Preparation And Properties Of Novel Wheat Straw Based Slow/Controlled Release Fertilizer

Agricultural production must guarantee the high yield and optimize the nutrient use in the view of economic and environment while the problem of the population, resources and environment become prominent increasingly. Slow/controlled release fertilizer could significantly improve the nutrient use efficiency and minimize the negative impact on the environment. Therefore, it has been received extensive attention.Wheat straw is an abundant and renewable biomass resource and is rich in cellulose, which can play an important role in many fields. However, most of the wheat straw has been discarded, incinerated or even utilized ineffectively. Obviously, it is not only the huge waste of natural resources, but also the serious pollution of environment. The low-cost wheat straw is employed to prepare a novel slow/controlled release fertilizer based on superabsorbent. The introduction of wheat straw is not only environmentally-friendly, but also can effectively reducing the cost of slow/controlled release fertilizer. Therefore, in consideration of the economic and ecological environment, the development of novel wheat straw-based slow/controlled release fertilizer has important practical significance for the development of sustainable and efficient agriculture.In this thesis, a series of superabsorbent based on wheat straw were developed by copolymerization with anionic, cationic, and nonionic monomers, and were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). Novel straw-based slow/controlled release fertilizers with water retention were prepared by the methods of adsorption and coating with the superabsorbent. The nutrient contents were determined and the release behavior in the soil was investigated. The influence of the products on soil condition and the degradation of the coating materials were investigated. The main results are as follows:1. A multifunctional slow-release fertilizer was prepared by recovery of ammonium onto pretreated wheat straw-g-poly(acrylic acid-co-2-acrylamide-2-methyl propane sulfonic acid) superabsorbent by adsorption. The adsorption studies with ammonium indicated that a good affinity for ammonium, the system can reach equilibrium within40min, and the adsorption capacity was7.15mmol L". The product with good water-retention and slow-release capacities could regulate soil acidity. However, the nitrogen (N) content of the product was11.2%. 2. The pretreated wheat straw-g-poly(acrylic acid-co-2-acrylamide-2-methyl propane sulfonic acid)/poly(diallyldimethylammonium chloride) semi-IPN amphoteric superabsorbent was prepared, and employed to prepare slow-release fertilizers by adsorption of ammonium and phosphate, respectively. The results of adsorption studies showed that the adsorptions with both ammonium and phosphate were quickly and spontaneously, and the physical adsorption is dominant. The nitrogen (N) and phosphorus (P2O5) contents of the fertilizer products were10.0%and15.9%, respectively. The product has slow-release and water-retention properties.3. A coated slow-release nitrogen and boron fertilizer was prepared based on urea in attapulgite and alginate matrix and chemically modified wheat straw-g-poly(acrylic acid)/attapulgite superabsorbent composite containing urea and borax used as the coating material. The contents of the nitrogen (N) and boron (B) of the product were23.3%and0.65%, respectively. The product based on the wheat straw and attapulgite with slow-release have great water-retention capacity and economical, nontoxic, environmentally-friendly property, which could be applied in agriculture and horticultural, especially for potato cultivation in arid region.4. A double-coated slow-release nitrogen and phosphorus fertilizer was prepared. Specifically, poly(acrylic acid-co-N-hydroxymethyl acrylamide)/wheat straw superabsorbent composite was used as the outer coating, and wheat straw/sodium alginate blends as the inner coating. The contents of nitrogen and phosphorus were20.6%and9.9%, respectively. The product has the preferable slow-release property, and could improve the water-holding capacity of soil. The introduction of wheat straw and N-hydroxymethyl acrylamide into the superabsorbent network could improve the degradation of the coating materials. The inner and outer coating material based on wheat straw not only could render the product environmentally-friendly property and lower the production cost, but also could provide an approach for valuable utilization of crop straw.5. A novel low water solubility macromolecular fertilizer, poly(dimethylourea phosphate)(PDUP) was "designed" and formulated. A coated controlled-release fertilizer based on PDUP and poly(acrylic acid-co-2-acryloylamino-2-methyl-l-propanesulfonic acid-co-N-hydroxymethyl acrylamide)/wheat straw superabsorbent composite was developed with nitrogen content of18.1%. The introduction of N-hydroxymethyl acrylamide as the cross-linking agent made the coating materials with good degradation and could control the release of nutrient while avoiding the pollution of soil and environment.