ABSTRACT
Many factors of soil degradation threaten the potential production capacity in these areas. Nutrient depletion, wind and water erosion and salinity are very common issues. Although dryland farming has known significant changes in the past few decades in many parts of the world, mainly with a shift from traditional agriculture to more intensive cropping, nutrient inputs and management, especially nitrogen, remains the main concern for crop production. The use of fertilizers is at its low levels in many countries. In china, deficiency of nitrogen is reported to be almost everywhere, and that of phosphorus affects at least one third of the arable lands (Li et al. 2009a). About 68–M ha of dryland soils in Pakistan with less than 300–mm have a negative nutrient balance (Shah and Arshad 2006). Nitrogen use efficiency (NUE) is considered more critical than that of other nutrients as it is highly affected by the amount and distribution of rain during crop season. Nitrogen is also related to organic matter dynamics, and the latter affects also water status necessary for nutrient bioavailability and uptake under water stress conditions. Therefore, this chapter will put more focus on nitrogen dynamic as it is the major critical factor in dryland agriculture.
