Early July crop water needs

Water use will be lower than expected for early July due to less mature crops.

Much of North/Northwest Indiana and Southern Michigan are below the mean for precipitation since crop emergence, so Michigan State University Extension would expect the need for irrigation in some areas. Water use will be lower than expected for early July due to less mature crops.

To avoid getting behind on available water, irrigators are encouraged to apply irrigation water to make up the deficit between crop water use and rainfall for the previous week. Purdue Extension Educator Bob Yoder of Marshal County Indiana was quick to remind me of a common 2012 situation, many producers in the spring of 2012 forced their crop to grow root into moisture at soil depth to meet their water needs. As the drought continued into the summer it was difficult to irrigate enough water to supply the plant without the soil moisture reserve.

Reference Evapotranspiration (rET.) was about 1.3” for most of Northern Indiana and Southern Michigan in the last week of June. In Indiana, rET. estimates from ET Gauges are available from the Purdue Agricultural Center stations and the data can be found at iClimate. Michigan Enviroweather network has links for rET. estimates and related tool for each of the 87 sites. The data could be used in the county it originates from or adjacent counties as long as actual rainfall information from the field is available.

Early season rooting depth of our crops limits our irrigation application volumes. Application of 0.75” or less are common this time of year to avoid pushing water below the effective roots zone, but avoid making too many small (less than 0.4”) application that are less effective and may aggravate disease. Corn at V-6 stage has an expected effective rooting depth of 20”. At V-10 stage we would expect corn to have a 23” effective rooting depth. By VT-16 (tassel) stage we would expect corn to have full effective rooting depth of 36” or more. Soybeans at V-3 stage have an effective rooting depth of 16”. Soybeans at R-1 stage have almost all of their effective rooting depth of 24”.

Forage crop nearing full growth and earlier season crop like potatoes have water use at or just above rET. and would have used about 1.3” of water last week. Soybeans at v-3 stage would have used 60% of the rET. for a weekly water use of just over 0.75”inches. Some soybean fields will near R-1 stage this week and will have a water removal equal to our rET. of 1.3” for the week.

Corn at v-6 stage would have used 40% of the rET. for a weekly water use of just over 0.5”inches. Corn at V-10 stage would have used 75% of the reference E.T. for a total water use of just less than an inch for the week. Corn at V-12 stage will have a water removal equal to our rET. of 1.3” for the week.

For more information on irrigation water use and when to irrigate see fact sheet #3 “Irrigation Scheduling tools”.

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