不同施氮量下覆膜滴灌玉米相对根长密度模型研究

为探明施氮量对宁夏引黄灌区覆膜滴灌玉米根长密度(RLD)的影响,设置5个施氮水平和1个对照(CK,不施氮与不覆膜)进行试验,测定玉米RLD,建立不同施氮量下相对根长密度(NRLD)模型,并加以检验。结果表明:不同施氮处理的玉米RLD分布区域均随土层深度的增加而减小,且大部分集中在0～20 cm土层;随着施氮量的增加,RLD分布区域明显扩大; NRLD分布满足三阶多项式函数模型,模拟曲线的决定系数R2为0.951,模型检验结果R2为0.845,均方根误差(RMSE)为0.248,拟合效果好,但该多项式模型不能保证NRLD在相对取样深度Zr为1时达到0,故对玉米NRLD分布多项式模型进行优化。优化模型验证结果显示,各施氮处理RMSE不大于0.308,CK、N0、N1、N2、N3和N4处理的标准化均方根误差分别为0.242、0.193、0.184、0.226、0.208和0.273,R2分别为0.903、0.953、0.920、0.944、0.962和0.898,具有较高的拟合度,解决了NRLD在Zr=1时达到0的问题。本研究可为宁夏引黄灌区膜下滴灌玉米NRLD分布拟合、根系养分吸收和施肥管理提供理论参考。

Effects of Nitrogen Application Rate on Root Length Density of Maize under Drip Irrigation with Mulch

The objective was to establish the root length density (RLD) distribution relation model of maize at different nitrogen rates, and explore the effects on RLD of maize under drip-irrigation with plastic film in Ningxia. The relationship was improved between the spatial distribution characteristics of maize root system and nitrogen absorption. The interaction was promoted between maize root and soil. The nitrogen fertilizer application rate of maize was optimized under the condition of water and fertilizer integration. There were five nitrogen fertilizer application rates and the treatment of no application of N fertilizer and no mulching as control (CK) in this experiment. The experiment plot was in farm of Pingjibao which was located in Yinchuan City, Ningxia, Northwest China. The RLD of drip irrigated maize was measured. The model of relative root length density (NRLD) was established and verified at different N application rates. The results showed that the RLD distribution of drip-irrigation maize was decreased with the increase of depth of soil layer in the N fertilization treatment. The vertical distribution of root length in the 0~20cm soil layer was the largest. The RLD distribution range of maize was expanded significantly with the increase of N fertilizer application rate. The NRLD value of maize in all treatments were consistent with cubic polynomial function. The determination coefficient of simulation curve was 0.951. The results of the evaluation showed that determination coefficient of linear relationship between simulated and observed values of NRLD was 0.845, and the root mean square error (RMSE) was 0.248. The fitting result of cubic polynomial function had a good effect. But it should be noted that the polynomial model could not guarantee that the value of NRLD reached zero at the Zr was equal to 1. Therefore, the cubic polynomial model of NRLD maize was optimized and verified. The verification results of the optimized model showed that RMSE in all nitrogen treatments was not more than 0.308, the standardized root mean square error (nRMSE) were 0.242, 0.193, 0.184, 0.226, 0.208 and 0.273, and determination coefficient values were 0.903, 0.953, 0.920, 0.944, 0.962 and 0.898, respectively. It not only had a higher fitting degree, but also solved the problem that the value of NRLD reached zero at the Zr was equal to 1. It was more suitable to simulate NRLD distribution of drip-irrigation under plastic film of maize for different nitrogen rates. All these results given can also provide a theoretical reference for nutrient absorption and fertilization management of drip-irrigated maize root system in the irrigation area of Ningxia.