Ridge-furrow plastic mulching with a suitable planting density enhances rainwater productivity, grain yield and economic benefit of rainfed maize

Soil surface mulching and planting density regulation are widely used for effective utilization of limited rainwater resources and improvement of crop productivity in dryland farming. However, the combined effects of mulching type and planting density on maize growth and yield have been seldom studied, especially in different hydrological years. A field experiment was conducted to evaluate the effects of mulching type and planting density on the soil temperature, growth, grain yield (GY), water use efficiency (WUE) and economic benefit of rainfed maize in the drylands of northern China during 2015-2017. Precipitation fluctuated over the three years. There were four mulching types (NM, flat cultivation with non-mulching; SM, flat cultivation with straw mulching; RP, plastic-mulched ridge plus bare furrow; RPFS, plastic-mulched ridge plus straw-mulched furrow) and three planting densities (LD, low planting density, 45.0x10(3) plants/hm(2); MD, medium planting density, 67.5x10(3) plants/hm(2); HD, high planting density, 90.0x10(3) plants/hm(2)). Results showed that soil temperature was higher with RP and lower with SM compared with NM, but no significant difference was found between RPFS and NM. More soil water was retained by soil mulching at the early growth stage, but it significantly varied at the middle and late growth stages. Maize growth was significantly improved by soil mulching. With increasing planting density, stem diameter, net photosynthetic rate and chlorophyll content tended to decline, whereas a single-peak trend in biomass yield was observed. Mulching type and planting density did not have significant effect on evapotranspiration (ET), but GY and WUE were significantly affected. There were significant interacting effects of mulching type and planting density on biomass yield, GY, ET and WUE. Compared with NM, RPFS, RP and SM increased GY by 57.5%, 50.8% and 18.9%, and increased WUE by 66.6%, 54.3% and 18.1%, respectively. At MD, GY increased by 41.4% and 25.2%, and WUE increased by 38.6% and 22.4% compared with those of at LD and HD. The highest maize GY was observed under MD+RPFS (7023.2 kg/hm(2)), but the value was insignificant under MD+RP (6699.1 kg/hm(2)). Similar trends were observed for WUE under MD+RP and MD+RPFS, but no significant difference was observed between these two combinations. In terms of economic benefit, net income under MD+RP was the highest with a 9.8% increase compared with that of under MD+RPFS. Therefore, we concluded that RP cultivation pattern with a suitable planting density (67.5x10(3) plants/hm(2)) is promising for rainwater resources utilization and maize production in the drylands of northern China.