Authors:

Richard L. Snyder, Biometeorologist
Stephen R. Grattan, Plant-Water Relations Specialist
Larry J. Schwankl, Irrigation Specialist
Cooperative Extension
Department of Land, Air and Water Resources, Davis

UC Cooperative Extension
Division of Agriculture and Natural Resources
Leaflet 21466 If you have comments or suggestions, please email lawrweb@ucdavis.edu

Last reviewed December 19, 2002

Drought Tips for Vegetable and Field Crop Production

Introduction

Evidence of drought in North America is clear from climate studies. A tree-ring analysis in Nebraska showed that serious droughts have occured on the average of every 24 years since the 12th Century. These droughts, however, were not cyclical and, hence, they could not be predicted. In the Nebraska study, a drought period averaged 13 years, which should alarm Californians since droughts here during the past century were typically 1 or 2 years in duration. Clearly we need to be prepared for much more serious droughts than we have recently experienced.

Most of our water is used in agricultural production and we need to use that water wisely. This publication describes various strategies to maximize production of vegetable and field crops under a limited water supply. Drought Strategy for Deciduous Orchards, UC Leaflet 21453, gives tips for deciduous tree crop drought management. In that leaflet and in this leaflet the techniques presented can improve water management in any season regardless of the amount of water available for irrigation.

Crop production and profits can be maximized during periods of limited water supply by (1) reducing the area planted, (2) improving irrigation efficiency, (3) applying accurate preseason irrigations, (4) reducing soil surface evaporation, and (5) deficit irrigation. In addition, selecting the crop and planting time that uses the least water, after economic considerations, could lead to substantial water savings. The objective of these strategies is to maximize the amount of irrigation water that contributes to plant production and to minimize nonessential losses.

The water conservation strategies listed above can be implemented to avoid prolonged water stress on the crop. Crop growth and yield can be severely affected by water deficits during a drought. When soil-water is moderately deficient, plants reponds by reducing growth (mild stress). Although yields may be acceptable, a smaller crop and yield will result if this stress continues all season. As water deficits become greater, stomata (pores in the leaves) close to reduce water losses. Although this response is a plant's method of conserving water, stomatal closure also restricts the intake of carbon dioxide (CO2) by the leaves, which reduces photosynthesis (severe stress). Severe stress usually reduces crop yield, specially if it occurs during sensitive developmental periods.

Many management strategies depend on water stress, which occurs when a crop is unable to extract water from the soil at the evapotranspiration rate. Evapotranspiration (ET) is the sume of evaporation from the soil surface and evaporation from the crop leaves (transpiration). The ET rate is usually expressed in inches per day and depends on weather and crop factors. Soil water-holding characteristics partly determine when plant water stress will occur.