Foliar application of urea ammonium nitrate increases summer maize yield and reduces nitrogen input and soil nitrogen surplus

Objective Base application plus one or two topdressing practices of urea is a conventional fertilization method in summer maize production of Huang-Huai-Hai Plain, which is time-consuming and laborious, and high in N loss risk. We studied the feasibility and appropriate amount of spraying urea ammonium nitrate liquid fertilizer (UAN), combing with the currently promoted micro-sprinkler irrigation technology.

Methods Field experiments were conducted in Taian City, Shandong Province in 2019 and 2020, with summer maize hybrids Denghai 605 (DH605) and Denghai 518 (DH518) as test materials. The treatments included furrow application of urea-N 210 kg/hm² (Ur), sprinkler application of UAN-N 126 kg/hm² (U1, reducing N by 40%), 168 kg/hm² (U2, reducing N by 20%), and 210 kg/hm² (U3), as well as a no nitrogen fertilizer control. At the tasseling stage (VT) and physiological maturity stage (R6), plant samples were taken to analyze N content and dry matter accumulation in different parts for the calculation of N absorption, reallocation, and utilization efficiencies. Before sowing and at the sixth leaf stage (V6), the twelfth leaf stage (V12), tasseling stage (VT), milk stage (R3), and physiological maturity stage (R6), soil samples from 0–20 cm, 20–40 cm, and 40–60 cm depth were taken to analyze the nitrate and ammonium nitrogen content for the calculation of N residue and surplus in soil.

Results The grain yields of hybrid DH605 and DH518 in U3 treatment were significantly higher than in U2 and Ur, while those in U1 were significantly lower than U2 and Ur. The grain yield and net income of hybrid DH605 under U3 were 6.71% and 11.75% higher than under Ur, while those of DH518 under U3 were 7.57% and 13.61% higher than under Ur, respectively. The dry matter accumulation, N accumulation, N transport and post-anthesis N assimilation amount all reached peaks in U3 treatment (P<0.05). Compared with Ur, the U3 treatment increased the N recovery rates of the two hybrids by 20.78 and 19.22 percentage points, N agronomic use efficiencies by 4.57 and 4.99 kg/kg, respectively. U2 treatment was recorded similar grain yields in the two hybrids with Ur, but enhanced plant N accumulation, transport and post-anthesis N assimilation, so led to significant higher N recovery and agronomic efficiencies than Ur. At the VT stage of maize, the NO₃⁻-N content in 20–40 cm soil layer increased with the increase of UAN application rate. From VT to R6 stage, the NO₃⁻-N content in 0–20 cm soil layer of each treatment showed a decreasing trend, with the highest decrease in Ur treatment. At the R6 stage, UAN treatment soils were recorded lower NO₃⁻-N content in 40–60 cm soil layer than Ur treatment, weakened the potential risk of NO₃⁻-N leaching. Compared with Ur, U3 decreased the N surplus in DH605 and DH518 experiment by 43.63 and 40.36 kg/hm² on two year average, and U2 decreased those by 48.25 and 51.91 kg/hm², respectively.

Conclusions With 20% less of conventional N input, foliar application of urea ammonium nitrate liquid fertilizer with sprinkler irrigation stimulates the nitrogen accumulation and reallocation, and increases the nitrogen recovery and agronomic efficiencies while increase maize yield, and decrease the soil nitrogen surplus and NO₃⁻-N leaching risk, achieving the target of fertilizer reduction and profit improvement in summer maize production.