Early Drought Management Tips for Pasture-based Livestock Producers

Matt Poore, Seth Nagy, Dale Monks, Miguel Castillo, NCSU Cooperative Extension

Due to the recent drought a large portion of the NC corn crop has been severely damaged. A few weeks ago it looked like most fields would be a complete loss, but after some significant rain the crop has perked up and is back to growing, but many fields have little if any grain due to unfavorable conditions during pollination.

Corn silage, hay or grazing for salvage of grain crops. Drought-damaged “Corn for Grain” with very low grain yield may be most effectively harvested as silage. In areas where silage is produced it will be common to find custom harvesters that can help harvest this material.

If silage harvest is not possible it is also possible to make hay out of corn. It has to be cut with a roller type hay conditioner, or a rotary mower for efficient drying. This works well when the drought lingers. Note that about half the nitrate will be degraded in corn silage, but this will not occur if the corn is made into dry hay. Nitrate is concentrated in the lower stalk of the plant, so increasing cutting height to 12 to 18 inches will result in a considerably lower concentration of nitrate in the resulting silage. The material could also be baled wet and wrapped with plastic to produce “balage”.

It is also possible to graze corn fields if cattle are nearby and temporary fencing is available. Make sure if the fields are grazed that there are few poisonous weeds present, and make sure you remove cattle once most of the corn is utilized. We have had situations where cows did well in these systems until corn was mostly utilized but then they started eating sicklepod on the field borders which can kill cows.

Corn stover. Corn Stover makes a surprisingly good feed for cows, and may be useful as a cattle feed following drought. It is low in protein and high in fiber and requires both energy and protein supplementation. During the drought of 2007 a very large amount of corn stover was harvested as part of the “Golden Hay” program that helped sustain the beef industry during that severe drought and feed shortage. Many farmers now regularly bale corn stover, and if the drought continues we can expect more to be baled this fall. It is critical to consider the value of nutrient removal when corn stover (or silage/hay) is harvested, as the soil nutrients present in the stover will have to be replaced.

Soybeans. In situations where heat and drought has resulted in a high level of biomass but low bean yields there may be a benefit to grazing or harvesting for forage. As long as the leaf is on the plant it will be of good feeding value to cattle. As soybeans mature the stalks get unpalatable to livestock, so harvest should be done as early as possible.

Soybeans can be cut and wilted to 50% moisture for baleage. Soybeans to be cut for dry hay should be handled carefully because the leaves dry out faster than the stems, resulting in a potentially high level of leaf shatter. Round bales of soybean hay take up water readily, so covered storage of some kind is recommended.

Agrochemical concerns. Make sure to identify post-application times for any chemicals used in salvaged row crops. Glyphosate has a 14 day post-application waiting period in soybeans and 7 day waiting period in corn before harvesting for forage or grazing. This information can be found in the VA Tech Field Crops Pest Management Guide.

Crop Insurance. If considering salvaging row crops for forage the farmer should contact their crop insurance agent. Often you can salvage fields but leave a designated strip for determining insurance payments.

Feed analysis. It is critical to sample and analyze forages for nutritive value, and also to screen for high levels of nitrate. It is well known that nitrate and aflatoxin are both likely to be elevated in corn forages silage as a result of drought stress.

Consider analyzing standing corn for nitrate now to help guide harvest, but analyze corn forages for aflatoxins and nutritive value once the silage is harvested and fermented. There is little sense in screening standing corn for aflatoxin due to difficulty sampling and potential changes in toxin level after sampling.

Sampling standing corn for nitrate. It may be desirable to sample standing corn to determine nitrate levels to plan alternative uses. Sampling would be primarily to determine nitrate levels. This may be in preparation for grazing or for chopping for silage or hay. According to Dr. Ronnie Heiniger, Corn Specialist at NCSU, “Corn that has suffered drought from much of the growth phase from V5 to VT will have lower nitrate levels than that which only suffered dry weather from V10 to VT”. Also “The potential for nitrates in the forage is highest where heavy manure applications or high levels of N fertilizer have been used.”

If you suspect high nitrate in a field and want to check it, select 10 plants at random from different areas of the field. Cut at 6 inches above the soil level, and remove the next 12 inches of stalk (from 6” to 18” above the ground, removing leaves and ears). Chop the 12 inch stalk sections into one inch pieces and mix in a bucket. Mix carefully and submit a one gallon ziplock bag full to the NCDA&CS forage lab. Go to this website to submit samples.

When asked for type of analysis on the form, the drop down menu has an option of “Nitrate Only” which is a free analysis. If nitrate is above 1% on a dry matter basis consider delaying chopping or grazing. Grazing is less risky than feeding silage or hay with the same level of forage nitrate. This is because the animals eat more selectively and slower during grazing, and the nitrate is also released from the plant cells into the animal’s stomach at a slower rate.

After rainfall you can expect nitrates to be elevated in corn and other crops because the root system is able to uptake more nitrogen than the damaged plant is prepared to use. It is strongly recommended to wait at least two weeks after adequate moisture to harvest such crops.

The other scenario in which to consider sampling is routine sampling of corn silage for ration balancing. There is $10 charge at the NCDA&CS Forage Lab for nutrient analysis, and nitrate is included. We strongly recommend all silage harvested during or following drought be analyzed because the energy value is usually less than normal corn silage, but the silage may be higher in moisture content and protein than is typical. Take care in obtaining a good sample by exposing the surface of the silage in the bunker, pit, or ag bag. Sample from multiple locations in the top third, middle third and bottom third of the exposed face. Mix in a bucket and submit a one gallon sample to the lab. It is difficult to obtain a good representative sample of the entire silo using this technique, so consider taking regular samples during feeding and adjust rations accordingly.

Interpreting Nitrate levels. Make sure you know how to interpret the nitrate levels you receive. Note that the NCDA&CS lab reports nitrate ion levels, while other labs may report ppm nitrate-N. Variations among labs in how they report nitrate levels can sometimes lead to misinterpretation of the levels presented. To convert from ppm nitrate N to % nitrate, multiply by 0.00044. To convert from % nitrate to ppm nitrate N, multiply by 2272. Cattle can tolerate 0.5% nitrate in the diet if they are slowly adapted to it. Higher levels may initially cause problems, especially in pregnant cows. After a month of adaptation, cattle can tolerate higher levels, but care should be taken even with well adapted cattle when levels exceed 1%. Ask your extension agent or veterinarian for help if nitrate levels are above 0.5% in forage intended for feeding.

Commercial labs. While the NCDA&CS lab provides a valuable forage analysis service, commercial labs often provide quicker sample turnaround and can analyze for additional forage nutritive characteristics that NCDA&CS does not test for. Dairy farmers often use these more specialized analyses. Many farmers in our area use either Cumberland Valley Analytical Services or Dairy One for commercial forage analysis and each are certified labs that do a good job.