Effects of long-term wheat straw returned to field on crop yield and soil chemical properties in soybean-wheat rotation areas

Abstract: Wheat straw returning is one of the main ways to improve soil fertility. Long-term straw returned to field combined with chemical fertilizer can maintain soil fertility. It should be combined with crop rotation system and fertilization management to maximize advantages and avoid disadvantages. The impact of straw returned to field on crop yield and how to fertilize when straw returning are the issues of great concern to agricultural producers. In order to clarify the effect of long-term straw returned to field in wheat-bean rotation on crop yield and soil nutrient, this paper conducted the experiments in the long-term positioning experimental station in Heihe district of Heilongjiang province, and adopted split-plot test method. The main treatment was straw returning to field and non-returning to field, secondary treatment was different fertilization for low, medium and high level. The experiment started in 1980 with wheat-soybean-wheat and wheat-soybean rotation models. The effects of wheat straw returning to field and different fertilization levels on crop yield under wheat-soybean rotation conditions were investigated for 38 consecutive years (1980-2018). The results showed that there was no significant difference in years of yield of wheat, soybean or wheat planted every other year after wheat straw returning. The medium-fertilizer was 7.42%-10.81% higher than that of low-fertilizer area on soybean with continuous fertilization, achieved significant difference level. The yield of wheat increased by 14.52%-19.33% in high-fertilizer area compared with low-fertilizer area. The effect of wheat straw returning on soybean yield was 5.91% higher than that of non-returning in the early stage (1-6 season) and 7.52% higher in the late stage (7-16 season). The yield of wheat increased by 0.31% and 0.22% in early stage (1-5 seasons) and late stage (6-16 seasons) compared with non-returning to field. Generally speaking, after wheat straw returning to the field, the frequency of crop yield reduction in the early stage is high, while the frequency of yield increase in the later stage is high. In Heihe area, the long-term application of wheat straw to field had no significant effect on soil organic matter, total nitrogen, alkali nitrogen, total phosphorus, available phosphorus and total potassium, while the content of available potassium increased significantly. Long-term fertilization had a significant impact on soil nutrients. High fertilizer level could significantly increase the contents of soil organic matter, total nitrogen, alkali nitrogen and total phosphorus. Long-term fertilization also reduces soil pH value, leading to acidification of soil.