Tropentag, October 6 - 8, 2009 in Hamburg "Biophysical and Socio-economic Frame Conditions for the Sustainable Management of Natural Resources"

How Does Traditional Harvesting of Young Leaves for Vegetable Use Affect Seed Yields of Cowpea Variety Mixtures in Eastern Uganda?

¹Georg-August-Universität Göttingen, Department of Crop Sciences, Institute of Agronomy in the Tropics, Germany
²National Semi Arid Resources Research Institute (NaSARRI), Serere, Uganda
³International Center for Tropical Agriculture, CIAT at ICRAF, Kenya

Abstract

Cowpea (Vigna unguiculata) is one of the top four leafy vegetables in Uganda grown for both its seed and leaves. Cowpea is usually grown in intercrop with maize, sorghum, cassava or mung bean but sole cropping is also practised. Lack of improved varieties, low soil fertility and insect pests are among the most important constraints to cowpea production in Uganda leading to low seed yields (200-400 kg ha^-1). Although, young leaves are an essential source of protein and micronutrients for the resource-poor subsistence farmers and their consumption is more popular than of seeds in the eastern and northern districts, leaf yield levels had never been researched and documented. This study was performed within the “ProNIVA” project conducted by the World Vegetable Center (AVRDC) and partners, to improve cowpea's use as leafy vegetable among other traditional African vegetables. Mixtures containing up to four experimental cowpea varieties with contrasting growth habits and morphology were grown in intercrop with maize during the first cropping season of 2008 at three locations in Soroti (Serere, Kikota) and Kumi (Kogili) districts. Young tender leaves were harvested every two weeks starting at one month until flowering. ANOVA for the leaf and seed yield data was performed using the SYSTAT procedure GLM. The results of these three trials indicated that accumulated dry matter leaf yield from 3-4 harvests and seed yield ranged from 34.7 to 70.9 kg ha^-1 and 33.4 to 551.2 kg ha^-1, respectively. The leaf-harvesting strategy (25-50% defoliation) employed by farmers reduced seed yield at Serere and Kogili by 43.4% and 46.6%, respectively, but it increased seed yield at Kikota by 8.2%. At Kikota, cowpeas could develop much more vigorously because the maize suffered severely from drought. Seed yield components (pod number, seeds per pod and 100-seed weight) were not significantly affected by leaf-harvesting. Seed yield of mixtures was less affected by leaf-harvesting, unlike single varieties, possibly due to compensation effect. Overall, harvesting both leaf and seed was superior by 1.34 g DM per plant to harvesting seed alone .

Keywords: Defoliation, traditional leafy vegetables, Uganda, variety mixtures, Vigna unguiculata

Contact Address: Joshua Okonya, Georg-August-Universität Göttingen, Department of Crop Sciences, Institute of Agronomy in the Tropics, Grisebachstraße 6, 37077 Göttingen, Germany, e-mail: joshua.okonyagmail.com