How to identify and adopt cleaner strategies to improve the continuous acidification in orchard soils?

Extensive fertilization is a major factor of soil acidification worldwide and especially in China, where farmland soil pH has been declined significantly and resulted in soil deterioration. However, the status of fruit orchard systems is currently unclear. Therefore, we choose pomelo as a case study to analyze the current status, characteristics and improvement of soil acidification in orchards according to element and charge balances. The survey results showed that the soil pH in pomelo orchards continued to decrease from 2010 to 2018 and caused yields to decrease when the soil pH was lower than 4.5. In this period, the total soil acidification rate of pomelo orchards increased significantly from 29.6 to 39.6 keq H+ ha−1 yr−1. In addition, 67.0, 21.8 and 25.3% of soil acidification was caused by chemical fertilization, fruit harvest and pruning, respectively, and 19.8% of that was buffered by manure application. Reducing the inputs of nitrogen and phosphorus and increasing their nutrient use efficiencies can significantly reduce the soil acidification rate and product acid footprint (soil acidification rate per unit product) and increase the economic income/cost ratio. By using a structural equation model, the effects of nutrient use efficiency and the acid footprint on the income/cost ratio were 0.111–0.136 and −0.341 to −0.354, respectively. Scenario analysis further showed that the trade-off between soil acidification and economic benefits can be best circumvented in orchards while reducing greenhouse gas emissions based on the 'balanced fertilization +50% nitrogen substituted by manure +100% return of pruned parts' strategy.