The Impact of Sunn Hemp Cover Cropping on Belowground Organisms and Nutrient Status Associated with a Cucumber

Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Andrew G. Hashimoto, Director/Dean, Cooperative Extension Service/CTAHR, University of Hawai‘i at Mänoa, Honolulu, Hawai‘i 96822. An equal opportunity/affirmative action institution providing programs and services to the people of Hawai‘i without regard to race, sex, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or status as a covered veteran. CTAHR publications can be found on the Web site . Summary A field trial was conducted to examine the impact of growing sunn hemp (Crotolaria juncea) on belowground organisms such as plant-parasitic and beneficial nematodes and nematode-trapping fungi associated with a cucumber (Cucumis sativus) agroecosystem. Populations of plant-parasitic nematodes were not different between sunn hemp-cucumber and bare-ground cucumber plots at the end of cover crop season, but were greater (P < 0.05)* in the sunn hemp–cucumber plots at the end of cucumber harvest due to the greater cucumber plant stand in sunn hemp plots. Bacterial-feeding nematodes were found at higher densities in sunn hemp plots after its incorporation into the soil. Numbers of nematode-trapping fungi were also greater in plots containing sunn hemp. Despite the greater (P < 0.05) plant stand in sunn hemp plots compared to bare-ground cucumber plots, there were no significant differences in marketable yields. Potential reasons for the outcome and additional use of sunn hemp are discussed. Cerruti R Hooks, Khamphout Chandara, Declan Fallon, Koon-Hui Wang, and Roshan Manandhar CTAHR Department of Plant and Environmental Protection Sciences, Khamphout Farms, Kunia, Hawai‘i