COVER CROPS in South African Vineyards

CHAPTER 1 INTRODUCTION

organic carbon in the soil is 0.9% or more. For soils with a clay content of less than 6%, the application of nitrogen may be unnecessary if the carbon content of the soil exceeds 0.6%. Besides increasing water loss, high soil temperatures also accelerate microbial breakdown of organic matter. Organic matter is likewise broken down faster when the soil is aerated during mechanical cultivation.Therefore, soil-cultivation practices that keep the soil cool and do not aerate the soil excessively should be used, to facilitate the slow release of nutrients and to promote the build-up of organic matter. The results discussed in Effect of Cover Crops on Soil Carbon and Minerals in Chapter 7 (p124) show that soil carbon can be increased by planting cover crops, irrespective of climate or soil type. Soil carbon was also increased by winter-growing grasses in the work row. Effect of Cover Crops on Soil Carbon and Minerals in Chapter 7 (p124) also describes this impact of cover crops on nutrients such as nitrogen in the soil and the vine. It is important to note that the impacts of cover crops on soil are more strongly influenced by soil type than by climate, so readers should consult the section of Effect of Cover Crops on Soil Carbon and Minerals in Chapter 7 (p124) which deals with the soil type that most closely matches their own, and not only focus on the section pertaining to their region. Whereas cover crops can enhance soil fertility and improve growing conditions for grapevines, cover crops can also potentially compete with vines for resources. Effect of Cover Crops on Grapevine Nutrition and Performance in Chapter 8 (p140) examines the interaction between cover crops and the growth of grapevines, specifically root distribution, vegetative growth, and grape yield and quality. Pests When it comes to pests, cover crops can be a two-edged sword. On the one hand, cover crops can reduce the impact of pests directly, for example through releasing biofumigants, or indirectly, through providing habitat for predators. On the other hand, cover crops may be a breeding ground for pests that invade grapevines. Whether a cover crop has a positive or negative effect on pests in a vineyard will depend on the pest profile of that specific site, as well as on

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