1. Crop Management Strategies for Low Water Availability.

The High Plains is a temperate semi-arid region with highly variable rainfall. Extended periods of drought are common. In general, crop management strategies attempt to maximize the total water available to the crop and to maximize transpiration by minimizing soil evaporation. Summer fallow, the practice of controlling all plant growth during the non-crop season, was quickly adopted in the region to increase the chances for successful establishment and development of winter wheat (Triticum aestivum L.) and to stabilize wheat yields. The substitution of herbicides for tillage to control plant growth during fallow resulted in an increase in summer fallow storage efficiency from less than 20% to about 40%. Greater water storage efficiency was achieved by terminating fallow in the spring and planting a summer crop. Cropping intensification replaces soil evaporation with crop transpiration. Intensified systems in the region generally produce two crops in three years or three crops in four years through the addition of summer crops. However, cropping intensification that eliminates summer fallow can have negative consequences. Elimination of the summer fallow can result in a significant reduction of available soil water at wheat planting and subsequent wheat yield. Using soil water in the spring to determine whether or not to use summer fallow prior to winter wheat seeding has been proposed as a dynamic approach to reduce the frequency of summer fallow. Skip-row planting patterns have proven to be beneficial in several full-season summer grain crops, e.g., corn (Zea mays L.), particularly in lower yielding environments. Reduced plant density may also be used to lower the risk of crop failure. Increased use of annual forage crops in the crop rotation reduces the risk of total crop failure resulting from a lack of sufficient rainfall during the critical flowering and early grain fill period in grain crops.