Effect of conventional and optimized nitrogen fertilization on spring maize yield, ammonia volatilization and nitrogen balance in soil-maize system

【Objective】 Two field experiments were conducted in spring maize at Changwu county(CW) of Shaanxi province and Lishu county(LS) of Jinlin province, to compare the effects of optimized and conventional N fertilization on crop yield, NH3 volatilization, and N balance in soil-spring maize system. The objective of the paper was to quantify the N saving potential and NH3 mitigation potential in spring maize under optimization N fertilization. 【Methods】 NH3 volatilization was monitored in situ with a Drger-Tube Method(DTM), which was corrected by a micrometeorological flux method in previous work. Three N treatments: CK(no N application), Ncon(conventional N fertilizer, N 250 kg/hm2 at CW and N 300 kg/hm2 at LS) and Nopt(optimized N fertilization, N 200 kg/hm2), were designed at the two sites. 【Results】 Except CK treatment(7.9 t/hm2 at CW and 3.8 t/hm2 at LS), no significant difference of maize yield between Ncon and Nopt was found at both sites(10.6-10.8 t/hm2 at CW and 9.5-9.6 t/hm2 at LS). In contrast, apparent N recovery was significantly higher in Nopt(44.3%-44.5%) than in Ncon(33.6%-36.4%). Compared with Ncon, apparent N recovery increased by 8.1percentage points and 10.7 percentage points in Nopt at CW and LS, respectively. No obvious NH3 loss was detected during the basal fertilization period with uniformly incorporated fertilizer into soil, combined with later precipitation at both sites. However substantial NH3 volatilization, accounting for 16%-22% of N applied, was found at the two sites during N top-dressing period. Reduced N application of N 30 kg/hm2(CW) and N 100 kg/hm2(LS) could significantly reduce NH3 volatilization(N 8 kg/hm2 at CW and N 15 kg/hm2 at LS). Calculated N balance results showed regional difference for N surplus and apparent N loss between CW and LS sites. For apparent N mineralization, N 97 kg/hm2 was observed at CW site, while only N 16 kg/hm2 at LS site. The Nopt significantly decreased N surplus N 48-88 kg/hm2 compared with Ncon. At CW, about 46% of N surplus was as 0-1 m residual soil N, and 54% of N surplus lost to environment, and NH3 volatilization accounted for 15%-30% of total N loss. At LS, about 65% N surplus existed as 0-1 m residual soil N, 35% of N surplus lost to environment, and NH3 volatilization accounted for 54%-75% of total N loss. Nearly N 140 kg/hm2 of residual soil N in Ncon treatment at LS, while parts of residual soil N may be lost due to N leaching and/or nitrification/denitrification. Compared with Ncon, the Nopt treatment significantly decreased N 30-40 kg/hm2 of N loss. The N loss results also showed large amounts of N unaccounted for(other N loss) was not NH3 loss but a considerable amount of N leaching, and/or denitrification.【Conclusions】 Out results reveal that there is a N saving potential of N 50-100 kg/hm2 or 20%-33% of conventional N rate in major spring maize production area of China without yield loss but significant less N loss to the environment.