The impact of humic acid compound fertilizer on sweet potato variety Jishu 25: A comprehensive study on dry matter, root yield, and starch properties

Abstract

In recent years, although humic acid (HA) compound fertilizers have been applied in sweet potato production, limited research has specifically addressed their impacts on dry matter (DM) accumulation, starch yield and starch properties, particularly in varieties with high starch content. To assess these effects, five treatments were designed for the high-starch variety Jishu 25 as follows: no fertilizer application (CK), chemical fertilizer with 75–60–180 kg ha−1 N-P2O5-K2O (F1), 750 kg ha−1 HA compound fertilizer with 2.6 % HA and 10–8–24 N-P2O5-K2O (F2), chemical fertilizer with 112.5–67.5–157.5 kg ha−1 N P2O5 K2O (F3), 750 kg ha−1 HA compound fertilizer with 3 % HA, and 15–9–21 N-P2O5-K2O (F4). The results indicated that F2 and F4 reduced the DM distribution ratio in leaves and stems, concurrently increasing DM accumulation in tuberous roots compared to F1 and F3. These HA fertilizer treatments enhanced the activities of AGPase, UGPase and SSS in tuberous roots during the middle and late growth stages, resulting in elevated total starch content and amylopectin content at harvest. Both types of HA fertilizers decreased the D [4,3] of starch particles, but exhibited minimal effects on PV, HPV, CPV, To, Tc and ΔH. The highest tuberous root yield and starch yield were observed after applying F2 continuously for two years. In conclusion, for optimizing starch yield while preserving its quality, the application of 750 kg ha−1 HA compound fertilizer with 2.6 % HA and 10–8–24 N-P2O5-K2O proved to be most advantageous for sweet potato producers cultivating this high-starch variety in regions with a similar climate in northern China.