The Moisture Environment

Summary

Drought as an environmental factor in crop production is not taken in its ­catastrophic connotation. Catastrophic droughts as a problem in agriculture are a dealt with at the political, engineering or the economical levels. For the plant breeding program drought is defined as insufficient moisture supply which causes a reduction in plant production. It is the gap between crop demand for water and the supply of water. The agricultural drought on the larger scale of the region is approached at the meteorological level where the Palmer Drought Severity Index is the classical estimate. It is based on precipitations and temperature and is useful only on a longer time span such as months or weeks.

At the field level estimates of drought which affect crop production must be more precise and resolute. Here the major approach to estimates has been developed by classical accounting the energy balance of the crop. The account considers the incoming energy load on the crop brought about by solar radiation and the dissipation of this energy mainly by reflection, heat and evaporation of water (see also Chap. 2). Thus evapotranspiration and crop water use can be estimated and crop water deficit assessed in the field even on a short time scale of days or hours. The crop energy balance is driven by both environmental and crop factors. Crop factors can be genetically manipulated by plant breeding and therefore they constitute a prime subject of interest in this book.