Thursday, 30 September 2021 10:55

Harvest silage quickly or wait?

Written by  Ian Williams
By mid-September, grass silage making season is well underway. By mid-September, grass silage making season is well underway.

By the middle of September, the grass silage making season will be well underway.

It will start on permanent cropping land with farmers harvesting annual ryegrass crops before the area is replanted in maize, and will continue on dairy farms as they move past balance date and begin to develop a pasture surplus. Well-made, high-quality grass silage is one of the most valuable feeds available to farmers. It will be high in energy and protein, and as a stored feed it can be one of the most flexible feeds in the farmer's toolbox to fill summer feed deficits. I am going to go into the mechanics of making great silage as this is well covered elsewhere (see https://www.pioneer.co.nz/inoculants/product-information/how-to-make-quality-pasture-cereal-and-lucerne-silage-guide/making-quality-silage or https://www.dairynz.co.nz/feed/supplements/grass-silage/ ). 

While we all understand the mechanics of making high quality silage, it is hard to put them into practice. We know good planning and good communication with the silage contractor increases the chance of making high quality grass silage. However, it is hard to plan for the biggest risk factor to making great silage - the weather. Good planning and communication increase the chance that the contractor will be available when the grass is at optimal quality. However, it all comes to nothing if the weather doesn't play ball, when the question is often asked, "Do I take my silage early (i.e. cut followed by little or no wilting) or do I leave it a bit later when the weather might be more stable?"

Too dry or too wet?

Theoretically, the ideal harvest drymatter for pasture silage is somewhere above 28%, as this is where the risk of losses through leachate are significantly reduced (see Figure 1).

Figure 1. Leachate losses from pasture silage vs pasture drymatter (from Bastiman & Altmann, 1985)

Leachate from grass silage is particularly problematic. Not only is it full of soluble sugar (and therefore energy) that can be used by the cow to produce milk, it is also very dangerous to aquatic life due to its high biological oxygen demand (BOD). Depending on the concentration of leachate, a small amount of Leachate (1 litre) in a large amount of water (10,000 litres) can threaten fish survival. Because of this, every regional council requires farmers to prevent silage leachate from entering waterways. It is important to see what the rules are for your region and make sure that you comply.

Practically speaking, the ideal harvest drymatter window is somewhere between 25% - 40% DM. Below 25%, the leachate losses increase substantially, while harvesting too dry can also be problematic. Over-wilted grass (above 40%) is difficult to compact into a bunker or stack, therefore increasing the aerobic losses.

Harvest time and quality

The next question then is "If it is not too smart to cut the grass and harvest it too wet, is it better to leave it growing until a safer weather window comes along? And if I do this, how much quality do I lose?" A former DairyNZ scientist, Dr Justine McGrath, published some data which shows the loss of grass quality over time (see Figure 2).

Figure 2. Pasture quantity vs quality (from McGrath et al, 1998)

This clearly shows that while there is quality loss as the pasture matures, the loss of quality isn't that great over a 2-week period and some of the loss in quality is compensated for by a gain in quantity.

So, if the weather doesn't allow to harvest the silage at the perfect time, it isn't a disaster. To reduce the risk of leachate loss, it is better to wait a couple of weeks and harvest when the weather allows for the grass to be sufficiently wilted, to ensure reduced risk of leachate loss.

Ian Williams is a Pioneer forage specialist. Contact him at This email address is being protected from spambots. You need JavaScript enabled to view it..

More like this

Optimising returns

Last month, in response to some pretty scary price rises, I wrote about the need to control costs. 

Grow another paddock

Farming is becoming increasingly complex. Until recentyl, farmers had relatively few issues to focus on: feeding cows, producing milk and hopefully making enough money to feed their family and pay off their mortgages.

Controlling feed costs

Everywhere I go, whether it be in town or on farm, I hear a similar topic being discussed. It’s the fact prices have risen and as a result farmers and growers have become very focused on controlling on-farm costs.

The potential of under-sowing forage maize

Given that New Zealand farmers are being expected to improve their environmental footprint, some trials in the UK around under-sowing in growing forage maize crops may have some benefits here too, particularly in the south.

National

Ruralco's got your back

Rural trader Ruralco has launched a new campaign, recognising and appreciating the farming sector.

Optimising returns

Last month, in response to some pretty scary price rises, I wrote about the need to control costs. 

Machinery & Products

Amazone's one-pass operation

Ag machinery maker Amazone has paired up its Precea precision air seeder and Combi-Disc 3000 compact disc harrow to deliver…

New grassland products

Grassland specialist Pöttinger has released a new portfolio of products and innovations for the new mowing season.

» The RNG Weather Report

» Latest Print Issues Online

Milking It

Oat juice, not milk

OPINION: New Zealand's best loved brand Whittakers has launched its first 'plant-based' chocolate but it hasn't left a sweet taste…

Heat wave

OPINION: The heat wave that hit Europe last week has forced a rethink among UK dairy farmers who normally graze…

» Connect with Dairy News

» eNewsletter

Subscribe to our weekly newsletter