With the rapid development of modern industry, rapid population expansion, and deterioration of water resources, the problems of drought and desertification have become increasingly prominent. The development of water-retaining agents is an effective way for scientists from various countries to solve these problems.
In 1974, the Northern Research Institute of the United States Department of Agriculture first invented the super absorbent resin obtained by starch-acrylonitrile graft polymerization and then hydrolyzed, and its water absorption rate is remarkable.
In 1978, Japan's Sanyo Corporation applied super absorbent resin to the sanitary products market. The market behavior prompted scientific research to pay more attention to this new field. The agricultural and forestry application of water-retaining agent requires a longer inspection and evaluation time, and the promotion and marketization process is longer than that of industrial products. In addition, the initial production scale is small and the price is extremely high. It is only in recent years that large-scale applications have been obtained. Thing.
Super absorbent polymer is a collective name for a class of functional polymer materials with high water absorption characteristics, and the full English name is super absorbent polymers (SAP). SAP is generally classified according to raw materials and synthesis methods. Has developed starch, cellulose and synthetic resin series. Synthetic resins include polyacrylate, polyacrylamide and polyvinyl alcohol.
Agricultural SAP is commonly called water retaining agent at home and abroad. It is different from other SAPs in terms of synthetic raw materials and performance requirements. At present, there are only two types in the world: starch grafted acrylate polymer cross-linked product (referred to as starch grafted type) and acrylamide-acrylate copolymer cross-linked product (referred to as polyacrylamide type).
Due to the cross-linked molecular structure of the water-retaining agent, the water absorbed by the molecular network cannot be squeezed out by simple physical methods, so it has strong water retention. It is like a miniature reservoir for seeds and plant roots to absorb slowly, and it can release and absorb water repeatedly.
Water-retaining agents, if used in combination with pesticides, rooting powder and fertilizers, can also make them slowly released and improve utilization. It will not burn and explode, is also non-toxic and corrosive, and the degradation products are beneficial and harmless to plants and soil.
Generally speaking, the lower the degree of cross-linking of the polymer of the same composition, the higher the relative water absorption rate and rate, the worse the water retention, stability and gel strength, and vice versa. The water-retaining agent used in the layout does not pursue high water absorption rate, but pays more attention to the gel strength. However, coating and root dip generally require a higher water absorption rate.
Polyacrylamide type has higher cost than starch graft type, but it has a longer life span and is the mainstream product of water retention agent. There are three forms: granule, powder and flake. Granules and flakes have better permeability and have a longer life span compared to powders. The powder form is suitable for coating and root dip.
The soil mixing is generally mixed with 0.05-0.1% of the dry soil weight of the cultivated layer, and then water is poured; or the water is retained to absorb enough water to form a saturated gel, and then the volume ratio of the soil to the saturated gel is 5%-15%. It is suitable for the horticulture industry with high economic value, and generally has the lowest cost in hole or furrow application. A 20cm potted plant only needs 1g. In arid areas, especially seasonally arid southern hills and mountainous areas, the use of polyacrylamide for fruit trees is the most economical, and the water retaining agent needs 3-6kg. Rice tray-type seedling raising is equivalent to 150-250g starch grafted water-retaining agent per 667m2 of the field. Not much water-retaining agent is required for coating. It forms a seed coating agent with nutrients, pesticides and fine soil. The water-retaining agent generally contains 5%-20% and the particle size is above 120 mesh. This requires specialized technical support. It is suitable for coating rice, corn, rapeseed, flue-cured tobacco and forest seeds.
Dip root is to put 40-80 mesh water retention agent in a water container at a ratio of 0.1%, stir and absorb water for about 20 minutes before using, and take out bare root seedlings after soaking for 30 seconds. It is best to wrap it with plastic film. 1kg of water retention agent can treat at least 2000 seedlings.
The water retaining agent is suitable for all plants in all regions. It can improve soil structure and resistance to compaction, improve soil permeability and have a certain thermal insulation effect. Effectively improve the utilization rate of water and fertilizer for seeds and plants. Ziwu is strong and strong, with well-developed root system. Plant growth and disease resistance have increased accordingly. The use of mixing soil can save water by 50%-70%. During the growth period, the water retention agent saturated gel can withstand 40 consecutive days of no rain. In the north, autumn water can even be used in the coming spring. The nutrition is not easy to lose, and the fertilizer saving is more than 30%. With other measures, the fruit trees can bear fruit one year in advance, increasing the yield by 20%-30%. The yield of general horticultural crops increased by more than 10%. Rice tray-type seedlings have a high yield rate and are easy to cast and plant. Coating improves the emergence rate by more than 10%. Dipping roots can prevent roots from drying out, prolong the wilting period, and increase the survival rate by 15%-20%.
Water-retaining agent is not a water-generating agent, nor does it work without a certain amount of rainfall or boiling water. When mixing soil in northern areas is used, there will be 300 seedlings raining throughout the year, and the best cost-effectiveness ratio of mixing soil is 0.1% of the dry soil weight. The water absorption rate of water retaining agent will be significantly reduced when it encounters metal ions. Unless it is compound fertilizer, mailing fee and urea, generally do not mix it with ordinary phosphate fertilizer and potash fertilizer. All places should be used scientifically according to soil quality, plant characteristics and rain conditions.
It should be noted that although cross-linked polyacrylate has strong water absorption capacity, it is not a real water-retaining agent, and its stability and salt resistance are poor. If it contains more sodium ions, it is harmful to soil and plant growth.