Drought/dry summer corn and soybean forage harvest options and management strategies

Harvest of Drought-damaged Corn

Livestock producers have been asking questions about the feasibility of grazing, green chopping, or ensiling drought-stressed corn. The strongest take-home lesson for livestock producers with drought-damaged corn is to not be too hasty to 'get in to the corn field.' As long as the corn plant is still alive it will be accumulating some additional dry matter. Each developmental stage of corn growth -- stalk elongation, ear formation, and grain fill -- will add several tons per acre of dry matter to the potential harvested product.

In addition to the dry matter considerations, other factors also should be assessed. Stage of development or condition of growth also has an influence on the feed value of the harvested crop. Compared to normal corn, corn that would yield about 20 to 40 bu./A would have about the same pound for pound feed value. Very poorly pollinated stalks with 0 to 20 bu/A yield potential would have about 80 to 90 percent the feeding value of normal corn. Short, barren stalks would have only about 70 to 80 percent the feed value of normal corn.

In what form will the corn be harvested and used? The three most practical options for using drought-damaged corn are green chopping, ensiling, and storing as dry stover. Each system has some advantages and disadvantages. Producers should consider the herbicides or insecticides used in their corn production. Growers should carefully check the label for any restrictions that may affect harvest or harvest timing

Green chopping corn provides an immediate source of feed for dry lot, or supplement on pasture. A disadvantage may be a potentially high level of nitrates in the drought-damaged, fresh forage. Producers are encouraged to have fresh chopped corn tested for nitrates at a nearby commercial feed testing laboratory if there is any concern about high levels.

Chopping corn for silage provides a less immediate feed source, but a form that can be stored and fed over a longer period of time. One of the main management challenges of harvesting drought-damaged corn for silage is cutting the plant at the proper moisture content for the type of silo structure in which the forage will be stored. Corn should be stored at 65 - 70 percent moisture in a bunker or trench silo and at 60 - 65 percent moisture in upright silos. In plants with at least some grain, the dry down rate of the grain will provide a rough guide for predicting whole plant moisture.

Using the 'milkline' on the maturing corn kernel may be the best visual indicator. Until the milkline is half and preferably 3/4 or more of the way down toward the tip of the kernel, the whole plant moisture will likely still be greater than 70 percent.

Hybrids vary somewhat in this trait. Plants with no grain, and some live green leaf tissue still evident, will have surprisingly high moisture content (75 - 80 percent); too high for direct cut and ensiling. In some cases even when all the visible leaves have turned brown, the whole plant moisture is still above 70 percent moisture. Plants that have actually died will lose moisture very quickly and could drop below 50 percent moisture in a short time; too low in this case for proper ensiling.

An accurate moisture test from a representative field sample is an important piece of information needed to manage a corn crop for silage. Moisture determinations can be made at a nearby feed testing laboratory, or with a home check using an accurate scale and a microwave oven or heat lamp to dry the sample. Use caution when drying forage at home. Plant material nearing the dry matter state and when dry is combustible. Special precautions should be taken to avoid permanent damage to microwave ovens. Nitrates are less of a concern when drought damaged corn is ensiled because some of the nitrate is converted to other forms of nitrogen in the ensiling process.

Harvesting drought-injured corn as silage will not be a good option for everyone. Making good silage from a normal corn crop requires some degree of skill and attention to detail. If you do not already have the harvest machinery, a silage storage structure in good condition, experience in making corn silage, and a well-defined plan for silage use then making silage from drought-damaged corn may be a high risk venture.

Too often producers who are looking for the 'cheap way' choose to store silage in a wide, low pile on the ground, possibly even bounded on each side by a row of large round hay bales. These piles may seem to be low cost initially but spoilage and waste is often high and as a result the 'cost' per ton of usable, good quality silage is higher than expected.

Drought-damaged corn has dried quickly in many areas. Corn that has dried below 55-60 percent moisture is not a good material for ensiling. Rather, it should be considered for possible stacking or baling as dry corn stover. Timeliness is not quite as critical when harvesting stover. It should be dried to 20 percent moisture or less to avoid spoilage in storage, and should be harvested before excessive leaf loss occurs. High nitrates can be a concern in stover. If you're concerned, have a nitrate test done on a representative sample. A few other suggestions are to store stover at a dry location near the site of feeding, and provide for limited access to stover during feeding to stretch feed supplies and minimize feeding waste.

Soybeans

Soybeans may be considered a viable alternative forage, especially in two situations:

  1. when alfalfa or clover are in short supply due to winter-killing, or
  2. when an early-killing frost or other drought-induced condition terminates soybean growth prior to normal grain maturity.

Both situations could exist in Iowa this year.

The effect of soybean harvest maturity on yield, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and ether extract (EE) concentrations of the whole plant forage was determined in a recent Wisconsin study. They found that soybeans produce reasonable yields of forage that are comparable in quality to alfalfa harvested in the first-flower stage. Maximum dry matter yields of soybean harvested for forage was 4.1 tons/acre compared to 2.7 tons/acre for seeding year alfalfa and 4.5 ton/acre for second year alfalfa harvested from adjacent fields.

Harvest maturity has the greatest effect on the yield and quality of forage produced. Soybeans were harvested at four growth stages starting at initial flowering (R1) and ending just prior to maturity when the pods had reached maximum weight and the leaves had turned yellow (R7).

Dry matter yields increase linearly with advancing maturity at harvest, from 1.1 ton/acre at R1 to 3.3 ton/acre at R7. Quality parameters showed a curvilinear change in that crude protein concentrations declined from 20.1 percent at R1 to 18.1 percent at R3 but then increased to 19.2 percent at R7.

Based on these and other studies we recommend that soybean forage be harvested between stages R6 and R7. At this stage, seeds completely fill the pods and the lower leaves of the plant are just beginning to turn yellow. At this time the plant has achieved its maximum dry matter yield and is just beginning to decrease in moisture content. Harvesting soybean forage during early reproductive development (R1-R5) can produce high quality forage but dry matter yields are often less than 1/3 the yield when harvested at R6-R7. Unless forage is in very short supply, we do not recommend harvesting at these earlier maturity stages.

Producers should consider the herbicides or insecticides used in their soybean production. Growers should carefully check the label for any restrictions that may affect harvest or harvest timing.

Soybean forage can be harvested as either silage or hay. Leaf shatter can be excessive when dried and baled at safe dry-hay moisture conditions. Store soybean hay inside or under cover. If harvested as a silage, follow good silage production practices. It is advisable to allow the forage to wilt to approximately 55-65 percent before ensiling alone, or to mix the direct cut soybean forage with corn forage before ensiling. In the Wisconsin study, soybeans direct cut at R1 to R5, had approximately 80 percent moisture, and at R7 it was 66 percent moisture. Test soybean hay or silage before feeding to help make better feeding decisions.

This article originally appeared on pages 154-155 of the IC-490(21) -- September 15, 2003 issue.

Updated 09/14/2003 - 1:00pm