Summer drought noticeably limits corn silage production by reducing ear size and stalk growth. As few as four consecutive days of visible wilting during vegetative growth can reduce grain or forage yield by as much as 5 to 10 percent. Yield losses of 40 to 50 percent are possible if high temperatures and limited rainfall coincide with silking and reproductive stages.
Factors to Consider
- Potential forage yield
- Timely harvest
- Moisture content
- Nitrate accumulation
- Estimate potential forage yield. It’s difficult to accurately predict the forage yield potential of drought-stressed corn. With 70 to 80 percent barren ear condition, expect to harvest about 1 ton of 70 percent moisture silage for each foot of crop height per acre. Corn measuring 5 feet tall could yield 4 to 6 tons of 70 percent moisture forage per acre.
- Manage harvest timing. Drought-stressed corn plants usually have few developed ears and brown or dead leaves that lose quality, tonnage and dry matter. If air temperatures stay above average, the corn plant will dehydrate rapidly and ultimately die. Timely harvest is essential to capture the most value from the crop. Focus on harvesting the crop at the optimum moisture content in order to limit dry matter losses from defoliation of dry leaves and harvest losses due to lodging and to ensure optimum silage fermentation.
- Monitor moisture content. Under drought conditions, the plant’s appearance may be misleading. Start monitoring moisture content early in the drought, and harvest when corn reaches recommended levels. Waiting too long to harvest and allowing the moisture level to fall below 60 to 65 percent may cause silage heating and dry matter loss. Dry forage may also encourage the growth of molds and yeasts.
- Beware of nitrate accumulation. Nitrates harmful to livestock can accumulate in corn plants under drought stress, especially in fields grown with high nitrogen applications. Nitrates accumulate under drought stress because plant metabolism slows and soil nitrates taken up by the plant are not converted to proteins. These unconverted nitrates accumulate in the lower stalks. This situation is magnified when rain does occur, because nitrates in the root zone are rapidly absorbed along with the moisture. Delay chopping for three to five days following a significant rainfall during a drought season to allow time for plants to convert the nitrates to protein.
- Reduce nitrates in harvested silage. To reduce nitrates, raise the cutter bar to 12 inches to avoid harvesting the lower portions of the corn stalk where nitrate levels are highest. This may reduce tonnage by about 15 percent, but the portion harvested will have better quality. The fermentation process reduces nitrate content by 30 to 50 percent, so be sure to harvest and pack silage properly for optimum fermentation.
- Test silage before feeding. Allow silage to ferment long enough to allow nitrates to convert to safer compounds, reducing livestock exposure to feed containing nitrates. Test silage before feeding to ensure that nitrate concentrations are not at a toxic level. Consult your nutritionist if you have any concerns about feeding drought-stressed silage.
Proper harvest management under drought conditions can help growers salvage as much silage quality and yield as possible. If your silage fields are under moisture stress, contact your local Mycogen Seeds customer agronomist or trusted agronomic adviser for management advice.