Slow-release nitrogen and boron fertilizer from a functional superabsorbent formulation based on wheat straw and attapulgite

To improve fertilizer use efficiency and minimize its negative impact on environment, a slow-release nitrogen and boron fertilizer with water-retention was prepared. Wheat straw was used as skeletal material in copolymerization on which acrylic acid monomer can be grafted to form superabsorbent composite. Urea and borax were introduced to provide nitrogen (N) and boron (B) nutrients, respectively. The product possessed a core/shell structure. Its core was urea in attapulgite and alginate matrix, and the shell was chemically modified wheat straw-g-poly(acrylic acid)/attapulgite (CMWS-g-PAA/APT) superabsorbent composite containing urea and borax. The effects of the amount of cross-linker, initiator, chemically modified wheat straw and attapulgite on water absorbency were investigated and optimized. The water absorbency of superabsorbent synthesized under optimal conditions was 186 g g−1 in tap water. Ammonia-selective electrode and inductively coupled plasma results showed that the contents of the nitrogen and boron of the product were 23.3% and 0.65%, respectively. The water retention capacity and the slow-release behavior of N and B of the product were investigated. The results showed that the product with slow-release and water-retention capacity, being economical, nontoxic in soil and environment-friendly, could be found good application in agriculture and horticultural.