Response of yield, water and fertilizer use efficiency of sweet potato to different drip fertigation regimes under mulching conditions in a humid region of East China

Developing precise irrigation and fertilization regimes is essential for sustaining sweet potato productivity, particularly in humid regions where rainfall variability complicates soil nutrient and water resource management. A two-year field experiment was conducted to investigate the effects of different soil matric potentials (SMP) and potassium (K) application rates on crop growth, yield, and water and potassium use efficiency in a representative humid region of East China with uneven rainfall distribution in 2019 and 2020. Five soil matric potential levels i.e. S1: –15 kPa, S2: –25 kPa, S3: –35 kPa, S4: –45 kPa, and S5: –55 kPa were designed in both 2019 and 2020. In 2020, under the optimal SMP regime (S2) identified in 2019, five potassium application rates i.e. K1: 75 kg ha–1, K2: 150 kg ha–1, K3: 225 kg ha–1, K4: 300 kg ha–1, and K5: 375 kg ha–1 were evaluated as a single factor. Results showed that in 2019, the S2 treatment achieved the highest storage root yield (statistically equivalent to S1) and maximum water productivity (WPc), while significantly improving irrigation water productivity (WPI) by 59.4% compared to S1. In 2020, S2 maintained the highest numerical yield, though both yield and WPc exhibited no significant differences compared to lower thresholds (S4 and S5). For K application rates, the K3 treatment significantly increased storage root yield compared to the K1 and K2 treatments (P  0.05) but significantly increased by 60.9% compared to K5 (P < 0.05). Meanwhile, its potassium partial factor productivity (PFPK) significantly increased by 54.4% – 81.3% compared to these excessive K treatments (P < 0.05). In conclusion, integrating a consistent potassium rate of K3 (225 kg ha⁻¹) with climate-adaptive SMP thresholds—S2 (−25 kPa) for dry or normal years and lower thresholds for wet years—presents a promising strategy for sustainable production.