The decision of when to irrigate is very important. Many times the first irrigation is started late, causing the crop to stress due to a lack of water. If irrigation is delayed until visible stress symptoms (such as plant wilting) appear, the crop has already suffered some amount of damage.
How long it lasts and when the stress occurs will determine how the crop's development is affected and whether the result will be a lower yield and/or poor quality, which reduces the profit potential for the producer.
The University of Arkansas irrigation scheduling computer program is a very good tool for determining when to water crops such as corn, soybeans, cotton, and grain sorghum so moisture stress can be avoided or at least reduced.
The program is designed to require a limited amount of readily available data and to be straightforward and easy to use. A regional location for the farm, the names of the fields, the type of crops planted, emergence dates for the crops and a start date for when the soil moisture is estimated will have to be entered for each field. This should be done at or soon after planting; information can be changed later if needed.
The initial data entry should take no more than five minutes per field once the user is familiar with the program.
The farmer then has to keep up with the maximum daily temperature, the amount of rainfall received, and when fields are irrigated. Recording of the data begins on the date selected for estimating the beginning soil moisture conditions and continues until the crop is near maturity. The maximum daily temperature can be obtained from a local newspaper, radio, or television report and Arkansas farmers can automatically download temperatures from the nearest weather station through the Internet.
Since rain can vary so much over a farm, the rainfall measurement should be taken from rain gauges in or near the fields.
The data does not have to be entered every day, but the data should be entered at least once a week. Entering data through the season should take only about 30 minutes a week for up to 20 fields.
An allowable deficit is set for each field, and it is used to determine when the crop has reached the point that it needs to be irrigated. The program keeps up with the daily crop water use. If the allowable deficit is 2 inches, the program will recommend irrigation when the crop has used approximately 2 inches of water from the soil.
The program presents recommended allowable deficits that have been determined from research studies and on-farm demonstrations. Once the data is entered, the scheduling program can predict when irrigation is needed over the next 10 days. The prediction is based on the expected maximum temperatures and no rainfall occurring in the 10 days.
The irrigation scheduling program is used by many Arkansas farmers and by growers in at least five other states. It is also used in the Cooperative Extension Service's Research Verification programs for soybean, cotton, corn and grain sorghum.
Drainage, soil type and rainfall should be considered for individual fields. When these conditions are combined with the farmers' judgment, the irrigation scheduling program can be a valuable asset in coordinating labor and water resources to satisfy crop water needs.
First-time users of the program usually think it is causing them to water too early and maybe too often. In most cases, by the end of the season, they see the benefit of improved yields by following the programs recommendations on when to irrigate.
The computer program can be downloaded from the Internet at no charge by going to www.aragriculture.org/computer/schedule/default.asp. The program is also available on compact disk (CD), through an Arkansas county Extension office for a cost of $15.
If you have questions or suggestions on topics please contact me: Phil Tacker, 501-671-2267 (office), 501-671-2303 (fax), 501-944-0708 (cell), or firstname.lastname@example.org (e-mail).
Phil Tacker is a University of Arkansas Extension ag engineer.