Effect of wheat straw return to soil with zero-tillage on maize yield in irrigated oases

Yield capability is a key factor for crop growth and yield formation. The response of yield capability of crops to straw return to soils usually has been important in establishing highly efficient cropping systems and optimizing cultivation practices. A field experiment was carried out in a typically irrigated oasis region in 2009-2012 to determine the effects of yield capability of maize with different treatments of wheat straw return to soil and different tillage operations. The tillage operations included (i) no tillage with straw standing (NTSS), where no tillage was combined with 25 cm length wheat straw standing in the field after wheat harvesting in the previous fall; (ii) no tillage with straw covering (NTS), where no tillage was combined with 25 cm length wheat straw chopped and evenly spread on the soil surface at wheat harvest in the previous fall; (iii) tillage with straw incorporation (TIS), where 25 cm length wheat straw was incorporated into the soil through conventional deep tillage (30 cm) at wheat harvest in the previous fall; and (iv) conventional tillage (as control), where conventional deep (30 cm) plow was done with wheat straw removed from the field. The results showed that compared with the control, wheat straw return treatments reduced leaf area index (LAI) and leaf area duration (LAD) of maize before the large bell mouth stage. However, it increased LAI and LAD of maize after silking, which effectively delayed senescence. No tillage with straw standing and straw covering (NTSS and NTS) had the best effects on senescence delay among all treatments. Mean leaf area index (MLAI) increased by 12.8% under NTSS, 19.1% under NTS and 7.0% under TIS. Similarly, total LAD increased by 12.9% under NTSS, 18.6% under NTS and 6.8% under TIS. Specifically, the increase in MLAI and LAD under NTSS and NTS treatments was the highest. No tillage with straw retention improved mean net assimilation rate (MNAR) of maize growth season, which was 10.7% greater under NTSS treatment than under the control. But NAR of maize increased before silking, and decreased after silking under treatments of no tillage with straw retention, compared with the control. Straw return treatments had higher grain yield than the control, which increased by 13.0% under NTSS, 15.6% under NTS and 7.9% under TIS, with NTS had the best effect on grain yield increase. There was a high significant positive correlation between grain yield and MLAI, ear number (EN) and kernel number per ear (KNE), a significant positive correlation between grain yield and harvest index (HI), but no correlation between grain yield and MNAR. Increased MLAI, EN, KNE and HI were the main reasons for high grain yield of maize under wheat straw return conditions. No tillage with 25 cm length straw mulching over the soil surface (NTS) was the most suitable straw return strategy for optimal yield capability. Based on the results therefore, no-tillage with 25 cm length straw return to soil was recommended as the most feasible cultural method to optimize yield capability of maize ration with wheat in irrigated oasis regions.