COVER CROPS in South African Vineyards

CHAPTER 4 COVER-CROP ESTABLISHMENT

3,50

3,00

2,50

2,00

1,50

1,00

0,50 Dry matter in tonnes per hectare

0,00

Zero

Standard Black oats

Double

Zero

Double

Standard Grazing vetch

FIGURE 4.4. Effect of three fertiliser regimes on dry-matter production of two cover crops in the Olifants River valley. Adapted from Fourie et al (2005).

The average dry-matter production of black oats without fertilisation was only 22% of dry-matter production of black oats given standard fertilisation. Therefore, it is essential to fertilise grasses, especially on sandy soils.However, doubling the amount of fertiliser only increased the dry-matter production of black oats by 15%, compared to the standard application. Standard fertilisation applied to black oats in this study was similar to that applied in a study by Assefa and Ledin (2001) where oats was grown on a heavy clay soil with high organic matter. They found that fertilisation significantly increased the dry-matter production of oats compared to no fertilisation. This supports the finding that fertiliser will increase the dry- matter production of a grass on all soils. Although doubling the application rate further increased dry-matter production of black oats in the Olifants River valley trial, it is costly. More research is needed to determine the ideal amount of fertiliser for grasses on different types of soils. Dry-matter production of grazing vetchwas not significantly different with no, standard, and double fertilisation. It seems that 10 milligram/kilogram phosphorus and 78 milligram/kilogram potassium in the top 300-millimetre soil layer of this sandy soil could supply in the needs of grazing vetch.This is much lower than the 15.5 milligram/kilogram to 23.2 milligram/kilogram

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