Modeling the effects of plant density on maize productivity and water balance in the Loess Plateau of China

Loess Plateau of China is an area with serious soil evaporation and large inter-annual rainfall variations. Water stress is the major limiting factor for crop production in local area. Optimizing plant density is one crucial management in semi-arid dry land areas where crop growth is constrained by precipitation and a high evaporative demand. The Agricultural Production System Simulator (APSIM) was parameterized and tested with two years datasets, and then used to investigate long-term rainfed maize productivity and water balance with the historical weather records. Model application showed that water use and yield were varied because of the plant density and the inter-annual variability of precipitation. Plant density presented no influence on the evapotranspiration (ET) in extremely dry years, dry years and mild wet years but a significantly (P<0.05) influence in normal and extremely wet years. In extremely dry years, the grain yield and (WUE) were all significantly (P<0.05) decreased when plant density increased. The grain yield and WUE showed a parabolic relation with the plant density except extremely dry years. On average, the maximum yield and WUE were 6715kgha−1 and 1.81kgm−3 at 52500 plants ha−1 (D2) in dry years, 7857kgha−1 and 1.92kgm−3 at 67500 plants ha−1 (D3) in normal years, 8937kgha−1 and 2.19kgm−3 at 67500 plants ha−1 (D3) in mild wet years，and 9713kgha−1 at 82500 plants ha−1 (D4) and 2.25kgm−3 at 67500 plants ha−1 (D3) in extremely wet years, respectively. However, no significant difference was obtained for average yield or WUE when compared traditional density of 52500 plants ha−1 (D2) with higher plant density. Compared with the traditional plant density of 52500 plants ha−1 (D2), the increase of plant density significantly (P<0.05) reduced soil evaporation, only with the exception of extremely dry years. In order to get long term average benefits in the study area and similar agro-ecological zones, plant populations should not exceed 32500 plants ha−1 (D1) in extremely dry years, indeed, lower may be better. A plant density of 52500 plants ha−1 (D2) in dry years and 67500 plants ha−1 (D3) in normal years, mild wet years and extremely wet years are recommended as the optimum value, respectively.