Wholecrop wheat silage

Dr. Aidan Cushnahan, Milk Technologist, Greenmount Campus, College of Agriculture, Food and Rural Enterprise

Wholecrop wheat silage is being used increasingly by dairy farmers as a complementary forage to grass silage, especially as part of a total mixed ration in complete diet feeding systems. The successful preservation of wholecrop wheat silage depends on making an accurate assessment of dry matter content prior to harvesting and paying attention to detail when harvesting and filling the clamp. The following article will deal with these factors in more detail.

There are two distinct systems for ensiling wholecrop wheat:

Fermented wholecrop - harvested at 35 - 45 percent dry matter. The majority of ensiled wheat crops in Northern Ireland are preserved using this method.

Urea treated wholecrop - harvested at 50 - 60 percent dry matter. The urea is converted to ammonia in the silo which inhibits the action of spoilage organisms.

The feeding value of wholecrop wheat is highly dependent on achieving the optimum balance between the increasing starch level in the ripening grain and the decreasing digestibility of the straw. Decisions on when to cut are therefore critical and should be based on assessments of dry matter content. It is important to monitor dry matter content on a regular basis as this gives an indication of the nutritive value and quality of the crop.

The following guidelines should be observed for fermented and urea treated wholecrop wheat:

FERMENTED WHOLECROP SHOULD BE HARVESTED AT 35 - 45 percent DRY MATTER (growth stages 71 - 85). The crop colour at this stage is changing from green to yellow and the texture of the grains has changed from watery to cheesy (soft Cheddar).

UREA TREATED WHOLECROP SHOULD BE HARVESTED AT 50 - 60 percent DRY MATTER (growth stages 85 - 92). Crops at this stage should be surface dry and the grains will be difficult to indent with a thumbnail (hard Cheddar). It is important not to apply urea to crops with a dry matter of less than 50 %. If this occurs, a foul smelling unstable product is likely to be produced.

The preferred method of harvesting is using a precision chop harvester fitted with a combine harvester header (which may require some adaptation) so as to minimise grain losses through shredding. Cutting height can vary between 7.5 and 15 cm (3 and 6 inches) depending on the quality of the crop. Chop lengths of approximately 25 mm (1 inch) can aid consolidation in the clamp. Ensure that the trailer door and sides are boarded or sheeted to minimise grain loss.

There are a number of additives available which can be applied to fermented wholecrops at harvesting. A number of these products have been shown to improve the stability of the resultant silage upon exposure to air. The cost of these additives can vary considerably, therefore careful selection is very important to ensure that any additive used is cost effective.
Urea should not be applied to crops which have been undersown with grass as this will interfere with the fermentation. In situations where urea is being added, thorough mixing of the urea into the crop is essential for a successful preservation. This is best achieved by applying urea through the crop stream on the harvester. However there may be practical difficulties with this method due to the application rates involved (40 KG/ tonne dry matter). Other methods of application include using a fertiliser spreader on tipped loads and mixing well with the harvested material before ensiling.

ANY FORM OF UREA OTHER THAN FEED GRADE UREA SHOULD BE TESTED FOR PURITY BEFORE USE.
IT IS ALSO VITALLY IMPORTANT TO ENSURE UNIFORM DISTRIBUTION OF UREA THROUGHOUT THE CROP SINCE A LUMP OF PURE UREA CONSUMED BY A RUMINANT IS TOXIC AND CAN CAUSE DEATH.

Provided the dry matter content of the harvested crop is within the target ranges outlined, whole crop wheat will not produce any effluent. Under such conditions a silo is not required for storage - hard standing is adequate.

When clamping fermented whole crop wheat, a narrow clamp is considered advantageous as this reduces spoilage due to secondary fermentation which takes place during feeding out. The crop should be filled quickly in thin layers, consolidating well as it is filled. The clamp should be double sheeted and sealed effectively with the top sheet being weighted down with tyres or bales. If tyres are being used on an outside clamp it may be advisable to net the clamp to avoid potential damage by birds.

Similar measures are used to store urea treated wholecrop wheat, provided both crop and urea have been mixed adequately. The crop only requires moderate consolidation and the clamp should be thoroughly sealed to prevent ammonia escaping.

Wholecrop wheat can be successfully preserved by regularly monitoring crop dry matter content prior to harvesting and paying attention to detail when harvesting the crop and filling the silo. Particular care should be taken if the crop is being treated with urea to achieve an even distribution of urea through the crop. Further information on producing wholecrop wheat silage can be obtained by contacting your local Farm Development Division Adviser.