Popis: |
The advantages of windbreak in terms of reducing soil erosion and providing tree products for farmers in the Sahel are well known. There is less certainty about the effect of shelter on crop growth, the degree of competition for water and light between windbreak and crop, and almost no information on the amount of water a windbreak transpires over a year. Field measurements of millet (Pennisetum typhoides) growth and microclimate behind a young double row neem (Azardirachta indica) windbreak at the ICRISAT Sahelian Centre, Sadore, Niger, were carried out in 1988 and 1989. Measurements of tree transpiration were made using a commercial sap flow meter, along with measurements of tree heights, stem basal areas and leaf areas. The reduction in wind speed produced by the windbreak changed over the season, as a result of the reduction of the porosity of the lower half of the windbreak by the growth of the millet crop on the windward side of the windbreak. Maximum shelter was found at 6h at the beginning of the cropping season and 3h during the middle and end of the season, where h is the height of the windbreak. Factors influencing the magnitude of shelter are discussed. |