Effects of Integrated Fertilization on Soil Fertility and Kiwifruit Productivity in Luvisols

Comparative evidence on the performance of urea and ammonium nitrate within integrated organo-mineral fertilization systems in acidic Luvisols under humid subtropical kiwifruit production remains limited. This study evaluated compost (30 t ha−1 + P150K120) combined with urea or ammonium nitrate (0, 90, 120, and 150 kg N ha−1) in non-degraded (ND) and moderately degraded (MD) acidic Luvisols during a three-year field experiment (2022–2024) arranged in a randomized complete block design (RCBD) with five fertilization treatments and four replications. Integrated fertilization significantly increased soil organic carbon (SOC), water-stable aggregates (WSA), and nutrient availability. Stepwise regression showed that NO3−–N explained 72.9% of yield variation, while inclusion of P2O5, SOC, and K2O increased explained variation to 93.8%. In ND soil, yield increased from 7004 to 20,139 kg ha−1 under Base + N150, but the increase over Base + N120 was small and non-significant. Urea generally resulted in higher yield and greater NUE than ammonium nitrate, whereas effects on fruit quality were less consistent. The highest NUE occurred under Base + N120 with urea (0.99) and declined at higher N rates. Overall, Base + N120, particularly with urea, provided the most favorable balance between soil improvement, kiwifruit productivity, and nitrogen use efficiency.