Nitrogen use efficiency of rice as affected by the type of urea fertilizers and soil properties in Burkina Faso

The loss of nitrogen (N) can be very high in rice (Oryza sativa L.) fields, particularly in the irrigated rice cropping systems with very poor water control. Previous studies have reported low (30%) N use efficiencies (NUE) using broadcast application method of fertilizer N (Urea) in irrigated cropping systems. This low N use efficiency is associated with low yields. This thesis is addressing strategies to increase NUE and rice yields in irrigated system. The effect of urea fertilizer type (prilled urea and urea supergranule) on rice yield performance was investigated in five studies. Field and pot experiments were carried out in a pilot irrigated scheme of Sourou valley located in the north western part of Burkina Faso. The studies were conducted in 2012 and in 2013. The main objective of the study was to optimize nitrogen use efficiency of irrigated rice production by reducing losses from rice field. The amounts of total nitrogen, phosphorus and potassium uptake increased in the rice plant with the use of urea supergranule compared to prilled urea during the different rice growth stages. Acid soil recorded higher N, P and K uptake compared to alkaline soil. Maximum nutrient uptake was observed at flowering stage. Soil total N content was higher with the use USG in acid soil than alkaline soil. Root development and the number of tillers increased with the use of USG in acid soil compared to alkaline soil. The highest and lowest ammonium concentrations in floodwater were recorded with the use of PU at 26 kg N ha -1 (2.8 mg l -1 ) and USG at 52 kg N ha -1 (2.26 mg l -1 ) in the wet season of 2012. The overall concentration of ammonium in floodwater was higher with the use of PU (1.34 mg l -1 ) than USG (0.98 mg l -1 ) during the wet season of 2013. iii The increases in grain yield following urea deep placement with USG were 8 to 18% relative to broadcasting method with PU. The straw yield increased with the use of USG relative to PU also ranged from 10 to 27% during the three cropping seasons. The use of USG with FKR 62N produced the highest numbers of tillers and panicles, leading to higher yields. The application of USG increased grain N uptake by 3%, P uptake by 6% and K uptake by 80% over PU in the wet season of 2012. The increase in grain N, P and K uptake with USG over PU were 25, 16 and 42 %, respectively in the wet season of 2013. The highest grain N and P uptake was obtained with USG. The agronomic efficiency (AE) significantly by 39 and 46% increased with USG application in the two wet seasons. The physiological efficiency (PE) and recovery efficiency (RE) varied between rice varieties during the three seasons. During the dry season AE, PE and RE were not significant with the use of urea fertilizers. The combined effect of USG and phosphorus did not affect rice yield. The increases in grain yield with phosphorus application relative to the control ranged from 25 -107% during the wet and dry seasons and the highest yield was recorded at 50P. The increases in AE with USG 1.8 g over USG 2.7 were 48.93% in the wet season of 2012 and 24.43% in the dry season of 2013.

Source: KNUST