| Heilongjiang Province is a typical cold paddy area and it is also the main rice production area in China.In 2017,more than 23 million tons of rice straw were produced in Heilongjiang Province.Nearly half of the straw was wastedand the rate of returning to land reached only about 10%.Researches showed that after rice straw was returned to the field,crops absorb a large amount of organic matter and nutrients released after decomposition of straw.Not only could we reduce the application of chemical fertilizers,increase economic efficiency,but it was also an important measure to cultivate soil fertility.At present,there are still many reports on rice straw returning in Heilongjiang cold region,but there was a lack of systematic research on the effect of straw returning on the physical and chemical properties of paddy soil and plant growth and development.In this experiment,different rates of nitrogen application were combined with two methods of straw returning.The experiment design was as follows.Straw powder returning:T1,Nitrogen-free;T2,Nitrogen fertilizer with 35%postponed in application;T3,Nitrogen fertilizer with 20%postponed in application;and T4,Nitrogen fertilizer with 20%postponed in application and calcium magnesium phosphate fertilizer.Bundle straw returning:ST1,Nitrogen-enhanced 20%;ST2,Nitrogen fertilizer with35%postponed in application;ST3,Nitrogen fertilizer with 20%postponed in application;and ST4,Nitrogen fertilizer with 20%postponed in application and calcium magnesium phosphate fertilizer.The research mainly studied the effects of the two different straw returning methods on soil basic nutrients,nutrient accumulation in plants,and the rice yield.The main resultswere as follows:1.When the nitrogen level was the same,the method of smashing and returning to the soil in the current season had a greater increase in the basic nutrient content in the soil than that in the whole plant.In the same manner of returning to soil,the 6.5:3.5 shift of nitrogen fertilizer treatment for alkaline nitrogen,available phosphorus,and available potassium increased significantly more than nitrogen,nitrogen-free treatment,nitrogen fertilizer shift,8:2 and increased calcium magnesium phosphate fertilizer treatment.Total nitrogen and organic matter were also the largest increase.The increase of calcium,magnesium and phosphate fertilizers was significant for the improvement of available nutrients for total nitrogen and organic matter.Therefore,straw returning with the appropriate amount of nitrogen postponed in application could effectively improve basic soil nutrients.2.The method of powder straw returning had a larger effect on nutrient and dry matter accumulation in plants than the bundle straw returning method.Under the same returning method,T2(nitrogen fertilizer with 35%postponed in application)had a significantly larger effect on nutrient and dry matter accumulation in plants than other treatments.T4 had no significant effect on the nutrient and dry matter accumulation in plants.Therefore,straw returning with the appropriate amount of nitrogen postponed in application could promote the absorption of nutrients and the accumulation of dry matter in rice,especially the transfer of nutrients to grain after heading.3.Comprehensively,yield under powder straw returning was higher than that under bundle straw returning,and there was a significant difference under T2.The highest yield was achieved when the 2basal panicle fertilizer was applied at 65 kg/hm~2 and 35 kg/hm~2,respectively.T4 had no significant effect on the yield.Rice yield was significantly positively correlated with panicle number,grain number per panicle and dry matter after heading.It was extremely negatively correlated with the seed-setting rate and the 1000-grain weight.Although nitrogen-enhanced treatment increased the number of panicles,it reduced the seed setting rate and the number of grains per panicle,which means coordinating different factors was the guarantee of high yield. |
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