Effects Of Rice Straw Returning And NPK Fertilizer Application On Soil Nutrients And Rice Yield

Heilongjiang province is the main japonica rice production area in cold region of China,and the total rice yield in Heilongjiang province accounted for 13.7%of the national total rice yield in 2020.With the continuous increasing of rice yield,the amount of rice straw also increases.In order to avoid environmental pollution caused by a large number of straw burning in the open air,the scientific and effective implementation of rice straw returning is very important for the sustainable development of rice.The"14th Five-Year Plan"for Circular Economy Development and the no.1 Central Document in 2021 clearly required that more straw should be returned to field and cultivated the black soil.Rice straw returning can compensate for the potential soil fertility consumption and provide nutrients for rice growth instead of reduced fertilizer.At the same time,reasonable fertilization is an important cultivation measure to ensure the supply of soil nutrients,improve soil fertility and increase crop yield.Therefore,the combination of rice straw returning and NPK fertilizer is beneficial to improve soil quality and yield of rice in cold region.This test was conducted in the Northeast Agricultural University in 2021,in the school test base,by pot cultivation,Rice straw returning was taken as main factor,two treatments were set including no rice straw returning（S0）and rice straw reurning（SR）.Fertilizer application was taken as sencondary factor,five treatment were set including no N（PK）,no P（NK）,no K（NP）,no NPK（F0）,NPK fertilizer（NPK）.The NPK content in soil,NPK content of rice plant,photosynthetic parameters,the change of rice yield index were measured under no straw returning and straw returning treatments to study the effect of straw returning and NPK fertilizer on soil nutrient and rice yield.This study provided theoretical basis and reference for analyzing the effects of rice straw returning and NPK fertilizer on soil fertility and yield contribution in cold region of northeast China.The test results show that:（1）Straw returning and NPK fertilizer had significant effects on soil nitrogen.Straw returning for 6 consecutive years significantly increased soil total nitrogen,NH₄⁺-N and NO₃^--N contents.Under straw returning,combined application of NPK fertilizer had no obvious effect on soil total nitrogen and NO₃^--N,but significantly increased NH₄⁺-N contents.Under straw returning,combined application of NPK fertilizer significantly increased soil total nitrogen,NH₄⁺-N and NO₃^--N contents.（2）Straw returning and NPK fertilizer had significant effects on soil P.The contents of total P and available P in soil were significantly increased by straw returning for 6 consecutive years,the contents of total P and available P in soil were significantly increased under straw returning and no straw returning,especially with NPK combined application.（3）Straw returning and NPK fertilizer had significant effects on soil K content.The contents of total K and available K in soil were significantly increased by straw returning for 6 years,but the effects of straw returning combined with NPK fertilizer on soil total K and available K contents were not obvious,and the contents of total K and available K in soil were significantly increased under no straw returning.（4）Rice straw returning and NPK fertilizer had significant effects on the NPK contents in rice grains.The nitrogen,phosphorus and potassium content of rice grain was significantly increased by straw returning for 6 consecutive years,but the combined application of NPK fertilizer had no significant effect on grain nitrogen content.The combined application of NPK fertilizer had no significant effect on grain nitrogen content,but significantly increased grain phosphorus and potassium content.（5）There was a correlation between soil NPK levels and plant NPK levels.There was a significant positive correlation between soil nitrate,total nitrogen and nitrogen content in roots,stems,leaves and grains.There was a significant positive correlation between soil available P content and P content in roots,stems and leaves.There was a significant positive correlation between total P in soil and P in stem,and a significant negative correlation between total P in soil and P in grain.There was a significant positive correlation between soil available K content and K content in roots and stems.There was a significant positive correlation between soil total K content a nd K content in roots,stems,leaves and grains.（6）SPAD and Phi2 increased firstly and then decreased with the growth period,and reached the peak at heading stage.VH+firstly decreased,then increased and then decreased,and reached the peak at the filling stage.Phi NPQ firstly decreased and then increased,and reached the peak at the filling stage.At the filling stage,the combined application of NPK fertilizer significantly decreased SPAD and v H+,and significantly increased Phi2 and Phi NPQ under straw returning condition,while the combined application of NPK fertilizer had no obvious effect on SPAD and v H+,significantly decreased Phi2 and significantly increased Phi NPQ under no straw returning.（7）Rice straw returning and NPK fertilizer had significant effects on grain NPK accumulation and yield of rice.Straw returning for 6 years significantly increased grain NPK accumulation,and straw returning and no straw returning combined with NPK fertilizer increased grain NPK accumulation.The plant height,tiller,effective tiller,grain number per panicle and dry matter weight of root,stem and leaf of rice were significantly increased and thousand-grain weight of rice decreased with and without rice straw returning.Rice yield was significantly increased by applying NPK fertilizer in rice straw returning and no straw returning conditions,but the variation of rice yield was not consistent between years.