Optimized ridge-furrow technology with biochar amendment for alfalfa yield enhancement and soil erosion reduction based on a structural equation model on sloping land

Water scarcity and water-related soil erosion are severely exacerbated by inappropriate human activities and global climate change. Hence, to find a suitable technology to mitigate drought and soil erosion, three consecutive field experiments were conducted to explore the impact of ridge-furrow cropping with biochar amendment on soil water storage, runoff, sediment yield, soil nutrient losses, alfalfa (Medicago sativa L) fodder yield, crop water productivity (WPc), and economic benefit from 2019 to 2021. This experiment was conducted in a split-plot design, taking biochar amendment patterns (no biochar amendment and biochar amendment at a rate of 3× 104 kg ha−1) as a main plot and ridge-furrow technologies (traditional planting, open-ridging, and tied-ridging) as a split-plot. The combination of biochar amendment with ridge-furrow technology, especially tied-ridging technology, increased soil water storage, and captured runoff, sediment, and related soil nutrient losses, consequently increasing alfalfa fodder yield, WPc, and income. During this study, compared to traditional planting, open-ridging depicted an increase in soil water storage by a range of 9.8–39.6 mm, an alfalfa fodder yield boost ranging from 9.8% to 38.6%, and a WPc increase ranging from 0.1 to 16.5 kg ha−1 mm−1. On the other hand, tied-ridging showed greater improvements with soil water storage increasing by 29.1–65.1 mm, alfalfa fodder yield growing by 11.6–44.4%, and WPc advancing by 0.9–17.5 kg ha−1 mm−1. The mean decrease in runoff, sediment, and nutrients (total nitrogen, total phosphorus, and organic matter) loss for open-ridging was 17.9%-37.7%, 46.4%-75.5%, and 40.4%-75.3%, respectively, while for tied-ridging, it was 22.3%-55.5%, 62.1%-87.6%, and 49.0%-87.3%, respectively. Compared to no biochar amendment, soil water storage, alfalfa fodder yield, and WPc for biochar amendment increased by 9.1%-20.4%, 5.8%-52.7%, and 4.6–7.8 kg ha−1 mm−1, respectively, while runoff, sediment, and nutrients loss for biochar amendment decreased by 32.2%-40.9%, 25.5%-55.5%, and 35.9%-53.3%, respectively. Structural equation modeling analysis indicated that the significant direct effect of biochar amendment and ridge-furrow technology on WPc was 0.20 and 0.62, respectively, whereas the significant direct effect of runoff and actual crop evapotranspiration on alfalfa fodder yield was −0.40 and 0.94, respectively. Tied-ridge cropping combined with biochar addition was a highly suggested approach for addressing soil erosion and enhancing alfalfa fodder yields in the Loess Plateau in China. This technology could mitigate soil water scarcity and soil erosion, and give farmers the confidence to invest in this technology in dryland regions.