Management Of Urea Supergranule (Usg) Application To Improve Growth And Yield Of Rice (Oryza Sativa L) In Some Paddy Soils Of Togo And Ghana

Nitrogen (N) is known to be a major limiting crop nutrient which is required in large amounts as compared with other major nutrients. In rice (Oryza sativa L.) cropping, urea is the main source of N which is applied to the crop because of its relatively low cost and its high N concentration (46%). However, low N use efficiency is always associated with urea application under paddy fields because of its high N loss, mostly through ammonia (NH3) volatilization. The split application of prilled urea (PU) has for a very long time being the common strategy for reducing urea-N losses but its efficiency has been of much concern of late. The present study addresses the increase in rice yield and nitrogen use efficiency (NUE) using the urea supergranules (USG) deep placement. The study comprised of (i) a greenhouse experiment carried out in the Sinna Garden, University of Ghana to evaluate the effect of USG application at different depths on ammonia volatilization, rice yield and NUE in some paddy soils, (ii) a field trial conducted in 2017 in the irrigated scheme of Zio valley in Togo to determine the efficiency of USG and its optimum rate to improve rice yield and NUE in three paddy soils and (iii) an open field pot experiment to determine the effect of seedling age and time of application of USG on rice yield and NUE. The first experiment comprised four paddy soils: Canne and Voudou series that belong to Oxisols (USDA) were sampled in Togo, and Akuse and Bumbi series that belong to Vertisols (USDA) were sampled in Ghana. Six modes of urea application were formulated as treatments: prilled urea (PU, 1.8 g pot -1 ) applied at soil surface and urea supergranule (USG 1.8 g) applied at soil surface (0 cm) 4, 8, 12 and 16 cm depths and a control without N application. Rice variety IR-841 was planted and a closed chamber device method was used to trap NH3. The results indicated significant decrease in ammonia loss with deep placement of USG over surface split application of PU in the different paddy soils. Regardless of the depth of USG application, the type of paddy soil significantly affected the cumulative ammonia loss which varied from 8% of N applied in Canne series to 14% in Bumbi series. Ammonia loss decreased drastically with depth of USG application (37% of applied N at the soil surface to 0% at 16 cm depth). The USG deep placement significantly increased rice yield and agronomic use efficiency (AE) over PU in the different paddy soils