Date of this Version
Extension Circular EC783, Revised May 2014
Technology implementation in agricultural water management can significantly enhance crop water productivity and result in soil, water, and energy conservation. Over the years a number of newer and cost-effective technologies/tools have been developed to measure soil water status. Deciding which technique should be used depends on the purpose of the measurements, soil and crop conditions, desired accuracy, cost and durability of the sensor, ease of operation and interpretation of the data, and other factors.
This Extension Circular defines soil matric potential and describes principles and operational characteristics of one of the electrical resistance-type soil moisture sensors for irrigation management. It describes proper installation, maintenance, data downloading, interpretation, and use in irrigation management decisions. Examples show how soil matric potential can be used for irrigation management in various soil textures. The information, data, and recommendations made in this publication are based on long-term field research conducted by the first author at the UNL South Central Agricultural Laboratory, Clay Center, Neb., and other locations in Nebraska.
Water in the soil influences plant growth and yield along with many other variables and management operations, including performance of tillage operations, planting, nutrient uptake, soil temperature, and field hydrologic components (runoff, deep percolation, drainage). Measurement of soil water status (soil water content or soil water potential) is essential in agriculture for research and development and for routine onfarm monitoring of a current crop's status in terms of water stress so informed decisions about irrigation management can be made. Accurate determination of soil water status is a fundamental element of agricultural water management, and a fundamental component in studies related to soil water movement, crop water stress, evapotranspiration, hydrologic and crop modeling, and other agricultural practices. Irrigation management requires knowledge of when and how much water to apply to optimize crop production. Too much or frequent irrigations may cause anaerobic soil conditions and promote undesirable chemical and biological reactions in the soil, which can substantially reduce yield quantity and quality, and waste water resources. Conversely, too light or infrequent irrigation applications may cause drought conditions which also may reduce crop yield quantity and quality. Irrigation management requires the quantitative knowledge of when and how much water to apply to optimize crop production, which also requires utilizing technology for soil water status measurements.
Effective irrigation management requires that soil water status be accurately monitored over time in representative locations in the field. For optimum yield, soil water in the crop root zone must be maintained between desirable upper and lower limits of plant available water. Proper irrigation management will help prevent economic losses caused by over- or under-irrigation; leaching of nutrients, pesticides, and other chemicals into the groundwater and other water bodies; and wasting water and resources. This publication discusses one of the newer electrical resistance methods to quantify soil water status through measurement of soil matric potential, and its practical applications in irrigation management.