Biotic resistance theory suggests that diverse cover crop mixes may be more effective at weed suppression than a cover crop monoculture. However, evidence for this has so far been inconsistent. To investigate, we designed a trial to explicitly test the role of cover crop diversity in weed suppression by comparing eight cover crop mixes that varied in species diversity, functional diversity, and composition. Mixes contained either one, four, or eight species, in equal proportions. Three mixes contained only cereal species, three contained only legumes, and two contained a mix of cereals, legumes, and brassicas. Research was conducted on two farms in South Africa's winter rainfall region, replicated over 2 yr. Indicators of resource uptake by each mix in terms of light, soil N, and water were measured at three time points throughout the season, approximately 50, 85, and 110 d after emergence (DAE). Aboveground biomass (dry weight) of cover crops and weeds within each mix was measured twice, at approximately 70 and 120 DAE. Regression analyses indicated that cover crop biomass was key to resource uptake and weed suppression, and that early‐season N and later‐season light availability had the strongest influence on weed biomass. Neither species diversity nor functional diversity affected resource uptake or weed suppression by cover crops. These results indicate that it is important to consider the competitiveness of individual species when designing cover crop mixes. Diverse mixes remain valuable to perform multiple functions but may contribute to weed problems if composed of poorly competitive species.

Several legume tree and shrub species of the genus Prosopis from South and Central America have been distributed around the dry regions of the world over the past 200 years. The first documented introduction of Prosopis in Kenya was in 1973, since when it has spread widely, adversely affecting natural habitats, rangelands and cultivated areas. P. juliflora is the most common naturalised species in Kenya, but P. pallida also occurs. In contrast to their undesirable effects as invasive weeds, many Prosopis species are valuable multipurpose resources in their native range, providing timber, firewood, livestock feed, human food, shade, shelter and soil improvement. The pods, which are high in sugars, carbohydrates and protein, have been a historic source of food for human populations in North and South America providing flour and other edible products. However, this indigenous knowledge has not followed the Prosopis trees and the fruit are unused or provide only fodder for livestock in most of Africa and Asia. Although Prosopis will not easily be eradicated in Kenya, a degree of control may be achieved through intensive utilisation of tree products and by improved management. In 2005, a project was launched in Kenya to develop income-generating activities using Prosopis. A workshop in 2006 explored the possibility of producing locally-acceptable food from Prosopis flour. Taste tests and feedback on the different recipes indicated that all of the food made with 20% Prosopis f lour had a pleasant taste. Preliminary analyses of Prosopis f lour samples from Kenya indicate good nutritional properties, but also the presence of aflatoxins and Ochratoxin A. Further study is required to determine toxin levels in freshly harvested pods, and in pods and flour after various periods of storage, and to develop appropriate harvesting and storage methods to maximise nutritional benefit and minimise risk to human health.

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This paper investigates how transformative agroecology may contribute to the critical reframing of social–ecological relationships, and how this might in turn create a foundation for bottom-up peace formation in fragile environments, within which rural communities are often habituated to conditions of control, violence and mistrust that drive social division. Here, we consider the value of social farming in reforging relationships through which social–ecological change may be negotiated and alternative sources of agency and identity may be cultivated in order to transcend entrenched patterns of division. Three case studies are presented, drawing on primary data from participatory action research with farming communities in Zimbabwe that also consider the differential attitudes and experiences of agroecological and conventional farmers. The study finds that, where agroecological farmers were exposed to more plural ways of thinking, being and acting together, levels of autonomy from coercive structures were increasing, as were both a sense of efficacy and optimism to effect social–ecological change. This was particularly pronounced where collective processes to shape physical landscapes were forging bonds of solidarity, reciprocity and trust. In these cases, agroecological farmers were increasingly able to envisage a future together shaped by collective endeavour, evidenced by changing attitudes and relationships with one another and their environment. The paper explores the extent to which farmers in each location were able to instrumentalise resilience and agency for everyday peace, and the variances found according to historical context and local power dynamics that represent barriers to change.