Abstract
<p>Adverse environmental conditions have contributed to perpetual poor cabbage (<em>Brassica oleraceae var. capitata</em>) yields in sub-Saharan Africa. Elsewhere, net covers have been reported to provide a low-cost technology with the potential of modifying the microclimate around a crop for better performance. Two experiments were therefore conducted over a span of two seasons to determine the effects of agronet covers on microclimate modification and subsequent cabbage yield and quality. The treatments comprised cabbage plants grown under either fine mesh (0.4 mm pore diameter) or large mesh (0.9 mm pore diameter) agronet covers maintained permanently closed, or opened thrice weekly from 9 am to 3 pm and a control treatment where cabbage was grown in the open field. Net covering generally modified the microclimate by raising temperatures, relative humidity and volumetric water content but lowering photosynthetic active radiation and diurnal temperature range compared to control. The use of agronet covers resulted in better cabbage performance. The large mesh (0.9 mm) enhanced leaf stomatal conductance and chlorophyll content, and improved fresh and dry weight as well as head quality. Results of this study present the use of agronet covers as a potentially effective technology for use by small-scale farmers in protected cabbage culture in sub-Saharan Africa.</p>
Highlights
Cabbage (Brassica oleraceae var. capitata) is an important vegetable mainly grown by resource restrained smallholder farmers for food
Averaged over the two seasons, mean temperatures were 23.4 oC under 0.4 mm agronet used permanently, 21.1 oC under 0.4 mm agronet opened thrice weekly, 19.1 oC under 0.9 mm agronet used permanently; 18.7 oC under 0.9 mm agronet opened thrice a week and 17.9 oC under the control. This corresponded to 5.5 oC, 3.2 oC, 1.2 oC and 0.6 oC increase in temperatures following the use of 0.4 mm agronet permanently, 0.4 mm agronet opened thrice a week, 0.9 mm agronet permanently and 0.9 mm agronet opened thrice a week, respectively compared to the control treatment
Relative humidity and volumetric water content remained higher in agronet covered than in uncovered treatments throughout the study
Summary
Cabbage (Brassica oleraceae var. capitata) is an important vegetable mainly grown by resource restrained smallholder farmers for food. Despite the important role of cabbage, average yields per unit area of the crop is estimated at 15 tons ha-1 in Kenya (HCDA Report, 2008) and 30 tons ha-1 in sub-Saharan Africa (Allemann & Young, 2008), figures that fall far below the worldwide average production of 50 tons ha-1. Adverse ecological conditions including constant fluctuations in temperature, relative humidity, soil moisture and light factors have been cited among the major constraints to optimal cabbage production in many parts of Africa (Levasseur et al, 2006). In most sub-Saharan countries, cabbage is still mostly grown in open fields.
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