An assessment of urea-based fertilisers for reducing nutrient leaching from contrasting soils under wheat crops

This study assessed the effects of different urea-based fertilisers on nutrient leaching, wheat yield and nitrogen (N) use efficiency (NUE) in two clayey, alkaline soils from Morocco and two sandy, acidic soils from Nigeria. The study was carried out in a controlled environment room under optimum conditions. Columns of the soils were sown with spring wheat, treated with different urea-based fertilisers applied basally and on the soil surface, and leached four times with a dilute salt solution. In the soil with the highest soil N supply, all of the fertilisers increased N leaching compared to when no fertilisers were applied. Furthermore, including inhibitors with urea or having urea in a slow-release format did not affect N leaching compared to when N was applied as straight urea. In soils with lower soil N supply, applying straight urea did not affect N leaching compared to the control with no N applied. However, including a urease inhibitor with urea caused an increase in N leaching. The inhibitor may have allowed the urea to penetrate deeper into the soil before being hydrolysed, decreasing ammonia (NH3) volatilisation losses from the soil surface and increasing the concentration of mobile N below the root zone available for leaching. Including a nitrification inhibitor with the urease inhibitor or having urea in slow-release format brought N leaching back down to background levels. Although yields were similar, the dual inhibitor proved better for maintaining NUE than the slow-release fertiliser in two of the four soils. Therefore, urea with a urease and nitrification inhibitor is the reccomended fertiliser for reducing N losses via leaching while simultaneously maintaining NUE. However, the extent of these changes are likely to vary depending on experimental conditions such as seeding rates, fertiliser rates, method of application and experimental set-up.