Study On Soil Organic Matter Effect On Soil Nitrate Nirtrogen Leaching Losses In Ningxia Yellow River Irrigation Area

The return flow is becoming the major pollutant source deteriorating the quality of the Yellow River in Ningxia Irrigation Area, and the leaching of the nitrate nitrogen is also the source of the return flow pollution. Search the technology which can control the nitrate nitrogen leaching have the significance to ensure the quality of the Yellow River. We make the research based on the typical paddy testing in the Irrigation Area, the nitrate nitrogen leaching loss in different soil layers of paddy winter-spring fallow period and growth period is measured by the method of resin-core, soil percolate is extracted by the device of soil solution extracting, soil organic matter and soil active organic matter in the relevant soil layers is also measured at the same time. The influence of the nitrate nitrogen leaching loss and the dynamic change of SOM and ASOM and the correlation is analyzed under the situation of applying pig manure on the basis of the normal fertilization. Main results are as follows:1) During the winter-spring fallow period, the nitrate nitrogen leaching loss of three treatment is 0.66 kg/ hm²,0.73 kg/ hm²,0.79 kg/ hm² respectively at the depth of 30 centimeter, and is 0.67 kg/ hm²,1.01 kg/ hm²,0.95 kg/ hm² respectively at the depth of 60 centimeter, and is 0.99 kg/ hm²,0.89 kg/ hm²,0.87 kg/ hm² at the depth of 90 centimeter. Contrast with CK, the increased proportion is 10.61%,19.70% respectively in the treatment of T₁,T₂ at the depth of 30 centimeter,and is 50.75%,41.79% respectively in the treatment of T₁,T₂ at the depth of 60 centimeter; the reduced proportion is 10.10%,12.12% respectively in the treatment of T₁,T₂ at the depth of 90 centimeter. From this aspective, the nitrate nitrogen leaching loss is increased at the depth of 30centimeter and 60 centimeter, and reduced at the depth of 90centimeter. Contrast with the 60 centimeter, the increased rate is higher in the 30 centimeter significantly. In the growth period of the rice, the nitrate nitrogen leaching loss of three treatment is 17.05 kg/ hm²,17.77 kg/ hm²,17.67kg/ hm² respectively at the depth of 30 centimeter, and is 15.81 kg/ hm²,15.03 kg/ hm²,13.61 kg/ hm² respectively at the depth of 60 centimeter, and is 17.65 kg/ hm²,16.33 kg/ hm²,15.22 kg/ hm² at the depth of 90 centimeter. Contrast with CK, the increased proportion is 4.22%,3.64% respectively in the treatment of T₁,T₂ at the depth of 30 centimeter,and is 4.93%,13.92% respectively in the treatment of T₁,T₂ at the depth of 60 centimeter; the reduced proportion is 7.48%,13.77% respectively in the treatment of T₁,T₂ at the depth of 90 centimeter. From this aspective, the nitrate nitrogen leaching loss is increased at the depth of 30centimeter, and reduced at the depth of 60 centimeter and 90centimeter. Contrast with T₁, the increased rate is higher in T₂ treatment significantly.2) The daily average nitrate nitrogen leaching loss is better than nitrate nitrogen leaching loss on the evaluation of nitrate nitrogen leaching severity. From transplanting to peak tillering stage, especially to formal tillering stage is the major stage of the nitrate nitrogen leaching, and is the critical period of controlling nitrate nitrogen leaching, the leaching loss account for 37% to 50% of the total leaching loss in this period. Application of organic manure can avoid leaching of the surplus nitrogen in the earlier stage, can make the nitrate nitrogen distribution balanced in tillering, jointing, boot and postulating stage, can ensure the nutrient is absorbed by the rice toot system. 3) The dynamic change of soil organic matter (SOM) and soil active soil organic matter (ASOM) is founded in the growth period of rice, and two of them is decreased with the deepen of the soil layer, and the content of them in the harvest is higher than the transplanting. The leaching of SOM and ASOM is also founded in the growth period of rice. The growth and decline state of SOM and ASOM is presented in the different soil layer, and the change is delayed with deepen of the soil layer. The peak of SOM is earlier than CK in the layer of 30 centimeter, and later than CK in the other layer with applying the organic manure. Two peak of ASOM is emerged in the early and later period respectively, and the lower value is lasted in the vigorous growth period. The rangeability of ASOM is increased with deepen of the soil layer in the growth period; SOM is preserved in the harvest because of the inactivation which can improve the content of SOM.4) During the winter-spring fallow period, the correlation is positive remarkable between the nitrate nitrogen leaching loss and SOM,ASOM in the depth of 30 centimeter, the coefficient is 0.8623and 0.8469 respectively. In the growth period of the rice, the correlation coefficient is 0.4792,0.0692 respectively at the depth of 30 centimeter; and is 0.3711,-0.1865 respectively at the depth of 60 centimeter; and is 0.3981,-0.1277 respectively at the depth of 90 centimeter. The nitrate nitrogen leaching loss with the correlation of SOM is higher than ASOM, this results is differect with other study which showed ASOM have the higer indicative function than SOM.5) The lower value of SOM and ASOM is found in Ningxia Yellow River Irrigation Area, there is 95% of SOM under 15mg/kg, and the biggest value is only 19.04mg/kg;there is 76% of ASOM is between 1.0mg/kg and1.5mg/kg, and only 11% of ASOM is higher than 1.5g/kg. The serious residual of nitrate nitrogen is found in Ningxia Yellow River Irrigation Area, the biggest value is 44.61mg/kg, and the average is 19.84 mg/kg. Straw returning and applying manure technology is advised with the consideration of the formal study results and the using of straw and manure. The leaching loss is reduced and the yield is increased by using these technologies.