Dryland agriculture occurs in many parts of the world. It is quite difficult to give a precise definition to dryland agriculture. Enhancing dryland productivity is a lesser constraint in developed countries where agricultural practices benefit from advanced research and technologies. Nutrient sources in poor drylands are from organic sources and fertilizer use in developing countries is of appreciable use only in the more favorable rainfed areas. Fertilizer input in dryland agriculture varies with soil and climate, but is, in general, very low in rainfed farming in developing countries. In rainfed dryland farming, crop adaptation and yield are correlated to root mass. Dryland agriculture is constrained by many interacting factors, but the main one remains the limitation of water, which in turn affects soil nutrient bioavailability, organic matter dynamics and the overall productive capacity. Limitation of water is not only in terms of total amount of rainfall, but also in terms of its erratic distribution with regard to crop growth stages.