Effects Of Straw Mulching On The Temporal And Spatial Distribution Characteristics Of Soil Nitrogen And Phosphorus In Black Soil Area

The black soil area is an important commodity grain base in China,and is also a famous production area of corn and soybean.The sustainable development of agriculture in this area has great significance to national food security.For natural factors and unreasonable use,soil degradation in this area is serious,and soil properties such as soil fertility and soil water storage capacity deteriorated gradually.Straw returning plays an important role in reducing soil erosion,improving soil structure,increasing soil fertility,adjusting soil temperature and enhancing water use efficiency.Thus,it has been widely used to solve soil degradation in black soil area and regulate rationally and use efficiently soil resource.In previous studies,the research on influence of straw mulching amount combined with mulching time on soil nutrient was less.Therefore this paper took farmland in black soil area of Northeast China as the research object and measured soil nitrogen and phosphorus content under different straw mulching amounts combined with mulching time,analyzed temporal and spatial distribution characteristics of soil nitrogen and phosphorus content under different straw mulching amounts and mulching period and evaluated effects of straw mulching amounts and mulching period on soil nitrogen and phosphorus and crop with comprehensive index method.The results revealed temporal and spatial distribution mechanism of soil nitrogen and phosphorus under straw mulching in black soil area,and dete rmined the optimal combination of straw mulching amount and mulching period in studied area,which could provide reference for application of straw mulching technology and efficient use of soil resources in studied area.The main conclusions were as follows:(1)Straw mulching in three-leaf period could increase the soil nitrogen content(nitrate nitrogen,ammonium nitrogen and total nitrogen)during the whole growth period.Except for40-60 cm soil layer,content of soil nitrate nitrogen increased with the increase of straw mulching amount in other soil layers.As the depth of the soil layer changed,the soil nitrate nitrogen content in the rest of the growth period except for the branching period gradually decreased as a whole.The soil ammonium nitrogen content had no obvious change with soil depth and growth period,and increased with the increase of straw mulching amount under same straw mulching period.With the change of growth period,the soil total nitrogen content did not show obvious changes on the whole.When straw mulching amount was 1.2 kg/m~2 in three leaf-stage,the total nitrogen content in different soil layers and growth stages was the highest.(2)The soil available phosphorus content in 0-30 cm soil layer first decreased and then increased with the change of growth period,and the one in 30-60 cm soil layer did not show obvious change.When the straw mulching amount was 1.2 kg/m~2,the soil available phosphorus content increased.When the straw mulching amount was 0.8 kg/m~2,the soil available phosphorus content increased in the seedling and branching stages,and decreased in other growth periods.When the straw mulching amount was 0.4 kg/m~2,the soil available phosphorus content decreased.Under the condition of the same straw mulching period,the soil total phosphorus content gradually increased with the increase of straw mulching amounts,and did not show obvious change with the growth period and soil depth.(3)Contrasted with the control,soil nitrogen and phosphorus content in 0-60 cm soil layer under 1.2 kg/m~2straw mulching amount and three leaf-stage mulching condition showed significant difference,the increase range was between 12.11%-134.32%.The proportion of soil nitrate nitrogen and ammonium nitrogen content to total nitrog en in the whole growth period of soybeans,straw mulching treatment were overall higher than the control,and the proportion of soil available phosphorus content to total phosphorus content is lower than the control.The proportion of soil nitrate nitrogen and available phosphorus to the total nitrogen and total phosphorus content also increases with the increase of the amounts of straw mulching.The Perason analysis showed that the soil nitrate nitrogen and ammonium nitrogen were highly positive correlatio n,nitrate nitrogen,ammonium nitrogen and total nitrogen were negatively correlated,and available phosphorus was positively correlated with total phosphorus as a whole.The RDA analysis shows that straw mulching time,mulching amount and available phosph orus in 0-60 cm soil layer averagely explain 35%,27.3%and 26.2%of the change in soil total nitrogen and phosphorus,and soil nitrate nitrogen was the main influencing factor of crop growth and yield.(4)The comprehensive evaluation of soil nitrogen and phosphorus and crop effect showed that the optimal combination of straw mulching amount and straw mulching period in studied area was TM3.