Maize yield and root morphological characteristics affected by controlled-release diammonium phosphate and Paecilomyces variotii extracts

Application of conventional phosphorus (P) fertilizer poses great concern due to its low P efficiency and potential eutrophication of P in sensitive waters. A novel biostimulant, Paecilomyces variotii extract (ZNC), with functionality of improving nutrient uptakes of crops, was integrated with diammonium phosphate coated with biobased polyurethane polymer in a three-year field trial. The objectives were to explore the effects and mechanisms of the controlled-release diammonium phosphate (CRP), ZNC and their combination on P use efficiency (PUE), economic benefit, soil P supply, and root growth and yield of maize (Zea mays L., Zhengdan ‘958’). The experiment consisted of five treatments: regular diammonium phosphate (DAP); CRP with release longevity of three months (CDAP); regular diammonium phosphate combined with ZNC (DAPZ); CRP combined with ZNC (CDAPZ); and no added P fertilizer (Control), each with three replicates. The results indicated that CDAP and DAPZ treatments significantly increased average yield by 9.65 % and 3.56 %, and PUE by 7.72 % and 3.32 %, respectively, when compared with DAP treatment. Similarly, the average soil available-P of CDAP and DAPZ treatments was increased by 10.0 % and 45.9 % at 0−40 cm soil depth. Furthermore, CDAP and DAPZ treatments significantly increased maize total root length by 178.2 % and 223.6 %, and bleeding sap rate by 23.3 % and 32.5 %, respectively, at the jointing stage. However, the average maize yield and net income of combined CDAPZ treatment had no significant difference relative to CDAP and DAPZ treatments. Moreover, the total root length of CDAPZ treatment was reduced by 16.0 % and 27.8 %, compared to CDAP and DAPZ treatments. Hence the application of CRP or ZNC could increase maize yield by improving soil P supply intensity to meet maize P demand and promoting root morphological characteristics and vitality. However, the combination of CRP and ZNC did not demonstrate significant synergies on yield improvement and root growth promotion. Further research is needed for the development and application of biostimulant enhanced fertilizer as a green environmental technology.