Using inoculants to improve the nutrient value of slurry

With consistent pressure on the industry to reduce greenhouse gas emissions, farmers are embracing the opportunity to increase available nitrogen and reduce ammonia volatilisation from slurry through the simple addition of an inoculant.

The Government has set targets for the agricultural industry to reduce ammonia emissions by 16% by 2030 and to achieve this, farmers will need to change their farming practices. Improved slurry management is one practical method that can help, while also offering financial benefits to the business.

Maximising the value of slurry​

Midlands based agronomists Jonathan Dolbear and Graham Harris work for BCW a Frontiercompany based in the West Midlands area and have been monitoring

the success of using slurry inoculants on several clients’ farms, carrying out pre and post treatment slurry analysis. Both agronomists are enthusiastic about the results and the opportunities slurry inoculants present to farmers.

There are two clear benefits to be had from maximising the nutrient availability in slurry.

1. Better utilisation of the material already available on-farm
2. Environmental benefits – including reduced ammonia and greenhouse gas emissions

Input costs are a large part of growing a crop and even if fertiliser prices come down, Mr Dolbear says there has still got to be an interest in better utilising manure through tools such as inoculants.

“Farmers have effectively paid to create that slurry by producing forage and feeding it to the cow and so it’s in their best interest to get the most out of it,” he explains.

The benefits of using slurry inoculants​

To understand the full extent of the benefits of using a slurry inoculant, BCW collated data from a number of farms where they are using SlurriN PRO.

“Last autumn, we started monitoring the available nitrogen (N) and sulphur (S) levels in the slurry before and after treatment,” explains Mr Dolbear.

“Once we’d taken the initial sample, we treated slurry for three months on the basis that although you’ll start to get a response in one month, to see the real benefits producers need to wait two to three months,” he says.

“The farmers we’ve worked with have put two months’ worth of treatment in at the start and then topped it up for the last month. Post treatment, a dribble bar was used to apply the slurry, so we took samples from the back of the machine.

“The pre-treatment available N was 1.28kg/m3 and post treatment it increased to 1.75kg/m3. I also noticed some differences in S; it had almost tripled the available nutrients,” explains Mr Dolbear.

The inoculant gives producers the opportunity to reduce artificial N input based on the uplift in slurry available N post treatment. However, he stresses that the benefits can be lost if the slurry is not appropriately applied. Techniques such as splash plating will increase ammonia volatilisation and negate the improvements.

“The financial benefit of using this inoculant equates to £40/ha in terms of N and S inputs1,” he adds.

Mr Harris looked into the savings his farmers that were using the inoculant had seen. While he used a different metric to measure this, his overall findings were similar to Mr Dolbear. “On a 100 cow per month basis, SlurriN PRO definitely covered the cost of the treatment and put money back in the bank,” says Mr Harris.

“I have calculated a standard gross saving of around £138/month for 100 cows, based on a saving in fertiliser costs and using standard book values.”

The treatment can work on different dairy systems, although the biggest benefits will be for fully housed herds because of the constant slurry production. The inoculant can be added to the store for both winter and summer slurry production, but the management required is slightly different.

“My trial farms were autumn block calving and so the cows go out to grass in the spring,” says Mr Harris

“They’ve stopped using the inoculant now because there isn’t the slurry going into the lagoon. However, if cows were housed over summer, it’s better to make monthly treatments, because you’re taking slurry out of the lagoon at regular intervals whereas in the winter you can dose it up in a couple of hits.”

Environmental benefits of using a slurry inoculant​

Lientjie Colahan, technical sales support at Lallemand Animal Nutrition, the company that has developed SlurriN PRO, says that as well as offering efficiency benefits in terms of enhanced nutrient availability, slurry inoculants also tick the environmental box.

“When slurry is spread, a process called volatilisation can happen, which means that ammonium (NH4+) is converted into ammonia (NH3) and released into the atmosphere. However, treating slurry with a biological inoculant will increase the total N, but will also increase the proportion of organic N in the slurry, and organic N is not volatile or leachable.”

SlurriN PRO contains enzymes and bacteria that promote the development of beneficial microorganisms in slurry, meaning it can help to reduce ammonia emissions and increase N use efficiency.

“From November 2020 to February 2021, a trial was carried out in a slatted dairy housing system and showed that slurry inoculated with SlurriN PROreduced ammonia emissions on average by 32.5%,” says Mrs. Colahan.

“The organic N content of the slurry was also greatly improved. With more N being incorporated into the bacteria’s cells, there is less opportunity for N leaching after the slurry is spread. This form of N then mineralises over time supplying N to the plant.”

Mrs Colahan explains that the inoculant is simple to use.

1. One sachet treats 200,000 litres of slurry or the equivalent of 1 months’ slurry production from 100 dairy cows
2. The sachet should be mixed with 10 litres or more of clean water at room temperature and mixed evenly into the liquid fraction of the slurry
3. Avoid putting it in where parlour washings enter the store because your dairy hygiene products may kill the bacteria within the inoculant

“Correctly stored and applied slurry inoculant can be a cost-effective way of nutrient management, utilising a resource readily available on-farm and replacing a proportion of bagged fertiliser while potentially reducing ammonia emissions.” she concludes.