If the success of my career was based on convincing farmers to harvest corn silage when it has reached the proper stage of maturity, I might have wound up selling shoes for a living. In September 1966 (was it really more than 50 years ago?), I was telling farmers to wait until corn was well-dented before starting silage harvest, and now we’re nearing the end of the 2015 growing season and I’m saying the same darned thing.
I used to think it was solely because farmers were worried about wet fall conditions hampering harvest, and that’s a factor in the Northeastern U.S. However, I’m a lucky guy and have worked with dairy farmers from coast to coast in the United States and Canada as well as in a number of other countries including Mexico, China, Japan and Australia. And wherever I go, low dry matter corn silage is an all-too-common problem. Even in central Mexico where harvest temperatures are over 100 degrees Fahrenheit and corn dries down at least 1 percent point per day with zero chance of rain, I found corn silage being ensiled at well under 30 percent dry matter.
The corn plant is patient – why isn’t the farmer?
One reason given for harvesting corn before the kernels are well-dented is to prevent the stalk from becoming lignified and thereby reducing fiber digestibility. This seems logical – except that it’s just not true: Corn remains highly digestible until the plant is at least 35 percent DM and perhaps a few points higher than this.
In fact, some recent Dupont-Pioneer research found that the yield of grain, starch, digestible NDF and milk per acre were all maximized at 40-41 percent whole plant DM. I’m not recommending delaying harvest until 40 percent DM, but (especially when corn is silage-processed) farmers would be better to miss the ideal maturity by a few points on the high side – say 38 percent DM – rather than chopping at less than 30 percent DM.
Several years ago Cornell University compared two hybrids, a conventional hybrid and a leafy one, at 29 percent and 34 percent DM. They found much higher starch content in the more mature corn silage, and they found no meaningful difference in stover digestibility. In fact, although the difference wasn’t statistically significant, stover digestibility was actually a bit higher in the 34 percent DM corn. Waiting for corn to mature to 33-35 percent DM is all gain and no loss.
Adapting management to new technologies
Every year an increasing percentage of the U.S. corn crop harvested for silage is processed, either with conventional silage processors or silage shredders. Both types of processors are intended to be used with corn that’s at the proper maturity for silage harvest. That’s because one of their major advantages is more completely breaking up corn kernels, thus making the energy in the kernels more available to dairy cows and other ruminants. It makes little sense to spend the time and money to produce corn kernels only to have them pass through the animal’s digestive system and wind up in the manure.
One of the problems encountered when harvesting corn for silage at less than 30 percent DM is effluent production. The Environmental Protection Agency takes a dim view of silage effluent, especially when it becomes a water pollutant. That’s why the Nutrient Management Plans required of large dairies include strict regulations on the handling of silage runoff, including effluent. Processing immature corn doesn’t improve starch availability because there are no mature kernels to break up – often very little starch is in the kernels at this stage – and it may considerably increase silage effluent.
One study found an increase of over 100 percent in gallons of effluent per ton of silage when dough stage corn was processed. That’s why I tell farmers that if they have to harvest immature corn – due to an early frost or other unavoidable situation – they should increase the spacing on the processor rollers from the 1-3 mm normally recommended for processed corn silage. Silage processing is a significant advance in harvesting technology – but not if you harvest corn before it’s time.
Hybrid selection is a key
September may seem like a strange time to be discussing corn hybrid selection, but most farmers are now within a couple of months of ordering next year’s seed corn. If you continually are challenged by immature corn silage you should consider one of two changes: Either plant corn earlier in the spring – if you’re currently planting later than recommended – or switch to earlier-maturing hybrids. For most farmers changing hybrids is a lot easier than changing planting dates. Back in the old days farmers paid a price in quality and yield by moving to earlier hybrids. But plant breeders have done a great job of improving the performance of early-maturity hybrids, to the extent that there’s now very little quality difference between 85 RM (RM=relative maturity) and 90 RM hybrids.
In fact, if the 85 RM hybrid is harvested at 33-35 percent DM while the 90 RM one is harvested at 30 percent DM or less, the early hybrid will usually make more milk per ton.
How about yield? In general, later-maturity hybrids have more leaves per plant and therefore a bigger factory and the potential for higher yield. A corn field is essentially a production facility that converts sunlight energy into edible plant energy. However, the small yield difference between 85 RM and 90 RM hybrids when harvested at the same stage of maturity all but disappears when the 85 RM hybrid is 33 percent DM while the 90 RM hybrid is at 30 percent DM. Three percentage points is the approximate difference in dry matter content we’d expect to see between 85 and 90 RM hybrids since during a normal fall corn dries down at half to two-thirds of a percentage point per day. So, five days of relative maturity would be about 3 percent difference in dry matter. Consider these things as you harvest corn this fall, and as you order seed corn for 2016.
Cover Photo: Abeleao/istock