COVER CROPS in South African Vineyards

CHAPTER 6 EFFECT OF COVER CROPS ON WATER USE

Olifants River valley A trial in the Olifants River valley was conducted over ten years at the ARC Infruitec-Nietvoorbij research farm near Lutzville in theWest Coast District of theWestern Cape. This is a semi-arid region with sandy soils, and cover crops can only be grown under full-surface micro-sprinkler irrigation.

860 840 820 800 780 760 740 720 700 680 660

Irrigation water supplied in millimetres

Sown Sown two- Sown Sown two- annually yearly annually yearly

Mechanical control

Sown Sown two- annually yearly

Chemical Mechanical

control

control

Henog rye

Saia black oats

Pink serradella

No cover crop

FIGURE 6.3. The amount of irrigation water per hectare per annum required in vineyards with and without cover crops under full-surface micro-sprinkler irrigation in the Olifants River valley. Adapted from Fourie (2015). Results of water use are shown in Figure 6.3.The vineyard required an average of 813 millimetres of water per hectare per year when no cover crop was present. When rye, black oats, or pink serradella was sown annually, and chemical control started just before bud-break, the average water requirement was approximately 733 millimetres per hectare per year.This reduction is due to the water-saving summer mulch created by the cover crops. When chemical control of the cover crops was left until grapevine berry set, the average water requirement was approximately 819 millimetres per hectare per year, which is similar to the requirement when no cover crop is present.This is due to the additional water needed for the cover crops to mature and set seed. For black oats, mechanical cultivation of the work row from just before bud-break was included as a treatment.The water requirement was similar to

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