Yield Enhancement of Pigeonpea [Cajanus cajan (L.) Millsp.] through Drip Irrigation and Fertigation Management

Performance of crop can be explored by manipulating the various agronomic practices. Among these water and nutrient are the most important production factors that play a vital role in augmenting the productivity of crop (Saritha et al., 2012). Major constraints limiting pigeonpea yield are dry spells during vegetative stage coupled with terminal drought during reproductive stage and poor crop nutrition which ultimately results into flower drop and formation of immature pods and this ultimately results into drastic reduction in yield (Deol et al., 2018). In recent years the availability of water has become a crucial factor as its demand is increasing in agricultural sector, industrial sector and for domestic use. Further the availability of water for irrigation purpose is declining abruptly while at the same time the demand for irrigation water has been increasing at the faster rate due to increased cropping intensity. In this scenario adoption of modern agronomic practices like drip irrigation and fertigation is the need of hour to augment the efficient use of water and fertilizer and enhance the yield of pigeonpea (Vimalendran, 2013). Drip is an efficient irrigation system as it wets the soil only in the root zone and maintains optimum moisture content (Ramani, 1991). The adoption of drip irrigation may increase the yield potential of crops by thrice with the same amount of water thus saving about 45 to 50 per cent of irrigation water and increasing the productivity by about 40 per cent (Vimalendran, 2013).
        
In drip fertigation water soluble fertilizers along with the water are applied in precise quantity as per the need of the plant directly in the active root zone of the crop where the concentration of active roots is high (Sivanappan et al., 1985). Hence not only water and nutrient can be saved in this technology but also helps to upsurge the crop productivity with quality farm produce as compared to conventional method. Taking into consideration these points the present field investigation was undertaken with an objectives to enhance the yield of pigeonpea through judicious use of water and nutrients.

The field experiments were conducted for two consecutive years during kharif seasons of 2018 and 2019 at the experimental farm of AICRP on Irrigation Water Management, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani. The soil of experimental field was dominated by higher clay content (57.80 per cent) with slightly alkaline in reaction (soil pH:7.63), normal in salt content (EC:0.36 dSm^-1), low in available soil nitrogen (176.66 kg ha^-1), medium in soil organic carbon (6.1 g kg^-1) and available soil phosphorus (12.43 kg ha^-1) and very high in soil available potassium (621.28 kg ha^-1).
        
The experiment was laid out in split plot design with four drip irrigation levels in main plots viz. I₁ : 0.6 ETc, I₂ : 0.8 ETc, I₃ : 1.0 ETc and I₄ : Conventional method (surface irrigation of 60 mm each at critical growth stages like bud initiation, flowering and pod formation stage as per the situation) and in sub plots four fertigation levels viz. F₁: Control (no application of fertilizer),  F₂: 80%  RDF,  F₃: 100%  RDF (25:50:25 NPK kg ha^-1) and F₄:120% RDF and replicated thrice on the same site with same randomization during both the years of investigation. The rainfall received was 781.4 mm in 21 rainy days and 970.4 mm in 53 rainy days during 2018 and 2019 as against the normal rainfall of 883.6 mm in 43.2 rainy days (Dakhore et al., 2020). Thus the actual rainfall received during both the years of experimentation deviated from the normal rainfall indicating deficit rainfall of 11.56 per cent during 2018 and 9.82 per cent excess rainfall during 2019.
        
The crop variety BDN-716 was sown at the spacing of 150 cm × 30 cm for drip treatments and at 90 cm × 50 cm for conventional method on 25/6/2018 and 25/6/2019 during first and second year of study respectively. The drip irrigation was scheduled at alternate day on the basis of crop evapotranspiration (ETc) as per the treatments. ETo (reference crop evapotranspiration) values were calculated as per the FAO Penman Monteith method (Allen et al., 1998) by using “Phule Jal” mobile app developed by Gorantiwar et al., (2018). The fertigation was given through water soluble fertilizers viz. urea (46% N), mono ammonium phosphate (12:61:0 NPK) and sulphate of potash (0:0:50 NPK) in 10 splits at an interval of ten days, out of which  20% N and 40% P in two splits at 0-30 DAS, 30% N, P and 25% K in three splits at 31-60 DAS, 30% N, P and 40% K in 3 splits  at 61-90 DAS and 20% N and 35% K in two splits at 91-120 DAS through soluble fertilizers.
        
Data pertaining to seed yield and straw yield were further subjected to calculations on harvest index and economic analysis. Water use efficiency was calculated by dividing the yield (kg ha^-1) with total water use (mm). Nutrient use efficiency was assessed by two indices suggested by Rolf Hardter and Thomas Fairhurst (2004). 

The data pertaining to seed yield, straw yield, biological yield, nutrient use efficiency, water use efficiency and economic aspect of pigeonpea as influenced by drip irrigation and fertigation during the course of investigation were critically interpreted and results of the same with appropriate justification are presented below.
 
Yield and economic studies
 
Data related to seed yield, straw yield, biological yield and harvest index of pigeonpea as influenced by different drip irrigation and fertigation during kharif seasons of 2018, 2019 and pooled mean are presented in Table 1.
 

 
 
Effect of irrigation levels
 
Drip irrigation scheduled at 0.8 ETc recorded significantlyhigher seed yield harvest index, gross monetary return, net monetary return and benefit cost ratio during kharif seasons of 2018, 2019 and pooled mean, however it was at par with 1.0 ETc in respect of seed yield, gross monetary return and net monetary return during second year of experimentation (Table 1 and 2) and during both the years in respect of benefit cost (B:C) ratio. The probable reason for higher seed yield might be the availability of optimum moisture level that had contributed to better proliferation of roots and aeration throughout the crop growth period and helped in better translocation of assimilates from source to sink and produced higher seed yield and harvest index These results are in conformity with the earlier findings reported by Kumbhar et al., (2015). The higher yield might have reflected in fetching higher GMR, NMR and B:C ratio.
 

        
Significantly higher straw yield and biological yield of pigeonpea was observed in drip irrigation regime scheduled at 1.0 ETc and was comparable with 0.8 ETc during both the years of experimentation and in pooled mean. The benefit of drip irrigation over surface irrigation is that better turgid condition is maintained by the plant during day time and this might have resulted in wider opening of stomata for longer time and helped in better exchange of gases. Meanwhile leaves might have remained turgid and produced more leaf surface area and this condition favoured in more absorption of solar radiation and ultimately resulted in higher photosynthetic activity which in turn contributed in harnessing higher biological yield. These results are in close conformity with the earlier findings reported by Shirgapure et al., (2018).
 
Effect of fertigation levels
 
Drip fertigation @ 25:50:25 NPK kg ha^-1 (F₃) recorded significantly higher seed yield, GMR and NMR of pigeonpea and was comparable with 20:40:40 NPK kg ha^-1 (80% RDF) during both the years of investigation and in pooled mean (Table 1). Whereas, drip fertigation @ 20:40:20 NPK kg ha^-1 (F₂) recorded significantly higher harvest index and B:C ratio  however, it was at par with 25:50:25 NPK kg ha^-1 (F₃). The probable reason for increased yield might be the better availability of major plant nutrients like NPK in the soil solution that proved beneficial in better translocation of assimilates from source to sink and produced higher seed yield which in turn reflected in realizing higher harvest index. These findings are in conformity with the earlier findings reported by Vanishree et al., (2019).
        
Drip fertigation @ 30:60:30 NPK kg ha^-1 (F₄) produced significantly higher straw yield and biological yield of pigeonpea closely followed by 25:50:25 NPK kg ha^-1 (F₃) during both the years of investigation and in pooled mean. This might be due to beneficial effect of split application of water soluble fertilizers in higher amount that helped in better uptake of nutrients and resulted in higher vegetative and reproductive growth of plant, which in turn contributed towards higher straw and biological yield. These results are in agreement with the earlier findings reported by Chandrasekhar (2013).
 
Interaction effects
 
Treatment combination of drip irrigation at 0.8 ETc and 100% RDF (I₂F₃) recorded significantly higher seed yield, GMR and NMR of pigeonpea during kharif seasons of 2018, 2019 and pooled mean, however it was comparable with treatment combination of 0.8 ETc and 80% RDF (I₂F₂), 1.0 ETc and 80% RDF (I₃F₂) and 1.0 ETc and 100% RDF (I₃F₃) (Table 1A, 2A and 2B). The higher seed yield might be due to the beneficial effect of scheduling of drip irrigation at alternate day along with split application of water soluble fertilizers which helped to maintain the optimum soil moisture in the root zone and readily increased the availability of major plant nutrients like NPK directly in the rhizosphere. This synergistic effect helped in better translocation of assimilates from source to sink and produced higher seed yield. These results are parallel to the earlier findings reported by Shruti and Aladakatti (2017). Whereas treatment combination of drip irrigation at 0.8 ETc and 80% RDF (I₂F₂) recorded significantly higher harvest index and B:C ratio, however it was at par with treatment combination of 0.8 ETc and 100% RDF (I₂F₃) 1.0 ETc and 80% RDF (I₃F₂) and 1.0 ETc and 100% RDF (I₃F₃) (Table 1B and 2C).
 



 

 

 

 
Water use efficiency (WUE)
 
The data related to mean water use efficiency as influenced by different drip irrigation and fertigation levels during kharif seasons of 2018 and 2019 is presented in Table 3.
 

 
Effect of irrigation levels
 
The water use efficiency in all drip irrigated treatments were higher as compared to conventional method of irrigation (surface irrigation), which might be due to better increase in yield of pigeonpea and higher nutrient use efficiency. The drip irrigation scheduled at 0.8 ETc recorded higher WUE followed by 0.6 ETc during both the years of investigation. Combination of drip irrigation at 0.8 ETc and 100% RDF (I₂F₃) recorded higher WUE followed by 0.8 ETc and 80% RDF (I₂F₂). The probable reason for this might be the synergistic effect of drip irrigation and fertigation which resulted in significant saving of irrigation water, increased yield and higher nutrient use efficiency under these combinations which eventually contributed in higher WUE. Similar trend was reported by Singh et al., (2018a) in Bt.cotton.
 
Effect of fertigation levels
 
With increase in fertigation level, WUE increased up to certain level and thereafter it showed declining trend. Thus higher WUE was noticed with application of 25:50:25 NPK kg ha^-1 (F₃) followed by drip fertigation @ 20:40:40 NPK kg ha^-1 (F₂) during both the years of study. This might be due to beneficial effect of split application of plant nutrients that helped in better nutrient uptake and finally resulted in higher yield which in turn reflected in higher water use efficiency in drip fertigation at 100% RDF followed by 80% RDF. These findings are in conformity with the earlier findings reported by Singh et al., (2018).
 
Nutrient use efficiency
 
The data pertaining to nutrient use efficiency viz., partial factor productivity and nutrient use efficiency/agronomic efficiency as influenced by different drip irrigation and fertigation levels during kharif seasons of 2018 and 2019 are furnished in Table 4 and 5.
 

 

 
Effect of irrigation levels
 
Drip irrigation at 0.8 ETc recorded higher values of partial factor productivity during both the years of investigation (Table 4). Drip irrigation scheduled at alternate day might have prevailed optimum soil moisture condition at 0.8 ETc and that have helped in better uptake of nutrient and resulted in increased yield and ultimately contributed in higher partial factor productivity. It is clear from Table 5 that higher value of agronomic efficiency/nutrient use efficiency was observed in drip irrigation at 0.6 ETc (8.91 kg kg^-1 nutrient) followed by 0.8 ETc (8.91 kg kg^-1 nutrient) during first year and at 0.8 ETc (12.05 kg kg^-1 nutrient) during second year of study.
 
Effect of fertigation levels
 
Higher values of partial factor productivity of nutrient were observed in drip fertigation with 20:40:20 NPK kg ha^-1 (F₂) during both the years of investigation (Table 4). Similar trend was observed in case of nutrient use efficiency/agronomic efficiency (Table 5). Thus with increase in the fertigation levels the partial factor productivity of nutrient and nutrient use efficiency/ agronomic efficiency decreased indicating that drip fertigation with 20:40:20 NPK kg ha^-1 (F₂) was found optimum in realizing the economical yield. These findings are in accordance with the views of Deolankar and Berard (1999). 

From the present investigation, it can be concluded that drip irrigation at 0.8 ETc scheduled at alternate day along with 20:40:20 NPK kg ha^-1 in ten splits through water soluble fertilizers out of which  20% N and 40% P in two splits at 0-30 DAS, 30% N, P and 25% K in three splits at 31-60 DAS, 30% N, P and 40% K in 3 splits at 61-90 DAS and 20% N and 35% K in two splits at 91-120 DAS was found promising for realizing higher productivity and profitability of pigeonpea.