Water Yam (Dioscorea alata L.) is Able to Grow in Low Fertile Soil Conditions

Abstract

The effect of fertilization on growth of water yam (Dioscorea alata L.) is not fully understood. The importance of nitrogen application has been demonstrated; however, the required minimum amount remains unknown. This study examined growth of water yam under low fertile soil conditions on Miyako Island, Okinawa Prefecture, Japan, from April 2013 to January 2014. Growth with urea application (N treatment) and without urea (control) was compared. N treatment had no effect on growth or tuber yield in soil with poor organic matter. Although yellowish leaves were observed in control plants, they continued to grow till the end of harvest. The findings suggest that water yam (cv. No. 511) is able to grow under poor fertile soil conditions such as the Holocene limestone soil of Miyako Island. The δ¹⁵N values of the N-treated plants suggested that nitrogen was absorbed from the urea; however, the source of nitrogen in the control plants was not identified. Moreover, the δ¹⁵N values of the control plants decreased with growth as in sweet potato, which are known to associate with nitrogen-fixing endophytes. In line with this, growth comparisons of N-treated and control plants suggest that water yam also absorbs nitrogen from the air, although further clarification is required.