Effects of adding proportions of functional absorption materials on performance of new slow-release urea

Nitrogen fertilization enhances crop productivity. However, common nitrogen fertilizers have some drawbacks (e.g., high risk of nitrogen leaching and ammonia volatilization) which lead to environmental and economic problems. The development and application of new types of high-efficiency fertilizers such as matrix-based slow-release fertilizer is a possible solution to these drawbacks. Matrix-based slow-release fertilizer has the advantages of simple production process, low cost and stable performance. The added proportion of modified functional absorption materials affects the performance, effective component content and production cost of slow-release fertilizers. However, little is known about the relationship between the added proportion of functional absorption materials and performance of slow-release urea. The objective of this study was to assess the effects of added proportion of functional absorption materials on the performance of a new materials-based slow-release urea. The tested functional absorption materials were modified zeolite and bentonite by using organic polymer. The nitrogen loss characteristics and field crop performance of the functional absorption materials-based slow-release urea (SRU) were analyzed using sand leaching, ammonia emission chamber and field maize experiment methods. Experimental treatments mainly consisted of common urea (CU, as control), and six SRUs added 1%, 2%, 3%, 4%, 5% and 6% functional absorption materials, respectively. Then nitrogen release characteristics of urea were described using the first-order kinetic model. In field conditions, soil in the plough layer (0-20 cm) and ear leaves of maize were sampled at silking stage for measurement of soil available nitrogen concentration, leaf chlorophyll content and nitrate reductase activity. The optimal added proportion of functional absorption materials in slow-release urea was calculated using a polynomial model. Results showed that the highest nitrogen leaching ratio occurred at the first leaching-i.e., 81.6% in common urea treatment and 27.7%-42.8% in SRU treatments. The cumulative nitrogen leaching ratio in common urea treatment reached 100% at the sixth leaching, while that in SRU treatments reached 90% only at the twelfth leaching. Slow-release urea with 6% functional absorption materials had the best performance of reducing nitrogen leaching. The nitrogen release characteristics was fitted by the first-order kinetic equation-N_t=N₀(1-e^-bx), where N_t is cumulative nitrogen release ratio, N₀ is the maximum cumulative nitrogen release ratio, b is nitrogen release ratio constant, and x is the number of leaching. Nitrogen release ratio constant (b) of SRU treatments was 67.4%-82.6% lower than that of CU treatment, while cumulative ammonia emission of SRU treatments was 15.8%-39.3% lower than that of CU. Available nitrogen content in the plough layer of maize field increased with increasing proportion of functional absorption materials, which also increased leaf chlorophyll content and nitrate reductase activity in maize. SRU increased maize biomass and grain yield. Calculation based on a polynomial model showed that the highest plant biomass (15 829 kg·hm^-2), shoot biomass (164.0 g·plant^-1), root biomass (26.9 g·plant^-1) and grain yield (6 769 kg·hm^-2) were obtained in SRU treatments with 5.28%, 4.80%, 5.24% and 4.76% functional absorption materials, respectively. Overall, slow-release urea with 5% functional absorption materials had better performance in terms of nitrogen loss reduction via leaching and ammonia emission reduction, maize nitrogen nutrient improvement, and then maize biomass and grain yield increase.