Development of deficit irrigation program for improving the water use efficiency, growth, and yield of groundnut in the semiarid tropical region of India

In this study, we assessed the efficiency of a deficit irrigation program (DIP) on groundnut (Arachis hypogaea L.) yield and economic profits. The DIP was designed to combine frequency and volume of irrigation to develop an appropriate irrigation water management (IWM) strategy for groundnut. Two field experiments were conducted at the Agricultural College and Research Institute, Madurai, Tamil Nadu, India, with a bunch variety of groundnut, VRI 2, under a randomized block design (RBD) with three replications. The treatments included DIP in combination with a foliar application of pink-pigmented facultative methylotrophic bacteria (PPFM). The irrigation frequencies adopted for the first set of treatments were high frequency (5/5), medium frequency (7/5), and lower frequency (7/7) starting from 14 days after sowing (DAS). The effects of early water stress on groundnut pod yield and water use efficiency were investigated in a second experiment by starting irrigation at 21 DAS. The number of irrigation frequencies and irrigation volume was fixed to develop an easily readable irrigation chart for end-users. The number of irrigation frequencies was fixed as three, and the volume of irrigation was fixed as a depth of 3 cm. In the first experiment, a mini mobile pumping unit was used for scheduling irrigation frequencies; in the second experiment, the surface drip method was used. In both experiments, we also assessed the effects of foliar application of PPFM, widely used as a growth stimulant for several crops, especially under drought conditions. Overall, we observed that DIP led to up to 25.6% water saving compared to surface irrigation. Use of the DIP at the medium frequency with PPFM spray had a significantly positive influence on water use efficiency (WUE) and irrigation water use efficiency (IWUE) compared to conventional drip irrigation (CDI). Compared to surface irrigation (SI), DIP had a positive impact on growth parameters, yield attributes, and economic profitability with a higher benefit-cost ratio. Additionally, there were only minor differences between deficit irrigation (DI) results starting from 21 DAS and 14 DAS. Irrespective of the irrigation techniques, PPFM application had a positive effect on the yield attributes and WUE. Our results indicated that DI at a medium frequency (7/5) with PPFM spray, starting from 21 DAS under drip fertigation, is the best irrigation management innovation (IMI) strategy for optimum utilization of irrigation water without significant reduction in pod yield. This management had a positive influence on WUE and IWUE of summer groundnut in sandy clay loam soil. However, the exact scheduling of the irrigation may differ in different environments as well as soil types. Nevertheless, we propose that the application and further optimization of the DIP devised in this study would help the farmers attain a similar yield using a lower amount of irrigation water and lead to significant economic profits for the farmers.