Objectives Maize shows fertilizer deficiency during seedlings growth under current drip irrigation technology. This study was performed to explore the effects of adding humic acid or citric acid to starter fertilizer on maize seedlings growth, and provide a theoretical basis for increasing P fertilizer use efficiency.

Methods Drip-irrigated maize field trials were conducted in Shihezi, Xinjiang in 2020 and 2021. In the experiment, ‘no phosphorus fertilizer’ was used as the control, all fertilizer top-dressed from jointing stage in 8 times (CF); 30% of NPK fertilizer was applied after maize sowing as starter fertilizer and the remained was fertigated in 8 times (DSF), humic acid or citric acid was combined applied with 30% of starter fertilizer (HSF, CSF). The total root length, dry matter and P accumulation of maize at seedling, jointing, tasseling and maturity stages, and maize yield was determined.

Results The starter fertilizer treatments (DSF, HSF, CSF) significantly increased total root length, root length density and root weight density at the maize seedling stage, compared with CF, and the root enhancement effect of starter phosphate fertilizer was such that CSF>HSF>DSF in 2020 and 2021. DSF, HSF and CSF increased maize yield by 4.60%, 8.77% and 9.82%; increased the apparent utilization rate of P by 3.21%, 9.13% and 7.66 percentage points; increased agronomic use efficiency of P by 28.05%, 53.51% and 59.91%, and increased the partial factor productivity of P by 4.60%, 8.77% and 9.82%, respectively. The maize yield, apparent utilization rate of P, agronomic use efficiency of P and partial factor productivity of phosphorus revealed that HSF≈CSF>DSF treatment in 2020 and 2021.

Conclusions Applying 30% of total fertilizer as starter fertilizer and topdressing the remaining exhibited significant yield increase effect. Adding humic acid or citric acid to starter fertilizer further stimulated the root growth and P uptake and accumulation of maize, improved maize yield and phosphate fertilizer use efficiency.