Effects of Plant Density and NPK Application on the Growth and Yield of White Guinea Yam (Dioscorea Rotundata Poir)
Studies were conducted at Evboneka, Edo State, Nigeria in a forest zone to examine the effect of increasing plant population and NPK application on the growth and tuber yield of Dioscorea rotundata (Poir) cv “Obiaoturugo”. This study involved three trials. The first was conducted in 2010 involving five plant densities (10000, 13333, 17778, 20000 and 266667 plants per hectare (pph)) laid in a randomized complete block design (RCBD) and replicated four times. The second trial was conducted in 2010 involving five NPK application rate (0, 100, 200, 300 and 400 kg NPK 15:15:15 ha-1 ) using RCBD and replicated three times. In the third trial, the best three plant densities (10000, 13333 and 17778 pph) from the first trial were re-evaluated with the best two NPK application rates (200 and 300 kg NPK ha-1 ) and control (0 kg ha-1 ) from the second trial using a 3 x 3 factorial arrangement fitted into RCBD with three replicates. Results from the plant density trial revealed that increasing plant density significantly resulted in increased fresh tuber yield and decreased in number of tuber per stand, tuber size, % unmarketable tuber and multiplication ratio (MR). Based on MR, the best tuber yield was produced from 10000 pph, followed by 13333 and 17778, which were statistically comparable. Results from the fertilizer trial showed that the application of 300 kg ha-1 had the highest tuber yield (19.16 t ha-1 ) statistically similar to 200 kg ha-1 (19.12 t ha-1 ). There was no significant interaction effect on agronomic traits assessed as both factors acted independently on yam plants. Increasing plant density and NPK application rate resulted in increased degree of foliation and leaf area index (LAI). These parameters imparted higher photosynthetic capacity and translocation leading to higher total dry matter production and tuber yield. A plant density of 10000 pph and 300 kg ha-1 could be most profitable and also bring about a considerable increase in growth and tuber yield of yam.