How to get top quality feed from whole-crop
When should whole-crop cereals be harvested to achieve
the best yield and produce a top quality feed for stock?
Jessica Buss reviews the results of an SAC project
PROVIDING whole-crop is harvested once crops reach the soft to hard dough stage, there is a four or five-week window for cutting without reducing yield or quality much below the maximum.
This is true for winter wheat, spring wheat, winter barley and spring barley, according to a study at SAC, part-funded by FSL Bells.
SAC senior adviser Chris McDonald says during the study the four cereals were harvested weekly to monitor changes in yield as the crop matured. Each harvest was reported weekly in farmers weekly last autumn.
Crops were grown in trial plots and managed as on a typical arable unit. "Winter wheat received three fungicides, two of which included a strobilurin type.
"This maintained green leaf area on the crop for a much longer period. Without fungicides grain yield would be lower."
Dry matter yields in all crops increased weekly, peaking at about two to three weeks before conventional grain harvest (see graph).
"The greatest increase in growth occurred early in the trial, when plants had the most green leaf area for photosynthesis and a longer day length for growing.
"The final decline in yield resulted from shedding of grain and straw leaves and the plants requirement for respiration."
Crop dry matter was influenced by rainfall and heavy dew, leading Mr McDonald to believe that growth stage is a better indicator of optimum harvest date.
Energy content (ME) of the crops was measured in straw and heads separately. For the heads, starch was also tested. Results show ME value of straw fell each week in almost all cases, but initially this was more than compensated for by an increase in ME of the heads.
The most economic harvest date must be when the yield of energy (ME) peaks, adds Mr McDonald. The pattern of ME yields/ha and the proportion of ME yield of the straw and heads differed for each crop at each growth stage (see bar charts).
"As grain texture became more doughy the rate of increase in ME slowed, peaking when grain became harder and started to ripen. This suggests that cutting whole-crop at the traditional arable silage stage, when the grain is at the milky-ripe stage, will produce a lower ME feed than later cut whole-crop."
For all crops, starch content reached a plateau as the grain filling period came to an end and ripening began, with little change from then on. This was very close to the maximum level at optimum harvest date for yield of ME.
For each crop there was a period when dry matter, ME and starch yields/ha peaked. Although the optimum growth stage for cutting whole-crop was slightly different for each cereal, it tended to be at a fairly late growth stage, he adds. In all crops it was well beyond the milky ripe stage when whole-crop is traditionally cut.
"For each crop, dry matter, ME and starch yields increased at a higher rate during the early period of grain filling. Following this period the rate of increase in each of these slowed which would suggest there is a fairly wide window of four to five weeks when whole-crop can be cut without significantly reducing yield or quality," says Mr McDonald.
But to maximise yield and quality, ensure whole-crop is not cut before the start of this window, which at this site was when grain was at the soft to hard dough stage. However, harvesting whole-crop at this stage using a forage harvester without a cereal cracker would result in a large proportion of grains passing through the animal undigested.
The development of a cereal cracker fitted inside forage harvesters now allows mature cereal crops to be successfully harvested for feeding to cattle with all grain cracked, so it is better used by stock, explains SAC beef specialist Basil Lowman.
The benefit of harvesting cereals at a more mature stage is an increase in dry matter and in particular starch yields/ha compared with conventional arable silage cut at the green/milky grain stage.
"Even when reducing yields by 10%, to allow for the high yields recorded by hand harvesting the studys small plots, it still produces higher ME yield/ha compared with taking three cuts off a grass silage field," says Dr Lowman.
"The other important difference is the starch content of whole-crop cereals, compared with much lower starch in grass/clover silage, with starch being a critical component in the overall ration, particularly for finishing beef cattle."
However, this very high energy and starch content, particularly for the heads themselves, reveals a potential storage problem for whole-crop.
It is likely to suffer rapid post-opening deterioration, causing a major reduction in feed value and risking poisonous toxins developing.
The use of an effective additive is essential, not to preserve the crop while it is enclosed in the pit but to avoid the high risk of severe, rapid deterioration when the pit is opened, he advises. *
Crop Growth Date of
Winter barley Ripe Aug 9
Winter wheat Hard dough Aug 23
Spring barley Early ripe Aug 23
Spring wheat Soft dough Aug 23
For each cereal crop, dry matter, ME and starch yields peak at a fairly late growth stage, says Chris McDonald.
• Milk development When grain is squashed a watery, milky and at a later stage sticky substance appears.
• Dough development In the early dough stage grain contents are of a soft cheese consistency and following on from this the texture becomes drier and more like a bread dough. At the hard dough stage, grain contents are dry and cannot be squeezed out.
• Ripening The grain hardens.