Effects of Green Manure Cover Crops on Weed Suppression at Mashare and Liselo, Namibia

Abstract

Small-scale farming communities in northern Namibia often encounter poor soil fertility and financial constraints. They don’t afford buying mineral fertilizers and herbicides, thus highlighting the need for cost-effective cropping systems that enhance productivity. While green manure cover crops (GMCCs) have been extensively studied elsewhere and shown to boost productivity, information on their use remains limited in Namibia. Experiments were conducted over two seasons (2016/2017-2017/2018) at Mashare Irrigation Training Center (MITC) and Liselo Research Station (LRS), which have different soil types, to explore the effects of rotating Pearl millet and maize with various GMCCs on crop weed populations. The experiments compared the effects of rotating nine different GMCCs with Pearl millet and maize separately against monocropping of Pearl millet and maize. Results showed that weed density varied across treatments and locations, with the highest densities observed in certain rotations, such as Pearl millet-pigeon pea and maize-pigeon pea, while the lowest densities were found in rotations involving lablab and velvet bean. This is indicative that lablab and velvet bean suppressed weeds better than all other GMCCs, while pigeon pea was vulnerable to weed infestation. Lablab exhibited the highest biomass yields. Overall, rotating Pearl millet and maize with cover crops demonstrated greater benefits compared to monocropping, emphasizing the need to identify suitable cover crops for specific niches to optimize productivity.