Nitrogen Use by Yam as Affected by Mineral Fertilizer Application

Abstract

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 Côte d'Ivoire using 15N (15NH415NO3) labeled fertilizers to monitor N uptake and fertilizer use efficiency in D. alata. The 15N‐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 15N‐labeled fertilizer applied at 90 and 130 d after planting was not significantly different but the year affected 15N recovery by the plant. The maximum 15N recoveries calculated from the sum of the 15N 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.