Effects of Tillage and Organic Fertilizer Application on Crop Yield and Water Use in a Potato-Maize Double Cropping System in the Longdong Region

The traditional monocropping system in the Longdong Loess Hilly Region suffers from low production efficiency and underutilization of water and thermal resources. To address these limitations, this study introduced an early-maturing potato-maize rotation model aimed at breaking through the constraints of the original cropping system and fully leveraging the region's water and thermal resource potential. To further optimize the productivity and sustainability of this new model, this research focused on investigating the effects of different tillage and fertilization practices on the photosynthetic characteristics, water use, yield, and economic benefits of the potato-maize double cropping system. These findings were expected to provide the key technical support for enhancing annual farmland productivity.

During the 2023-2024 growing season, using early-maturing potato (cv. Helan 15) and early-maturing maize (cv. Kewo 028) as test materials, four treatments were established: traditional tillage (TT), traditional tillage+organic fertilizer (TTO), vertically rotary sub-soiling (VT), and vertically rotary sub-soiling + organic fertilizer (VTO). Aboveground and belowground biomass, photosynthetic characteristics, yield and yield components were measured, and water use efficiency and economic benefits were calculated too.

Compared with TT, VT and VTO treatments significantly increased aboveground biomass and tuber yield at potato maturity, as well as stalk weight and ear weight at maize maturity. VT and VTO also increased the number of tubers per plant, tuber weight per plant, and marketable tuber rate in potato, while enhancing the number of kernels per row and 100-kernel weight in maize. Under VTO, potato and maize yields reached 32 853-33 879 and 8 289-9 860 kg·hm^-2, respectively, resulting in an annual total yield (converted to grain equivalent) of 15 065-16 431 kg·hm^-2. Compared with TT, VT and VTO increased potato yield by 21.5%-24.5% and 30.4%-36.2%, maize yield by 4.2%-10.3% and 9.3%-16.2%, and total annual yield by 11.2%-15.4% and 17.8%-23.5%, respectively. Furthermore, VT and VTO synergistically enhanced photosynthetic capacity. During key growth stages of both crops, these treatments significantly increased leaf SPAD values, net photosynthetic rate, stomatal conductance, and transpiration rate, while decreasing intercellular carbon dioxide (CO₂) concentration and improving instantaneous water use efficiency. Specifically, VT and VTO improved water use efficiency in potato by 15.4%-19.6% and 21.3%-32.5%, and in maize by 7.3%-10.4% and 13.4%-15.3%, respectively. Annual precipitation use efficiency increased by 3.0%-3.1% under VTO and 2.7%-3.4% under VT. Economically, VTO and VT increased net income by 19.9%-31.8% and 32.7%-40.5% compared with TT, though VTO was 6.3%-9.6% lower than VT. With the exception of economic returns, VTO outperformed VT in all other metrics evaluated and demonstrated greater potential for soil improvement, supporting its role in advancing agricultural sustainability.

In promoting the early-maturing potato–maize double cropping system in the Longdong Loess Hilly Region, the combination of vertically rotary sub-soiling with organic fertilizer (VTO) represented the most effective approach for synergistically enhancing crop productivity and ecological benefits. This practice not only provided robust support for the stable implementation of the potato–maize double cropping system but also contributed to achieving the high-yield goal of an annual "ton-grain hectare" (10 000 kg·hm^-2). Although the economic return of VTO was slightly lower than that under VT in the short term, it demonstrated significant technical value and long-term potential in promoting efficient and sustainable use of resources in regional dryland farming systems.