Study on prolonged effect of humic acid-urea (long-term urea) on maize

To prolong the fertilization effect of urea on crop output, a special maize-humic acid-urea fertilizer (long-term urea) was studied via pot culture and field experimentation, based on our former results on the application of humic acid derived from coal as urease inhibitor. In terms of maize yield, the optimum ratio of urea to humic acid (HA4) is in the range of 32.5∶1~121.7∶1. Humic acid-urea (long-term urea, UHAⅢ) inhibits soil urease activity during maize seedling stage by 24.1%, and soil urease activity inhibition is much stronger at seedling stage than at other growth stages of maize. Alkali-hydrolysis N contents in soils treated with UHAⅢ are increased significantly by 31.58%~32.73% compared to those in soils treated with common urea. This indicates that UHAⅢ has strong ability to supply nitrogen at late growth stages of maize over the control. Maize yield, output-investment ratio and nitrogen using ratio in maize with UHAⅢ treatment are increased by 40%, 40% and 39.70%, respectively compared to the control treatment. This indicates that UHAⅢ can enhance and prolong the effect of urea, which can be used as special maize nitrogen fertilizer.