The Releasing Characteristic And Effects On Soybean Yield Of Slow-release Ureas

Through laboratory and field simulation, the differences of nitrogen release characteristicamong sulfur-coated urea and self-made slow-release ureas and common urea were studied in thisresearch. The effects of slowing-release ureas on soybean were studied as well to provide theorybasis for slow-release urea application in soybean production using pot and filed experiment. Thecontent of NO₃-N was determined by leaching simulation experiment in laboratory. The change ofresidual urea-N content, NH₄⁺-N content and NO₃^--N content with time in soil were tested in fieldsimulation experiment. The effects of slow-release urea on N accumulation, dry matteraccumulation and yield of soybean were determined in pot experiment and field experiment.The main results are as following:1.The slow-release function of sulfur-coated urea was the most obvious under leaching condition,the leaching amount of NO₃-N was maximal after 31 days, and the amount was higher than othertreatments at each period during 66 days. The inhibitor in self-made slow-release urea couldrestrain conversion of urea to NO₃^-N in the first 9 days,.2. Slow-release urea 1 and sulfur-coated urea had the effects of slowing release under fieldconditions. Residual urea amount was 33.3% higher than common urea in the first 31 days. After46 days, the amount fell to the same level as common urea. Residual urea amount in sulfur-coatedurea treatment was always higher than that of common urea and slow-release urea 1, and thecontents of NH₄⁺-N and NO₃^-N were much higher during later period under this treatment.3. In pot experiment, N accumulation amounts at the treatments of N25^*3, slow-release urea 1and sulfur-coated urea were significantly higher than the treatment of N75 from R4 to R6 period. Infield experiment, N accumulation amount of sulfur-coated urea was 84% of control plot at seedlingstage, 94.7% at florescence, and 108.3% at pod stage, Showing that sulfur-coated urea had morepersistence of supplying nitrogen to soybean than common urea, furthermore, it was beneficial fornitrogen distributing to seed.4. The law of dry matter accumulation was similar with that of N accumulation in potexperiment. Top dressing nitrogen at R4 to R6 stage were beneficial to dry matter accumulation insoybean shoots at later growth stage, and also beneficial to dry matter transferring to seed. In fieldexperiment, applying sulfur-coated urea was beneficial to total dry matter accumulation at latergrowth stage, and it was also beneficial to dry matter transferring to seed. 5. In pot experiment, the yield of N25^*3 was 18.2% higher than N75, significant at 5%, butthe factors of yield was not different. The yield of sulfur-coated urea increased by 16%, notdifferent with N75, but the 100-seed weight increased by 2.6%, significant at 5%. The 100-seedweight of slow-release urea 1 treatment increased 4.3% compared with N75, significant at 5%.In field experiment, the yield of sulfur-coated urea increased by 7.5%, but there was no significantdifference with common urea plots.