The Pruning Paradox in Coffee Agroecosystems: Enhancing P Balance While Accelerating K Loss Under Different Fertilization Practices

Abstract

This study evaluated the effects of canopy pruning, fertilizer type, fertilizer rate, and their interactions on nitrogen (N), phosphorus (P), and potassium (K) nutrient balances in an Arabica coffee agroforestry system. A 2 × 3 × 3 factorial experiments arranged in a completely randomized design with four replications (72 experimental units) was conducted at UB Forest, Malang, Indonesia (1,300 m above sea level) on an Inceptisol. The experimental factors consisted of pruning (pruned and unpruned), fertilizer type (organic, inorganic, and combined), and fertilizer rate (low, medium, and high). Nutrient balances were calculated as the difference between total nutrient inputs (initial soil nutrient stocks and fertilizer inputs) and outputs (final soil nutrient stocks, harvested yield, and litter), and analyzed using three-way analysis of variance (ANOVA) followed by Duncan’s multiple range test at the 5% significance level. Pruning exerted contrasting effects on nutrient balances by significantly increasing the P balance (244.50 vs. 225.03 kg ha⁻¹; P < 0.01) while decreasing the K balance (6,415.59 vs. 9,683.45 kg ha⁻¹; P < 0.01), whereas the N balance was not significantly affected. Fertilizer rate significantly influenced N and P balances, with the high fertilizer rate producing the greatest nutrient surpluses (911.40 kg N ha⁻¹ and 466.55 kg P ha⁻¹), whereas the low fertilizer rate resulted in the only negative P balance (−32.28 kg ha⁻¹). Fertilizer type did not significantly affect the balances of N, P, or K. A significant pruning × fertilizer rate interaction was detected only for the P balance, indicating that the effect of pruning depended on fertilization intensity. These findings demonstrate nutrient specific trade-offs associated with canopy pruning, improving P retention while accelerating K depletion. Integrating pruning practices with adequate K replenishment and balanced fertilizer application is therefore essential to maintain long-term soil fertility and nutrient sustainability in Arabica coffee agroforestry systems.