Studies On Nutrient Release Characteristics And Applied Effects Of Plant Oil Coated Urea

Nitrogen fertilization plays an important role in agricultural development, especially in food production. The contribution rate of chemical fertilizers application in the increase of food prodution are about50%in the world and more than40%in China. The maximum application amount of nitrogen internationally recognized is225kg/ha. Nitrogen use efficiency in developed countries ranged46%～68%. Nitrogen dose applied for single season crops in China excessed250kg/ha and nitrogen use efficiency was only30%～35%, lower than the average in the world. Excessive application of nitrogen fertilizers not only wasted resources, but also polluted the environment. To reduce nitrogen loss and improve nitrogen utilization has become a key link of farmland nitrogen management. The development and application of coated urea is an emerging technique to improve nitrogen use. efficiency. The synthetic polymers currently used as film materials were expensive and may cause secondary pollution in the soil, which has become a major limiting factor for the development of slow release fertilizer. Coated urea was prepared with plant oil as the main film material by spouted-spraying methods. Nutrient release characteristics and application effects of the prepared coated urea were studied. The main results were as follows:1Two kinds of coated urea as POU1(N:38.2%), POU2(N:33.3%).were preparated with large granular and oxidized plant oil by self-made spouted-spraying device.2SEM images showed that plant oil can form a complete film on the glass plate and urea granular. Mixed barrier layers on the surface of POU1coated with plant oil-drying additives and POU2coated with a complete plant oil film and plant oil-drying additives were observed. The latter was more completed. The film formed on the surface of urea granules had layered overlay structure, play the role of the physical barrier of the nutrient release.3The results of the continuous dissolution test showed that nitrogen leaching amount of POU1, POU2were significantly less than that of the commercial coated urea(CCU)(P<0.05), nitrogen leaching amount of POU2was significantly less than that of POU1. The results of soil column leaching test showed that accumulated total nitrogen leaching amount of POU1, POU2were significantly less than that of the CCU in the first three leaching and significantly less than that of normal urea in the first six leaching (P＜0.05), implying that POU1and POU2possessed sustained-release properties.4. The results of simulated ammonia volatilization test with the same nitrogen doses showed that maximum ammonia volatilization rate of POU1and POU2were only25%-30%of that of CCU. The accumulative nitrogen losses through ammonia volatilization of POU2was significantly (P<0.05) lower than that of CCU and normal urea (NU) treatment, indicating that plant oil coated urea could effectively reduce ammonia volatilization rate and nitrogen losses in soil.5The results of the pot experiment with the same nitrogen doses excepted the control showed that shoot nitrogen concentrations of POU2treatment were higher than these of NU treatment, the difference was significant (P<0.05) in some cases. After three harvest, the total biomass and the amounts of nitrogen, phosphorus, potassium accumulated in shoots of POU1and POU2treatments were significantly (P＜0.05) larger than these of NU treatment, POU2was significantly (P<0.05) larger than these of CCU treatment. It was also obtained that the apparent nitrogen use efficiency of POU1and POU2treatments were significantly (P<0.05) higher than that of CCU treatment or NU treatment. Plant oil coated urea, especially POU2, could improve nitrogen status of ryegrass plant, promote plant growth, increase nitrogen, phosphorus and potassium uptake in shoots and apparent nitrogen use efficiency.6The results of the field experiment showed that grain yields of the treatments fertilized (except only potassium treatment) were significantly higher than that of no fertilizer treatment (P<0.05). Grain yields of plant oil coated urea treatments (PPN, POU1:POU2:NU=0.3:0.4:0.3) were significantly higher than that of NU treatments (P<0.05). Nitrogen contents in shoots at the tillering stage, in straw at the harvest time and in brown rice of PPN treatments were significantly higher than that of NU treatments (P＜0.05). Nitrogen, phosphorus accumulated in straw and in brown rice and total nitrogen, phosphorus (except N5P2Kc treatment) accumulated in aboveground organs of PPN treatments were significantly higher than that of NU treatments (P<0.05). Potassium accumulated in brown rice of PPN treatments were significantly higher than that of NU treatments (P<0.05). With nitrogen application of82.5kg/ha-247.5kg/ha, apparent nitrogen use efficiency of PPN treatments were significantly higher than that of NU treatments (P＜0.05). These results indicated that plant oil coated urea could improve nitrogen status of rice, promote nitrogen, phosphorus and potassium uptake in shoots, increase rice grain yield and apparent nitrogen use efficiency, meanwhile, it could be applied in practice. According to the response of grain yield to nitrogen application under PPN treatment conditions, the appreciate nitrogen doses ranged from96.3kg/ha to139.6kg/ha, and were regarded as the recommandation.