Singh, 1997). Ground floor of the experimental orchard was kept weed free and the plant protection measures against insect pests and diseases were adopted uniformly for all plants in the experimental block, following the recommendations given for ‘Nagpur’ mandarin cultivation in central India. 2.4. Measurements and analysis The volumetric soil water content was monitored twice in a week (1 day prior and 1 day after irrigation) using a neutron moisture meter (Troxler Model-4300, USA). The water content was measured at 0–0.2 m, 0.2–0.4 m, and 0.4–0.6 m soil depths, installing 2 access tubes per plant (3 plants per treatment) at a distance of 0.45 and 0.90 m from the plant stem. The depth wise mean soil water content was calculated. Four number of ceramic cup tensiometers per plant (3 plants per treatment) were placed at 0.2, 0.4, 0.6 and 0.8 m depths below the soil surface to measure soil water suction. Soil samples were collected from 0 to 0.2, 0.2 to 0.4 and 0.4 to 0.6 m soil layers, at the sites located at a distance of 0.5, 0.75 and 1.0 m from plant stem, at beginning (November) and end (June) of irrigation seasons. One plant basin from each replicated plot (4 plants per treatment) was taken for soil sampling. Each soil sample was analysed for EC (soil:water ratio of 1:2), pH (soil:water ratio of 1:2) and available nutrients (N, P, K, Ca, Mg, Fe, Mn, Cu and Zn), by following the standard procedures (Tandon, 2005). The depth wise mean values of EC, pH and available nutrients were calculated. Five to seven months old leaf samples (3rd and 4th leaf from tip of non-fruiting branches) at a height of 2.0 m from ground surface were collected surrounding the plant canopy at the end of irrigation seasons and analysed for macronutrients (N, P, K) and micronutrients (Fe, Mn, Cu, and Zn). The leaf samples were thoroughly washed and dried at 65 ◦ C for 48 h. The dried samples were powdered homogenously and then digested in tri-acid mixture of 2 parts HClO4 + 5 parts HNO3 + 1 part H2 SO4 . Analysis made in acid extracts of leaves consisted of N by auto-nitrogen analyzer (Model2410, Perkin Elmer Inc., USA), P using vanadomolybdo-phosphoric acid method, K by flame photometry and micronutrients (Fe, Mn, Cu and Zn) by atomic absorption spectrophotometer (Model-908, GBC Scientific equipment, Australia). The leaf nutrient concentrations were calculated as dry weight basis of leafs. The net photosynthesis rate (Pn ), stomatal conductance (gs ) and transpiration rate (Tr ) of leafs were recorded fortnightly, in 1 h interval from 9 am to 5 pm on a clear-sky day by CO2 gas analyser (model-301PS, CID Bio-Science, USA) during irrigation

seasons. Four mature leaves per plant (3rd or 4th leaf from tip of shoot) from exterior canopy position (one leaf in each North, South, East and West direction) and two plants per treatment were taken for these measurements. Leaf water use efficiency (LWUE) was calculated as Pn divided by Tr of leafs (García-Sánchez et al., 2007). The plant height (distance from ground surface to top of plant crown), stem height (distance from ground surface to base of first branch on stem), canopy diameter (mean of canopy spread diameter measured in north–south and east–west directions), stock girth diameter (stem diameter measured at 0.1 m above ground surface) and scion girth diameter (stem diameter measured at 0.1 m above bud union) were recorded annually. Plant canopy volume was estimated using the following formula (Obreza, 1991): Vpc = 0.5233 H (D)2

(3)

where Vpc is the plant canopy volume (m3 ), H the plant canopy height (difference between plant height and stem height) in m and D the mean plant canopy spread diameter (north–south and east–west) in m. The number and weight of fruits harvested from each experimental plant (3 plants from each replicated plot) were recorded and the mean yield per plant under various treatments was calculated. Irrigation water productivity (IWP) was worked out in terms of fruit yield (kg plant−1 ) per unit quantity of irrigation water applied (m3 plant−1 ). Five fruits per experimental plant were taken randomly and their quality parameters (juice percent, acidity, total soluble solids) were determined. Juice of fruits was extracted manually using juice extractor and juice percent was estimated on weight basis with respect to fruit weight. The juice acidity was determined by volumetric titration with standardized sodium hydroxide, using phenolphthalein as an internal indicator (Ranganna, 2001) and total soluble solids (TSS) was measured by digital refractometer (Atago model-PAL 1, Japan).

2.5. Statistical analysis The data generated were subjected to analysis of variance (ANOVA), and separation of means was obtained using Duncan multiple range test (DMRT), according to the methods described by Gomez and Gomez (1984).

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3. Results and discussion 3.1. Soil water variation Fig. 2 shows the mean monthly volumetric water contents observed in 0–0.2, 0.2–0.4 and 0.4–0.6 m soil layers under various irrigation treatments. All the DI treatments except irrigation at 40% Ecp resulted in significantly (P < 0.05) higher water content in 0–0.2 m (26.1–29.1%) and 0.2–0.4 m (26.8–29.3%) soil layers in comparison to that under BI (25.7–27.2% and 26.5–28.4%, respectively). The soil water content at both 0–0.2 and 0.2–0.4 m depths increased with increasing irrigation regime from 40% Ecp to 100% Ecp . Moreover, the water content in 0–0.2 m and 0.2–0.4 m soil layers increased invariably in all irrigation treatments during January and February, due to some unseasonal rainfall of 11.5–20.0 mm in these months. The difference in daily soil water fluctuation at 0–0.40 m soil between any two irrigation events was estimated to be higher under BI (1.2–6.4 mm) than that under DI (0.8–4.8 mm), indicating higher evapotranspiration (ET) of basin-irrigated plants. The higher ET of basin-irrigated plants was probably due to the higher leaf transpiration rate caused by increased soil water content (28.7–29.2%) in root zone up to 2–3 days after irrigation, coupled with higher evaporation from larger wetted surface area under this irrigation method. Likewise, the range of soil water depletion at 0.2 m depth between any two irrigations increased with increasing irrigation regime with DI. This indicated the higher ET of drip-irrigated plants under high regime of irrigation. However, the magnitudes of soil water fluctuation in 0–0.2 soil layer was observed to be significantly (P < 0.05) higher than that in 0.2–0.4 and 0.4–0.6 m soil layers with DI. The higher fluctuation of water content in top 0.2 m soil under DI was due to the maximum plant water uptake from this soil layer, indicating the confinement of effective root zone of mandarin plants in this soil. Our observation marginally differs from the earlier observation of Autkar et al. (1988), which concluded that the effective root zone of 5- to 7-yearold basin-irrigated ‘Nagpur’ mandarin plants exists in top 0.30 m soil. The shallow rooting system of drip-irrigated plants in our study might be caused due to higher soil water content in upper layer (0–0.20 m) under frequent water application (alternate day) through drip. The similar result of development of shallow rooting system under DI was earlier reported in sweet orange (Kanber et al., 1996). The soil water content at 0.4–0.6 m depth under DI decreased irrespective of irrigation regime. However, BI showed an increasing trend of soil water content at 0.4–0.6 m depth, in spite of the irrigation application for top 0.30 m soil layer in this treatment. This was due to the percolation of irrigation water from top 0.30 m soil, probably caused by transport of water through preferential pathways (cracks and fissures) developed in this shrinking and swelling type clay soil at low soil water content (50% available soil water) under BI. Moreover, the increase in soil water content at 0.4–0.6 m depth under BI was relatively higher during April to June than November to March, indicating the higher percolation under higher quantum of water application during summer months (April–June). 3.2. Changes in EC and pH of soil The electrical conductivity (EC) of soil (0–0.2, 0.2–0.4 and 0.4–0.6 m depth) at the end of irrigation season was observed to be higher by 0.01–0.71 dS m−1 over that at beginning of irrigation (Table 4). Under DI, the maximum salinity build-up was observed in top 0.2 m soil. This happened due to the higher evaporation rate from wetted surface area, coupled with lower leaching of soluble salts from this soil layer with low water application rate under DI (Abu-Awwad, 2001). The higher salt accumulation in surface soil under DI had also been documented earlier in avocado (Gustafson

83

et al., 1979) and pistachio (Butt and Isbell, 2005). However, at the end of irrigation season, the salinity development in 0–0.6 m soil layer under DI (0.77–1.01 dS m−1 ) was within the salinity tolerance limit of ‘Nagpur’ mandarin plants (1.3 dS m−1 ), as reported by Ram et al. (1993). In basin-irrigated plots, the EC value increased up to 0.04 dS m−1 at 0–0.4 m soil, whereas at 0.4–0.6 m soil, EC reduced by 0.71 dS m−1 . The reduction of salinity in top 0.4 m soil under BI was attributed to higher leaching of soluble salts from this soil layer by flooding of irrigation water in the plant basin under this treatment. The substantial losses of soluble salts from top soil layer of orchards causing lower soil EC under surface irrigation was earlier reported by Myhre et al. (1991) in ‘Valencia’ orange. On the other hand, the highest increase in EC value at 0.4–0.6 m soil under BI reflects the accumulation of salts in sub-soil layer under this irrigation method. At the end of rainy season (November), the salinity level of soil reduced to initial values (0.64–0.83 dS m−1 ), indicating that the monsoonal rainfall (700–800 mm) takes place in this region is sufficient to leach out the accumulated salts from soil. The pH values of drip-irrigated soil at 0–0.2, 0.2–0.4 and 0.4–0.6 m depths decreased by 0.3–0.8, 0.1–0.4 and 0.1–0.2 units, respectively, at the end of irrigation season over that at the beginning of irrigation (Table 4). The lowering of soil pH can probably be attributed to acidic conditions in the soil induced by ammoniumbased fertilizers (urea and urea-phosphate) applied to citrus plants in our study. The chemistry behind soil acidity under application of ammonium-based fertilizers is that during nitrification of ammonium (NH4 + ) to nitrate (NO3 − ) in the presence of soil microbes, two H+ ions get released in soil, which is acidic in nature (Eq. (4)). + NH+ + 2 O2 → NO− 3 + H2 O + 2 H 4

(4)

The lower acidity of soil caused by application of ammonium-based fertilizer was earlier observed by He et al. (1999) in citrus. The pH value in top 0.2 m soil under BI showed a similar trend as DI. However, the magnitude of decrease in pH of basin-irrigated soil at 0–0.2 m was lower (0.3 units) than that of drip-irrigated soil. The lower acidification of 0–0.2 m soil under BI in comparison to drip irrigation probably reflects the higher loss of ammonium-based fertilizers from soil surface to atmosphere through denitrification and ammonia volatilization under BI. The pH value in 0.2–0.4 and 0.4–0.6 m soil layers was observed to increase by 0.1 and 0.4 units under BI. Similar findings of increase in pH with concomitant increase in salinity in sub-soil layers under surface irrigation (flooding) was earlier reported by Myhre et al. (1991) in citrus. However, the pH of different soil layers followed the similar trend of EC, at the end of rainy season. 3.3. Changes in available nutrients in soil The changes in available macronutrients (N, P and K) at 0–0.20, 0.20–0.40 and 0.40–0.60 m soil depths under various irrigation treatments show that the nutritional status of top 0.20 m soil improved (Table 5). This happened due to the application of NPK-based fertilizers to the plants during irrigation season. The magnitudes of incremental N, P and K in 0–0.20 m soil layer was marginally higher in drip-irrigated plots (15.0–32.5, 0.5–2.1 and 9.9–21.0 mg kg−1 , respectively) compared to that in basin-irrigated plots (9.0, 0.3 and 9.7 mg kg−1 , respectively). The increase in N, P and K showed a decreasing trend with soil depth under DI, whereas the reverse trend was observed under BI. The better availability of plant nutrients in 0.20 m upper soil under DI was probably facilitated by optimum soil–water and low soil pH, coupled with lower nutrients leaching from this soil layer under this irrigation method compared with BI. Moreover, the increase in nutrients contents at both 0–0.2 m and 0.2–0.4 m soils was higher at higher level of DI. The higher nutrients availability in effective root zone of the plants under DI indicated a greater efficacy of fertilizer application

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c Soil water at 0.4 -0.6 m depth (%, v/v)

31 30 29 28 27 26 25

40% Ecp

60% Ecp

80% Ecp

24

100% Ecp

Basin irrigation

Field capacity

23 Nov.

Dec.

Jan.

Feb.

Mar.

Apr.

May

June

May

June

b

31

Soil water at 0.2 -0 . 4 m depth (%, v/v)

Month

30 29 28 27 26 25 40% Ecp 100% Ecp

24

60% Ecp Basin irrigation

80% Ecp Field capacity

23 Nov.

Dec.

Jan.

Feb.

Mar.

Apr.

Month

a Soil water at 0-0.2 m depth (%, v/v)

31 30 29 28 27 26 25 24

40% Ecp 100% Ecp

23 Nov.

Dec.

60% Ecp Basin irrigation

Jan.

Feb.

80% Ecp Field capacity

Mar.

Apr.

May

June

Month Fig. 2. Mean soil water content in 0–0.2 m (a), 0.2–0.4 m (b), 0.4–0.6 m (c) soil depths under various irrigation treatments in ‘Nagpur’ mandarin during 2006–2009. The vertical bar at each data point represents the standard error of mean.

Table 4 Changes in EC and pH of soil in different soil layers of ‘Nagpur’ mandarin orchard under various irrigation treatments.* Soil depth (m)

Treatments +

EC (dS m−1 ) 0–0.2 0.2–0.4 0.4–0.6 # pH 0–0.2 0.2–0.4 0.4–0.6

DI at 40% Ecp

DI at 60% Ecp

DI at 80% Ecp

DI at 100% Ecp

BI

+0.08b z +0.05a +0.01a

+0.14c +0.08b +0.01a

+0.16c +0.12c +0.03b

+0.17c +0.14d +0.04c

+0.02a +0.04a +0.71d

−0.3a −0.1a −0.1a

−0.5b −0.3b −0.1a

−0.6c −0.3b −0.2b

−0.8d −0.4c −0.2b

−0.3a +0.1a +0.4c

#

* + # z

Mean of 2006–2007, 2007–2008 and 2008–2009. DI: drip irrigation; BI: basin irrigation. Plus sign (+) indicates gain and minus sign (−) indicates loss in EC and pH of soil. Data within a row followed by same letters do not differ significantly at P < 0.05.

P. Panigrahi et al. / Agricultural Water Management 104 (2012) 79–88

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Table 5 Changes in available macronutrients (N, P and K) in different soil layers of ‘Nagpur’ mandarin orchard under various irrigation treatments.* Soil depth (m)

Treatments +

N (mg kg−1 soil) 0–0.2 0.2–0.4 0.4–0.6 # P (mg kg−1 soil) 0–0.2 0.2–0.4 0.4–0.6 # K (mg kg−1 soil) 0–0.2 0.2–0.4 0.4–0.6

DI at 40% Ecp

DI at 60% Ecp

DI at 80% Ecp

DI at 100% Ecp

BI

+19.0c +8.5b +0.4c

+21.0d +9.0b +0.4c

+32.5ab +9.5b +0.3b

+9.0a +11.5c +13.3b

+0.5b +0.2a +0.1a

+1.4c +0.3b +0.1a

+1.8d +0.3b +0.1a

+2.1ab +0.4c +0.2b

+0.3a +0.8d +1.2c

+9.9a +7.6a +3.9a

+13.5b +9.4b +4.8b

+19.5c +12.7c +5.1b

#

* + # z

+15.0b z +7.5a +0.2a

+21.0d +16.4d +6.9c

+9.7a +12.9c +14.5d

Mean of 2006–2007, 2007–2008 and 2008–2009. DI: drip irrigation; BI: basin irrigation. Plus sign (+) indicates gain in available-N, P, and K in soil. Data within a row followed by same letters do not differ significantly at P < 0.05.

through this irrigation system, and suggests some further studies to optimize the fertilizer doses for drip-irrigated mandarin plants grown in central India. However, the N, P and K contents in 0.4–0.6 soil under BI were observed to be higher by 12.1–13.1, 1.0–1.1 and 7.6–10.6 mg kg−1 , respectively, over that under DI. This was probably due to higher deposition of leached out nutrients than the combination of plant use and losses (leaching, denitrification) of such nutrients from this soil layer under BI. The magnitudes of available micronutrients (Fe, Cu, Zn, Mn and Cu) in different soil layers decreased, irrespective of irrigation treatments (Table 6). The highest decrease in concentration of available micronutrients at top 0.4 m soil was observed with DI at 100% Ecp , followed by DI at 80% Ecp . The higher loss of micronutrients in soil under DI at 100% Ecp in comparison to other treatments might be caused due to higher plant uptake of these nutrients induced by lower soil pH under this treatment in this alkaline soil. The consistent decrease of micronutrients in soil suggests the application of appropriate quantity of micronutrients-based fertilizers to mandarin plants. As the changes of micronutrients concentration within the soil layers did not show any significant variation under BI, the leaching of such nutrients is not highly expected during the irrigation seasons. 3.4. Leaf nutrient composition Nutrient composition of leafs showed a differential response to irrigation treatments (Table 7). All the DI regimes produced the higher concentrations of N (1.92–2.37%), P (0.095–0.152%) and K (1.58–1.98%) in leafs over that with basin-irrigated plants (1.73% N, 0.092% P and 1.49% K). The higher leaf-N, P and K was caused by higher plant uptake with increased availability of such nutrients in soil under DI. The concentrations of leaf nutrients increased with increase in irrigation regime from 40% Ecp to 100% Ecp with DI. However, the amount of N, P and K in leafs was adequate in all the DI treatments, when compared to the foliar diagnostic chart developed for optimum ‘Nagpur’ mandarin productivity (1.70–2.81% N, 0.09–0.15% P and 1.02–2.59% K) in central India condition (Srivastava and Singh, 2008). This reflects some scope of curtailment of NPK-based fertilizer doses applied under DI over that recommended for surface-irrigated ‘Nagpur’ mandarin plants. The concentration of micronutrients (Fe, Mn, Cu and Zn) in leafs was observed higher under DI (Fe, 99.1–108.1 ppm; Mn, 48.2–57.3 ppm; Cu, 8.7–13.1 ppm; Zn, 10.3–14.2 ppm), with maximum value at DI at 100% Ecp , in comparison to BI (Fe, 98.4 ppm; Mn, 46.3 ppm; Cu, 8.2 ppm; Zn, 9.9 ppm). However, the effect

of irrigation treatments on micronutrient composition in leafs was statistically insignificant (P > 0.05), possibly due to the suboptimum availability and lower solubility of these nutrients in soil–water continuum. Overall, in all irrigation treatments except DI at 80% Ecp , the leaf micronutrient (Mn, Cu and Zn) content was less than their threshold values (54.8–84.6 ppm Mn, 9.8–17.6 ppm Cu and 13.6–29.6 ppm Zn) required for optimum productivity of ‘Nagpur’ mandarin (Srivastava and Singh, 2008). 3.5. Leaf physiological parameters The mean values of net photosynthesis rate (Pn ), stomatal conductance (gs ) and transpiration rate (Tr ) of leafs were significantly influenced by irrigation treatments (Table 8). The Pn value was higher at higher level of irrigation under drip, indicating the negative effect of soil water deficit on Pn of citrus plants (Tomar and Singh, 1986; Vu and Yelenosky, 1988). Moreover, the highest reduction in Pn value was calculated in between DI at 80% Ecp and 60% Ecp (0.68 ␮mol m−2 s−1 ), followed by that in between DI at 60% Ecp and 40% Ecp (0.47 ␮mol m−2 s−1 ). The higher reduction of Pn in between 80% and 60% Ecp irrigation treatments indicated the existence of threshold limit of soil water deficit with DI at 80% Ecp , resulting in optimum Pn of mandarin plants under this treatment. The basin-irrigated plants exhibited a marginally higher Pn value (2.03 ␮mol m−2 s−1 ) than the plants with DI at 60% Ecp (2.45 ␮mol m−2 s−1 ). However, the difference in Pn values between DI at 40% Ecp and BI was insignificant (P > 0.05). The gs and Tr values decreased with decreasing irrigation regime from 100% Ecp to 40% Ecp with DI. The highest values of gs and Tr in DI at 100% Ecp attributed to higher soil water content in root zone of plants under this treatment. However, the highest per cent reduction in gs and Tr was observed in between 100% Ecp and 80% Ecp , whereas, the Pn reduced to higher extent in between 80% Ecp and 60% Ecp . The maximum reduction in gs and Tr at higher irrigation level compared to Pn reflects the higher sensitivity of the former parameters to soil water deficit than the later one. Moreover, the reduction of gs (12.5–17.4%) was comparatively higher than that of Tr (7.7–16.2%), with corresponding irrigation regimes. The lower reduction of Tr could be probably due to the contribution of residual or mesophyll conductance (movement of water through intercellular spaces and mesophyll cells of leafs) to transpiration of leafs (Davies and Albrigo, 1994). Leaf transpiration depends on total conductance (stomatal conductance + mesophyll conductance) of leaf. As water stress occurs, the stomatal closure restricts the entry of both CO2 and water fluxes from surrounding atmosphere to

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P. Panigrahi et al. / Agricultural Water Management 104 (2012) 79–88

Table 6 Changes in available micronutrients (Fe, Mn, Cu and Zn) in different soil layers of ‘Nagpur’ mandarin orchard under various irrigation treatments.* Soil depth (m)

Treatments +

Fe (mg kg−1 soil) 0–0.2 0.2–0.4 0.4–0.6 # Mn (mg kg−1 soil) 0–0.2 0.2–0.4 0.4–0.6 # Cu (mg kg−1 soil) 0–0.2 0.2–0.4 0.4–0.6 # Zn (mg kg−1 soil) 0–0.2 0.2–0.4 0.4–0.6

DI at 40% Ecp

DI at 60% Ecp

DI at 80% Ecp

DI at 100% Ecp

BI

−1.60b z −1.41a −0.37a

−1.80c −1.41a −0.51b

−2.20d −1.60b −0.50b

−2.51ab −1.72c −0.72c

−1.40a −1.41a −1.43d

−0.42b −0.31b −0.15a

−0.60b −0.32c −0.20b

−0.91c −0.40d −0.22c

−1.12d −0.50ab −0.22d

−0.28a −0.29a −0.29ab

−0.08a −0.07a −0.04a

−0.12b −0.07a −0.05a

−0.15c −0.09b −0.07b

−0.16c −0.12c −0.09c

−0.06a −0.07a −0.09c

−0.06a −0.06a −0.06a

−0.07a −0.06a −0.05a

−0.12b −0.08b −0.05a

−0.14c −0.12c −0.06a

−0.05a −0.06a −0.06a

#

* + # z

Mean of 2006–2007, 2007–2008 and 2008–2009. DI: drip irrigation; BI: basin irrigation. Minus sign (−) indicates loss of micronutrients in soil. Data within a row followed by same letters do not differ significantly at P < 0.05.

Table 7 Mean leaf nutrients composition of ‘Nagpur’ mandarin under various irrigation treatments.* Treatment

+

DI at 40% Ecp DI at 60% Ecp DI at 80% Ecp DI at 100% Ecp BI * + z

Macronutrients (%)

Micronutrient (ppm)

N

P

K

Fe

Mn

Cu

Zn

1.92b z 2.08b 2.35c 2.37d 1.73a

0.095b 0.098c 0.141d 0.152ab 0.092a

1.58b 1.73c 1.97d 1.98d 1.49a

99.1a 102.5a 106.4a 108.1a 98.4a

48.2a 52.3a 55.6a 57.3a 46.3a

8.7a 10.1a 12.7a 13.1a 8.2a

10.3a 12.7a 13.9a 14.2a 9.9a

Mean of 2006–2007, 2007–2008 and 2008–2009. DI: drip irrigation; BI: basin irrigation. Data within a column followed by same letters do not differ significantly at P < 0.05.

leaf, but mesophyll conductance remains same and transpiration reduces disproportionately to stomatal conductance. The gs and Tr values of basin-irrigated plants exists in between that with DI at 80% Ecp and DI at 100% Ecp . The magnitude of leaf water use efficiency (LWUE, ␮mol CO2 fixed per mmol H2 O transpired) increased with increase in irrigation regime from 40% Ecp to 80% Ecp , and then decreased at 100% Ecp with DI. However, the LWUE value in DI at 100% Ecp existed in between that in DI at 40% Ecp and DI at 60% Ecp . The higher LWUE in DI at 80% Ecp is due to the marginal decrease in Pn value (0.22 ␮mol m−2 s−1 ) associated with the higher decrease in Tr value (0.42 mmol m−2 s−1 ) under this treatment over DI at 100% Ecp . These results are in concurrence with the findings of Vu and Yelenosky (1988) in Valencia orange and Ribeiro et al. (2009) in Satsuma mandarin.

3.6. Plant growth response The annual increase in vegetative growth parameters was significantly affected by irrigation treatments (Table 9). The mean of incremental height (0.51–0.62 m), stock girth (42–51 mm), scion girth (40–49 mm) and canopy volume (0.681–1.231 m3 ) of the plants registered under DI except irrigation at 40% Ecp was significantly higher (P < 0.05) than that with basin-irrigated plants (plant height, 0.46 m; stock girth, 40 mm; scion girth, 38 mm and canopy volume, 0.627 m3 ). The lower growth performance of mandarin plants under DI at 40% Ecp over BI was due to higher plant water stress caused by lower soil water availability in root zone under the former treatment (350–410 mm m−1 soil depth) than the later one (510–660 mm m−1 soil depth). All the growth characteristics increased with increasing irrigation level with DI. The

Table 8 Net photosynthesis rate (Pn ), stomatal conductance (gs ), transpiration rate (Tr ), and leaf water use efficiency (LWUE) of ‘Nagpur’ mandarin under different irrigation treatments.* Treatments

Pn (␮mol m−2 s−1 )

gs (mmol m−2 s−1 )

Tr (mmol m−2 s−1 )

LWUE

+

1.98a z 2.45b 3.13c 3.35c 2.03a

36.45a 41.65b 48.95c 59.25ab 55.45d

1.67a 1.81a 2.16b 2.58c 2.21d

1.18b 1.35c 1.44c 1.29c 0.91a

DI at 40% Ecp DI at 60% Ecp DI at 80% Ecp DI at 100% Ecp BI * + z

Mean of 2006–2007, 2007–2008 and 2008–2009. DI: drip irrigation; BI: basin irrigation. Data within a column followed by same letters do not differ significantly at P < 0.05.

P. Panigrahi et al. / Agricultural Water Management 104 (2012) 79–88

87

Table 9 Annual incremental plant growth parameters of ‘Nagpur’ mandarin under various irrigation treatments.* Treatments

Plant height (m)

+

az

DI at 40% Ecp DI at 60% Ecp DI at 80% Ecp DI at 100% Ecp BI * + z

Stock girth diameter (mm)

Scion girth diameter (mm)

a

0.40 0.51c 0.58d 0.62d 0.46b

a

38.2 42.4c 48.5d 51.3ab 40.7b

Canopy volume (m3 ) 0.503a 0.681c 1.018d 1.231ab 0.627b

37.1 40.3c 46.6d 49.9ab 38.4b

Mean of 2006–2007, 2007–2008 and 2008–2009. DI: drip irrigation; BI: basin irrigation. Data within a column followed by same letters do not differ significantly at P < 0.05.

higher increase in plant growth parameters with higher irrigation regimes is attributed to more quantity of photosynthate formed by increased rates of net-photosynthesis in leafs under these treatments. 3.7. Yield parameters and irrigation water productivity Table 10 shows the numbers of fruits per plant, average fruit weight and fruit yield produced in various irrigation treatments. The maximum number of fruits (242 plant−1 ) was harvested in DI at 100% Ecp , followed by DI at 80% Ecp (235 plant−1 ). However, the heavier fruits were recorded with DI at 80% Ecp (148 g fruit−1 ) than DI at 100% Ecp (136 g fruit−1 ). The increased number of fruits with DI at 100% Ecp could be a reason for smaller fruits in this treatment. Both fruit number per plant and mean fruit weight decreased with decreasing irrigation regime from 80% Ecp to 40% Ecp with DI. The basin-irrigated plants produced marginally higher number of fruits with higher weight as compared to DI at 40% Ecp . The highest fruit yield was recorded in DI at 80% Ecp (34.78 kg plant−1 ), followed by DI at 100% Ecp (32.91 kg plant−1 ). The possible reasons for higher fruit yield under DI at 80% Ecp may be that the water deficit (15–20% available soil water depletion) in root zone under this treatment suppressed the vegetative growth of the plants without bringing much effect on leaf photosynthesis rate and the citrus plants invested higher quantity of photosynthates towards reproductive growth (fruiting) than vegetative growth. The fruit yield decreased with decreasing irrigation level from 80% Ecp to 40% Ecp , resulting from less number of fruits with lower fruit weight under lower regime of DI. However, the yield obtained from DI at 40% Ecp (15.07 kg plant−1 ) was significantly (P < 0.05) lower than that with basin-irrigated plants (23.18 kg plant−1 ). This could be caused by lower photosynthesis rate of leaves under continuous soil water deficit prevailed under DI at 40% Ecp compared to BI. The similar results of lower fruit yield with higher level of deficit irrigation were earlier reported by Pérez-Pérez et al. (2008) in ‘Lane late’ orange and García-Tejero et al. (2010) in ‘Salustiana’ orange. The mean annual quantities of water applied under different irrigation treatments indicate that the water consumed under DI at

80% Ecp (6.965 m3 plant−1 ) was 29% lower than BI (Table 10). Earlier studies also demonstrated the reduction of water consumption up to 30% in lemon grown in central Tajikistan (Tashbekov et al., 1986), 30–40% in ‘Verna’ lemon in Spain (Sánchez Blanco et al., 1989) and 15% in ‘Salustiana’ orange in Spain (Castel et al., 1989) under DI over conventional BI method. These variations are due to the nature of citrus cultivars studied under varied soil–climate and the methods used in scheduling irrigation. The IWP was computed to be maximum under DI at 80% Ecp (4.993 kg m−3 ), followed by DI at 60% Ecp (4.675 kg m−3 ). The higher water productivity resulted in DI at 80% Ecp was attributed to higher increase in fruit yield with comparatively less increase in irrigation water use under this treatment over other treatments. An improvement in IWP with optimal DI regime was also earlier reported in citrus (Pérez-Pérez et al., 2008; García-Tejero et al., 2010). All DI treatments resulted in higher IWP (3.780–4.993 kg m−3 ), with minimum value at DI at 100% Ecp in comparison to that with BI (2.361 kg m−3 ). 3.8. Fruit quality Fruit quality (juice content, acidity and total soluble solids) assessment under various irrigation treatments showed that the juice content increased with increasing irrigation level from 40% Ecp to 100% Ecp with DI (Table 10). However, the highest total soluble solid (10.2 ◦ Brix) with lower acidity (0.83%) in juice was observed in DI at 80% Ecp . The higher juice content is one of the reasons for dilution of soluble solids concentrations in fruits with DI at 100% Ecp (Davies and Albrigo, 1994). Moreover, the higher TSS and lower acidity in fruits with DI at 80% Ecp and 60% Ecp was probably caused by enhanced transformation of acids to sugars in dehydrated juice sacs, which is required to maintain the osmotic pressure of fruit cells under mild water deficit condition prevailed under these treatments (Huang et al., 2000). Earlier studies also demonstrated the higher TSS in citrus fruits under soil water deficit condition in root zone of plants (García-Tejero et al., 2010). However, the basin-irrigated plants produced the fruits with higher juice content (37.5%) and higher TSS (9.8 ◦ Brix), with lower acidity (0.86%) than that with the fruits produced in DI at 40% Ecp (juice content, 36.4%; acidity, 0.88%; TSS, 9.5 ◦ Brix).

Table 10 Annual fruit yield, water productivity and fruit quality of ‘Nagpur’ mandarin as affected by various irrigation treatments.* Treatment

IWU (m3 plant−1 )

Yield parameters −1

DI at 40% Ecp DI at 60% Ecp DI at 80% Ecp DI at 100% Ecp BI * + z

−1

No. of fruits plant

Average fruit weight (g)

Fruit yield (kg plant

110a z 172c 235d 242d 168b

137a 142b 148b 136a 138a

15.07a 24.42b 34.78c 32.91c 23.18b

IWP (kg m−3 )

) 3.482 5.223 6.965 8.706 9.814

Mean data during 2006–2009; IWU: irrigation water used; IWP: irrigation water productivity. TSS: total soluble solids; DI: drip irrigation; BI: basin irrigation. Data within a column followed by same letters do not differ significantly at P < 0.05.

4.327b 4.675c 4.993c 3.780b 2.361a

Quality parameters TSS (◦ Brix)

Juice (%)

Acidity (%)

+

36.4b 38.8c 40.2d 40.4d 37.5a

0.88c 0.84a 0.83a 0.86b 0.86b

9.5a 10.1c 10.2c 9.7b 9.8b

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4. Conclusions DI is found as a potential water saving technique for ‘Nagpur’ mandarin cultivation in central India. The higher leaf nutrient (N, P and K) content of drip-irrigated plants is associated with the increased nutrients availability in their effective root zone. The sub-optimum micronutrient content in leafs and their reduction in soil during the experimental years advocate for the application of required amount micronutrients-based fertilizers to mandarin plants. The higher salinity development in surface soil of drip irrigated plots indicated the lower leaching of soluble salts under low water application rate with drip irrigation in high clay content soil of the experimental site. However, the salinity development under drip with sufficient water application had no clear-cut effect on plant performance. Among net-photosynthesis, stomatal conductance and transpiration rate of leafs, the stomatal conductance was found most sensitive to soil water deficit, reflecting the scope of its use a tool for efficient irrigation scheduling in drip-irrigated citrus. All the DI regimes except irrigation at 40% Ecp proved superior to BI, in relation to plant growth, fruit yield and fruit quality, with highest irrigation water productivity under DI at 80% Ecp . The overall reduction in growth and yield under DI at 40% Ecp over BI was apparently due to low photosynthesis rate caused by sub-optimum soil water content in root zone of plants under the former treatment. Irrigation water quantity of 1.2–4.5, 5.6–9.8 and 12.5–21.3 l plant−1 day−1 applied through drip system in between December to June is sufficient to grow 5-, 6- and 7-year-old mandarin plants, respectively, in central India condition. The significant (P < 0.05) variation of soil water content at 0–0.20 m depth under DI suggests that irrigation scheduling based on soil water deficit measured in 0–0.20 m soil layer through drip may be used for ‘Nagpur’ mandarin. The overall results of the present field investigation demonstrate that the adoption of optimal DI regime (80% Ecp ) could save a substantial amount of irrigation water over traditional BI in ‘Nagpur’ mandarin cultivation. This will help in bringing more area under irrigation, resulting in higher production of quality citrus fruits. Further studies related to optimizing the quantities of NPKbased fertilizers and micronutrients applied through DI system for ‘Nagpur’ mandarin is suggested. Acknowledgement The authors acknowledge the help rendered by Mrs. Jayashree, T-2-3 of National Research Centre for Citrus, Nagpur, India, in analysing the chemical properties of soil samples. References Abu-Awwad, A.M., 2001. Influence of different water quantities and qualities on lemon trees and soil salt distribution at the Jordan Valley. Agric. Water Manage. 52, 53–71. Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper No. 56, Rome, Italy. Amberger, A., 2006. Soil Fertility and Plant Nutrition in the Tropics and Subtropics, first ed. IFA/IPI, Paris, France/Horgen, Switzerland. Autkar, V.N., Kolte, S.O., Bagade, T.R., 1988. Distribution of active rooting zones in Nagpur mandarin and estimates of water requirement for Vertisoles of Maharashtra. Ann. Plast. Physiol. 2 (2), 219–222. Butt, C.M., Isbell, B., 2005. Leaching of accumulated soil salinity under drip irrigation. Trans. ASAE 48 (6), 1–7. Castel, J.R., Buj, A., Ramos, C., 1989. Comparison of drip and border irrigation of mature Salustiana orange trees. Invest. Agr. Prod. Prot. Veg. 4 (3), 393–412. Chartzoulakis, K., Michelakis, N., Stefanoudaki, E., 1999. Water use, growth, yield and fruit quality of ‘Bonanza’ oranges under different soil water regimes. Adv. Hort. Sci. 13 (1), 6–11. Davies, F.S., Albrigo, L.G., 1994. Citrus. CAB International, Wallingford, UK. Fereres, E., Goldhamer, D.A., Parsons, L.R., 2003. Irrigation water management of horticultural crops. HortScience 38 (5), 1036–1042.

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