Monday, July 9, 2012

Harvesting Barren and Poorly Pollinated Corn

Poor corn pollination can be caused by numerous factors including drought, hail, frost, corn rootworm silk feeding, and foliar diseases. Often poorly pollinated corn can be utilized by livestock systems involving cattle. Corn forage quality is influenced by pollination success. In general if some kernels are developing, it is better to wait with harvest. But, if the plant is barren, then harvest can occur at any time.

Forage quality of normally pollinated corn

Corn has two peaks in forage quality: one at pollination and one at harvest maturity. Forage quality as measured by Milk per Ton is high during vegetative phases prior to flowering (Figure 1). Like all forages, quality decreases after flowering. Unlike other forages, quality improves beginning around R3. The early peak in forage quality at pollination is high in quality but too wet for ensiling. The later peak is more familiar, and is the one we typically manage for when producing corn silage because it maximizes biomass yield and quality.

Figure 1. Corn silage yield and quality changes during development. 

Forage quality of barren and poorly pollinated corn

The first peak in Figure 1 occurs around flowering and will continue if pollination is unsuccessful. Drought stressed corn has increased sugar content, higher crude protein, higher crude fiber and more digestible fiber than normal corn silage. Drought generally reduces yield and grain content resulting in increased fiber content, but this is often accompanied by lower lignin production that increases fiber digestibility.

If pollination is poor yet some kernels are developing, the plant can gain dry matter and farmers should wait with harvest. Coors et al. (1997) evaluated the forage quality of corn with 0, 50 and 100% pollination of the kernels on an ear during 1992 and 1993. These years were not considered “drought” stress years, but they can give us an idea as to quality changes occurring due to poor pollination. These plots were harvested in September.

A typical response of corn to stress is to reduce grain yield. Bareness reduced whole-plant yield by 19% (Table 1). Kernels on ears of 50% ear fill treatments were larger and tended to more than make up for reduced numbers (Albrecht, personal communication). With the exception of protein, as ear fill increased, whole-plant forage quality increased.

Table 1. Forage yield and quality of corn with differing amounts of pollination grown at Madison in 1992 and 1993 (n= 24).
%% of control%%%%%
100 (control)1007.549267754
LSD (0.05)60.31111
derived from Coors et al., 1997

Harvesting and Handling Barren Corn

Farmers often can increase biomass yield in a field of barren corn by double-cropping. If corn is barren and it has been determined that pollination and fertilization of kernels will not or did not occur, then the barren corn can be harvested at anytime and another crop planted. 

Before harvesting check with your crop insurance agent and follow their instructions for collecting adjustments. Also, make sure that there are no herbicide restrictions on the forage for livestock feeding. Aflatoxin and other grain quality problems are insurable causes of loss, so growers can receive indemnities for problems.  Continue to protect insured crops from further damage – you cannot graze an insured crop or chop it for forage or silage without first receiving permission from your crop insurance agent, or you will forfeit indemnities.  You do not have to use the forage yourself, but can sell it.  The same applies if you decide to terminate the insured crop and plant a new crop – you must first receive permission or you will forfeit any indemnity. Farmers who insured their corn for silage can receive an indemnity not only if their silage yield is low, but also if their silage is grain deficient.

The harvesting challenge is that green, barren stalks will contain 75-90% water. If weather remains hot and dry, moisture content drops, but if rain occurs before plants lose green color, plants can remain green until frost.

Barren corn is difficult to harvest because it is rank and too wet for silage storage structures. Arlington UW-ARS staff have had some success using a discbine to cut barren corn into a windrow. The windrow would need to dry for a few hours to desiccate the forage. A forage chopper with a hay pickup attachment is then used to gather and chop the windrow into a wagon for transport to a storage structure for ensiling.

Grazing is an option, but be careful about nitrate toxicity problems. If grazing, consider potential for nitrate toxicity. This is especially likely to be a problem if growth was reduced to less than 50% of normal and/or high levels of nitrogen were applied.

Forage moisture

If the decision is made to harvest the crop for ensiling, the main consideration will be proper moisture for storage and fermentation. The crop will look drier than it really is, so moisture testing will be critical. Be sure to test whole-plant moisture of chopped corn to assure yourself that acceptable fermentation will occur. Use a forced air dryer (i.e. Koster), oven, microwave, electronic forage tester, NIR, or the rapid "Grab-Test" method for your determination. With the "Grab-Test" method (as described by Hicks, Minnesota), a handful of finely cut plant material is squeezed as tightly as possible for 90 seconds. Release the grip and note the condition of the ball of plant material in the hand.
  • If juice runs freely or shows between the fingers, the crop contains 75 to 85% moisture. 
  • If the ball holds its shape and the hand is moist, the material contains 70 to 75% moisture. 
  • If the ball expands slowly and no dampness appears on the hand, the material contains 60 to 70% moisture. 
  • If the ball springs out in the opening hand, the crop contains less than 60% moisture. 
The proper harvest moisture content depends upon the storage structure, but is the same for drought stressed and normal corn. Harvesting should be done at the moisture content that ensures good preservation and storage (Table 2).

Table 2. Recommended moisture content (%) for corn stored in various types of storage structures.
Horizontal bunker silos70-65
Bag silos70-60
Upright concrete stave silos65-60
Upright oxygen limiting silos60-50
derived from Roth et al., 1995

Literature Cited

Coors, J. G., Albrecht, K. A., and Bures, E. J. 1997. Ear-fill effects on yield and quality of silage corn. Crop Science 37:243-247.

Roth, G., D. Undersander, M. Allen, S. Ford, J. Harrison, C. Hunt, J. Lauer, R. Muck, and S. Soderlund. 1995. Corn silage production, management, and feeding. NCR 574, American Society of Agronomy, Madison, WI. 21 pp.

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