There is simply no end to the importance of water.  Those two little hydrogen atoms covalently bonded to oxygen are often the cause of emotional highs and lows in agriculture.  We usually think of water’s importance to sustain crop growth, activate herbicides, and to improve or negate soil nutrient availability to “make” a crop.  However, water is just as important on the backside of the growing season in the form of internal plant or grain moisture, which often dictates when a crop will be harvested for optimum yield, quality, and storability.  This is certainly the case for corn harvested as silage. 

            Many years ago someone once told me that any idiot can harvest good corn silage.  At the time, we really didn’t know a whole lot about corn silage other than you do everything the same as corn for grain except chop it when that funny little black layer appears at the kernel-cob interface.  Through research and experience maintaining high producing dairy herds we now know much more about corn silage and are still making knowledge breakthroughs with each passing year.  Further, corn breeders and seed marketers are offering designer corn silage hybrids.  No, this is not a world of your father’s corn silage but one where corn silage has become an industry in and of itself.  An early research finding of this spawning industry was that harvesting corn silage at the proper whole plant moisture is the key to optimizing yield, feed quality, and often storability.  Miss the proper harvest moisture and everything that was done right for the previous four months can be compromised. 

            Corn silage is complicated animal.  Total yield increases up to the point where kernel black layer is reached and the plant begins to desiccate, which is generally around 60 percent moisture.  However, delaying harvest until maximum dry matter yield is achieved reduces nutrient availability.  Often, kernels become hard and remain undigested by the animal.  Researchers often cite 65 to 68 percent moisture as optimum for maximizing corn silage quality.  Often silage that is over 70 percent or under 60 percent moisture results in the greatest problems from a feeding and storage standpoint.     

            Storage structure type often dictates whole plant harvest moisture with the realization that some tradeoff is going to be made for quality and yield.  Corn silage put into upright silos is often done so at moisture levels between 60 and 65 percent to prevent seepage.  The thought process is sound but it comes with the realization that some loss of inherent feed quality may occur (less starch availability and higher lignin content).  Kernel processors help to alleviate some of these quality losses.  Corn silage is generally harvested at higher moisture levels for bunker silos to improve packing characteristics (ideally 65 to 70 percent moisture) but with the expense of maximizing dry matter yields.  Harvesting corn silage at over 70 percent moisture increases the chances for improper fermentation and the formation of butyric acid. 

            So how does a person know when corn has reached the optimum whole plant moisture for harvesting?  This, in my opinion, remains the weakest link in the corn silage management chain.  There is no easy way to estimate plant moisture by simply eyeballing the plant (although methods to do just that are currently being studied).  Kernel milkline was once thought to be the answer, but hybrid variation has disposed with that criterion for all but as a means to trigger more rigorous and precise methods of moisture estimation.  Throughout Wisconsin, corn silage “dry down” days are offered to producers as a means to have field plant samples chopped and tested for whole plant moisture.  They have proven popular and effective but are not without the inherent errors that go along with limited sample size and testing procedures.  These efforts do, however, help to prevent major errors in estimates of whole plant moisture caused by environmental conditions or hybrid phenotype. 

            Yes, each year we generally complain about too much or too little rain to plant or grow a crop.  But remember, at the end of the crop year it’s still all about the water, especially for harvesting high yields of quality corn silage.