28 March 1997


Silage making, Dutch-style. Norman Dunn reviews the latest thinking on how to improve grass conservation in the Netherlands

TALK to almost any Dutch dairy farmer about silage making and you get the sort of enthusiastic response that most people associate with a favourite hobby.

Its this intense interest in achieving the highest possible silage quality that has translated into the undesirable ammonium nitrogen content in Dutch silage dropping from 12%-13% to 6%-7% in the last 15 years. Average dry matter content is now 45% and mean wilting time out in the field has been slashed from four days in the early 80s to just two days in the last few years.

Grass silage samples inspected at the Laboratory for Soil and Crop Analysis (BLGG, Oosterbeek) where some 75% of all farms send one or more samples yearly, now test-out at 18% crude protein, with between 9.20 and 10.75 MJ of ME/kg dry matter. Other averages include 24% crude fibre with digestible organic matter at 76%.

"Its a national campaign for silage quality, if you like," explains forage expert and farm adviser Henk van Dijk from the PR Research Station for Cattle, Sheep and Horse Husbandry. He advises farmers to:

&#8226 Rotate grazing and silage making in fields through the season.

&#8226 Cut at 18-25cm (7-10in) grass height.

&#8226 Stay weather-flexible by keeping individual cuts of silage small.

&#8226 Always condition and wilt, and aim for a minimum 40% dry matter.

&#8226 From mowing to getting the grass into the clamp should ideally take a maximum two days per cut.

&#8226 Thorough consolidation and careful sheeting at the end of each harvesting day is critical.

Mr van Dijk says these basic rules have been responsible for the steadily increasing quality standards. For instance, theres a radio report for silage makers every day right through the season. This features a numbered code representing the risk factor for up to three consecutive days good wilting weather.

The majority of Dutch dairy farm swards are permanent, with up to 95% perennial ryegrass, and the usual fertiliser applications – including slurry – supply from 300-400kg/ha of pure N (240-320 units/ac) each season.

In the Netherlands, grazing and mowing for silage is nearly always integrated on dairy farms. At a national average stocking rate of 1.7 cows/ha (0.68/ac) of grass and forage, the cows traditionally get two grazings and then the field is shut-up for silage. Then its back to grazing again with 80% of fields giving a second cut before the end of the season.

"By advising that the size of individual cuts be tailored to the farms or contractors capacity to get the grass into the clamp within two, or at the most, three days, we ensure a basic flexibility. Thats not possible where large areas are cut in a single operation," says Henk van Dijk.

"This means our farmers are only mowing from 3-8ha (7.5-20ac) at any one time, and integrated grazing/ensilaging gives about three weeks between cuts on the average dairy farm."

With such small areas, cutting can easily be delayed for a few days without serious bottlenecks in the harvest.

"If it looks like rain, we say Dont cut. This means only about 10% of Dutch silage makers bother with additives. The only time we advise their use is where rain means that, three days after mowing, the dry matter has still not passed the 35% mark."

The rule is to cut and condition, and then immediately spread the grass as thinly as possible over the field surface with two or three turning operations within the ideal 48 hours. Between 65% and 70% of Dutch silage is taken-in using self-loading wagons with chopping knives.

These give a 10-15cm (4-6in) chop length. About 25% of the remaining silage in the Netherlands is collected by conventional forage harvesters, with the remainder packaged in large rectangular and round bales. As in England, most big baling is done by contractors.

"A good stand of perennial ryegrass, fertiliser and grazed along the lines of our national programme, will yield 2.5-3.5t/ha (1-1.4t/ac) dry matter per cut," says Mr van Dijk.

One-day wilting

"I would say were getting a general silage sample that can offer a minimum of maintenance plus 10-12 litres daily with milk recorded dairy cows that average 7500 kg milk per lactation. But it would be wrong to say were completely satisfied," points out Dr Frank Driehuis, microbiologist with the Dutch national institute for animal science, ID and health (ID-DLO).

"Remember that our climate is not much better than Britains as far as the risk of silage being rained-on is concerned – so we want to further reduce the risk of this happening by aiming for a one-day 40% to 45% dry matter silage harvest."

This goal is achievable, feels Dr Driehuis, with more efficient and higher capacity mowing and conditioning. "Weve tested a mower-conditioning system that gives us the sort of treatment and spread in a single pass that will lead, we think, to even shorter wilting times."

The system, developed by Greenland in cooperation with research institutes including the Dutch IMAG agricultural engineering centre, features a pair of horizontal rollers fitted onto the mower.

The lower roller comprises nylon brushes, and the top roller is an open cage with steel bars forming a V-profile. The top roller turns faster than the lower one, forcing grass into the bristles. The result, according to Dutch trials, is a very efficient stripping of the wax cuticle, and a crimping of stalks and leaves every 1.5cm – without actual breakage and related leaf loss.

The thin mat of conditioned grass is then deflected onto a distributing roller, which spreads the material across the whole cutting width.

Next, he says, will come more care of the material once its in the clamp. There is a fair amount of nutritive loss and spoilage through moulds, yeasts and uncontrolled aerobic fermentation when air gets into the clamp. Dr Driehuis puts such losses in his country at about 5% on the average farm.

Here, Dr Driehuis feels that there may indeed be a case for additives in the future. "A biological additive that can control such aerobic deterioration would be very valuable and we think we have found an organism with Lactobacillus buchneri – a strain isolated from maize silage."

In the case of maize silage, this organism has kept material open to the air stable for up to 33 days, instead of just two days before spoilage started in untreated silage. This occurs through the bacteria converting some lactic acid to acetic acid, which in turn inhibits the action of undesirable organisms.

With high dry matter grass and L. buchneri, the increase in acetic acid is relatively low, but trials have shown substantial increases in lactic acid doing the same stabilising job.

New bacillium

Ryegrass silage at 50% dry matter tested at Lelystad took more than 320 hours to start heating when it had been inoculated with L.buchneri whilst control samples took 125 hours. This relatively new bacillium – now incorporated in a range of commercial additives under the Biotal label from Cardiff-based manufacturers of the same name, and available throughout Europe – increased aerobic stability in chopped maize silage by up to 20 times when compared with untreated material.

Further improvements in the future could also introduce other inoculants into the Dutch system. As Dr Driehuis points out, fermentation times are very slow in the average high dry matter Dutch clamp, taking from 3 to 6 months before the pH has reached its final level. "This means that we have losses in dry matter and in protein (amino acid) quality whilst the pH is slowly sinking," he explains.

Inoculants (Pioneer Hi-Bred No 1188 Enterococcus faecium and Lactobacillus plantarum strains) have, in Dutch trials, been successful in lowering pH to the final level in high dry matter grass silage (42% to 56% dry matter) within three weeks from ensiling.

"All this means that we still have substantial room for improvements towards making the best quality silage possible," concludes Dr Driehuis. &#42

Farm adviser Henk van Dijk

Mowing, conditioning and then spreading over every square yard of the field, with two or three turning operations within 48 hours. That is the present technique advised for the Netherlands high dry matter grass silage.


&#8226 Rotate grazing and silage making in fields through season.

&#8226 Cut at 18-25cm (7-10in) grass height.

&#8226 Stay weather-flexible by keeping individual cuts of silage small.

&#8226 Always condition and wilt. Aim for a minimum of 40%DM.

&#8226 Clamping cut grass should ideally take a maximum two days per cut.

&#8226 Thorough consolidation/sheeting at the end of each harvesting day is vital.

For harvesting silage with minimum labour, 65% to 70% of grass silage in the Netherlands is taken-in by self-loading wagons fitted with choppers.