宁夏黄灌区稻田冬春休闲期硝态氮淋失量

对宁夏黄灌区稻田设置不同有机肥处理：常规施肥（CK）；常规施肥条件下分别施用4500 kg/hm2（T1）与9000 kg/hm2猪粪（T2），采用树脂芯法测定了稻田冬春休闲期30 cm、60 cm、90 cm处的硝态氮流失量。结果表明，常规施肥条件下，90 cm处硝态氮淋失量最大，分别为T1、T2的1.10与1.13倍；在常规施肥基础上增施猪粪，硝态氮最大淋失量出现在60 cm土层，T1、T2的流失量分别为4.47 kg/hm2与4.21 kg/hm2，分别为该层CK淋失量的1.50与1.42倍。灌区稻田常规施肥基础上增施有机肥，能够减少硝态氮向深层淋失；但60 cm土层处硝态氮淋失量增加，为硝态氮的深层淋失提供了基础，但在灌区水旱轮作模式下，下季旱作灌水量明显减少，加之作物吸收，硝态氮淋失也将明显降低。

The nitrate-nitrogen leachingamount in paddy winter-spring fallow period

Fertilizer nitrogen mainly remains in the form of nitrate nitrogen. If not taken up by crops, it will be leached downward to subsoil by rainfall and irrigation water, negatively impacting soil and water system. Ningxia Irrigation District is the representative irrigation farming region in the upper stream area of the Yellow River. The paddy-upland rotation is still the typical agricultural model in this irrigation district. the crude farming methods are used in the paddy planting, such as uncontrolled irrigation and excessive fertilization, therefore there is a high accumulation of the residual nitrate nitrogen in soil after the harvest. During the long fallow period in the irrigation district; the residual nitrate nitrogen tends toward leaching due to freeze-thaw and wind erosion under the condition of winter irrigation in order to keep the soil moistures. The resin core technique has been applied to study the nitrogen mineralization in recent years. This method can absorb the leaching nitrate nitrogen directly and do not need to estimate the leakage; moreover causes slight disturbance to the soil, and therefore has been considered as an ideal method to study the nitrate nitrogen leaching losses in field. A filed experiment was conducted in paddy of Ningxia Yellow River irrigation district with three treatments including normal fertilization (CK), 4500kg/hm²(T₁)and 9000 kg/hm²(T₂)pig manure, respectively, on the basis of the normal fertilization. The undisturbed soil columns were obtained by driving the different length stainless steel tube into the soil vertically after the harvest. The stainless steel tubes are 42, 52, 102 centimeter long and the length of the wedge surface is 10 centimeter. The three different length stainless steel tubes are one unit; three units were set up for each experimental plot. The cut-and-dried aluminum plastic plate, resin bag, aluminum plastic plate, antiskid axis were sequentially enclosed in after removing the 2 centimeter soil at the bottom. The stainless steel tubes were cultivated on the original place. The soil samples, collected around the stainless steel tubes, were classified into 3 groups according to depth (0-30, 30-60 and 60-90 cm).The soil nitrate-nitrogen, ammonium nitrogen, organic matter and active organic matter content were measured at the start and end of the assay. The nitrate nitrogen leaching losses of soil at the depth of 30, 60, 90 cm were measured by the method of resin core in the fallow period. For the normal fertilization, the largest nitrate nitrogen leaching loss was found at the depth of 90 centimeter, which is 1.10 and 1.13 fold higher than T₁ and T₂, respectively. However, the largest nitrate-nitrogen leaching losses in T₁ and T₂ appeared at the depth of 60 centimeter, which are 4.47kg/hm² and 4.21kg/hm² respectively, and 1.50 and 1.42 fold increases compared to CK, respectively. Application of organic manure can reduce the nitrate nitrogen to leach downward to subsoil on the basis of the normal fertilization. The increase nitrate nitrogen leaching losses at the depth of 60cm seems to facilitate the further leaching, however, in the mode of the paddy-upland rotation, because the irrigation amount is normally reduced during the upland period and also the nitrate nitrogen is absorbed by crops, the leaching losses will thus be significantly decreased.