Tree-crop interaction of Single Scattered Trees under arid and semi-arid (rainfed and irrigated) areas are discussed in bio-economics terms. The result suggests crop suplementarity with Prospois cineraria associated with wheat and chick peas. However, the opportunity cost of keeping trees of Acacia nilotica and Zizyphus mauritiana are more than the value foregone for growing wheat and chick peas. A strong biological and financial competition exist between trees of Acacia and Zizyphus and agricultural crops of wheat and chick pea.