Silage is only as good as the fresh grass it is made from

Silage can never be as high a quality of forage as the grass from which it was initially made.

This was the key take-home message delivered by renowned forage specialist Dr. Dave Davies courtesy of his presentation to the recent ‘Making Silage Sense’ webinar hosted by Alltech.

“This is why it is so important that the quality of the fresh forage ensiled is maximised,” Davies explained.

According to Davies, preparation for silage making should begin as early in the year as possible.

“All dead grasses should be cleaned off silage swards prior to them being closed off. Sheep can do an excellent job in this regard. Grass type is also very important when it comes to making top-quality silage. Perennial ryegrasses have been shown to perform well under Irish and UK conditions in this regard.

“But specifically where silage is concerned, the varieties within the swards should have heading dates that are within seven days of each other.”

Davies confirmed that grass should be cut for silage when no more than 10% of the plants’ stem is visible.

“As stem levels increase, so do fibre and lignin levels,” he added.

Soil fertility will drive grass growth. Davies confirmed a soil pH of 6.5 as being optimal for grass swards.

“For swards containing 30% plus clover, this figure should be slightly higher,” he stressed.“Regular soil analysis is critically important. The results should be used to determine the fertiliser programmes used for all silage-making operations. Applying five tonnes of lime per hectare will increase soil pH levels by 0.4units.”

According to Davies, fertiliser application is all about timing when it comes to maximising grass and subsequent silage quality. He confirmed that slurry must be spread a minimum of eight weeks before cutting if applied to the soil surface. This figure can be reduced to six weeks if slurry injection or trailing shoes application systems are used.

“If slurry is spread too late, subsequent contamination of the soil with clostridial bacteria will impact negatively on the quality of the fermentation achieved,” Davies commented.“The same principle holds if soil contamination becomes an issue. Mowing grass to almost ground levels can have unwelcome consequences.”

Davies advised a first-cut fertiliser nitrogen application of between 80–140kg per hectare.

“Legumes require little or no nitrogen to be applied at all. A grass sward containing 30% clover can fix up to 150kg of nitrogen per hectare during a normal growing season,” he said.

“Sulphur is the fourth most important fertiliser requirement of a grass crop. In the past, all of the sulphur required by plants was present in the air, courtesy of the sulphur dioxide created in a range of manufacturing processes.

“This is no longer the case. A grass test can assess plant sulphur levels. If required, then an application of up to 40 kg of sulphite equivalent per hectare is recommended.”

Davies also highly advised grass testing to assess grass crude protein and free nitrate levels in the days running up to harvest.

“These tests should be used to gauge trends,” he commented.“Optimal fermentation will take place if crude protein and free nitrate levels are in the region of 17% and 0.15%, respectively.

“The accuracy of any grass test is very dependent on the freshness of the grass submitted. If the time lag between cutting and testing goes beyond 24 hours, the accuracy of the results coming back will fall significantly.”

Davies justified the use of chemical nitrogen fertiliser on silage crops at present, not specifically on the overall yield response received, but on the increase in crude protein nitrogen levels contained within the silages produced.

“Improving the levels of crude protein in silage reduces the amount of protein required, courtesy of bought-in concentrates,” he stressed.

“Grass testing will also allow the farmer to gauge the efficiency of the fertiliser nitrogen applied. If free nitrate levels are significantly above 0.15%, then too much nitrogen was applied in the first instance.

“Conversely, if the free nitrate figure is well below the 0.15% figure, then too little fertiliser was applied to the crop. Cows are designed to eat forage,” Davies concluded.

“High-quality silage can deliver numerous performance - and health-related benefits for dairy cows. But, in order to achieve this, forage quality must be maximised.”

InTouch feeding specialist Aislinn Campbell also addressed the webinar. She highlighted the fact that many cows are kept indoors throughout the year.

“This puts even more emphasis on the need to get silage quality consistently right,” she said.

“There is no point in getting first cut silage right and then forgetting about the cuts that follow.”

Campbell defined good-quality grass silage as a forage with a dry matter of 30%, an ME of around 12 and a crude protein value of at least 14%.

“It may not be possible for every dairy farmer to achieve these targets on a consistent basis,” she concluded.

“However, it should be feasible for every milk producer to improve the quality of the silage they make on a consistent basis.”

A follow-up webinar will be held on Thursday, April 29. The event will commence at 7.30pm and will focus on harvesting silage and reducing silage slippage. The final webinar in the series of three will be held in October.