Rice-wheat (RW) farming systems of north-west (NW) India are critical to the country's food security. Current farming practice involves intensive tillage for both crops, puddling for rice, manual transplanting of rice, in situ burning of rice residues, and removal of wheat residues for fodder (with remaining residues burnt). As a result, yields have declined, and the sustainability of these systems is threatened by soil degradation, ground water depletion, air and groundwater pollution, increasing farm labour scarcity, and high production costs. This has led to strong advocacy by agricultural scientists for conversion to conservation agriculture (CA), featuring direct drilling of wheat into rice residues, and dry seeding of rice. Therefore, a cropping system experiment was initiated to evaluate the effects of tillage and rice residue management on crop performance, components of the water balance, and water productivity, in a dry seeded RW system. The trial consisted of two tillage treatments, conventional tillage (CT, dry tillage, 2-3 passes) and zero tillage (ZT) for both rice and wheat, and two wheat mulching treatments (none, 6-7 t ha-1 of rice straw mulch). This thesis reports the finding for the first 2.5 years (five crops), commencing with wheat sown in November 2011. The field observations were also used to validate the APSIM cropping system model, which was then used to further explore the effects of tillage and mulch on crop performance components of water balance. There was no effect of tillage associated with wheat, nor rice, or of mulching of wheat on individual crop and total system yield (rice equivalent yield, REY, 13.3 t ha-1) in the first year. In the second year, REY of the systems with ZT dry seeded rice (ZTDSR) was significantly lower than that of the systems with CTDSR, due to lower yield of ZTDSR. Wheat yield declined over the three years, irrespective of tillage and mulch treatments, due to less favourable weather conditions for wheat production. Rice yield declined in the second year due to weed pressure, disease infestation from neighbouring fields, and possibly other unidentified factors. The lower yield of ZTDSR than CTDSR appeared to be due to heavier weed infestation, suggesting that weed control in DSR could be more problematic in ZT systems. Rice straw mulch (6-7 t ha-1) significantly improved the performance of ZT wheat in terms of tillering, biomass accumulation and spike density, with the differences appearing early during the first crop. This suggested a direct effect of mulch by conserving moisture, rather than changes in soil properties, which can take years to develop. With soil matric potential-based irrigation scheduling, mulch delayed the time of irrigation, and reduced the number of irrigations in CT wheat by two in the first year, and by one in both ZT and CT wheat in the third year. There was no significant carry over effect of rice straw mulch in wheat on the performance of the DSR, regardless of tillage treatment; at the time of sowing ZTDSR, there were <2-2.5 t ha-1 of degraded rice straw on the soil surface, which rapidly disappeared under frequent wetting and drying in the hot and humid conditions. In the first 2.5 years, there was no evidence to support the hypothesis that crop performance of the double zero till RW system will decline over time in the absence of residue retention in comparison with the residue retained double ZT system; longer term studies are needed given the findings in maize-wheat systems the yield with ZT in the absence of residue retention begins to decline after several years of implementation.The APSIM model performed well in simulating growth and yield of both rice and wheat crops, soil profile (0-120 cm) water dynamics over 1.5 years (during rice, wheat and fallow phases), and evapotranspiration (ET) and drainage (below 120 cm) from wheat, but consistently over-predicted soil evaporation (Es) from both rice and wheat.
|Qualification||Doctor of Philosophy|
|Award date||26 Sep 2016|
|Place of Publication||Australia|
|Publication status||Published - 2016|