Wednesday, November 15, 2006
283-7
Green Manure Effects on Root-knot Nematodes (Meloidogyne javanica) and Following Taro (Colocasia esculenta) Crop.
Susan Miyasaka, Joseph DeFrank, Brent Sipes, and Andrea Blas. University of Hawaii, University of Hawaii, 875 Komohana St. #B1011, Hilo, HI 96720-2757
Taro is a tropical root crop that is grown for its corm, or starchy, underground stem. Corm weights can be reduced by 90% due to root-knot nematodes. To determine the potential benefits of green manures on dryland-grown taro, two promising crops, Sorghum x sudangrass hybrid [Sorghum x drummondii (Steud.) Millsp. & Chase) cv. Sordan 79] and sunn hemp (Crotalaria juncea L.), were grown for 1, 2, and 3 months in Pepeekeo , Hawaii . A weedy treatment and a weed mat treatment were included for a total of eight treatments and four blocks. Glyphosate was applied to kill green manures and then taro planted. Prior to planting of taro, nematode counts were taken and soil analyses were conducted. After 1 month of growth, tissue analyses of taro were conducted. Corm yields of taro were determined after 9 months of growth. Counts of root-knot nematodes differed significantly with the highest mean number in 1-month sunn hemp and the lowest mean numbers in 3-month sunn hemp and 2-month sorghum. Exchangeable potassium (K) differed significantly among treatments with the greatest level in 3-month sorghum followed by 2-month sorghum, and the lowest level in weed mat treatment. Significant differences in leaf K were found in taro grown for 1 month, with the highest K concentration in taro grown after 2-month sorghum and the lowest K concentration in taro grown after weed mat treatment. Green manures grown for 2 or 3 months had a beneficial effect on the individual fresh corm weight of the subsequent crop of taro. This beneficial effect could be due to lower initial numbers of root-knot nematodes or to greater exchangeable K in soil and in taro leaves, perhaps caused by slow release of nutrients during decomposition of green manure crops.