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Long-Term Fertilizer and Water Availability Effects on Cereal Yield and Soil Chemical Properties in Northwest China

^a Dryland Agricultural Institute, Gansu Academy of Agricultural Sciences, Lanzhou 730070, Gansu, P.R. China
^b Dryland Agriculture Institute, West Texas A&M Univ., Canyon, TX 79016
^c Texas Agriculture Experimental Station, Texas A&M Univ., Bushland, TX 79012

View larger version (79K): [in a new window]   Fig. 1. Changes of grain yield and water use efficiency (WUE) in a long-term (1979–2002) rainfed fertilization experiment in Pingliang, Gansu, China. CWSI is crop water stress index (1 – ET/PET), where ET is estimated seasonal evapotranspiration for wheat and corn, and PET is potential evapotranspiration.

View larger version (26K): [in a new window]   Fig. 2. Relationship between wheat grain yield and crop water stress (CWSI) in a long-term rainfed fertilization experiment in Pingliang, Gansu, China. A CWSI value of 1 or 0 would indicate full stress or no stress. ***Linear regression coefficient (R2) significant at 0.001 probability level.

View larger version (26K): [in a new window]   Fig. 3. Relationship between corn grain yield and crop water stress (CWSI) in a long-term rainfed fertilization experiment in Pingliang, Gansu, China. A CWSI value of 1 or 0 would indicate full stress or no stress. ***Linear regression coefficient (R2) significant at 0.001 probability level.

View larger version (41K): [in a new window]   Fig. 4. Estimated grain yield for different cropping systems based on probabilities of crop water stress index (CWSI) and grain yield–CWSI relationships. Probabilities, expressed by the relative frequency, of CWSI values are calculated based on 24 yr of estimated seasonal Evapotranspiration (ET) and potential evapotranspiration (PET) records. Regression functions in Fig. 2 and 3 were used to estimate grain yield related to probabilities of CWSI. Data points () are for minimum, 75% probability, 50% probability, 25% probability, and maximum CWSI values in 24 yr of records, respectively.

View larger version (36K): [in a new window]   Fig. 5. Estimated grain yield for different cropping systems based on probabilities of estimated seasonal evapotranspiration (ET) and regression function of grain yield to estimated ET. Probabilities, expressed by the relative frequency, of ET values are calculated based on 24 yr of crop seasonal precipitation plus rainfall amount estimated by assuming fallow efficiency in fallow periods of the various cropping system. Regression functions in Table 3 were used to estimate grain yield related to probabilities of ET. Data points () are for minimum, 75% probability, 50% probability, 25% probability, and maximum ET values in 24 yr of records, respectively.

View larger version (33K): [in a new window]   Fig. 6. Trend changes of soil fertility in long-term fertilizers experiment in Pingliang, Gansu, China. Data showed here were continuous from 1979 through 1991 and 1996 through 1998; soil samples for 1992–1995 were not analyzed (Dashed lines), and total P, available P, and available K for 1996 were not determined except total N and soil organic matter.