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Strategies with Drought-Stressed Corn
by Mike Hutjens

Hopefully, most readers do not need to read this column. But, some areas in Illinois and the Midwest have not received any rain since the first week of June. In July, Champaign, IL, received 2 inches while areas 60 miles north received five inches. Grain and hay markets are on the move with shelled corn breaking the $2.50 bushel target, soybeans potentially breaking through $6 a bushel, wheat over $3.50 a bushel, and Kansas hay up $20 a ton. Colorado hay prices have reached $180 to $200 a ton.

Bill called last week and asked when should he chop his barren stalk corn silage, what should he add, and what is its feed value? Drought stressed corn silage (and perhaps frost damaged corn silage in September) may be an alternative for your 2002-2003 dairy feeding program. Bill’s answers to his questions are listed below plus a few items to consider.

Question: When should drought-stressed silage be chopped?

Answer: Ensiling should occur at the same dry matter level as normal corn silage (30 to 35 percent dry matter) depending on your storage unit. The field problem is the milk line guideline may not be available (no ears and kernels may not reflect total plant dry matter). If the plant has green material, it is still alive converting sunlight and soil nutrient to plant nutrients even if not ear is present. Nutrients are stored in the plant; do not chop the corn plant. The best guideline is chop up several representative stocks and conduct a dry matter analysis on your farm using a Koster tester or microwave or send it to a commercial lab. Dry matter levels must be optimal for proper fermentation to occur.

Question: What is the feed value to drought-stress corn?

Answer: The good news is the feeding value (protein, energy, and mineral levels) will be similar to normal corn silage. The bad news is dry matter yield can be reduced by 10 to 50 percent. Ensile stressed silage and conduct a forage test, especially starch and soluble protein (these values will be different). Expect slightly higher NDF (neutral detergent fiber) levels, but a digestibility test may reflect higher than normal energy values.

Question: If drought-stress corn is good quality forage, should I buy from my neighbor?

Answer: In Illinois, drought stressed corn may be available for livestock managers to purchased from grain farms as the little to no corn grain will be harvested. One guideline is 1 to 1 ½ tons of 30 to 35 percent corn silage per foot of barren corn stalk. The best recommendation is to weigh several chopper boxes of stress corn silage and price it on a dry matter and yield base. Conservatively, reduce the value per ton of stressed corn silage by 10 to 15 percent compared to current corn silage prices or price the forage after fermentation and a silage test has been conducted (if you and the seller are willing). Be sure to deduct the cost of harvesting, transportation, and storage loss costs ($5 to $10 a ton). The fertility value of corn stalks (if the grain farmer would plow it down) is $25 to $35 an acre (for example, 4 to 5 feet corn with no grain contains 55 pounds of nitrogen, 12 pounds of P2O5, and 60 pound of K20).

Question: What about nitrates?

Answer: Nitrate nitrogen (N-NO3) will increase with drought stress. The plant’s photosynthetic surfaces (green material) are reduced and nitrates are not converted to plant protein and growth. Table 1 illustrates the typical nitrate levels in various parts of the corn plant. Checking with a major Wisconsin forage testing lab on August 1st, levels of nitrate nitrogen (be sure you are using the same unit of measurement) were not high except in the west Dakotas (over 5000 ppm or 0.5 percent on a dry matter basis). Nitrate-nitrogen levels over this guideline should be diluted down with other feeds. If animals are adjusted to high nitrate containing feed, health risks are reduced (gradually increasing the higher nitrate feed in the ration over a two week time period). Ensiling stressed corn silage can reduce nitrate levels by 15 to 50 percent. A commercial lab can analyze your fermented silage for $7 to $10 per sample (nitrate and moisture levels). Testing standing corn plants in the field is not recommended as it will vary daily due to soil type, moisture, and plant maturity changes. Chopping the corn plant 6 to 18 inches high will reduce nitrates, but significantly reduces dry matter yield (Table 1).

Question: What about adding dry corn or other additives to stressed corn silage?

Answer: Adding a research based effective silage inoculant is recommended to “jump-start” the fermentation process. Two reasons to inoculate drought-stress corn silage are listed below.

  • Silage will be variable in dry matter due to planting and heat stress effects.
  • Hot weather can reduce the normal bacteria found on the corn plant that could start the fermentation.

Research over the last ten years has clearly indicated an effective silage inoculant will return $3 to $6 for each one dollar invested in the inoculant (based on Kansas and Washington State data).

Adding dry corn is not recommended. It will reduce the moisture level of the corn silage that is a potential fermentation problem. Test the stressed corn silage after ensiling and have your nutritionist balance starch and nutrient levels prior to feeding. Do not add ammonia, urea, or other nitrogen additives as they delay the fermentation process (raises pH) and higher levels of nitrates (a source of NPN) may be present. Again, test and let your nutritionist balance for soluble protein. Adding wet brewers grain, liquid whey, or wet by-product (over 70 percent moisture) can increase silage moisture and improve fermentation if done correctly. Placing a lawn sprinkler will add water, but the amount will not be significant.

Question: Is ensiling stressed corn the best strategy?

Answer: Corn silage is the best alternative.

  • Avoids selective grazing (compared to pasture)
  • A uniform forage is fed (green chopping always the crop to change daily)
  • Ensiling reduced nitrate levels
  • Can be tested to develop a balanced ration.

If stress corn is green chopped and it heats in the wagon or bunk, some nitrate may be converted to nitrite (more deadly). If the plant is alive and late rains fall, expect plant nitrates to increase for several days as roots absorb moisture and nitrates and the plant is delayed/prevented in converting to nutrients. If ensiling of stress corn is your strategy, be aware higher levels of silo gas (nitrogen gases) will be released. Do not enter a silo unless you have supplemental oxygen or air tank or run the blower for several minutes before entering and continuously. Open up the silo room and barn to get proper ventilation to avoid silo gas accumulation. Making corn hay is difficult until a killing frost because the corn stalk retains moisture leading to moldy forage (corn hay should be under 20% moisture at baling).

Table 1. Nitrate-nitrogen levels at different sections of a normal corn plant (ear contains 22 ppm and is not included in any area below).

Distance from the roots (inches) Nitrate-nitrogen level (ppm)
0-12 6160
12-18 5613
18-24 3891
24-36 2194
36-48 1187
48-60 453
Over 60 16


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