Comparative advantages of three-crop systems in improving crop nutrient accumulation and soil fertility in Sichuan Hilly agroecosystems, China

The expansion of mechanized agriculture has accelerated the adoption of double-cropping systems in dryland regions, leading to a decline in the traditional three‑crop rotation system in the hilly arid areas of Sichuan. In its place, two‑crop rotations-specifically winter wheat–summer corn and winter rapeseed-summer corn-have gradually become more prevalent, resulting in a coexistence of both three-crop and two‑crop systems. Understanding the nutrient utilization patterns associated with these typical cropping systems in Sichuan’s hilly arid zones can offer a theoretical foundation for optimizing crop rotation and optimizing cropping structures in the hilly regions of southwestern China. This study was based on a three‑year field experiment conducted from 2021 to 2024, in which five cropping systems were established: winter wheat-spring corn-sweet potato (T1), winter wheat-spring corn-soybean (T2), potato-spring corn-soybean (T3), winter wheat-summer corn (T4), and winter rapeseed-summer corn (T5). For each cropping system, we measured crop biomass, nitrogen (N), phosphorus (P), and potassium (K) uptake, soil nutrient dynamics, and partial factor productivity of fertilizer (PFPF). The results showed that the three‑crop rotation systems exhibited significantly higher average annual biomass and N, P, and K uptake than the two-crop systems, with the winter wheat-spring corn-sweet potato rotation producing the highest average annual biomass among all treatments. In the three‑crop systems, fertilizer-to-productivity ratios increased, whereas soil N, P, and K levels declined, and partial factor productivity of fertilizer efficiency improved. These findings indicate that the three‑crop rotation system enhances nutrient acquisition and utilization, thereby laying a foundation for yield improvement. Compared with two-crop rotations, the three‑crop system exhibited greater soil nutrient uptake (including N, P, and K), higher biomass accumulation, and improved partial factor productivity of fertilizer. Among the five cropping patterns tested, the winter wheat-spring corn-sweet potato rotation performed the best and is therefore recommended for adoption in the hilly arid regions of the study area.