Research progress on water and fertilizer regulation technology and functional fertilizers

This paper reviewed the relevant technologies of research on water and fertilizer regulation, and the progresses in water retention and slow/controlled release fertilizers (WRSRF) which were made from super absorbent polymer (SAP), and provided basis for development and application of this kind of fertilizers in the future. Water and nutrient are the main factors restricting the dryland sustainable agricultural development in China. Regulating water by fertilizers, and promoting fertilizers by water to fully use the synergy effect of water and fertilizer are the key to improve water and fertilizer use efficiencies. At present, the implementation of water and fertilizer regulation (coupling) technology is mainly completed by agronomic measures and fertigation technology. In recent years, with the improvement and popularization of SAP, besides its effect of water absorption and retention, people have paid more attention to its fuction of nutrients conservation and slow release. Therefore, the research of WRSRF based on SAP has become a hot topic. SAP is different from common polymer in its highly hydrophilic property and moderate crosslinking network structure. Nutrients of ions or molecules in the resin can be temporarily fixed and released later by various combination forms. The soluble salts in soil have important influence on water absorbency of SAP except urea. WRSRFs can be made by using techniques of nutrient loading, compounding and coating. WRSRF is the integrated application and materialized carrier of the technologies of water and fertilizer regulation (coupling), water retaining and water saving by chemical agent, and fertilizer slow/controlled release technology. WRSRF has the functions of water absorbing and retaining, and nutrient release, and realizes the integration of water and fertilizer regulation at the same time and space, improves the use efficiencies of water and fertilizers, and has broad application prospects in agriculture, forestry, environmental restoration, ecological engineering and other fields. The future work is to seek more suitable raw materials and manufacturing processes for SAP to reduce costs; use molecular design to change the structure of SAP, modify its biodegradability, control the adverse effects of salt, and improve the water absorption, water retention and slow release properties of the fertilizer; strengthen the study of nutrient release mechanism and WRSRF evaluation methods, which are different from ordinary slow/controlled release fertilizers.