Influence of the irrigation, fertilization and groundwater depth on wheat yield and nitrate nitrogen leaching

The orthogonal tests were taken to analyzed the significant of the irrigation，fertilization and groundwater table depth on the wheat yield and the nitrate nitrogen leaching loss from March to July 2010, and the statistic geological method was taken in ArcGIS9.0 to analyze the spatial distribution of groundwater table depth (annual average in 2009) in Hetao irrigation district. The results were used to make the optimal (minimum) combination patterns of the three factors each other which were suited to the different area in Hetao irrigation district. The analysis results showed that the root surface (0–80 cm) soil water content was decreasing with the increasing groundwater table depth. When the groundwater table depth was over 2.0 m, the irrigation amount was the significant factor with the same value of groundwater table depth. The influence of the three factors on the wheat yield was in the order of groundwater table depth＞irrigation amount＞fertilization, and on the leaching loss of nitrate nitrogen was in the order of irrigation＞fertilization＞groundwater table depth. The groundwater table depth was an inducible factor, the irrigation amount was extremely significant and the nitrogen rate was significant on the nitrate nitrogen leaching, respectively. When the groundwater table depth was 1.5, 2.0 and 2.5 m, respectively, the combination patterns of three factors were irrigation (280 mm)+fertilization (Urea 150 kg·hm-2 and diammonium phosphate 165 kg/hm2), irrigation (320 mm)+fertilization (Urea 150 kg/hm2 and diammonium phosphate 165 kg/hm2) and irrigation (360 mm)+fertilization (Urea 255 kg/hm2 and diammonium phosphate 375 kg/hm2), respectively.