A meta-analysis of long-term effects of conservation agriculture on maize grain yield under rain-fed conditions

Conservation agriculture involves reduced tillage, permanent soil cover and crop rotations to enhance soil fertility and to supply food from a dwindling land resource. Recently, conservation agriculture has been promoted in Southern Africa, mainly for maize-based farming systems. However, maize yields under rain-fed conditions are often variable. There is therefore a need to identify factors that influence crop yield under conservation agriculture and rain-fed conditions. Here, we studied maize grain yield data from experiments lasting 5 years and more under rain-fed conditions. We assessed the effect of long-term tillage and residue retention on maize grain yield under contrasting soil textures, nitrogen input and climate. Yield variability was measured by stability analysis. Our results show an increase in maize yield over time with conservation agriculture practices that include rotation and high input use in low rainfall areas. But we observed no difference in system stability under those conditions. We observed a strong relationship between maize grain yield and annual rainfall. Our meta-analysis gave the following findings: (1) 92% of the data show that mulch cover in high rainfall areas leads to lower yields due to waterlogging; (2) 85% of data show that soil texture is important in the temporal development of conservation agriculture effects, improved yields are likely on well-drained soils; (3) 73% of the data show that conservation agriculture practices require high inputs especially N for improved yield; (4) 63% of data show that increased yields are obtained with rotation but calculations often do not include the variations in rainfall within and between seasons; (5) 56% of the data show that reduced tillage with no mulch cover leads to lower yields in semi-arid areas; and (6) when adequate fertiliser is available, rainfall is the most important determinant of yield in southern Africa. It is clear from our results that conservation agriculture needs to be targeted and adapted to specific biophysical conditions for improved impact

Lablab purpureus—A Crop Lost for Africa?

In recent years, so-called ‘lost crops’ have been appraised in a number of reviews, among them Lablab purpureus in the context of African vegetable species. This crop cannot truly be considered ‘lost’ because worldwide more than 150 common names are applied to it. Based on a comprehensive literature review, this paper aims to put forward four theses, (i) Lablab is one of the most diverse domesticated legume species and has multiple uses. Although its largest agro-morphological diversity occurs in South Asia, its origin appears to be Africa. (ii) Crop improvement in South Asia is based on limited genetic diversity. (iii) The restricted research and development performed in Africa focuses either on improving forage or soil properties mostly through one popular cultivar, Rongai, while the available diversity of lablab in Africa might be under threat of genetic erosion. (iv) Lablab is better adapted to drought than common beans (Phaseolus vulgaris) or cowpea (Vigna unguiculata), both of which have been preferred to lablab in African agricultural production systems. Lablab might offer comparable opportunities for African agriculture in the view of global change. Its wide potential for adaptation throughout eastern and southern Africa is shown with a GIS (geographic information systems) approach

On-farm evaluation and scaling-up of soil fertility management technologies in Western Kenya

Low soil fertility is a fundamental constraint to crop production in western Kenya. Although researchers have developed many soil fertility-improving technologies, the adoption of these technologies is low due to inadequate awareness of the technologies, poor access to requisite resources and unsuitability of the technologies to the farmers conditions. On-farm experiments were conducted during the 2002/2003 long rain cropping seasons in two village clusters in Vihiga and Kakamega Districts in order to: (1) introduce farmers to selected soil fertility-improving options and elicit farmers evaluation of the options; (2) assess the economics of the selected soil fertility management options under standard farming conditions; (3) compare the farmers evaluations with the results of an economic assessment. Five treatments were suggested to the farmers and through consensus, they ultimately chose to test three: (1) 5 tons ha?1 FYM (Farm Yard Manure); (2) 60 kg P ha?1 plus 60 kg N ha?1 (chemical fertilizers); (3) 2.5 tons ha?1 FYM plus 30 kg P ha?1 (chemical fertilizers). These were assessed concurrently with farmers accepted practice, using maize as a test crop. Farmers were involved in the routine management, monitoring and evaluation of the experiments, and field days were held to introduce more farmers to the technologies. The results of this investigation show that the application of 30 kg P plus 2.5 tons FYM ha?1 gave economically viable returns that remained viable even under a projected decline in maize yield and an increase in the price of fertilizers. This treatment was also the most preferred option of the farmers. The results of this study should be used for validation of the promising options and planning of future experiments