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

- Modelling was used to quantify yield of rainfed maize and water balance on the Loess Plateau.
- Plant density presented no significant (P > 0.05) influence on the evapotranspiration in dry years and mild wet years, but a significant (P < 0.05) positive influence in normal and extremely wet years.
- Soil evaporation was reduced significantly (P < 0.05) by increased plant density, only with the exception of extremely dry years.
- Plant density of 32500 and 52500 plants ha−1 are recommended in extremely dry years and dry years, respectively. In normal years, mild wet years and extremely wet years, 67500 plants ha−1 is recommended as the optimum value in order to get long-term benefit.

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 6715 kg ha−1 and 1.81 kg m−3 at 52500 plants ha−1 (D2) in dry years, 7857 kg ha−1 and 1.92 kg m−3 at 67500 plants ha−1 (D3) in normal years, 8937 kg ha−1 and 2.19 kg m−3 at 67500 plants ha−1 (D3) in mild wet years，and 9713 kg ha−1 at 82500 plants ha−1 (D4) and 2.25 kg m−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.