Slow-release urea of 60-day-release period is suitable for one basal application in early and late rice

ObjectivesSlow-release fertilizer is an important carrier for both single basal and reduction fertilization. This study explored the effect of controlled-release urea on nutrient absorption and yield formation of rice which could provide theoretical support for further increase rice yield and new fertilizer development.

MethodsField experiments in early and late rice were set up with five different treatments described as below:No N fertilization, split application of urea (50% of base fertilizer, 20% of turning green fertilizer and 30% of jointing fertilizer), single basal application of urea, single basal application of 60-day type urea and single basal application of 90-day type urea. Except no nitrogen treatment, all the other four treatments were fertilized with N 150 kg/hm². All the experimental fields were fertilized with P₂O₅55 kg/hm² and K₂O 130 kg/hm², which were supplied by calcium superphosphate and potassium chloride. Shoot and root samples of early rice were collected at jointing, booting, heading and filling stage for analysis of N, P and K. Flag leaves and grains of early rice were collected at filling stage and analyzed for N, P and K. Bleaching sap N contents and SPAD values were also measured at the same stage. The yield and yield components were also recorded after the early and late rice harvest.

ResultsThe highest yield of the early rice was 60-day type urea and split application of urea treatments, followed by the 90-day type urea and single basal application of urea treatments. The lowest yield occurred in no nitrogen application treatment. There was no significant difference in late rice yield between the 90-day type urea, 60-day type urea and split application of urea treatments. Too long period of nutrient release group, such as 90-day type urea, led to excessive nitrogen supply at filling stage, which showed insufficient filling and 1000-grain weight reduction. Application of the 90-day type and 60-day type urea increased shoots and roots N and P contents at jointing, booting, heading and filling stage of the early rice, and the highest value occurred in the 90-day type urea treatment. The N content of flag leaf and grain, bleaching sap N contents and SPAD values were all increased by application of the 90-day type and 60-day type urea in the early rice. Single basal application of 60-day and 90-day type slow-release urea increased soil alkali-hydrolysable N contents.

ConclusionSuitable slow-release urea has been proved available for single basal fertilization in rice production. The nutrient release period of 90-day type urea is too long to meet the requirement of rice, but that of 60-day type is appropriate for the purpose, with one basal application of 60-day type urea, the N uptake is increased and P uptake is synergistically increased at the same time. There is also potential to decrease the N and P fertilizer input using 60-day type urea.