Mr Copestake says there is a larger hectarage of maize being grown on arable farms this year, mainly as farmers looked for a crop to spring sow following the disrupted autumn drilling season.
“With winter cereal drillings down, maize fitted the bill in many areas allowing a spring crop which would allow a return to a normal autumn rotation,” he comments. “It also allowed a cereal break and in most parts of the country demand for maize silage, for livestock feed or AD plants, remains high.
“With crops in the ground and growing very well, the focus must turn to making the most valuable crop possible, and as with other arable crops the quality of the harvested material is paramount.”
Mr Copestake explains that users of maize silage want a high energy feed with a good level of dry matter which has been well fermented, all of which are affected by harvest date. At the same time, growers will want an early harvest to allow timely establishment of the successor crop.
Once the crop has got to 32% dry matter, there is little benefit in delaying harvest, as it will increase it’s dry matter content, but not bulk up any more. In addition, if the crop is too dry and has senesced too far, it will be more difficult to ensile.
Cutting too soon can mean an earlier harvest but can produce a lower dry matter product. Furthermore, sugars will not have been converted to starch, while the fibre to starch ratio will be higher which is equally undesirable in terms of quality.
“As a crop matures it dries out. Once dry matter increases above 32%, the digestibility of the vegetative part of the plant which contains 50% of the total energy declines as the plant lignifies, reducing overall energy content.”
He says that harvest date is greatly influenced by the variety grown. Early maturing varieties require fewer heat units to reach maturity.
“As there is a range of over 20 days between the time the earliest and latest varieties will be fit for harvest, the first thing to do is check the maturity class of the variety you are growing so you can understand where it sits in the range.”
He says the ideal time to harvest the crop is at a dry matter content of 32-35% and when cobs are mature and starch yield is maximised, with the target of a minimum 30% starch content.
“Harvesting crops too dry at above 35% can result in ensiling problems, which is something that must be avoided.”
As crops start to dry down at a rate of around 2% per week from the beginning of September, Mr Copestake advises walking and inspecting crops weekly and carrying out two simple tests.
“Walk well into the crop and look at plants in several locations in the main field. The first test is the dry matter of the growing plant. You should be looking to harvest when the stover is around 24% DM, when the lower part of the stems no longer have any moisture freely running from them when twisted. In addition, the leaves level with the cob will be beginning to turn brown.”
Regarding the cob, he says it should be around 55% DM which can be assessed by the thumbnail or milk line test, where grains in the middle of the cob will no longer bear the imprint of a thumb nail when pushed into it. Grains at the top of the cob will have a consistency of soft cheese while those at the bottom should be like hard cheese.
“Regular assessment of the growing crop will improve the precision of timing of harvest but it is also vital to keep talking to your contractor in the lead up to harvest to ensure the crop is actually harvested at the optimum time.
“Also make sure all steps are taken to make the best quality feed by focussing on the ensiling process as this will determine the quality of the end product and help reduce aerobic spoilage. There is little point harvesting at the optimum stage if the crop is poorly ensiled and fermented”, Mr Copestake concludes.