Preparation And Application Effect Of A New Type Of Water-retaining Slow-released Fertilizer

Modern agriculture uses fertilization to increase food production.However,the utilization of fertilizers is low due to volatilization,runoff,surface runoff,and soil.In addition,over-fertilization can also cause a series of environmental pollution problems,such as lake eutrophication and soil quality decline.At the same time,China also has a large number of arid,semi-arid,and desert areas.The low utilization rate of water and fertilizer resources not only causes a lot of waste of human,material and financial resources,but also these fertilizers may infiltrate into groundwater with rainwater,polluting drinking water.Therefore,the lack of water resources and the low utilization rate of fertilizers are the main factors restricting the development of agriculture in my country.In order to increase nutrient efficiency and increase food production,slow-released fertilizers（SRFs）are considered as a promising strategy to replace traditional fertilizers.Double-coated fertilizers（DCFs）,as one of SRFs,have great advantages in delaying nutrient release,reducing water pollution and increasing crop yields.However,the membrane shell of this kind of fertilizer is difficult to degrade,which will cause secondary pollution to the soil structure and the environment.In addition,the preparation process is complicated and the production cost is high.In order to solve the above problems,from the point of view of materials,this paper develops a new water-and fertilizer-management strategy--nutrient-water carrier（NC）.This new type of fertilizer is prepared with superabsorbent resin and the existing polymer slow-released fertilizer technology.NC has the characteristics of simple preparation process,strong ability of slow release and high water absorption rate.The specific research content is as follows:（1）Using carboxymethyl chitosan（CMC）,acrylic acid（AA）and poly（dimethylourea phosphate）（PDUP）as raw materials to prepare NC with the function of slow release of multiple nutrients by solution polymerization.The preparation conditions of the superabsorbent resin with the highest water absorbency rate of 791.26 g/g are: AA 7.20 g,AA neutralization degree 75%,10% NOCMC（AA mass ratio）,5% PDUP,0.6% APS,0.05%MBA,70 ℃ and reaction time 2.0 h.After loading 25% of the PDUP into the polymer network,the swelling degree（SD）of the optimal NC reached 482.59 g/g.FTIR,SEM,EDS and TG were used to characterize the optimized sample.The results showed that the nutrient content of NC exceeded 70 wt%.The NC with semi-interpenetrating network structure（semi-IPN）can significantly improve the water holding capacity of sandy soil,which is six times that of the control group.In addition,NC in sandy soil showed a positive synergistic effect on corn root length and seedling height.After 30 days,the cumulative release of N,P and K in NC reached 73.43%,49.93% and 79.95%.The results of the study show that NC can not only improve nutrient efficiency and prolong the fertilizer release rate,but also reduce the frequency of irrigation.It is expected to be widely used in semi-arid and arid regions.（2）Using CMC,AA,acrylamide（AM）and urea-formaldehyde（UF）as raw materials,NC was prepared by solution polymerization.On the basis of orthogonal experiment,the reaction parameters of NC were optimized by single factor experiment.The optimized preparation conditions of NC were: MBA 0.07%,KPS 0.8%,AM to AA mass ratio 0.30（total10.0 g）,CMC content 10%,AA neutralization degree 85%,reaction temperature 70°C,and reaction time 2 h.When the UF content is 20%,the maximum water absorption rate of NC can reach 143.50 g/g.FTIR,SEM,and EDS were used to characterize the optimized NC.FTIR and SEM results showed that UF was successfully loaded into the CMC-P（AA-co-AM）polymer network.The results of the pressure film experiment found that UF could reduce the water-holding capacity of the hydrogel network.The hydrostatic slow-release experiment showed that the cumulative release of N in 30 days was 31.19%.Therefore,NC has excellent water retention and slow and controlled release capabilities.（3）In order to study the practical application value of NC,a pot experiment of apple saplings was used.The effects of different fertilizer ratios and application time on the growth,nutrient use efficiency,soil nutrients and soil enzyme activities of apple saplings were analyzed,and the differences of NC and compound fertilizer application on the growth and soil nutrients of apple saplings were discussed.The results show that the combined application of NC and common fertilizer can effectively promote the absorption and utilization of nutrients by apple saplings,and is beneficial to improve soil nutrient content and biological properties.After T1 treatment,the utilization rate of N,P,and K in saplings increased by 11.22%,7.11% and 4.56%,respectively.The application of NC could significantly increase the soil nutrient content and soil enzyme activity,and the soil nutrient content and soil enzyme activity were significantly improved by T1 treatment.Urease and sucrase activities were significantly positively correlated with soil available potassium content;urease and phosphatase activities were also significantly positively correlated with soil total nitrogen content.Therefore,NC application is an effective measure to improve nutrient use efficiency and comprehensive soil fertility level in apple planting.