垄作覆膜对土壤无机氮流失过程的影响机理

Plastic mulching, as the prevail management to promote the crop yield, can influence the inorganic nitrogen accumulation and loss in soil, through changing the soil coverage, temperature and water content. Therefore, it is of great requirement to interpret the regulating mechanism of plastic mulching on soil inorganic nitrogen loss for the field of non-point source pollution in response to plastic mulching. This project will take the plasticulture of peanut, potato, maize in yellow brown and purple soil of in the Qingtang watershed located in Danjiangkou reservoir area, as the case study. Mineralization experiment in situ will be conducted to reveal the characteristics of temperature, soil water content and the coupling effects on net nitrogen mineralization in different soil layers,and the net nitrogen mineralization model could be constructed. Then, The relationship of soil inorganic nitrogen content and its influencing factors, such as net nitrogen mineralization and LAI, will be analyzed. The amount of inorganic nitrogen loss in different ways can be obtained by detecting the inorganic nitrogen content in runoff, interflow,leakage and sediment yield at the outlet of standard plot after each rainfall. Through analyzing the relationship of inorganic nitrogen loss and the factors of inorganic nitrogen accumulation, soil water content and precipitation,the effects of plastic mulching on the processes of soil inorganic nitrogen loss could be interpreted. The result of this project would provide some scientific information on assessing and managing non-point source pollution in the slope land under plastic mulching, and contribute to designing plastic mulching tillage cultivation and controlling non-point source pollution.

地膜在农业生产中的广泛应用改变了农田地表覆盖状况与土壤水热条件，影响着无机氮在土壤中的积累与流失；阐明覆膜对土壤无机氮流失过程的影响，对于揭示土壤侵蚀非点源氮素输出机理具有重要意义。本项目以丹江口库区广泛分布的土壤类型（黄棕壤和紫色土）与常见垄作覆膜种植作物（花生与玉米等）为例，拟以青塘河小流域为典型研究区，利用野外氮矿化试验、周期性观测与统计分析，探明覆膜条件下不同层次土壤净氮矿化的水热耦合效应，分层次对土壤净氮矿化量进行模拟，定量解析土壤净氮矿化量、叶面积指数等因素对土壤无机氮积累量的影响；结合原位径流小区天然降雨观测试验，建立不同流失途径下土壤无机氮流失量与土壤无机氮累积量、土壤含水量、降雨等因子之间的定量关系，以揭示覆膜对土壤无机氮流失过程的影响机理。研究成果有助于进一步认识土壤侵蚀的非点源环境效应，并对坡耕地覆膜耕作模式设计、防治水土流失非点源污染具有重要价值。

本项目以丹江口库区典型小流域为研究区，设置不同的覆膜处理方式，以垄作玉米为例开展田间原位观测试验，研究覆膜措施对玉米各生长期不同层次土壤氮矿化的影响及其对水热条件的响应，不同覆膜处理土壤中氮素流失及积累特征。主要结果如下：（1）覆膜显著提高了玉米拔节期、抽穗期和成熟期土壤含水量；覆膜处理对玉米苗期和拔节期的土壤增温幅度大于抽穗期和成熟期。（2）覆膜处理可显著增加整个玉米生长期内的土壤净氮矿化量，从而增加整个玉米生长期内土壤氮素的积累。其中，玉米苗期和拔节期净氨化过程明显，在抽穗期和成熟期以净硝化为主。（3）玉米不同生长期影响土壤净氮矿化量的主要因子分别是：土壤温度（苗期）、土壤含水量和温度（拔节期）、土壤含水量（成熟期）。从不同土层来看，影响土壤净氮矿化量的主要因子分别是： 土壤含水量和全氮含量（0～10 cm土层），土壤温度、含水量以及全氮含量（10～20 cm土层）、土壤温度（20～30 cm土层）。（4）渗流是无机氮淋失的载体，横坡垄作系统中渗流曲线呈“S”型，且能够通过指数函数模型较好拟合（R2 > 0.995）；以垄向坡度、坡向坡度和垄高为自变量，建立二次多项式回归模型可以较好预测总渗流量（R2>0.66且p<0.05）和稳定渗流量（R2 > 0.68且p< 0.05）（5）在各处理中，硝态氮是土壤无机氮淋失的主要形态；覆膜可减少土壤氮素淋失，玉米生长中途揭膜比全程覆膜的作用更明显。回归模型表明，苗期土壤硝态氮淋失的主要影响因子是土壤温度，其它各生长期的主要影响因子是降雨量。（6）覆膜相比未覆膜显著减少了径流量、泥沙量、总氮与总磷流失，覆膜增大了硝态氮流失，但是差异不显著。（7）坡改梯降低了胡家山小流域氮素输出负荷，但耕地氮素输出负荷相对增加；TN负荷强度在坡度较低区域较为稳定，坡度较大区域有所增加。.上述研究成果，有助于深入理解耕作模式对非点源污染的影响机理，也可为水源地非点源污染防治提供参考。