Growth, yield and water productivity of zero till wheat as affected by rice straw mulch and irrigation schedule

Intensive cultivation of rice and wheat in north-west India has resulted in air pollution from rice strawburning, soil degradation and declining ground water resources. The retention of rice residues as a surfacemulch could be beneficial for moisture conservation and yield, and for hence water productivity, inaddition to reducing air pollution and loss of soil organic matter. Two field experiments were conductedin Punjab, India, to study the effects of rice straw mulch and irrigation scheduling on wheat growth, yield,water use and water productivity during 2006'2008. Mulching increased soil water content and this ledto significant improvement in crop growth and yield determining attributes where water was limiting,but this only resulted in significant grain yield increase in two instances. There was no effect of irrigationtreatment in the first year because of well-distributed rains. In the second year, yield decreased withdecrease and delay in the number of irrigations between crown root initiation and grain filling. Withsoil matricpotential (SMP)-based irrigation scheduling, the irrigation amount was reduced by 75mmeach year with mulch in comparison with no mulch, while maintaining grain yield.Total crop water use(ET) was not significantly affected by mulch in either year, but was significantly affected by irrigationtreatment in thes econdyear. Mulch had a positive or neutral effect on grain water productivity withrespect to ET (WPET) and irrigation (WPI). Maximum WPI occurred in the treatment which receivedthe least irrigation,but this was also the lowest yielding treatment. The current irrigation schedulingguidelines based on cumulative pan evaporation (CPE) resulted in sub-optimal irrigation (loss of yield) inone of the two years, and higher irrigation input and lower WPI of the mulched treatment in comparisonwith SMP-based irrigation scheduling. The results from this and other studies suggest that farmers in Punjab greatly over-irrigate wheat. Further field and modelling studies are needed to extrapolate thefindings to a wider range of seasonal and site conditions, and to develop simple tools and guidelines toassist farmers to better schedule irrigation to wheat.