Evaluation of the effects of mulch on optimum sowing date and irrigation management of zero till wheat in central Punjab, India using APSIM

Abstract

Machinery for sowing wheat directly into rice residues has become more common in the rice-wheatsystems of the north-west Indo-Gangetic Plains of South Asia, with increasing numbers of farmers nowpotentially able to access the benefits of residue retention. However, surface residue retention affectssoil water and temperature dynamics, thus the optimum sowing date and irrigation management for amulched crop may vary from those of a traditional non-mulched crop. Furthermore, the effects of sowingdate and irrigation management are likely to vary with soil type and seasonal conditions. Therefore,a simulation study was conducted using the APSIM model and 40 years of weather data to evaluatethe effects of mulch, sowing date and irrigation management and their interactions on wheat grain yield,irrigation requirement (I) and water productivity with respect to irrigation (WPI) and evapotranspiration(WPET). The results suggest that the optimum wheat sowing date in central Punjab depends on both soiltype and the presence or absence of mulch. On the sandy loam, with irrigation scheduled at 50% soilwater deficit (SWD), the optimum sowing date was late October to early November for maximising yield,WPIand WPET. On the clay loam, the optimum date was about one week later. The effect of mulch onyield varied with seasonal conditions and sowing date. With irrigation at 50% SWD, mulching of wheatsown at the optimum time increased average yield by up to 0.5 t ha−1. The beneficial effect of mulch onyield increased to averages of 1.2–1.3 t ha−1as sowing was advanced to 15 October. With irrigation at 50%SWD and 7 November sowing, mulch reduced the number of irrigations by one in almost 50% of years,a reduction of about 50 mm on the sandy loam and 60 mm on the clay loam. The reduction in irrigationamount was mainly due to reduced soil evaporation. Mulch reduced irrigation requirement by more assowing was delayed, more so on the sandy loam than the clay loam soil. There was little effect of mulchon irrigation requirement for late October sowings.There were large trade-offs between irrigation input, yield, WPETand WPIon the sandy loam with regardto the optimum irrigation schedule. Maximum yield occurred with very frequent irrigation (10–20% SWD)which also had the greatest irrigation input, while WPIwas highest with least frequent irrigation (70%SWD), and WPETwas highest with irrigation at 40–50% SWD. This was the case with and without mulch.On the clay loam, the trade-offs were not so pronounced, as maximum yield was reached with irrigationat 50% SWD, with and without mulch. However, both WPETand WPIwere maximum and irrigation inputleast at the lowest irrigation frequency (70% SWD). On both soils, maximum yield, WPETand WPIwerehigher with mulch, while irrigation input was slightly lower, but mulch had very little effect on theirrigation thresholds at which each parameter was maximised.