ABSTRACT
A. Agro-environment and Soils The dryland agro-climate is encountered in several parts of the world. Such a climate is predominant in West Asia, North Africa, India, China and US Plains in the Northern hemisphere. In the Southern hemisphere, Australia, Southern African nations, Argentina and Brazil possess drylands. However, the intensity and expanse of drylands utilized for agricultural cropping varies widely. It is generally accepted that in dryland agroecosystems, firstly limiting levels of soil moisture dictates cropping patterns, then net nutrient availability in soil as well as its recovery and
crop productivity. Added to it, are the frequently observed soil nutrient dearth's and droughts. In certain other ecosystems, such as wetlands, water is neither limiting nor the driving factor. Unlike wetlands in the dryland agroecosystems water and its interactive effects along with nutrients determines productivity. Liebig's 'law of minimum', if applied selectively to nutrients, may confound our inferences, because quite often soil moisture is intricately linked to nutrient dynamics and its effects on crop productivity (Power, 1990; Jones, 1997; Ryan, 1997). Again, unlike irrigated ecosystems, farmers in dryland belts cannot regulate or alter soil moisture levels, or the timing of water inputs. Precipitations received in whatever pattern or intensity has to be efficiently utilized. The capacity of dryland soils to supply nutrients also varies depending on large number of other natural factors, such as soil parent material, extent of weathering, cropping patterns adopted etc.
