Why silage ground often has the poorest level of soil fertility and how to fix it

Catherine Hurley

Catherine Hurley

Recent grass silage tests that have been carried out have shown poor protein levels in the winter fodder in many cases, so much so that the feed may need to be supplemented when feeding certain groups of beef animals, according to a report by Head of Drystock for Teagasc, Pearse Kelly.

He says that silage ground often has the poorest level of soil fertility, with much of the nutrients taken out at cutting not being replaced at an appropriate rate.

To help rectify this, he says that forming a fertiliser plan without information on soil fertility levels is impossible, and that soil test results for the whole farm are essential. The cost of soil sampling is on average €1.50 to €2.50/acre.

“Although it costs money to increase fertility levels on low fertility soils, the returns in terms of grass production can be considerable,” he says.

He says recent soil samples taken from farms and analysed by Teagasc show that only 10pc had optimal soil fertility in terms of pH, phosphorus (P) and potassium (K), which is Index 3 for P and K and a pH of >6.2.

Although lime is often seen as the cheapest form of fertiliser available, only half of drystock farms in the country have applied lime in the last 10 years, according to Pearse. He says up to 20pc of nitrogen (N) fertiliser will be lost where lime is deficient in the soil.

“Where lime is deficient in soil, all other artificial fertilisers and slurry will not work as well,” he says.

He also says that Irish soil P and K statuses are also far below acceptable in many cases, with over 60pc of soils deficient.

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Rumen bacteria need sufficient protein, he says, so that they have enough nitrogen to properly function and digest the silage being fed efficiently.

“Without this animal performance will be at least reduced and it may in some cases lead to more serious problems."

Research carried out in Scotland shows that low-protein silage, which was fed to suckler cows had an impact on their rumen function due to poor fermentation, according to Pearse. This led to some cows actually dying.

Where insufficient protein levels are fed, he says the cow is forced to mobilise lean tissue rather than fat.

In the case the deficiency is prolonged it can result in poor calves born from thin, weak cows, which affects colostrum quality, performance of the calf and can also have long terms effects on fertility, he says. 

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