ObjectivesIn this study, effects of humic acid urea on maize dry biomass, grain yield, and the fate of fertilizer nitrogen were investigated. The result could provide a theoretical and practical basis for the prodection of humic acid fertilizer with better quality and higher efficiency.

MethodsZhengdan 958 was selected as the test maize cultivar, and the tested humic acid urea was synthesized in the laboratory . The experiment was carried out by using technique of the ¹⁵N-label and soil column culture. No nitrogen (CK), common urea (U) and humic acid urea (HAU) were included as treatments, and all fertilizer was applied into 0–30 cm soil layer as base fertilizer. After the harvest, the maize shoots were collected and divided into five parts: leaf, stem, bract, cob and grain. Then, the dry biomass, nitrogen contents and ¹⁵N abundance in all parts of maize shoots were determined, and ear traits were tested as well. The soil samples in different soil layers (0–15 cm, 15–30 cm, 30–50 cm, 50–70 cm, 70–90 cm) were collected after the harvest, and nitrogen contents and ¹⁵N abundance were determined subsequently.

ResultsThe dry biomass of shoots and individual organs, except bract, showed an ascending order as CK < U < HAU, no significant difference existed in the allocation ratio of dry matter in aboveground organs among the treatments. The aboveground dry biomass in HAU was 13.8% higher than that in U, and grain yield in HAU was 14.2% higher than that in U. The HAU enhanced grains per ear significantly (P < 0.05), while increased the hundred kernels weight slightly. The uptake amounts of total N and fertilizer N in each column in HAU were 0.989 g and 0.072 g more than those in U, respectively. The fertilizer nitrogen use efficiency in HAU was enhanced by 4.80 percentage points compared with that in U. The allocation proportion of fertilizer N and total N in different organs showed an ascending order as: bract and cob < stem < leaf < grain, and grain possessed 65.7%–74.2% of total N and 58.6%–60.5% of fertilizer N in shoots. The fertilizer N amounts accounted for 13.3%–30.9% of total N in individual organs. There was no significant difference in the total residue of fertilizer N between HAU and U. The residual amount of fertilizer N in 0–30 cm soil layer in HAU was higher than that in U, while the residual N in 30–90 cm showed an opposite trend. The loss rate of fertilizer N in HAU was 34.9%, which was lower than that in U by 5.1 percentage points.

ConclusionsUnder the experimental condition, the application of humic acid urea could improve the maize aboveground biomass and grain yield, and regulate the fate of fertilizer nitrogen by enhancing fertilizer N uptake and reducing its leaching to soil deeper than 15 cm.