Effects of NPK Fertilization on Growth, Fruit Yield, and Gross Output Value of Sapindus mukorossi ‘Yuanhua’

Balanced fertilization is essential for improving the growth and productivity of Sapindus mukorossi plantations. In this study, a three-year “3414” fertilization experiment was conducted in a six-year-old plantation of the new S. mukorossi cultivar ‘Yuanhua’ to evaluate the effects of nitrogen, phosphorus, and potassium fertilization on vegetative growth, fruit yield, yield stability, and gross output value. Fertilizer levels were set at 0, 300, 600, and 900 kg N ha−1, 0, 250, 500, and 750 kg P2O5 ha−1, and 0, 200, 400, and 600 kg K2O ha−1. NPK fertilization promoted tree height, ground diameter, crown width, and fruit yield compared with the unfertilized control. Among the 14 fertilization treatments, N1P1K2 produced the greatest mean annual increment in tree height, N1P2K1 produced the greatest ground-diameter increment, and N2P2K1 produced the greatest crown-width increment. Fruit yield was highest under N2P2K2 in 2021 and 2022 and under N2P2K1 in 2023. The highest three-year mean yield was obtained under N2P2K2, reaching 1278.93 kg ha−1, and the highest yield stability index was observed under N2P2K2 and N2P1K2. Gross output value showed a pattern consistent with fruit yield, with N2P2K2 producing the highest values in 2021 and 2022 and N2P2K1 producing the highest value in 2023. Among the tested fertilization combinations, N2P2K2, corresponding to 600 kg N ha−1, 500 kg P2O5 ha−1, and 400 kg K2O ha−1, showed the best overall performance for six-year-old S. mukorossi ‘Yuanhua’ plantations under the conditions of this study. These findings indicate that balanced NPK fertilization can improve vegetative growth, fruit yield, yield stability, and gross output value in S. mukorossi ‘Yuanhua’ plantations.