OPTIMIZING WATER AND FERTILIZER INPUT USING AN ELASTICITY INDEX: A CASE STUDY WITH MAIZE IN THE LOESS PLATEAU OF CHINA

Authors: LIU, WENZHAO - ISWC,CAS,CHINA; Zhang, Xunchang

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2006
Publication Date: 1/1/2007
Citation: Liu, W., Zhang, X.J. 2007. Optimizing water and fertilizer input using an elasticity index: A case study with maize in the Loess Plateau of China. Field Crops Research. 100(2-3):302-310.

Interpretive Summary: Optimizing water and fertilizer inputs under a given environmental condition remains a major challenge for improving crop productivity and maximizing water use efficiency (WUE). The objectives are to (i) develop a new approach to mathematically characterizing interrelations of grain yield (Y), evapotranspiration (ET), WUE, and soil fertility, and (ii) to further derive optimum combinations of water and fertilizer inputs using maize data of 1997 and 1998. The experiment had two factors (water supply and fertilizer input) with five levels each, among which 13 combinations were studied in triplicate. A maize cultivar (Zhongdan 2, Zea mays L.) was grown in a loessial silt loam in the hilly region of the Loess Plateau of China. Irrigation and fertilizers were applied at predetermined amounts as needed. Approaches of characterizing interrelations of Y, ET, and WUE were developed using crop-water production functions and an elasticity index (EI), and further extended to derive the optimal coupling domain of water and fertilizer inputs. As water supply increased, WUE reached its maximum before yield did. Yield responses to water and fertilizer inputs followed a quadratic function with a positive interactive term. The optimal coupling domain was of elliptic form with the maximum WUE and Y being the two end points on the long axis. The ellipsoid can be used by extension specialists to make fertilizer recommendations in the region given a seasonal water supply or precipitation forecast.

Technical Abstract: Identifying optimum combinations of water and fertilizer inputs under a given environmental condition remains a major challenge for improving crop productivity by maximizing water use efficiency (WUE) in areas where water resource is scarce. The objectives are to (i) develop a new approach to characterizing interrelations of yield (Y), evapotranspiration (ET), WUE, and soil fertility using an elasticity index, and (ii) to further derive the optimum combinations of water and fertilizer inputs using maize data of 1997 and 1998 as an example. The experiment was an incomplete factorial design with two factors (water supply and fertilizer input) with five levels each, and had a total of 13 treatments with three replicates each. A maize cultivar (Zhongdan 2, Zea mays L.) was grown in a loessial silt loam in the hilly region of the Loess Plateau of China. Irrigation was hand applied with a flow meter at predetermined amounts as needed, and fertilizers including nitrogen, phosphate, and yard manure were applied at planting and jointing at predetermined rates. Approaches on how to use the crop-water production function and elasticity index (EI) to characterize the interrelations of Y, ET, and WUE were presented, and further extended to derive the optimal coupling domain of water and fertilizer inputs by setting EI=1. As water supply (x2) increased, WUE reached its maximum (at x2=a) before yield did (at x2=b). Specifically, both WUE and Y increased when x2b. Yield responses to water and fertilizer inputs followed a quadratic function with a positive interactive term. The optimal coupling domain was of elliptic form with the maximum WUE and Y being the two end points on the long axis. The ellipsoid can be used to determine optimal fertilizer inputs for a given water supply, or vice versa. In addition, the maximum WUE and Y in 1997 were 27 and 21% lower than those in 1998, respectively, indicating that the higher than normal temperature in 1997 considerably reduced the maximum WUE and Y.