Nitrogen Use by Yam as Affected by Mineral Fertilizer Application

Soil fertility decline and high N demand during plant growth are cited as main causes of low yield in yam (Dioscorea spp.). As information regarding fertilizer N use in yam is lacking, a field experiment was undertaken in 2006 and repeated in 2007 in central Cote d'Ivoire using N-15 ((NH4NO3)-N-15-N-15) labeled fertilizers to monitor N uptake and fertilizer use efficiency in D. alata. The N-15-labeled fertilizer was added in two splits (at 90 and 130 d after planting) for a target tuber yield of 40 Mg fresh tuber ha(-1). The application of mineral fertilizers increased total biomass production and tuber yield as well as N uptake from native soil organic matter. The recovery of N-15-labeled fertilizer applied at 90 and 130 d after planting was not significantly different but the year affected N-15 recovery by the plant. The maximum 15N recoveries calculated from the sum of the N-15 recovery measured at both application dates were 46 and 23% in 2006 and 2007, respectively. Leaf dry matter and leaf N uptake were higher in 2006 than in 2007, but tuber dry matter was not different between years at the final harvest. Up to 170 kg N ha(-1) was returned to the soil through the fallen shoots, indicating an important recycling of N for soil fertility replenishment. Thus, crop succession or intercropping are encouraged in a yam cropping system. Our results also show that the application of mineral fertilizers had a strong priming effect on the native soil N in both years.