Effects of strip-collected chopping and mechanical deep-buried return of straw on physical properties of soil

Abstract: As a direct and effective way to utilize crop straw, long-term straw returning has the effect of improving soil fertility and physical properties. Straw returning in Heilongjiang Province can be divided into three types: mulching return, plough-layer return and deep-buried return, with different models having different effects on the soil. Covering soil with straw significantly increases humidity of the soil but reduces the soil temperature during seedling stage, thus, it has both positive and negative effects on soil physical properties, with different results in different researches. The return of straw to the plough layer can improve the physical and chemical properties of the soil, reducing the soil bulk density and increasing the soil water-storage ability. However, a large number of studies have concluded that plough-layer return can cause the soil to be fluffy and reduce water-retaining property because of the accumulating of the straw in the plough layer. It may cause the delay of crop emergence as well as reducing the crop yield for that the straw corruption may consume soil nutrients, resulting in insufficient soil nutrient during seedling growth. The technology of deep-buried return of straw can overcome the drawbacks of straw mulching and plough-layer return in agricultural production in North China. This technique can avoid problems of low ground temperature and delayed emergence of seedlings caused by mulching return in spring in cold areas and avoid problems of low quality of mechanical sowing and low emergence rate resulted from plough-layer return. Meanwhile, it can improve deep soil fertility and improve the soil physical properties. On the basis of deep-buried return, this paper puts forward the technology of strip-collected chopping and mechanical deep-buried return. The straw smashing and strip-collected machine is used together with moldboard plow to deeply bury the smashed straw under the plough layer. It can return the straw strips that are four times of the per unit yield deeply to the soil, forming the fertilization ditch which is separated by 180 cm. In the early stage, the effects of strip-collected chopping and mechanical deep-buried return of straw on crop growth and soil fertility change are studied. In order to clarify the soil physical properties after straw being concentrated into a strip returning, three treatments for comparative studies are carried out in this paper: normal tillage, plough-layer return and straw concentrated into a strip returning. The results show that after 3 years of continuous returning to the field, the soil consolidation rate and bulk density of 0-30 cm soil layer decrease by 1.17%-6.21% and 0.02-0.14 g/cm3 respectively, with gas tolerance and water holding capacity increased. The total soil porosity increases by 0.70%-5.98% and the effective porosity increases by 0.22%-2.69%, the difference being significant than the control group. As in the control group, the soil consolidation rate and bulk density of 0-20 cm soil layer decrease by 2.42%-4.30% and 0.09-0.12 g/cm3 respectively, with gas tolerance and water holding capacity increased. The total soil porosity and the effective porosity increase as well. The soil layer of straw concentrated returning is deep and interval work is conducted every three years. In the long run, the physical properties of the whole soil can be improved and the tillage layer can be thickened about 10 cm.