If you’re one of many Michigan farmers that drew a short straw for rainfall this growing season, you already know the impact hot, dry weather conditions had on your corn crop.
But if you’re making plans to salvage that crop in the form of corn silage, you need to be aware of major issues associated with nitrate accumulation in the plants and the potential for toxic levels of nitrates in corn silage.
The potential for excess levels of nitrates due to the prolonged moisture stress, high temperatures and low humilities during this year’s growing season could be compounded following the recent rainfall events over Michigan in the past two weeks.
High-producing corn hybrids having high amounts of nitrogen fertilizer and manure application prior to drought conditions will be prone to excess nitrate in harvested corn silage. As the corn plants recover, nitrates are taken up at levels greater than they can assimilate.
Those excess amounts of nitrate in the plant can be toxic to livestock. This is especially important if farmers are feeding green-chopped corn or corn silage. To minimize risk, generally wait two weeks before harvesting the silage.
Questions to ask before chopping:
Livestock producers would be well-advised to ask some questions prior to the chopper hitting the field to determine whether they have the potential for nitrate toxicity.
- Did the field receive heavy nitrogen fertilization or manure application? The more nitrogen that is available, the greater the potential for increased nitrate accumulation.
- Has recent weather been cloudy? Cloudy weather will increase the potential for nitrates due to reduced activity by enzymes that convert nitrate into amino acids and, later, proteins.
- Are there known deficiencies of nutrients such as phosphorus, potassium, molybdenum and manganese? If so, it could increase the concentrations of nitrate since root uptake of nitrate continues, but plant growth is limited, causing nitrates to accumulate.
- Has the field received rainfall after prolonged moisture stress? If rains arrive just prior to harvest it can increase the amount of nitrates in plant materials. To minimize risk, generally wait two weeks before harvesting the silage.
- If harvesting later in the fall, has the crop experienced any frost damage? This question is pertinent on all corn, including droughty corn. Plants can have elevated levels of nitrates if harvested two to six days following a heavy frost. Silages following heavy frost conditions should be tested and treated the same as drought-stressed corn silage.
Corn silage should be harvested at normal recommended moisture levels, regardless of growing conditions (see Table 1).
Drought can affect the whole plant moisture content. When drought slows plant growth and delays maturity, the moisture content will be higher than suggested by the appearance of the crop.
When a drought occurs at the end of the season, moisture levels may be lower than normal. Even though drought-damaged corn may appear dryer than normal, whole plant samples are the only sure-fire way to know the current moisture levels of the crop.
Harvest height is typically set at 4 inches. Increasing the height to improve silage quality is usually not profitable, since the improvement in quality rarely offsets the yield loss.
Corn silage samples can be submitted to the Michigan State University Soil and Plant Nutrient Laboratory to determine nitrate content of your plant materials. A representative sample should be dried and sent in a paper bag to the laboratory. Wet samples should be delivered directly to the laboratory.
What are safe nitrate levels?
The potential problems associated with high nitrate levels in corn silage include possible asphyxiation and death of animals consuming excess nitrates.
Founder, the inflammation of the hoof's internal connective tissue, can also affect livestock, especially dairy cows, causing lameness and off-feed problems. This condition may dramatically decrease milk production and result in high cull rates of affected cows.
When in doubt about potential nitrates in forages, always sample affected feedstuffs.
For more information, contact Phil Kaatz at [email protected] or 810-6678-0341.