A study of competitive effects between a Eucalyptus camaldulensis shelterbelt and an adjacent millet ( Pennisetum typhoides) crop

Despite wide acceptance that shelterbelts increase crop yields, reports also show that yields are reduced close to shelterbelts because of competition with the trees for light, soil moisture and nutrients. The yield of millet ( Pennisetum typhoides) grown adjacent to a Eucalyptus camaldulensis shelterbelt increased substantially by pruning the roots at a distance of 0.25 times the belt height (0.25 H) from the trees. Observations indicated that roots of Eucalyptus penetrated into the cropped area, mainly at depths 0–70 cm, up to a distance of at least 1.5 H. These roots were largely in the diameter classes of 1–10 mm. The highest depression of millet yield occurred between the edge and 1.5 H, which suggests that was indeed the zone of most active competition. Shading, which most of the time extended only up to about 0.5 H, also contributed to reduced yields very close to the belt.