Effects of gravel mulching on yield and multilevel water use efficiency of wheat-maize cropping system in semi-arid region of Northwest China

Gravel mulching technology has been applied in the arid and semi-arid regions of Northwest China for many years. However, systematic field studies concerning its effects on ecological effects and water productivity are insufficient. A field study was conducted during two consecutive cycles of Wheat-Maize cropping system in the Yangling District of Northwest China to evaluate water productivity and crop productivity with the four treatment combinations: CK (control, no mulching), WCK (CK plus 50 mm irrigation), GM (CK plus 8 kg/m(2) gravel mulching, covering 100% of soil surface) and WGM (WCK plus GM). Soil temperature, soil moisture, total biomass and yield were significantly increased, whereas CO2 emissions were decreased by gravel mulching treatment over the control. System yield improved by 19.87% and 15.59% by applying 50 mm irrigation, 53.58% and 43.18% by applying gravel mulching and 60.64% and 48.28% by applying gravel mulching and 50 mm irrigation over the control during both the cycle of Wheat-Maize rotation, respectively. Gravel mulching results in a positive contribution to annual net primary productivity (NPP) and net ecosystem exchange (NEP), and high-water use efficiency (WUE) were achieved under gravel mulching treatment for the two rotation cycles. Annual WUEeco and WUEyield significantly increased by 40.6% and 49.2% and 57.6% and 51.4% under the gravel mulching treatment over the control during the two cycles, respectively. However, during cycle 1 WUEveg and WUEbio did not significantly affected whereas during cycle 2 it affected, with a maximum value of 14.4 kg ha(-1) mm(-1) in WGM and 47.1 +/- 5.1 kg ha(-1) mm(-1) in GM, respectively. Taking into account crop yield, ecological effects and water use, covering the soil with gravel is an effective approach to enhance multi-level water use efficiency while increasing the productivity of wheat-maize cropping system in semi-arid regions of China.