Early season irrigation maximizes value of crop inputs

Spring irrigation can greatly improve germination, stand uniformity, herbicide activity and reduce nitrogen volatilization losses to air in dry soil conditions.

If you have irrigation available, consider applying water when a lack of rainfall threatens poor germination or poor use of your inputs. Most farmers appreciate a nice gentle rainfall the night after they finish planting or they have applied pre-emergence (soil applied) herbicides. Michigan State University Extension recommends that producers with irrigation can utilize their investment to make sure every irrigated field has the best chance for optimum plant populations, stand uniformity, and performance of herbicides and fertilizers.

The irrigated sandy loam soils of southern Michigan and northern Indiana need about a half inch of irrigation to wet the soil down to five to six inches. A single half inch application is often enough to germinate seed, assist in emergence (alleviate crusting) and incorporate fertilizers and soil applied herbicides. Heavier loam soils may need 0.7 inch to 1.0 inch of water to wet the top 6 inches of soil to accomplish these tasks.

One potential problem that can occur when irrigating only enough to aid a crop through emergence is the potential of a dry layer of soil developing beneath the root zone of the young seedlings. Subsequent downward root development may be restricted if the young roots desiccate and die in the dry zone before reaching adequate soil moisture at deeper depths. This situation is not very common, but irrigators need to be aware of this potential problem so that they can apply additional irrigation to prevent seedling stress. Double crop situations (soybeans or snap beans following wheat, second crop of snap bean crops) often require extensive watering to establish the second planting during the warmer and drier summer conditions.

Many soil applied herbicide labels recommend using irrigation to improve performance (or warnings to expect weed escapes if lack of rain leaves the herbicide on the soil surface). One example of this is the herbicide label from the commonly used pre-emergence corn herbicide, Bicep II Magnum. The label states the following: “Dry weather following an application of Bicep II Magnum or a tank mixture may reduce effectiveness. Cultivate if weeds develop.” This statement is followed by, “If available, sprinkler irrigate within two days after application. Apply half to one inch of water. Use lower water volumes (half inch) on coarse-textured soils, higher volumes heavier soils (one inch) on fine-textured soils.” Look to the product label for pesticides you use on irrigated field for information on use of irrigation to improve performance or for the rain fast period to assure you are not reducing performance by applying water too soon.

The economics of using irrigation to help incorporate soil applied herbicides are potentially very good in dry springs. The additional application cost alone is often greater than the cost of applying an inch of water. The cost of applying one half inch of water is between $1.00 and $4.00 per acre for most Indiana and Michigan producers. A post emergence rescue weed control program will often cost upwards of $15 -20 per acre.

In drought conditions, irrigating fields prior to post emergence weed control applications can often improve performance. Glyphosate-based herbicide labels often include the verbiage, “apply to only actively growing weed.” Drought-stressed weeds have difficulty absorbing and translocating the active ingredient where it is needed to provide effective weed control.

Not having the irrigation system ready to run was the reason most often cited for not addressing early season drought conditions. De-winterizing systems early and having pivots ready to run when you plant can make the difference between looking at a weed-free field with a uniform stand, primed for maximum yields or paying for more inputs and wishing the rest of the season you had a better start to the growing season.

For more information on maximizing the value of your inputs through the use of irrigation visit the St. Joseph County Michigan State University Extension website.

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