Background The low utilization rate of traditional urea fertilizer has caused serious waste of agricultural resources and non-point source pollution, and the shortage of water resources has also become one of the important factors restricting the development of agriculture in China. Therefore, water-retaining coated slow-release (WRCU) urea has become the inevitable trend of optimal application of soil nutrient resources and development of water-saving agriculture. However, the cost of the existing WRCU is too high, which limits its application in agriculture.

Methods A novel WRCU fertilizer was developed by using the transfer drum coating technique with large particle urea as the inner core carrier, blend (attapulgite∶fly ash=8∶2) as the inner layer, polyacrylic acid resin as the middle layer, and high water absorption resin as the outer layer, to explore the optimal composition ratio of WRCU. The nutrient release rate of WRCU was measured by the Kjeldahl method. Compressive strength of WRCU was measured by universal testing machine. The water retention properties of WRCU were determined by mass difference before and after water absorption from WRCU. Finally, a soil column drenching experiment was used to show the nutrient release characteristics of WRCU in soil media.

Results The optimal weight ratio of each component in WRCU is: 20% inorganic material (attapulgite∶fly ash=8∶2), 11% polyacrylic acid resin coating amount, 3% superabsorbent resin, the rest is large granule urea. At the same time, the compressive strength of WRCU is 81.59N, the maximum water absorption ratio is 641g/g, total nitrogen dissolution in soil column at 1 day was 12.25%, and the nutrient leaching of total nitrogen and urea nitrogen in 30 day was 81.27% and 47.62%, respectively; while the nutrient leaching of total nitrogen and urea nitrogen by uncoated macroparticles urea within 1d has reached 86.38% and 83.26%.

Conculsions The WRCU showed good slow-release effect of nutrients and water retention function, and the materials used were easily degradable materials and inexpensive, which made the promotion of WRCU in agriculture possible.