Effect of activated humic acid-urea on nitrogen use efficiency and its driving factors under wheat-maize rotation system

Humic acid-urea is an innovated fertilizer used widely in agricultural production in recent years. However, understanding on nutrient use efficiency of humic acid-urea under wheat-maize rotation system and its driving factors has so far been limited. In this study, the effects of activated humic acid-urea on wheat and maize growth, soil physicochemical properties, nitrogen use efficiency, soil nitrogen forms and contents were investigated in both field and incubation experiments. Three activated humic acid-urea treatments used in the experiments included mixed humic acid and urea (U+HA1), activated humic acid-urea (U+HA2) and activated and catalyzed humic acid-urea (U+HA3). For comparison with those urea treatments, no fertilizer application treatment (Control) and single urea application (Urea) were set up. Wheat and maize grain yields in U+HA2 and U+HA3 treatments were enhanced respectively by 15%–28% and 8%–10%, compared with Urea treatment. The application of activated humic acid-urea not only significantly reduced soil bulk density, pH and center diameter of soil granule, but also significantly increased soil specific surface area, electrical conductivity, organic carbon concentration and mineral nitrogen content. In wheat season, nitrogen recovery efficiencies with activated humic acid-urea treatments were markedly higher than that of Urea treatment. The rate of increase for wheat was 37%–91% and that for maize was 78%–93%. The trends in nitrogen agronomic efficiency and nitrogen partial productivity were then same for activated humic acid-urea treatments under wheat-maize rotation system. In addition, regression analysis showed that nitrogen recovery efficiency decreased with increasing soil nitrification, soil organic nitrogen mineralization and soil urease activity. However, it increased with increasing soil specific surface area. In the study, U+HA3 was the best treatment for crop yield, soil physicochemical properties, etc., which was therefore recommended for application in agricultural production. The results of the study provided the basis for the development and promotion of activated humic acid-urea used in agriculture.