Rain has been spotty across much of Ohio this summer and there are areas where corn was under moisture stress during the critical pollination period. As a result, this drought stressed corn has poor grain development and small cobs. Much of this corn may end up chopped for corn silage. Typically the most frequent questions about using drought stressed corn for corn silage revolve around nitrate toxicity, expected yield and quality.
In the August 16 issue of the CORN newsletter (http://agcrops.osu.edu/newsletter/corn-newsletter/potential-nitrate-problems-drought-stressed-corn) Peter Thomison and Laura Lindsey addressed the question of potential nitrate problems in drought stressed corn. When drought occurs during or immediately after pollination it raises the flag of potential nitrate accumulation. In drought conditions nitrates accumulate in the stalk of the plant, with the lower portion of the stalk having the highest concentration of nitrates. High and potentially toxic levels of nitrates are more likely to accumulate if high rates of nitrogen fertilizer or high rates of manure were applied to the crop. Testing for nitrates before chopping may be advisable in those conditions. If nitrate levels are high, raising the chopping height to 10-12 inches can be helpful, but obviously tonnage is going to suffer. If the nitrate accumulation is borderline high, then it probably is not necessary to raise chopping height because nitrate concentrations are reduced during the ensiling process, according to some sources, as much as one-third to one half of the nitrates may be converted to nitrous oxide compounds which leave the silage as a gas. Be aware that this gas, typically a yellow-brown in coloration, is very toxic and extreme care with regard to both people and animals should be taken. Vacate the area immediately if a cloud of this gas is observed.
Typically drought stress affects yield more than it affects the quality of corn silage. A University of Wisconsin Agronomy Advice publication from August 2007 compared corn silage yield and quality factors across 4 locations from 2003 through 2006. Each location had at least one drought year during that time frame and some locations had 2 drought years. When drought stress extended into the pollination period, similar to what we have experienced in some of our fields this year, the silage yield was reduced by 18 to 46% compared to non-drought years. To estimate yield potential use this procedure:
- Measure a distance equal to 1/1000th of an acre along one row and count the number of plants that will produce an ear. This number multiplied by 1000 equals the ears per acre. For 30 inch rows this distance is 17 feet 5 inches. Repeat this at several locations within the field and take an average to get ears/acre.
- Pick two ears at random from each measured area. Count the number of rows and the number of kernels per row on each ear. Get an average from all the areas measured. Multiply the average number of rows by the average number of kernels/row. This gives you the average kernels/ear in the field.
- Multiply the average kernels/ear by the average ears/acre. This gives you kernels/acre. Typically there are about 90,000 kernels/bushel in normal corn but drought stressed corn has smaller lighter kernels. Therefore take your kernels/acre figure and divide it by 100,000. This will give you an estimate of bushels/acre.
- A thumb rule for drought stressed corn is one ton of 30% dry matter silage for each 5 bushels of grain/acre.
Quality wise, according to a Penn State publication entitled “Managing Drought Stressed Corn” drought stressed corn silage as compared to normal corn silage may be higher in crude protein, lower in starch and energy, higher in fiber content, but often with higher digestibility of that fiber. Quality analyses presented in that publication showed drought stressed corn silage CP values ranging from 0.6 to more than 2 percentage units higher than normal corn silage, starch values were around 17% lower, energy as measured by net energy for lactation around 10% lower and NDF fiber values approximately 7% higher.
Regardless of whether drought stressed or normal corn is being harvested as corn silage there are a few key management practices that need to be followed to make good quality silage. The first and foremost is chop at the correct moisture concentration. If you don’t get this right, nothing else you do is likely to improve the situation. Optimum moisture range for bunker silos is 65 to 70%, for silage bags and for upright silos 62 to 68%. The microwave oven method is still one of the quickest, least expensive and easiest methods of moisture determination available. It involves collecting at least 4-6 representative corn stalks and chopping or cutting them into short lengths of less than 1 inch. Mix well and collect a representative sample from the total. Weigh out100 to 200 grams and spread it out on a microwave safe plate. Heat the sample for a minute and re-weigh. Shake and re-distribute the sample on the plate and heat for another 45 seconds to one minute. Repeat this heating and re-weighing process until the sample stabilizes and does not decrease in weight between cycles. Be careful as you approach the end point to avoid charring or burning the sample and adjust heating times accordingly. The moisture content is equal to the beginning weight minus the end weight divided by the beginning weight.
Other key management practices to insure good quality silage include:
- Chop at correct particle length. The theoretical length of cut (TLC) for processed corn silage is ¾ inch and if not processed the TLC should be ¼ to ½ inch. Drought-stressed corn has lower grain content and so will be less responsive to kernel processing.
- Use a proven inoculant. Severely drought stressed corn may have a high concentration of sugars which can result in increased spoilage at feed out. The buchneri inoculants are used to increase the aerobic stability of silage during feed out and could be very cost effective when used with drought stressed corn silage. Pack, pack, pack. Remove as much air as possible to create a favorable anaerobic environment. The guideline for packing is 800 pounds of packing weight for each ton of silage delivered to the silo or pile.
- Cover. This should be done as soon as the bunker is filled and the final packing had been done. Covering prevents oxygen from getting into the silage pack. Covering reduces DM and spoilage losses. University research trials have demonstrated that the oxygen barrier 2-step products have reduced losses more than covering with the 6 to 8 mil plastic.