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Harvesting

The optimum time to harvest is when the yield of starch is maximised, but the crop still contains sufficient moisture to compact easily in the clamp.

Maize is harvested in late September or early October (harvesting should be completed by 20th October). The exact harvesting date depends whether the tassels have started to flower or not, if the plant has stopped actively growing and if the leaves have started to turn yellow. The plant must be at least 2 metres high. At the lower part of the cob, the grains should have a similar texture to that of a hard cheese and the tip of the cob should be of a soft cheeses type texture. The individual grains should be solid at the wide end and cheesy when moving towards the tip. Only the tip may still be milky. The optimum harvest date is when the whole crop dry matter is between 28 – 32% and the cob dry matter is between 50 – 55%.

When the maize is cut it is important not to set the harvester too low. The optimum cutting height is 20cm above ground level. This is so because the lower part of the stalk contains a lot of water and has little feeding value.



Analysis of the Crop when Harvested in October:







Dry Matter


29.2tonnes/ha







Crude Protein


7.7%







pH


3.6







Ammonia


7.4%







Ash


3.0%







Starch


25.2% (of dry matter)




	 





Analysis of the Crop when Harvested in November (too late):







Dry Matter


	32.2tonnes/ha







Crude Protein


8.3%







pH


3.9







Ammonia


4.5%







Ash


3.5%







Starch


33.6% (of dry matter)




	 












Harvesting Maize








Kernels












Harvesting Maize with a Combine Harvester









The Source of Energy:



The energy in maize mainly comes in the form of carbohydrates (also main energy sources in all beef and dairy rations). The main types of carbohydrates are fibre, sugar and starch.




Fibre is mainly found in the leaves and stem so once the crop is fully grown, the amount of fibre does not change no matter when the crop is harvested.



Sugars from photosynthesis are deposited in the grains as starch while the crop matures: a shift in the sources of energy from sugar to starch is experienced. This is referred to as metabolisable energy or ME.



Therefore, the overall yield of energy from a standing crop of maize only increases slightly as the crop matures but a greater proportion of this energy will be derived from starch.




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