Crop Water Use Program for Irrigation
Cropping Systems Specialist
Commercial Agriculture Program
Commercial Agriculture Program
Senior Research Associate
Fisher Delta Research Center
AgEBB System Administrator
Commercial Agriculture Program
Water is an important factor that can affect crop yields. University of Missouri Extension developed an online application to help farmers produce higher crop yields by improving irrigation management. The Crop Water Use application can be run on an office computer or smartphone. To register, go to http://cropwater.org. This guide explains how to track soil moisture in fields for optimum yields and water conservation and gives information about how to use the application to that end.
Farmers with irrigation are usually able to harvest consistent yields, even in times of drought. Irrigation helps in periods of short-term crop water stress, which are common in Missouri summers in July or August. Farmers can prevent yield losses and conserve water resources with access to information on daily crop water use and by better understanding how much soil water can be stored for root uptake between rainfall and irrigation events in specific fields on their farms.
How does the application work?
The Crop Water Use program is designed to simplify calculations required for tracking soil moisture in fields. The application saves farmers time by automatically entering weather information for each field and making daily calculations used for irrigation planning.
In the New Field setup, farmers enter locations (latitude/longitude) and soil types for each field. This is a one-time job. Each growing season, farmers enter the crop and planting date for each field. The program predicts when fields need irrigation based on estimated soil water balance. The main information that the application needs from a farmer during the growing season is actual irrigation dates and rates.
The application estimates crop water use from weather data using an equation for calculating evaporation from soil and plants called evapotranspiration, or ET. The application also calculates daily soil water balances for each field. Reports include indexes to help farmers determine when to irrigate.
University of Missouri Extension automatically downloads data each day from a network of agricultural weather stations across Missouri. ET is calculated from temperature, humidity, wind and solar radiation. This application uses the standardized short crop Penman-Monteith Evapotranspiration equation, or ETo, which was developed by a committee of the American Society of Civil Engineers. ET is the amount of combined water lost from a reference crop, such as grass, and soil evaporation.
ETo is multiplied by a crop coefficient, which is specific for the crop and growth stage. The crop coefficients, with the exception of rice, are derived from United Nations Food and Agriculture Organization publication FAO-56. Beginning at planting, growth stages are predicted from heat units for corn, rice and cotton. Calendar days are used for soybean. This information is used to estimate daily crop water use, or ETc.
Irrigation is a management tool to protect against yield loss from crop water stress in years with low rainfall. In that regard, irrigation can be viewed as an insurance policy. The cost of installing irrigation depends on the water source and whether applications are made by flood, furrow or sprinkler. To be profitable, the value of higher crop yields from watering, averaged over several years, should exceed the cost of the irrigation. Irrigation applications when crops do not need them are a waste of water, energy and money. In a drought though, they can save a farm from financial ruin.
Most of the cost of irrigation comes from the equipment, which is a multiple-year investment. Wells, pumps, pipes, valves and sprinklers are fixed costs even in years when they are not used. Variable costs for irrigation include fuel costs, repairs and changes depending on how many inches of water are applied in a given growing season.
Before deciding whether 