Co-benefits of a customized nutrient management approach tailored to smallholder farming for cabbage (Brassica oleracea L.)

The inappropriate use of fertilizers in cabbage (Brassica oleracea L.) production is widespread worldwide; however, there are few easily implementable methods of fertilizer application rates suitable for smallholders. We established a nutrient expert system for cabbage (NEc) using data collected in China’s cabbage-growing regions from 2000 to 2023. The NEc addressed issues related to nutrient-application imbalances and excessive fertilization by optimizing N, P₂O₅, and K₂O usage based on yield responses, agronomic efficiency, and nutrient uptake. Additionally, field experiments were conducted to assess the utility of NEc in terms of yields, economic benefits, and nutrient-recovery efficiency compared to farmers’ practices (FP). The resulting database revealed a significant quadratic relationship (P < 0.05) between the yield response and agronomic efficiency. Quantitative evaluation of the fertility of tropical soils model, used to simulate optimal nutrient demands, reveals that the simulated nutrient requirements for N, P, and K increase linearly as the yield increases when the target yield is within 70 % of potential yield. In other words, to produce 1 Mg of cabbage, it requires 2.46 kg of N, 0.33 kg of P and 2.26 kg of K. The statistical results of collected data showed that optimal fertilization significantly (P < 0.05) enhanced cabbage yield, nutrient utilization efficiency, and net benefit. It was observed that fertilizer application rate exerted a direct and positive impact on these parameters. Field verification experiment demonstrated that NEc led to co-benefits, including a 7 % increase in yield, a 15.2 % increase in net profit, and improved agronomic efficiency (14.7 %∼101.2 %) compared to FP. The NEc approach enabled optimization of fertilizer applications based on specific production conditions, thereby enhancing cabbage yield, economic benefits, and nutrient-recovery efficiency. Thus, the NEc approach developed in this study was superior over traditional fertilization methods and is highly suitable for small-scale cabbage farming.