Effects Of Nitrogen And Phosphorus Regulation On Soil Nitrogen Distribution And Utilization In Paddy Fields

Nitrogen is the first of the three elements required for rice growth and development.At present,excessive nitrogen input in China has caused nitrogen fertilizer waste and environmental pollution.Straw returning to the field can effectively improve the soil.Under the condition of straw returning to the field,the reasonable combined application of nitrogen and phosphorus fertilizer can improve the soil nutrient balance,improve the fertilizer utilization rate,reduce the fertilizer loss,and alleviate the environmental pressure caused by excessive fertilization.Therefore,it is particularly important to reduce the environmental pollution caused by nitrogen loss without reducing rice yield and nitrogen use efficiency.From 2017 to 2018,through the positioned fertilization test in the agricultural park of Mianyang Southwest University of science and technology,under the condition of straw returning to the field,the split plot design was adopted to set four nitrogen fertilizer application levels:N0（no nitrogen fertilizer）,N1(90 kg·hm^-2),N2(150 kg·hm^-2),N3(270kg·hm^-2),and four phosphorus fertilizer application levels:P0（no phosphorus fertilizer）,P1(15 kg·hm^-2),P2(30 kg·hm^-2),P3(60 kg·hm^-2),The changes of nitrogen storage before and after rice planting,the vertical distribution characteristics of soil nitrogen in 0～1 m soil layer and the nitrogen use efficiency of Deyou 4727 were analyzed,and the nitrogen and phosphorus application scheme suitable for local rice cultivation and environment-friendly under straw returning was explored.The results show that:1.Under the condition of straw returning,nitrogen application in paddy field was beneficial to the accumulation of soil nitrogen in plough layer.In the two-year experiment,the total nitrogen storage in 0～40 cm soil layer after rice harvest was increased by 4.63%compared with that before planting 4.63×10^-3kg·hm^-2、48.24×10^-3kg·hm^-2.Fertilization and irrigation can promote the downward leaching of nitrate nitrogen.After harvest,the reserves are reduced by 46.46 kg·hm^-2and 206.43 kg·hm^-2respectively compared with those before planting.Ammonium nitrogen is easy to be enriched on the soil surface.Continuous drought and flood rotation will cause the loss of surface ammonium nitrogen.The reserves of ammonium nitrogen increased by 163.30 kg·hm^-2in 2017 and decreased by 102.33 kg·hm^-2in 2018.2.When the input of phosphorus fertilizer was low,the effect of increasing nitrogen fertilizer on the total nitrogen content of deep soil（60～100cm）was not significant.Under the conditions of P0 and P1,the total nitrogen content of deep soil（60～100cm）in N3 treatment was lower than that in N0 treatment by 0.19 mg·g^-1and 0.05 mg·g^-1respectively,but there was no significant difference;With the increase of phosphorus fertilizer input,the total nitrogen content of deep soil increased with the increase of nitrogen fertilizer application.Under P2 and P3 conditions,the total nitrogen content of deep soil（60～100 cm）under N3treatment increased by 0.16 mg·g^-1and 0.21 mg·g^-1respectively compared with N0 treatment,and the difference was significant.Increasing the application of nitrogen fertilizer will increase the leaching of nitrate nitrogen in deep soil and increase the accumulation of nitrate nitrogen in deep soil layer.The nitrate nitrogen content in deep soil（60～100 cm）of N3P2 treatment is 1.55μg·g^-1higher than that of N0P2 treatment,and that of N3P3treatment is 1.81μg·g^-1higher than that of N0P3 treatment.Proper application of phosphorus fertilizer promoted the absorption of nitrogen by rice and reduced the content of nitrate nitrogen in deep soil,which was the most significant under the condition of N2,and the decrease of P3 was 83.94%compared with P0.3.The response trend of rice yield to different nitrogen application rates in the two years was the same,which showed that it increased with the increase of nitrogen application rate.Continuous nitrogen application may reduce the yield increasing effect of nitrogen fertilizer.Compared with N0P0,the yield growth in 2018 under N1P0 treatment increased by 10.41%compared with that in 2017,and the yield growth under other treatments decreased by8.09%～25.99%.The response of rice to phosphorus is less than that of nitrogen fertilizer.The two-year field test results show that nitrogen fertilizer has a very significant impact on the yield of hybrid rice.In 2017,phosphorus fertilizer has a significant impact on the yield of hybrid rice,and in 2018,phosphorus fertilizer has no significant impact on the yield of rice.4.Under different phosphate fertilizer application conditions,the nitrogen grain production efficiency was different,and the highest was 0.94 kg·kg^-1under n1p0 treatment;Nitrogen harvest index and Nitrogen Agronomic use efficiency first increased and then decreased with the increase of nitrogen application rate;The partial productivity of nitrogen fertilizer decreased significantly with the increase of nitrogen application rate.Under the conditions of P0,P1,P2 and P3,the highest productivity was under N1 treatment,which were 82.89kg·kg^-1,71.89 kg·kg^-1,78.85 kg·kg^-1and 77.30 kg·kg^-1respectively.Under the conditions of 150 kg·hm^-2of nitrogen fertilizer and 30 kg·hm^-2of phosphorus fertilizer,the rice yield and nitrogen use efficiency can maintain a high level,and the soil nitrogen leaching loss is low.Therefore,this fertilization scheme is suitable for agricultural production under the conditions of similar soil fertility and straw returning to the field,and is friendly to the environment.