Comparison of nitrogen use efficiency of a newly developed sorghum hybrid and two improved cultivars in the Sahel of West Africa

In Sahelian areas such as Niger, West Africa, grain sorghum [Sorghum bicolor (L.) Moench] is grown under conditions of low soil nitrogen (N) availability on degraded land with little or no fertilizer N application. Nitrogen use efficiency (grain weight per unit of N supplied from soil and/or fertilizer) is reduced due to poor crop cultural practices, lack of appropriate cultivar, suboptimal yields and N losses or deficiency of other nutrients. However, little is known about traits that contribute to differences in land races and hybrids for their performances and the adaptive mechanism of N utilization on sandy soils in a high risk environment. A three-year study was conducted to examine the N use efficiency of three cultivars: hybrid NAD-1, and improved lines Sepan82 and IRAT 204 at different N levels to identify their specific characteristics and appropriate management systems to enhance productivity. Three cultivars differed in N extraction capacity from soil indigenous N, where external N was not applied. At 90 kg ha(-1) N and above, NAD-1 was more efficient in biomass production and grain yield than the two improved lines which were selected from land races, but biomass yields were similar. NAD-1 had higher N use efficiency as measured by partial factor productivity (increase in yield per unit applied N) compared to Sepan82 and IRAT 204. However, differences in agronomic efficiency, N recovery efficiency, physiological efficiency and biomass production efficiency did not differ significantly among cultivars. Harvest index and improved N uptake in NAD-1 were associated with high grain yield compared to Sepon82 or IRAT 204. Chlorophyll content of leaves estimated by a chlorophyll meter generally determined leaf N status up to 180 kg ha(-1) applied N. This may have potential as a management tool since optimum N application in the degraded Sahelian soils of West Africa and use of superior cultivars such as hybrids are extremely important in determining potential productivity.