Effects Of Snow Cover On Nutrients In Black Soil And Its Contribution

Black soil is a soil with high productivity and fertility,which plays an important role in the development of global agricultural production.Snow cover is the most common and important upper boundary condition of farmland soil during freezing-thawing period in seasonal permafrost areas in northern China.At present,many scholars have paid attention to the effects of water and heat,water and salt transport,land use mode and organic cover on soil fertility of black soil under snow cover,but no one has paid much attention to the effects of snow cover on nutrient composition and supply of black soil.Therefore,it is significant to study the influence of snow cover on the nutrient composition and supply of black soil.In this paper,outdoor repeated tests are set,black soil samples of Harbin city are taken,and six kinds of nutrients and physical and chemical properties of black soil are selected:Six soil properties,such as TOC,DOC and NO^3--N,were explored to explore the variation characteristics of nutrients under different snow depth and different cover time,and statistical methods were used to analyze the coupling relationship between nutrients in black soil.The main conclusions are as follows:（1）With different snow cover depth,SWC of black soil was significantly different with snow cover compared with bare soil control group.With the increase of snow depth,SWC of shallow black soil increased by 12.086%,20.848%,39.586%,35.893%and 33.403%,and SWC of deep black soil increased by 9.706%,16.939%,29.962%,28.540%and 27.189%,respectively.The influence of different snow depth on SWC of shallow and deep black soil was obviously different,and showed a significant increasing trend with the increase of snow depth.When mulching time is different,SWC of black soil tends to decrease significantly with the longer mulching time.With each month’s mulching time increased,SWC of shallow black soil decreased by 5.8%and that of deep black soil decreased by 5.9%.（2）When the depth of snow cover was different,the NO^3--N of black soil under snow cover was significantly different from that in bare soil control group.With the increase of snow depth,NO^3--N of shallow black soil under 10 cm and 20 cm snow cover increased by 5.861 mg/kg and 6.135 mg/kg,respectively,compared with bare soil.The NO^3--N of shallow black soil under 30 cm,40 cm and 50 cm snow cover decreased by 12.278 mg/kg,11.516 mg/kg and 10.254 mg/kg,respectively.The NO^3--N of deep black soil under 10 cm snow cover was the same as that of bare soil.However,NO^3--N in deep black soil under 20 cm,30 cm,40 cm and 50 cm snow cover decreased by 2.579mg/kg,13.432 mg/kg,12.515 mg/kg and 11.959 mg/kg,respectively.The effects of different snow depth on NO^3--N in shallow and deep black soil were significantly different,and showed a significant decreasing trend with the increase of snow depth.When the mulching time was different,the NO^3--N of black soil showed a significant decrease trend with the longer mulching time.When the snow depth increased by 10 cm,NO^3--N of shallow black soil decreased by 3.480 mg/kg and NO^3--N of deep black soil decreased by 3.092 mg/kg.（3）With different snow cover depth,compared with bare ground control group,snow cover has a significant difference on black soil DOC,but there is no obvious trend of change with snow cover depth.Compared with bare ground control group,TOC of shallow black soil under 10 cm and 20 cm snow cover increased by 0.301 g/kg and0.625 g/kg,respectively.TOC of shallow black soil under 30 cm,40 cm and 50 cm snow cover decreased by 0.61 g/kg,2.028 g/kg and 1.087 g/kg,respectively.TOC of deep black soil increased by 1.721 g/kg,2.004 g/kg,1.683 g/kg and 0.958 g/kg under 10cm,20 cm,30 cm and 50 cm snow cover,respectively,while TOC of deep black soil under 40 cm snow cover decreased by 0.042 g/kg,respectively.TOC of black soil decreased significantly with the increase of snow cover time.TOC of shallow black soil decreased by 0.332 g/kg with each additional month of mulching time,while TOC of deep black soil showed no obvious trend.（4）With different depth of snow cover,DOC in black soil was significantly different from that in bare soil control group.With the increase of snow depth,DOC in shallow black soil increased by 8.384 mg/kg,8.334 mg/kg,32.291 mg/kg,29.578mg/kg and 33.734 mg/kg,respectively,compared with bare soil.DOC in deep black soil increased by 4.104 mg/kg,7.929 mg/kg,24.751 mg/kg,21.501 mg/kg and 36.354mg/kg,respectively.The influence of different snow depth on DOC in shallow and deep black soil was significantly different,and showed an extremely significant increasing trend with the increase of snow depth.When the mulching time is different,the DOC of the black soil tends to decrease significantly with the longer mulching time.With each additional month of mulching time,the DOC of the shallow black soil decreases by9.057 mg/kg and that of the deep black soil decreases by 11.752 mg/kg.（5）The effects of different snow depth and different cover time on the variation of p H and NH⁴⁺-N of black soil were not significant on the whole,and there was no significant difference between each treatment.The influence of short-term snow cover on NH⁴⁺-N was not significant with the snow depth,which needed to be further studied by long-term snow cover observation.（6）SWC was significantly correlated with DOC,TOC,NO^3--N,NH⁴⁺-N and p H in soil nutrients under different depth of snow cover,and the correlation coefficient was large.Soil SWC showed a significant negative correlation with NO^3--N,and the number of times was the most,and was positively correlated with DOC,TOC,NH⁴⁺-N and p H,followed by the number of times of correlation with DOC.In soil nutrients under different depth of snow cover,DOC was significantly correlated with TOC,NO^3--N and p H,and the correlation coefficient was large.Soil DOC has a significant negative correlation with NO^3--N,and the number of times is the most,and it has a positive correlation with TOC and p H,followed by the number of times of correlation with p H.There was a significant negative correlation between NO^3--N and p H,and a significant positive correlation between NH⁴⁺-N and p H,and the correlation coefficient was large.In addition,TOC and NH⁴⁺-N had weak or no correlation with other nutrients.The purpose of this study was to explore the effects of different snow depth and covering time on soil nutrients and physical and chemical properties,to provide theoretical support for scientific evaluation of the effects of snow cover on soil properties,to provide basis for the protection of black soil resources and the sustainable development of human society,and to promote the utilization and research of snow resources.