Effects of humic acid on the root growth and its interaction with coated diammonium phosphate on yield of wheat

Coated diammonium phosphate (CDAP) and humic acid (HA) have improved crop phosphorus fertilizer use efficiency. However, the effects of different phosphorus concentrations and HA incorporation on wheat and their potential mechanisms are unknown. This study aimed to elucidate the impact of varying phosphorus concentrations and HA applied in combination with coated phosphate fertilizers on wheat growth and its yield. An incubation experiment was performed using different phosphorus (P) concentrations (P0%, P1%, P10%, and P100% in Hoagland nutrient solution) combined with two HA content (0 and 0.1 g L−1). Finally, the wheat pot experiments were presented with two HA application rates (0 and 45 kg ha−1) and two P levels (60 and 75 kg P2O5 ha−1) under the condition that two forms of P fertilizer (CDAP and diammonium phosphate (DAP)) were comprised. At the same P rate, the auxin (IAA) and cytokinin (CTK) content in wheat seedlings of HA-added treatments was increased by 11.30%- 40.33% and 12.03%-29.21%, respectively, compared with the HA-free treatment. The CDAP combined with HA that improved the wheat growth and increased the yield and P use efficiency (PUE) by 2.7%-4.3% and 6.7-7.1 percentage points. Furthermore, the interactions between the types of P fertilizer (DAP, CDAP) and the application rate of HA were recorded as being significant (p < 0.01) for the wheat yield. In conclusion, as an environmentally friendly fertilizer, the combination of CDAP and HA increased enhanced root growth, and then maximized yields and PUE, which is important for P resource conservation and environmental protection.