The water retaining agent is a super absorbent resin (SAP). From the raw materials, it can be divided into starch, cellulose, and polymer. Agricultural water-retaining agents are generally called water-retaining agents at home and abroad. They are different from other water-retaining agents in terms of synthetic raw materials and performance requirements. At present, water-retaining agents at home and abroad can be divided into starch grafted acrylate polymer cross-linked products (referred to as starch grafted type) and acrylamide-acrylate copolymer cross-linked products (referred to as polypropylene phthalamide type) according to their composition. In 1969, the U.S. Department of Agriculture's Northern Research Center (NRRC) first developed a starch-grafted polypropylene cyanide water-retaining agent, and used it for corn, soybean seed coating, and sapling transplanting in the mid-1970s. The development of water-retaining agents in my country began in the early 1980s, and the development speed is relatively fast. In 2000, the National Agricultural Technology Extension Service Center carried out experiments and demonstrations of Boya Water Retaining Agent on dozens of crops in 18 provinces, municipalities and regions across the country, discussed its usage and dosage, and achieved good results. It can be seen that the water retaining agent has become an important part of the water-saving agricultural technology system.
1. The characteristics of water retaining agent
1. Water absorption Different water retention agents have different water absorption capabilities. Generally speaking, ionic polymers have higher water absorption capacity than non-ionic polymers, and the higher the degree of ionization of the polymer, the stronger the water absorption capacity. The water absorption times of water-retaining agents are generally tens, hundreds or even thousands of times their own weight. Different water quality has a significant impact on the water absorption multiple of the water retaining agent. Compared with pure water, the water absorption multiple of the water retaining agent in tap water, river water, muddy water, and soil extract decreases. The water-retaining agent not only absorbs large amounts of water, but also has a fast water absorption rate. The ionic water-retaining agent has a slower water absorption rate than the non-ionic water-retaining agent. The particle size of the water-retaining agent also has a greater impact on the water absorption rate. Generally speaking, the smaller the particles of the same type of water-retaining agent, the faster the water absorption rate, and the easier it is to reach water absorption saturation.
2. Water retention There are two main ways to dehydrate water-absorbing materials, one is heating and evaporation, and the other is dewatering with force (such as pressure, centrifugal force, etc.). Water retention capacity is divided into natural water retention, thermal water retention, pressure water retention, and soil water retention due to different measurement conditions. The water-retaining agent becomes a hydrogel after absorbing water, and the evaporation rate of the absorbed water is obviously reduced under natural conditions, and it is not easy to separate under pressure, showing a strong water retention capacity. Professionals have measured the water retention performance of starch grafted copolypropylene phthalamide. The results show that the water retention rate of the water-absorbing gel is still as high as 97% after continuous centrifugation in a centrifuge with a rotation speed of 4000 cycles per minute for 1 hour, indicating that it has superior Water retention performance.
3. Repeated water absorption After the water retention agent is applied to the soil, it will encounter multiple dry and wet alternates with the growth and development of the crop. This requires the water retention agent to have good regeneration ability, that is, absorb water-release water-dry-and then absorb water. After repeated absorption of water, the water-retaining agent generally stabilizes after the water absorption ratio drops by 50% to 70%.
2. The application effect of water retaining agent in agriculture
1. Effect on the emergence rate and survival rate of transplanting. After field crops such as wheat, corn, soybean, peanut, potato, rape, millet, cotton, etc. are coated with water-retaining agent, the emergence can be 1 to 4 days earlier, and the emergence rate can be Increase by 8% to 47%. Relevant personnel have conducted experiments on tomatoes and corn and found that the water-retaining agent can increase the germination rate and the emergence rate. The reason is that the water-retaining agent improves the permeability of the soil, enhances the activity of microorganisms in the soil, prolongs the decomposition of chemical fertilizers, and increases the resistance of plants. The adsorption and absorption capacity of certain nutrient elements increases the amount of water infiltration. For transplanted crops, water retention agents can generally increase the survival rate of seedlings by 10% to 30%, even higher under certain conditions, and can shorten the slow seedling period by 2 to 7 days. After chestnut, apple, hawthorn, Chinese pine, poplar, locust tree, etc. are treated with water-retaining agent dipped in roots, their transplantation survival rate increases by 12%-60%, and the average survival rate of coniferous forest increases by 2.7%-22.39%. Broadleaf forest 1.8%～14.8%.
2. Effect on growth and development Water retention agent can promote the development of plant roots and above-ground parts, mainly in plant height, stem thickness, dry matter accumulation and root dry weight. Application of water-retaining agent in the soil furrow increases corn plant height by 8-10 cm, ear position by 2-3 cm, stem thickness by 0.2-0.3 cm, aerial root layer by 1 to 1.5, and longest aerial root by 7-10 cm. Researchers found that the use of water-retaining agents combined with micro-fertilizers can also delay the onset of kiwi yellow leaf disease and slow down the symptoms of the disease. The disease index is lower than that of micro-fertilizers alone.
3. Impact on yield and quality A large number of test results show that the application of water-retaining agents has a general yield-increasing effect on crops. According to the research results on several crops of the Chinese Academy of Agricultural Sciences, the yield increase after the application of water-retaining agent: 7.9%-17.8% for winter wheat, 8.0%-14.9% for corn, and 7.7% for millet. After applying BP water retaining agent, the yields of mulched wheat, mulched corn, peas, and potatoes were increased by 10.79%, 12.19%, 8.87%, and 8.25% respectively compared with the control field. Application of water retention agent in loamy cinnamon soil increased the number of stems per plant and the average tuber weight of sweet potato, and the field production increased by 4.6% to 31%. The number of peanuts per plant and the yield per unit area treated with SA type drought-resistant and water-retaining agent were significantly higher than the control, which increased the yield of peanuts by 7% to 15%. The application of water retention agent in rice can promote tillering and increase yield by 6.2%. The water retention agent treatment of sugarcane "Xintai Sugar No. 22" can increase the yield by 12.79% to 25.48%.
Third, the application prospect of water retaining agent
The application of water retaining agent as a new way to save water in agriculture and forestry production has extremely broad prospects. At present, the bottleneck restricting the application of water-retaining agents is the price. In the future, the chemical research field and the agricultural research field should jointly find ways to reduce the cost of water-retaining agents. After the price problem is resolved, it will greatly contribute to the sustainable development of agriculture in arid and semi-arid areas. In addition, the experimental results vary greatly due to different experimental locations, application times, and crop types. Intensive management of water-retaining agents must be explored. At present, water-retaining agents are generally used in the soil. With the popularity of soilless culture and the particularity of substrate cultivation, especially in the technology of vegetable plug seedlings, the special structure of the plug causes the seedlings to have a small nutrient area, and the water holding capacity and water retention of the substrate Sex has become an important limiting factor to improve the quality of seedlings, and it is even more necessary to apply water-retaining agents to solve the problem.