Water conservation in irrigated crop production has to be viewed as a systems approach to conserving water. As I stated in previous articles, I think water conservation starts with improving the performance of the soil.
Another key component to a systems approach to water conservation is choosing a dynamic crop rotation for your farm or ranch. The crops you choose to produce have to be profitable, provide a good agronomic rotation, be relatively high in water-use efficiency, and require less irrigation for high yields.
On our farm we’ve chosen an irrigated crop rotation of corn, field peas and winter wheat, followed by a diverse forage crop and edible beans. We added field peas to our irrigated rotation this past growing season.
I like this rotation for a number of reasons. We now have a rotation that includes all four crop types, warm-and cool-season grasses and legumes, which adds a lot of diversity to the rotation. With this rotation we can break up persistent weed and disease cycles, and rotate herbicides to lessen herbicide resistance in weeds.
We also have three fairly low-water-use crops in our system with the winter wheat, edible beans and field peas. The winter wheat and field peas’ water use is also during the portion of the growing season when we receive our most precipitation, on average. This helps lower our irrigation pumping requirements for these crops.
I also like this rotation from an agronomic perspective. I think this rotation will work well for the crops we grow. Planting our winter wheat following field-pea harvest allows us to get the winter wheat planted in a timely fashion. There also seems to be a synergism between winter wheat following the field peas where the winter wheat tends to have high yields.
I also like this rotation with the corn following the edible beans. The corn gets off to a better start by planting it into the edible bean stubble as opposed to planting the corn following the winter wheat stubble like we used to do. I think we will see higher corn yields with this new rotation.
The field peas tolerate the cooler temperatures when we plant them into the corn stubble in the early spring.
We also graze the corn stubble to eliminate some of the corn residues. The edible beans are planted into the diverse forage stubble, which has been grazed. This allows us to manage the winter wheat stubble and forage crop residues as well. We use livestock within this system to control the amount of residues we are planting into.
I also like the diversity this crop rotation provides from a soil-microbe standpoint. By planting all four crop types we’re increasing the diversity and populations of soil microbes in the soil. As we gain more knowledge of what these microbes can do for us I think this diversity will become increasingly important.
I think water conservation requires a systems approach to get the most out of our water resource. This systems approach requires soil that performs at a high level. This approach also requires careful consideration to the crops you are growing within your crop rotation.
Another component to water conservation we have implemented is to produce a forage crop following our irrigated winter wheat harvest.
I struggled with this decision, since we’re producing another crop on our irrigated acres that will require some irrigation. This contradicts our whole idea of conserving water, but I think the benefits to soil health will offset any additional irrigation required to produce the forage crop.
We decided to incorporate a forage crop into our rotation for many reasons. By producing a forage crop we can manage the amount of residue left in the field for our edible bean planting the following growing season.
We feel winter wheat residue is difficult to plant into if it lies in the field over the winter and early spring. Winter wheat residue tends to fall over at this point and getting our drill to consistently cut through them is difficult.
We felt by planting a forage crop and grazing the crop we could begin the degradation process of the winter wheat stubble earlier. By knocking down some of the stubble with the drill during planting of the forage crop, the soil microbes can begin consuming the stubble.
Growing a forage crop also creates a humid environment that helps deteriorate some of the wheat residue. The livestock will also consume some of the winter wheat stubble as they graze the forage crop.
The diverse forages following our winter wheat harvest also add more plant diversity into our rotation. We can maintain a living root in the soil for an extended period of time by planting these forages, which creates more organic matter in the soil.
We’re also able to produce more biomass on the soil surface. This should allow us to put more carbon into the soil and increase the organic-matter content of the soil.
If we can increase the organic matter content of the soil, our soil should perform at a higher level when it comes to moisture management. Increasing the organic matter should improve soil aggregation, water-holding capacity and improve soil structure. All these benefits improve the soil’s ability to infiltrate and store additional water.
These diverse forages should also improve the diversity and populations of soil microbes. This will result in increased nutrient cycling for the following crops. I think the end result of producing these forages will be healthier soil over time, which will give us a higher performing soil to work with.
The most water we’re pumped to produce these forage crops following winter wheat harvest has been 5 inches. During this time we didn’t receive any moisture at all during July, August and September. We had to water the forage crop to get germination established, and had to apply additional water during the growing season.
We have also had to water the forage crop very little following winter wheat harvest. At times there is enough moisture to get the crop germinated, and timely rains have fallen where we have pumped as little as 0.50 inches of irrigation water to produce the forage crop. Water use will vary depending on the precipitation received in the late summer and early fall.
I’m fairly confident that over time, the benefits of improved soil health will offset the irrigation required to produce these forage crops, and will result in a net decrease in the amount of irrigation we use in our rotation. We’ll learn more over time if our management decision is a good one.
In case you missed it, check out "Part 1" of the Keys to Conserving Water series.