Synthesis, evaluation and usage of a new generation of hydrogel-coated fertilizers with soil improving properties

Abstract

Salinity is one of the most severe environmental factors limiting the productivity of agricultural crops. Most crops are sensitive to salinity caused by high concentrations of toxic sodium chloride and other types of salts in the soil. Agricultural losses caused by salinity are difficult to assess but estimated to be substantial and salinization impact will continue to increase under climatic and anthropogenic variables. Secondary salinization of agricultural lands is particularly widespread in arid and semiarid environments where crop production requires usage of large amounts of inorganic fertilizers (e.g., ammonium sulfate, potassium nitrate, various phosphate and chloride fertilizers) to guarantee yield production. At least 20% of all irrigated lands are salt affected, with some estimates being as high as 50%. The situation will become worse with increasing world population.

Optimization of crop production under salinization required elaboration of a new generation of fertilizers.

We are proposing an effective granular fertilizer covered by a new type of hydrogels with a positive multi- effects to plant growth under saline drylands. Our findings showed that polymer hydrogels have a good ability to retain water and plant nutrients and release them to plants. The process of new type of polymer synthesis of hydrogel has been synthesized through polymerization of acrylonitrile, and maleic acid with formalin in the presence of glycerin. The formation of hydrogel used the copolymerization reaction of glycerin and a cross-linking agent formalin. Obtained product is more effective than others to water saving and gives slow release effects to fertilizers.

Free functional carboxyl groups in the composition disturb the balance of poorly soluble polyvalent cationic salts in the soil, in contrast to well-structured soils due to specific ion exchange. In contrast to the action of inorganic acids, dissolved salts are protected from recrystallization, and amorphous structures are formed. Thus, water easily penetrates into stratified areas where difficult-to-dissolve salts are formed. The low content of salts of polyvalent metals in the soil compared to acid functional groups in hydrogel completely destroys water-insoluble salts in the soil and prevents an increase in the total salt balance. The new type of hydrogel coated fertilizers became the formation of molecular pores in the crystalline layers in soil, and used as a water saving fertilizers product with the slow release effects.

Toxicological properties of these products were studied and it was determined that it belongs to a class of relatively less toxic substances. It was also found that the product does not have a negative effect on the dynamics of the number of beneficial microorganisms in the soil.