[Effect of returning corn straw into soil on soil fertility]

Three-year field micro-plot experiment was conducted to study the effect of applying corn root stubble, corn straw, and the ordure of cattle fed with corn straw to improve soil fertility in northern Liaoning province. The results showed that chemical fertilizers could significantly increase the corn production, while organic fertilizers mainly improved the soil physical and chemical properties so as to increase soil fertility. In comparison with no fertilizer treatment, combination of chemical fertilizers and organic materials could increase soil organic matter by 3.06%-27.78%. The increments of soil organic matter by using different organic materials were in order of 100% corn straw > 50% corn straw > mixture of cattle ordure and soil > cattle ordure > 33% corn straw > corn root stubble. For maintaining and increasing soil organic matter, corn straw was better than mixture of cattle ordure and soil, and secondly better than cattle ordure if they contained the same carbon content. In addition, comparing with applying chemical fertilizers only, combination of chemical fertilizers and organic materials increased soil labile oxidization organic matter by 10.91%-20.67%, increased extractable humic acid by 1.43%-14.28%, raised slack/stable ratio of bonded humus by 0.07-0.19, and raised HA/FA ratio by 0.07-0.24. Meanwhile, this combination improved the soil nutrient status of N, P, and K, and the status of soil moisture and porosity, which demonstrated the increase of activity of soil organic matter and the improvement of soil fertility. So directly adding straw into soil without removing after harvest in autumn should be actively recommended, and the amount of corn straw added into soil should be 30 to 50 percent of the total production of corn straw.