Yield and Tuber Quality of White Yam (Dioscorea Rotundata Poir) as Influenced by Fertilizer Application and Time of Harvesting

A field trial was conducted at the CSIR-Crops Research Institute (CRI) experimental fields to evaluate the effects of organic and inorganic fertilizers, and time of harvesting on the yield and quality of white yam (Dioscorea rotundata). The experiment was a 4x3 factorial arranged in a Randomised Complete Block Design (RCBD) with three replications. The treatments consisted of four fertilizer rates [(i) No fertilizer (ii) 4t poultry manure per hectare (iii) 300kg NPK 15:15:15/ha (iv) 2t poultry manure + 150kg NPK 15:15:15/ha and three harvesting times [(i) milking at 20 weeks after planting (WAP) (ii) milking at 24 WAP and (iii) harvesting at 32 WAP]. The combined application of organic and inorganic fertilizer gave significantly higher (p<0.05) total yield of yam than their sole application. All treated plots had higher (p<0.05) yields than the control. Harvesting yam early at 20 WAP yielded more seed yam and total yield than at 24 and 32 WAP. The combination of PM+NPK gave higher number of tubers of 2.12 per stand. Tuber length of 37.9cm was significantly higher (p<0.05) in PM treatment than 29.23cm for the PM+NPK amended treatment while at 24 WAP, PM+NPK was better in terms of tuber length than the control. The sole NPK amended treatment recorded higher yam mosaic virus (YMV) infection at 4MAP than all other treatments whereas leaf spot infection rate was greatest (20.1%) in the PM+NPK treatment as compared to in the control (7.3%). The study also revealed significant tuber weight loss of 23.8%, 19.0% and 16.7% for PM, PM+NPK and the control respectively, over a three month storage period. Yam harvested at 20 WAP had the greatest (p<0.05) weight loss. The interaction of fertilizer PM treatment and harvesting at 24WAP gave significant (p<0.05) weight loss compared to the control. Tuber weight was 36% and 41% higher at 32WAP than at 24 and 20WAP, respectively. Higher rotting rates were recorded under PM+NPK amended treatments compared to the other amended treatments and the control. The sensory evaluation showed that there was equal preference for boiled yam from PM+NPK amended treatments and the control at 20 WAP. The PM+NPK treatment yam was similar to the control in taste, aroma, sogginess and hardness at 20 WAP. At 24 WAP, only sole NPK treatment was slightly worse than control in taste. The treatments did not differ in mealiness. Sole NPK and PM were similar to the control in aroma and mealiness at 32 WAP. Proximate analysis showed that fertilizer amendment did not improve ash contend of yam at 20 WAP. Significantly higher level of carbohydrates was realized in PM treatment compared to the other fertilizer treatments at 20 WAP. Applying sole PM and NPK increased crude fibre content compared with the control and PM+NPK treatments. Significantly higher crude protein level (12.23%) was realized under PM+NPK treatment at 24 WAP. Highest moisture (66.1%) and fat (2.0%) contents were recorded under the NPK treatment plot at 24 WAP. The PM+NPK treatment gave the highest protein content of 11.7% than the other amended treatments but recorded lower fat content than sole PM and NPK at 32 WAP. However, moisture and potassium levels did not vary significantly at 32 WAP with fertilizer application. The application of PM+NPK was most profitable at all harvest times. It was profitable to harvest at 32 WAP and 20WAP under sole PM and NPK, respectively.

Source: KNUST