| With the rapid development of agriculture and rural economy in our country, the unscientific fertilizer into the field cause the problem of the agricultural non-point source pollution. farmland ecological environmental degradation, surface water eutrophication, groundwater nitrate pollution and farmland productivity reduce have become the most important domestic research emphasis. Winter wheat and summer maize rotation is the main planting patterns and playing an important role in food production in Guanzhong plain, Shaanxi province. A part of farmland of Shaanxi province exist a problem of nitrogen fertilizer excess, it significantly increases the soil nitrate accumulation in the soil, the risk of nitrogen leaching and the apparent loss. Currently, there are a lot of research about nitrogen leaching has carried out both in China and abroad, but most of the research is main focused on NO3--N, the other nitrogen leaching form(e.g., total nitrogen, etc.)has less attention. In fact, a study shows, the form of organic nitrogen is one of the main forms of nitrogen from the leaching water., On the other hand, there is no enough study about the effect of straw returned on N leaching and N budget under wheat-maize crop rotation system. Some results showed that straw returned treatment can increase production, reduce the leaching loss, the other results have reported that straw returned treatment can improves the soil water storage capacity, it causes greater leaching losses when rainfall or irrigation happened. Therefore, using the lysimeter method to conduct a 7-year long term experiment in Guanzhong Plain of Shaanxi Province, there are 6 treatments: CK(pure N: 0 kg/hm2), OPT- N(pure N: 165 kg/hm2), OPT(pure N: 330 kg/hm2), CON(pure N: 471 kg/hm2) OPT + N(pure N: 495 kg/hm2), OPT + S(pure N: 330 kg/hm2) on the basis of OPT treatment increase the straw 5000 kg/hm2 in every season. to investigate effectsof application of nitrogen fertilizer and incorporation of straws on nitrate leaching and N budget, the main conclusions are as follows:1.The effect of nitrogen fertilizer and straw returned on the yield of wheat-maize rotation systemin a 7-year long-term experiments from 2008 to 2014, it is concluded that winter wheat recommended N fertilizer is 150 ~ 191 kg/hm2, summer maize recommended N fertilizer is 180 kg/hm2, excessive N fertilizer not only cause a decline in the yield and nitrogen utilization efficiency,but also cause the waste of resources. optimum N application+straw returned treatment can significantly increase the yield of the wheat and maize, and the average crop increase was 92.4% under wheat-maize rotation system. And about 18% higher than OPT treatment. Effect of straw returned treatment is an increasing trend, in 1-2 year,the production effect is not obvious, since 3 years, the cumulative yield of wheat and maize were higher than OPT treatment, the yield reached 43.5 t/hm2 and 61.6 t/hm2 than OPT treatment by 15.4% and 15.4%, respectively. Over time, the utilization rate of total nitrogen also increased year by year, it illustate that the previous N fertilizer can be use by the back crop. Straw return treatment not only increased the yield and the accumulated utilization rate of nitrogen under wheat corn crop rotation system, but also reduce nitrogen waste.2.The effect of the different nitrogen application and straw returned on N leaching characteristicsThe mean annual precipitation is 550 ~ 600 mm in Guanzhong plain of Shaanxi province, according to the crop water requirement, roughly 2-3 times for irrigation. Leaching may happened between 2 to 5 times under wheat –maize rotation system, high intensity rainfall and continuous rainfall could result in leaching. The result of the concentration and the loss of dynamic change showed, the loss of NO3--N and TN show great similarity. the average loss of TN is 2.47 ~ 19.97 kg/hm2, average leaching rate of TN is 0.55% ~ 0.55%; the average loss of NO3--N in 2008 to 2014 is 2.29 ~ 18.76 kg/hm2, average leaching rate of NO3--N is 0.72% ~ 3.33%. TN and NO3--N leaching and the leaching rate showed a trend of increase with the increase of N application amount. Long-term monitoring results obtained under low nitrogen treatment the proportion of NO3--N was lower, under high N application treatment of the proportion of NO3--N was higher, and on straw returned treatment the ratio of NO3--N to TN was lower than no straw returned treatment, these showed that different nitrogen fertilizer and straw returned treatment affect N leaching form. Statistical results illustrated that anual loss of both TN and NO3--N showed great postive correlation with N application rate, the regression equation of the loss of TN(y), the loss of the NO3--N(z) and N application amount(x) is y=2.425e0.0045x(R2=0.796**);z=2.151e0.0043x(R2=0.793**). Straw returned treatment did not decrease the concentrations of NO3--N and TN, but generally reduced leaching amount. 3. 0-100 cm soil mineral nitrogen distribution in 2008-2014Every year after maize harvest in2008 ~ 2014, the accumulation amount of NO3--N in 0-100 cm soil was range from 17 to 322.6 kg/hm2, the accumulation amount of NH4+-N in 0-100 cm soil was range from 2.61 ~ 60.71 kg/hm2, larger contribution to the mineral nitrogen in the soil is NO3--N, and in the same soil profile, the accumulation amount of NH4+-N is not affected by N application amount or period of fertilizing. Long-term experiment results showed that using Index Regression Analysis model forecast the relationship between the accumulation amount of NO3--N, mineral nitrogen and N application l is more accurate. the regression equation of the accumulation amount of NO3--N(y), mineral nitrogen(z) and N application amount(x) were y=36.481e0.0037x(R2=0.809**);z=55.27e0.0031x(R2=0.801**). The straw returned treatment show no effect to mineral nitrogen significantly.4. Crop-soil N apparent budget in 2008-2014monitoring results for many years showed that the OPT treatment obtain higher yield than OPT- N, compared with the CON, OPT + N treatment it improved the utilization rate of nitrogen fertilizer, reduce the apparent N loss. Overall, OPT treatment is the most appropriate amount of nitrogen fertilizer to save fertilizer resources and reduce the potential environmental risk. Statistical results illustrated N surplus had a significantly positive relationship with the annual N fertilizer inputs. the regression equation is y=37.404e0.0054x(R2=0.8995**)use the F value analyses significance test, get 1% significance level, it illustrate that it is feasible to estimate surplus N in this region. Straw returned treatment put a great influence on nitrogen budget under wheat-maize rotation system. It increased the crop N uptake, N apparent utilization and makes the surplus of nitrogen and nitrogen loss dropped substantially.although did not reduce the residual nitrogen in the soil compared with OPT treatment. |
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