Application Of Slow-Release N Fertilizer In One-Off Fertilization On Single Crop Rice

Rice is an important crop, which has become critical for food security throughout China. Rice production in China, however, is facing so many problems such as low nutrients utilization and rural labor force shortage. It is commonly to find excessive fertilizer inputs but limited increase in crop yields in agricultural production recently. Farmers get fewer benefits from rice production due to all the above-mentioned phenomena. Under the current background of unreasonable fertilizations and rural labor force shortage in China, researches on key technologies for one-off fertilization on rice production are absolutely necessary. Five samples of Slow-Release N Fertilizers (SRF) were collected in the present work, which included three SRFs that are in sale at market and two SRFs that are prepared in the laboratories of scientific research institutes. The nutrient slow release features and their influencing factors were studied for all SRFs by using the water dissolution rate method and the soil cultivation method. Field experiments were also carried out to investigate effects of different SRFs on the enhancement of the rice yield during one-off fertilization for single crop rice. The results are listed as follows:1. According to the results of water dissolution rates, we noted that both coated 1 SRF and coated 2 SRF released nutrients in an S-shaped curve with an initial dissolution rate of 0.81% and 2.9%, respectively. The release cycles of coated 1 SRF and coated 2 SRF are theoretically calculated to be 106 days and 63 days. As the nutrient release features of coated 1 and coated 2 satisfied the requirement for the nutrient release of slow-release fertilizer, they can be used as alternative fertilizers for one-off fertilization on single crop rice. Compared with that for the above-mentioned SRFs, the nutrient release curve was parabolic-shaped for coated 3 SRF, which showed only 5.07% of the initial dissolution rate and 8 days of the theoretical release cycle. The results indicated that coated 3 SRF can not meet the demands of low-release fertilizer on nutrient release.2. According to the dynamic curves of nutrients release obtained from water dissolution rates, the actual values of nutrient release cycle for coated 1 SRF and coated 2 SRF were 75 days and 45 days, respectively, which were found to be lower than their theoretical values. SRFs in soils and in water showed similar patterns of nutrient release, although the SRFs in soils have higher nutrient release rates than that in water. Insignificant differences in the nutrient release rates were found between SRFs cultivated in Red soil and in Hu Songtian soil. However, the nutrient release rates of SRFs cultivated in flooded soil were found to be higher that cultivated in dryland soil.3. During soil cultivation, soil enzyme activities were found to be affected by both SRFs types and culture conditions. The dryland soils added with all SRFs have significantly higher urease activities than the flooded soils added with the same SRF. The soils applied with both coated 1 and coated 2 SRFs showed low urease activities, which increased with the increasing of the culture time. In contrast, the long-term sustained release fertilizer, urea-formaldehyde fertilizer and coated 3 SRF, which exhibited higher nutrient releasing rates, showed higher urease activities in soils. For coated 1 SRF and coated 2 SRF, there were no significant differences in urease activity when cultured in red soil and in Hu Songtian soil. However, the urease activities for the long-term sustained release fertilizer, the urea-formaldehyde fertilizer and the coated 3 SRF showed obvious differences when cultured in different soil types. Soil nitrate reductase activity was then detected and found to increase as cultivation time increased. The long-term sustained release fertilizer, the urea-formaldehyde fertilizer and the coated 3 SRF resulted in higher nitrate reductase activities than coated 1 and coated 2 SRFs, regardless of the cultivation time.4. Application of SRFs in the production of single crop rice did enhance rice production since it resulted in an increase in some factors related to crop yield such as the effective tillers of single crop rice, total grain number per panicle, effective panicle and plant height. However, application of SRFs showed insignificant effects on the grain weight. We found that coated 1 and coated 2 SRFs application promoted the nutrients uptake in rice. Indeed, there are no obvious differences between the single crop rice yield and equal N application rate treatments in Lincheng and Pengcheng of Changxing two experimental points. The improving effects of urea-formaldehyde fertilizer and coated 3 SRF were found to be unstable in both pilot sites. Besides, the application of urea-formaldehyde fertilizer led to reduced rice yields in both pilot sites.5. According to the results of both nutrient release characteristics and field experiments, it could be concluded that the application ratio of the coated 1 SRF or the coated 2 SRF should be higher than 60% to keep its rice yield comparable to or higher than that obtained from conventional fertilization when the application dosage of nitrogen is equal to that convention fertilization.6. Effects of the dosage and the proportion of SRFs applied in soils on rice yields were investigated. When the application dosage of nitrogen is equal to that convention fertilization, the application ratio of coated 2 SRF should be higher than 40% to keep its rice yield comparable to or higher than that obtained from conventional fertilization. However, when the application dosage of nitrogen is 20% lower than that in convention fertilization, the application ratio of the coated 2 SRF should be higher than 48% to keep its rice yield comparable to or higher than that obtained from conventional fertilization.