This year maize silage harvest is running 2-4 weeks later than normal in many districts.

The challenge for many dairy farm growers will be determining when to harvest their crop so they maximise maize silage yield and quality and still achieve timely regrasssing.

There are two reasons why this season’s maize crops are running late.

Many maize crops were planted later than usual – the delay largely caused by wet spring weather. Some crops were planted late because farmers did not commit to cropping until after Fonterra increased the payout forecast on November 9.

The growing season has also been cooler than usual.

Maize crops mature according to heat unit accumulation which is measured as growing degree days. Recent data from the Foundation of Arable Research (FAR)1 shows that cumulative growing degree days (from September 1) are similar to the long term average in Whangarei, Te Puke, Whakatane and Rangiora while all other areas are below the long-term average.

When maize crops are running late, farmers have two options – either harvest the maize crop early, or move the regrassing date later.

To decide which option is best for you, it is important to evaluate the economic and management implications of harvesting your maize crop prior to silage maturity versus late planting the new pasture.

Early harvesting maize

Ideal maize silage harvest occurs when the crop is in the range 30-38% whole plant drymatter. At this point the crop ensiles well and yield is maximised.

During the grain fill period silage harvest yield accumulation can be as high as 250kgDM/ha/day. Harvesting a crop a week early could potentially result in a yield reduction of up to 1.75tDM/ha.

Maize crops that are harvested below 28%DM are also more likely to have a less desirable fermentation and lose valuable nutrients as silage effluent (or seepage). Silage effluent wastes valuable nutrients which could have been used for animal production. It is also a powerful environmental pollutant.

If you have to harvest your maize prior to ideal silage harvest maturity, consider the following options to maximise fermentation quality and reduce the risk of run-off.

Lift the cutter bar.

The bulk of the moisture is held in the base of the maize stem. New Zealand trial data shows that lifting the cutter bar from 100mm to 300mm increases silage drymatter by 1.5% but decreases yield by 1tDM/ha. It is also calculated to increase silage metabolisable energy content by 0.15MJME/kgDM.

Use a long chop length.

A longer chop length means fewer cuts and release of fewer plant fluids. If you grab a handful of chopped material and squeeze it and fluid runs from your hand it will also run from the stack. Aim for a chop length of up to 19mm.

Consider adding grain or straw to the stack. About 14kg per tonne of grain, hay or straw per wet tonne of harvest material will be required to increase DM by 1%. If you are harvesting several paddocks, put the driest material on the bottom so that it can absorb any moisture that runs out of the top material.

Use a quality silage inoculant. Products like Pioneer brand 1132 provide the right strains of bacteria so you achieve a more efficient fermentation.

Late regressing

Harvesting your maize crop a week early could potentially result in a yield reduction of up to 1.75tDM/ha. Planting pasture a week earlier is unlikely to produce this amount of additional DM.

Late perennial ryegrass pasture establishment can be successful especially in drier areas where early establishment is often hampered by dry soil conditions.

If you need to late sow:

Make sure that you have treated seed on hand and your contractor is booked so you can direct drill immediately after maize silage harvest.

Assess clover planting depth carefully. As the season gets cooler clover is slower and more difficult to establish.

Consider using low rates of an N-P fertiliser at sowing to ensure fast early growth.

In cooler districts or where the maize harvest is very late, consider planting a shorter term pasture option or a winter cereal crop.

Annual or Italian ryegrasses are ideal for late planting because they have better cool season activity, a faster time to first grazing and will produce more winter feed than a perennial ryegrass pasture.

Oats and triticale can produce high drymatter yields and surplus feed can be made into baled or stacked silage in the spring. Talk to your local merchant to discuss the best cultivar choices for your district.

In summary, in most cases it will pay to wait the extra weeks until your maize silage crop reaches the ideal harvest maturity. If this is well past the recommended perennial ryegrass-clover regrassing date for your area, consider other winter pasture and crop options to maximise DM production.

1 FAR Maize Action 18th February 2010.

• Ian Williams is a Pioneer forage specialist. Contact: iwilliams@genetic.co.nz