Agricultural News
Maximum Soybean Yields Depend on Optimal Irrigation
Tue, 03 Jul 2012 14:42:06 CDT
The amount of irrigation required to achieve maximum soybean yield depends on many things such as yield potential of the cultivar, soil fertility, and weather conditions. In general, the amount of supplemental irrigation needed for soybean in Oklahoma may range from as little as 8 inches per year in the northeastern portion of the state to more than 13 inches in the southwest, says Chad Godsey, oilseed cropping specialist with Oklahoma State University.
Water stress at some stages of plant development will have a greater effect on soybean yield than at others. If adequate soil moisture is available to germinate and establish a good stand, moderate water stress in the early growing season has a mild effect on yield. If good subsoil moisture is available throughout the root zone, the plant root system will develop normally and irrigation should not be needed for the first six weeks after planting. However, if inadequate off-season rainfall has left the soil profile depleted of moisture below the seedbed, early-season irrigation may be necessary. Roots will not develop in dry soil. An initial profile of deep soil moisture helps ensure an adequate root system to carry the plant through heavy water use periods.
The most critical stage for water stress is the reproductive stage (Figure 1). Soybean plants during early reproductive stages can easily use 0.3 in of water day, perhaps more if conditions are hot and windy. If planting a MG III or early MG IV soybean, peak water use at reproductive stages will likely occur in mid to late June. In contrast if planting a MG in May or June peak water use will occur at the end of August. Inadequate moisture at this stage will result in a reduced number of fruiting sites, and poorly filled pods. Research has shown that a 10 percent reduction in water use by soybeans during flowering results in an 8 percent reduction in yield potential, while a 10 percent reduction in water use during pod filling leads to a 10 percent potential yield loss. When limiting irrigation water, it should be saved for flowering and pod set.
One online tool to help estimate crop water use can be found at the AgWeather Mesonet website. You can get up-to-date estimates of crop water usage on a daily basis by clicking here.
In order to do a good job with irrigation scheduling you need to make sure you understand the water holding capacity of your soil in the surface 3 to 4 feet, which is the effective rooting zone where the plant will utilize water from during the growing season. Applying more water than the soil will hold is a waste of resources and cash.
You can read Godsey's original article complete with charts and graphs by clicking here.
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