Scheduling tools help irrigators get the most out of rainfall
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EmailMichigan and Indiana will often get rainfall in late June and early July to the extent it will refill the root zone for corn and soybeans.
Surprisingly often, Michigan and Indiana will get rainfall late in June and early July to the extent it will refill the root zone for corn and soybeans. This full profile allows producers to start fresh as corn growth reaches its peak water needs just after tasseling early in July. Soybeans peak water needs happen late in July at flowering stage.
The most cost-effective water irrigators can utilize come in the form of rainfall at no energy or labor cost. Irrigation scheduling is a best management practice to make the most out of rainfall. Starting to irrigate too early leaves the producer without enough water holding capacity in the root zone to take advantage of future rainfall events. Starting too late condemns the producer to a race, trying to keep up as the crops move into higher water need times and the typical weather pattern becomes hotter and drier.
Soil types most commonly irrigated in Michigan and Indiana will have holding capacities between 3 and 5.5 inches within the 36-inch root zone of a corn plant or 2 to 3.5 inches in the common 24-inch root zone most often used for managing soybean irrigation. Rainfall or irrigation in excess of the water holding capacity of the soil within the root zone is unusable to the plant but does recharge the aquifer underneath.
The common question for most irrigators after major rainfall events is when do I restart irrigation? A quick look at water removal estimates shows depletion of the water bank within the root zone. Efficient water managers will want to have at least 1 inch of available capacity to take advantage of any rainfall in the forecast. If the reference potential evapotranspiration (RPET) is 0.2 inches per day, most producers will wait five days to create 1 inch of available water holding capacity to make use of any future rainfalls. If no rainfall is in the forecast, they will wait an additional four to five days and then apply 0.8 to 1 inch of irrigation. If no rainfall happens, they’ll continue to apply 0.8 to 1 inch of water every four to five days if the RPET stays near 0.2 inches per day.
There are several no-cost irrigation scheduling tools available that help and ensure optimal yields with as little irrigation use as needed. For more information on irrigation water use and when to irrigate, see Irrigation Fact Sheet #3, “Irrigation Scheduling Tools." If you are just getting started with irrigation scheduling, download “Soil Water Balance Sheet." These and other useful resources are available from the Michigan State University Extension Irrigation website.
Waiting longer to irrigate has the potential to decrease irrigation costs by taking advantage of any larger future rainfall, but also runs the risk of falling behind if we enter a drought period. A comparison of management methods over the last decade shows that the greatest potential for water and energy savings comes from irrigation scheduling on heavier soils in wet years. In dry years on sandy soil (low water holding capacity soils), the advantage of waiting is often outweighed by the disadvantage of falling behind.
|
|
Kalamazoo |
Kalamazoo |
Kalamazoo |
Oshtemo |
Oshtemo |
Oshtemo |
Spinks |
Spinks |
Spinks |
|---|---|---|---|---|---|---|---|---|---|
|
Year |
50% |
1.5" |
1" |
50% |
1.5" |
1" |
50% |
1.5" |
1" |
|
2005 |
1.0 |
3.0 |
4.5 |
1.0 |
3.0 |
4.5 |
3.5 |
3.5 |
5.0 |
|
2006 |
0.0 |
3.0 |
3.5 |
0.0 |
3.0 |
4.5 |
2.5 |
2.5 |
5.5 |
|
2012 |
10.0 |
11.5 |
12.0 |
10.5 |
11.5 |
12.0 |
12.0 |
12.0 |
12.5 |
|
2013 |
6.0 |
7.5 |
8.5 |
6.5 |
7.0 |
8.0 |
8.0 |
8.0 |
10.0 |
|
2014 |
1.0 |
3.0 |
3.5 |
2.0 |
3.0 |
3.5 |
3.5 |
3.5 |
5.0 |
|
2015 |
2.0 |
4.5 |
6.0 |
4.0 |
4.5 |
6.0 |
4.5 |
4.5 |
6.0 |
|
2016 |
5.0 |
7.0 |
7.5 |
6.0 |
7.0 |
8.5 |
7.5 |
7.5 |
8.5 |
|
Sum (inches) |
40.0 |
59.0 |
68.0 |
47.0 |
58.5 |
69.5 |
64.5 |
64.5 |
78.5 |
|
Average (inches) |
3.64 |
5.36 |
6.18 |
4.27 |
5.32 |
6.32 |
5.86 |
5.86 |
7.14 |
The above chart depicts a comparison of irrigation recommendations (Michigan State University Excel Irrigation Scheduling program) for wet, dry and average season over the last two decades over three soil types. The greatest potential water savings from using irrigation scheduling came in the wettest years on the soils with the greatest water holding capacity. Three different management practices were analyzed: waiting to irrigate until the profile was depleted 1 inch, waiting to irrigate until the profile was depleted 1.5 inches or waiting to irrigate until half of the plant available water was used. The least amount of water was used by systems that waited the longest to begin irrigating but does not take into account any yield losses from not being able to stave off drought over long dry periods.
