Improving of soil physical and chemical properties and increasing spring maize yield by straw turnover plus nitrogen fertilizer

Abstract: Improving plough layer is necessary for solving the problems of shallow and compacted plough layer and plough layer lack, which are caused by a long-term unreasonable tillage. In order to examine the effects of straw turnover and different nitrogen (N) additions to plough layer on the yield, soil physical properties, root morphology of spring maize in dry land, 6 treatments were conducted in Tieling of Liaoning Province from 2014 to 2015. The 6 treatments included straw turnover of 0 kg/hm2 and adding pure N of 0 kg/hm2 (S0F0), straw turnover of 9 000 kg/hm2 and adding pure N of 0 kg/hm2 (SN0), straw turnover of 9 000 kg/hm2 and adding pure N of 112.5 kg/hm2 (SN1), straw turnover of 0 kg/hm2 and adding pure N of 225 kg/hm2 (S0N2) (local traditional cropping pattern, CK), straw turnover of 9000 kg/hm2 and adding pure N of 225 kg/hm2 (SN2), straw turnover of 9 000 kg/hm2 and adding pure N of 337.5 kg/hm2 (SN3). The result showed that treatments of straw turnover and different N additions significantly influenced spring maize yields, soil physical properties and root morphology. The treatment of straw turnover of 9 000 kg/hm2 and N addition of 225 kg/hm2 had the highest yield, increasing by 1.10%-11.56% compared with none straw turnover. This increase in yield of spring maize was mainly contributed by the augmented 100-grain weight and grain number, as well as the decreased bald tip. The N addition did not promote the yield while improved the biomass of whole crop. On the same level of N addition, the spring maize yield of straw turnover treatment was 3.08%-3.56% higher than that of none straw turnover treatment, whereas the harvest index of straw turnover treatment was 2.43%-3.12% lower than that of none straw turnover treatment. Plough layer construction of straw turnover and N addition could significantly lower soil bulk density, especially in soil depth of 15-20 cm. Treatment of straw turnover plus N fertilizer to plough layer construction could also loosen top soil, and further enhance rainwater infiltration and soil water content, whereas the similar trend did not be observed for the treatment of N addition. The soil three-phase structure derived from SN2 treatment was the optimum, with 25% liquid phase, 25% gas phase and 50% solid phase, respectively. The root indices, including amount, length, volume and dry weight of root of spring maize, were better than the indices of none straw turnover treatment. On the same level of N addition, the amount, length, volume and dry weight of root of spring maize were 1.90%, 10.27%, 1.25% and 2.77% higher than the corresponding index of treatment of none straw turnover, respectively. Consequently, we suggest that the treatment of straw turnover of 9 000 kg/hm2 and N addition of 225 kg/hm2 is the optimum approach of plough layer construction and technology of straw turnover in the brown soil area of northern Liaoning Province, which is recommended to be applied in agricultural production.