The scent of freshly cut grass is a bit away at the moment. The cold weather hasn’t encouraged grass growth rates. Meanwhile, the abolition of milk quotas sees this country gear up for a milking boom, with Simon Coveney predicting that 300,000 extra animals will enter the system bringing the number of dairy cows in Ireland to close to two million. The diet of these cows is based predominately on grass, the cheapest source of animal feed available.

However, more important is how good the silage is on the farm. Grass, like any other crop, requires a good nutritional programme, as outlined in pages 8-9 of this Focus. The quality of silage is related to our variable weather conditions and how well the harvesting process is managed. The fundamental drivers of good-quality silage must be borne in mind when choosing the operations carried out during harvesting and the method of ensiling.

Although a lot of grass is mowed with large mowers, a number of smaller mounted mowers remain very popular. This may be the case where strong paddocks have to be cut for baled silage. They also give the farmer the option of targeting the mowing operations in evening time when grass sugar is at its highest after the day’s sunshine. The specifications and prices for these mowers are detailed on pages 10-12. We also compare the different strategies for making silage adopted by two Laois farmers (pages 4-5).

Focus on quality

According to Philip Cosgrave from IAS Laboratories, the results from the silage analysis carried out this year indicate that quality was down. The pH levels were a little higher than expected, but the main reason for the reduced quality is best put down to the low dry matter of many of the crops harvested last year, with a break in the weather just when the crop was ready to be cut.

Padraig O’Kiely, grass silage expert with Teagasc, explained that preparation is key to making good quality silage. He said a sugars test should be carried out before you cut to check if the grass is fit for ensiling. Teagasc centres around the country will facilitate this – just bring in a sample of grass and they will do the rest.

Once sugars are above 3%, the grass is suitable for ensiling. Sugars will increase if the grass is tedded out in fine weather. Padraig said a simple step of waiting until the dew is gone off the grass before you mow a field can lead to a reduction of up to a tonne of extra weight in water being ensiled.

The stage at which silage is cut is very important in order to improve your chances of harvesting higher DMD silage. Cutting silage just before it comes to seed is the recommended method. Many farmers want to go for a bulky crop, but Padraig warned: “Every week you delay harvest, 3% digestibility is being lost. A dead butt segment in silage has the same feeding value as straw and this situation should be avoided.”

Wilting will seriously aid grass dry matter percentage and reduce the amount of effluent produced in the pit. A balance has to be kept, however, because when making pit silage, 40% dry matter (DM) is too dry and is hard to roll – 28-30% DM is ideal.

IAS Laboratories offers a quick turnaround on pre-mowing tests for silage. The test analyses nitrate and sugar levels to help make the decision. High nitrate levels will act as a buffer to pH, which can affect the lactic acid fermentation desirable for quality grass. Nitrate levels can be high where the application of N has not been fully utilised by the growing silage crop. In a typical example, according to Philip, 80 units of N applied will typically take 40 days and one week before mowing. Higher DM grass will ferment at a higher pH. If the sample is in the lab by 12am the results are available that evening for farmers. The test costs are €20 for nitrates and €10 for sugars.

Important role

The harvesting machinery and settings have an important role to play in helping the silage fermentation. Philip adds that mowing in the evening is always desirable for higher sugar levels in the plant, particularly after a sunny day.

Tedding out silage is an area that some contractors and farmers overlook. Philip noted that the silage with the highest DM% generally comes from fields that have been tedded out for at least 24 hours. Again, the timing with the weather is critical.

Setting up the mowers, rakes and tedders is the primary objective of the operator. Machines that are cutting and raking soil are of no benefit. The bacteria in the soil causes butyric fermentation, which is not desirable for silage production. It is important that the rakes and tedders are not throwing soil into the sward. The machines need to cover the ground effectively, not losing any of the grass crop and flowing over the cut grass. Bumpy undulating fields cause difficulties in achieving this.

Heavy grass swards not tedded out will not reach their potential to wilt effectively in 24 hours. The main aim of the harvesting is to get the ideal DM in to the bale or pit. Harvesting water and blowing it up a chute is demanding on machinery energy requirements and creates problems with silage conservation. Silage is high cost on most farms to get harvested and even a higher cost if meal is needed to supplement poor silage all winter.

The ideal conserved silage should have the following analysis results: pH 3.8-4.0, DM% 28-30, DMD% 70+, Protein 13%.