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Long-Term Fertilization Effects on Crop Yield and Nitrate Nitrogen Accumulation in Soil in Northwestern China

^a The Key Lab. of Arid and Grassl. Agroecol., Lanzhou Univ., Ministry of Educ., Lanzhou, 730000, P.R. China
^b Inst. of Soil and Fert., Gansu Acad. of Agric. Sci., Lanzhou 730070, P.R. China
^c Agric. and Agri-Food Canada, Research Farm, P.O. Box 1240, Melfort, SK, Canada S0E 1A0
^d Gansu Agric. Univ., Lanzhou 730070, P.R. China
^e Inst. of Agric. Sci. of Zhangye Prefecture, Zhangye 734000, P.R. China

View larger version (31K): [in a new window]   Fig. 1. Regressions of cumulative grain yield (kg ha–1) of crops with years in wheat–wheat–corn rotation from 1982–2000, treated annually with various combinations of N, P, and K fertilizers and unfertilized check, without and with manure (M) on a calcareous sandy loam soil under irrigation near Zhangye, Gansu, China (LSD0.05 for differences between all treatments is 4.451).

View larger version (17K): [in a new window]   Fig. 2. Regressions of mean cumulative grain yield (kg ha–1) of crops with years in wheat–wheat–corn rotation from 1982–2000, treated annually with various combinations of N, P, and K fertilizers and unfertilized check, without manure (UM) and with manure (M) on a calcareous sandy loam soil under irrigation near Zhangye, Gansu, China (LSD0.05 for differences between main-plot treatments is 3.420).

View larger version (59K): [in a new window]   Fig. 3. Harvest index (ratio of grain yield to grain + straw yield) of crops from 1988–1997, treated annually with various combinations of N, P, and K fertilizers and unfertilized check, without and with manure on a calcareous sandy loam soil under irrigation near Zhangye, Gansu, China (LSD0.05 for differences between main-plot treatments is 0.005 for wheat and 0.007 for corn; LSD0.05 for differences among subplot treatments is 0.018 for wheat and 0.012 for corn).

View larger version (54K): [in a new window]   Fig. 4. Concentration of protein (g protein kg–1) in grain of crops from 1988–1997, treated annually with various combinations of N, P, and K fertilizers and unfertilized check, without and with manure on a calcareous sandy loam soil under irrigation near Zhangye, Gansu, China (LSD0.05 for differences between main-plot treatments is 2.8 for wheat and 1.9 for corn; LSD0.05 for differences among subplot treatments is 9.3 for wheat and 11.0 for corn).

View larger version (49K): [in a new window]   Fig. 5. Total N uptake (kg N ha–1) in grain + straw of crops from 1988–1997, treated annually with various combinations of N, P, and K fertilizers and unfertilized check, without and with manure on a calcareous sandy loam soil under irrigation near Zhangye, Gansu, China (LSD0.05 for differences between main-plot treatments is 16.9 for wheat and 18.5 for corn; LSD0.05 for differences among subplot treatments is 17.6 for wheat and 12.8 for corn).

View larger version (40K): [in a new window]   Fig. 6. Nitrate N mass (kg N ha–1) in different soil layers after 19 annual applications (1982–2000) of various combinations of N, P, and K fertilizers and unfertilized check, without and with manure on a calcareous sandy loam soil under irrigation near Zhangye, Gansu, China (for the 0- to 20-, 20- to 60-, 60- to 100-, 100- to 140-, and 140- to 180-cm depths, respectively, the LSD0.05 for differences between main-plot treatments is 0.6, 5.7, 8.1, 7.2, and 8.9, and the LSD0.05 for differences among subplot treatments is 1.5, 7.7, 9.6, 4.9, and 7.3).

View larger version (43K): [in a new window]   Fig. 7. Nitrate N mass (kg N ha–1) in the 0- to 180-cm soil depth after 19 annual applications (1982–2000) of various combinations of N, P, and K fertilizers and unfertilized check, without and with manure on a calcareous sandy loam soil under irrigation near Zhangye, Gansu, China (LSD0.05 for differences between main-plot treatments is 5.3; LSD0.05 for differences among subplot treatments is 13.3).