Cropping choices and water use relationships

Farm Forum

The precipitation from the recent snow storm provided welcome relief in terms of soil moisture. Standing stubble certainly showed its value as fields with stubble caught a uniform layer of snow that will help replenish dry soils with an inch or more of valuable moisture.

Depending on what moisture is received over the next month or so, farmers may be wise to consider the water/yield relationship for various crops as they are making planting decisions this spring. The USDA-Agricultural Research Service has conducted research exploring the moisture needed to produce the first bushel of grain and the bushels per inch of moisture for various crops. This information can be highly valuable when making cropping decisions when moisture is limited.

Corn is very efficient in using water as it can produce just over 10 bushels per additional acre inch, but also requires just over 9 inches of water to produce the first bushel. Grain sorghum, or milo, is also relatively efficient in producing bushels once the initial requirement is met, at 9 bushels per additional acre inch, but takes only 6.5 inches to produce the first bushel. That is why grain sorghum has historically been a popular crop in marginal rainfall areas. Grain sorghum lost some popularity in the 1990’s, partially due to a volcano eruption that resulted in cool summers for several years, above average rainfall during the same period of time (which favored corn production), and improved drought tolerance in corn hybrids. Summer temperatures have returned to higher levels in more recent years, and the uncertainty of rainfall may bring resurgence in the interest in sorghum.

Sunflower requires slightly more water to produce the first bushel/pound of grain than sorghum at 6.9 inches, and fewer equivalent bushels (6.3) per inch of additional water. Sunflower is marketed on a different price per unit structure than corn and sorghum, so it’s not directly comparable on a bushel/pound basis regarding yield.

Wheat, millet and soybean are fairly similar in both their water requirement to produce initial grain yield and efficiency in bushels per additional acre inch of water. To produce the first unit of grain, wheat requires 5.2 inches, millet 3.5 inches, and soybean 3.7 inches. With each additional inch of moisture, wheat will produce about 4.7 bushels, millet 4.2 bushels, and soybean 3 bushels. Again, the price per bushel of each crop varies, and if one were to evaluate each crop fairly regarding water use efficiency, this would need to be taken into account.

According to this research, field peas are a remarkable crop in that they require less than 1 inch of water to produce grain. They can produce 3 bushels of grain for each additional inch of moisture.

These numbers are not exact and each crop will perform best if moisture is available at the right time and suffer if it is short at a critical time, like corn at pollination and soybeans at flowering.

This information could prove valuable as producers are making cropping plans while they watch the skies and weather reports for more precipitation, which will be necessary for a successful growing season.