Ridge-furrow cropping of maize reduces soil carbon emissions and enhances carbon use efficiency

Effects of agricultural practices on rising atmospheric CO2 concentrations have led to a widespread desire to optimize conventional land use strategies to reduce soil carbon emissions (CE) from agricultural lands. Ridge tillage is a contour-based system that involves planting into ridges of soil. It differs from conventional tillage in soil carbon (C) retention over time and when combined with mulching has been widely viewed as an important support technology to increase soil water availability and improve soil productivity for maize (Zea mays L.) production in arid and semiarid regions. However, the combined effect of ridge, mulching and limited water irrigation on properties of carbon emissions is still unclear. A field experiment was conducted to study the effects of ridge, plastic-film mulching and limited water irrigation practices on amount of carbon emissions (CE), carbon emission efficiency (CEE), carbon emission per unit of evapotranspiration (WUECE) and maize grain yield (GY) advantages in maize growing areas in 2013 and 2014. The experiment comprised ridge cropping (R) or flat cropping (F) patterns and complete mulching (C, soil surface 100% mulched) or half mulching (H, soil surface 30% mulched) with plastic film, and three total irrigation levels (430, 490 and 550 mm) and totally consisting of 12 treatments. We find that ridge cropping significantly reduced CE by 1.1 t ha(-1) in 2013 and 1.0 t ha(-1) in 2014, and reduced WUECE by 1.12 kg ha(-1) mm(-1) in 2013 and 2.09 kg ha(-1) mm(-1) in 2014 but also enhanced CEE by 0.34 kg kg(-1) in 2013 and 0.14 kg kg(-1) in 2014 compared to maize flat cropping over a period of two consecutive years. Although, ridge copping reduced GY by 1.14 t ha(-1) in 2013 and 1.66 t ha(-1) in 2014, some improved agronomy managements were put forward to attempt to overcome this disadvantage. In contrast with complete mulching, the half-mulching system reduced CE, GY and WUECE and effectively enhanced CEE. The CE increased with increasing irrigation level and the middle irrigation maintained GY and enhanced CEE. A structural equation modelling (SEM) explored that ridge directly and negatively affected CE and also partly through the negative effect on GY in 2013, and negative effect on GY and ET in 2014. There was a positive synergistic effect on CE by combining GY and evapotranspiration (ET) in 2013. Anyway, ridge cropping with half mulching and middle irrigation was confirmed to be a combined and optimum management strategy for the enhancement of CEE by 0.43 kg kg(-1) higher in 2013 and 1.02 kg kg(-1) higher in 2014 compared to the corresponding mean level overall treatments and the reduction of WUECE was by 0.97 kg ha(-1) mm(-1) lower in 2013 and by 2.34 kg ha(-1) mm(-1) lower in 2014.