Energy input-output, water use efficiency and economics of winter wheat under gravel mulching in Northwest China

Gravel mulching has long been used to conserve water and enhance crop yield in the Loess Plateau of China. The climate change and water scarcity in the Loess Plateau of China may have an impact on the phenological changes of plants, thus affecting the growth process, biomass yield, energy input-output and economics of crops. However, focuses on the effects of gravel mulching on energy input-output and agricultural economics are less. Therefore, a 3-year field study of winter wheat was conducted with different gravel mulching practices in the Loess Plateau, China. The five treatments are: zero mulch (CK), 25% surface gravel mulch (M1), 50% surface gravel mulch (M2), 75% surface gravel mulch (M3) and 100% surface gravel mulch (M4), respectively. In addition, a set of indicator systems based on energy, economics and crop growth were proposed to better understand the effects of gravel mulching. Compared with the CK treatment, the gravel mulching treatments significantly prolonged the thermal time required for the plant growth and biomass accumulation and increased the growth rate of the Leaf area index (LAI), and ultimately improved the winter wheat yield. This effect was particularly evident during the jointing period of winter wheat. The results also showed that gravel mulching significantly increased energy use efficiency and net returns in economics. The four gravel mulching treatments significantly increased the biomass yield (4.9%–17.3% higher than the CK), net returns (12.1%–53.8% higher than the CK) and net returns water-use efficiency (WUEnre) (12.0%–53.4% higher than the CK). Accordingly, the energy productivity, net energy and net energy water-use efficiency (WUEene) were 2.2%–8.2%, 5.7%–19.8% and 7.1%–20.9%, respectively, higher than the CK under M1-M4. Overall, gravel mulching exerted positive influences on the economic returns and the energy use, vs their water use efficiency. Thus, gravel mulching is not only an effective way to improve crop growth and yield, but it also has the potential to improve economic benefits and energy efficiency within the context of climate change and water crises in the Loess Plateau, China.