Characteristics Of Water-Retaining Slow-Release Nitrogen Fertilizer In Swelling And Regulation Of Water And Fertilizer Release

Water and fertilizer have been the main factor limiting the development of the world’s agriculture,water to promote fertilizer,fertilizer to adjust water,water and fertilizer to coordinate the supply is the key to improve the utilization of water and fertilizer.Field crops are the main source of food,and the main promotion of the"Israeli model"of water and fertilizer control technology due to high investment only in the high economic value of fruits and vegetables.In order to meet the field crop water and fertilizer requirements,it is necessary to achieve water and fertilizer control through other methods.Super absorbent polymers are synthetic chemicals that can absorb hundreds of times their own weight in water.It is effective in reducing water loss and transpiration and enhancing water utilization in arid areas.In a previous study,we prepared a chemical reactive water-retaining slow-release nitrogen fertilizer（CSR-WN）using acrylic acid and urea as the main raw materials.Through the properties and synthesis conditions of CSR-WN,the optimal synthesis conditions for CSR-WN fertilizer were determined.It has superior water retention and nitrogen slow-release properties.Based on the above research background,this study investigated the relationship between water uptake,water loss and water-fertilizer synergistic release of CSR-WN by adjusting the ratio of hydrophilic groups in CSR-WN,fertilizer release environment,soil type and soil salinity.It is to reveal the regulatory role and mechanism of water and fertilizer regulatory factors on its water uptake,water and nitrogen synergistic release.The main results are as follows:（1）In terms of the swelling of CSR-WN,CSR-WN with n（-COO-）:n（-NH₂）=1:1,1:0.8had a strong swelling capacity,and its water-holding capacity and water-retention capacity in soil was enhanced.CSR-WN had better water-holding capacity and water-retention capacity in sandy loam than in loamy soil.The swelling behavior of CSR-WN in water followed the proposed first-order kinetics;CSR-WN maintained good reusability after five cycles.（2）The speed of nutrient release from CSR-WN in different pH buffers was influenced by the-COO-to-NH₂ratio,pH,and temperature.The nutrient release mechanism followed the Fickian diffusion in the Ritger-Peppas model.The release rate of CSR-WN with n（-COO-）:n（-NH₂）=1:0.8 was 3.61%～10.56%lower compared to CSR-WN with n（-COO-）:n（-NH₂）=1:0.2 after 77 days of release at 25℃.Except for n（-COO-）:n（-NH₂）=1:0.4,the nitrogen release rate of CSR-WN followed pH 4.0﹥pH 10.0﹥pH 5.6﹥pH 8.4﹥pH 7.0.The nitrogen release rate of CSR-WN increased by 10.07%～39.28%at 40℃compared with 25℃.（3）The speed of nutrient release from CSR-WN in soils under different salinity conditions was influenced by the ratio of-COO-to-NH₂,salinity conditions and soil acidity and alkalinity.The release mechanism followed the same Fickian diffusion in the Ritger-Peppas model.The release rate of CSR-WN with n（-COO-）:n（-NH₂）=1:0.8 was 5.70%～8.28%lower compared to CSR-WN with n（-COO-）:n（-NH₂）=1:0.2 after 70 days of release in neutral soils.Except for n（-COO-）:n（-NH₂）=1:0.6 of CSR-WN,the nitrogen release rate of CSR-WN in soil was directly proportional to soil salinity.The release rates of CSR-WN after70 days of release in alkaline soils were higher by 0.25%～2.77%than that in neutral soils.（4）The conversion rates of nitrogen released by CSR-WN into nitrate nitrogen in neutral and alkaline soils reached 0.26%～1.30%and 0.82%～3.89%,respectively.The conversion rates into ammonium nitrogen reached 0.28%～6.58%and 0.92%～6.61%,respectively.This is consistent with the overall change curves of nitrate and ammonium nitrogen content in CSR-WN cultivated soil.This was consistent with the overall change curves of nitrate nitrogen content and ammonium nitrogen content of CSR-WN incubated soil of the soil.（5）In terms of the degradation of CSR-WN,n（-COO-）:n（-NH₂）=1:1 was 36.23%～87.39%higher compared to n（-COO-）:n（-NH₂）=1:0.2 for CSR-WN in soil.The degradation rate of CSR-WN in alkaline soil is 12.48%～50.48%higher than that in neutral soil.（6）The addition of CSR-WN with n（-COO-）:n（-NH₂）=1:1 and 1:0.8 showed a significant effect on stem length and root length of maize seedlings.This work initially reveals the regulatory role and mechanism of water and fertilizer regulating factors on its water uptake and synergistic release of water and nitrogen.It will not only provide theoretical and technical guidance for the water and fertilizer regulation of CSR-WN fertilizer,but also accelerate the low-cost industrialization and application of water-retaining slow-release nitrogen fertilizer.