The importance of soil sampling

Grassland Agro's Campbell Hume(left) and Chris Wilson (right) discuss the details of this year's soil testing programme with Nathaniel McCollum
Grassland Agro's Campbell Hume(left) and Chris Wilson (right) discuss the details of this year's soil testing programme with Nathaniel McCollum

Good productive soils are the foundation of any successful farm system.

The ability of soils to supply nutrients at a time and in appropriate quantities for grass and crop growth is a key determining factor of how productive a field or farm can be.

Therefore, the management of soil fertility levels should be a primary objective on any farm.

“Fertiliser costs account for approximately 15-20 per cent of the total variable costs on many farms,” confirmed Grassland Agro’s Campbell Hume.

“Fertiliser costs represent good value for money when used correctly. However, fertiliser application rates that are either too low, too high, or not in balance with other soil fertility factors will yield lower returns on the investment made.

“With fertilisers staying expensive, it is vital that each kilo of fertiliser is managed as efficiently as possible with maximum return in grass growth and milk production. Two steps are required in order to achieve this: taking soil tests and using the results to plan fertiliser and lime applications. Both of these steps are equally important.”

Campbell went on to point out that a soil test is an indicator of the background soil fertility levels of pH, P and K, Mg, Ca and trace elements where required.

“Soil sampling and analysis is not a new technology,” Campbell further explained.

“However, it is important to remember that the primary function of soil testing on the farm should be to inform a farmer of the soil fertility status and to plan fertiliser applications,” Campbell continued. 

“Soil sampling and analysis cost money. Therefore, it is critical to ensure that the samples are taken correctly so that the results are accurate and usable.

“Soil pH is the first thing to get right. Due to the relatively high rainfall in Northern Ireland, it is a natural process for soils to become acid and for soil pH to drop. Regular applications of lime are required to counteract this natural process.

“The optimum soil pH for grassland is pH6.3. It is recommended to apply lime to raise the soil pH to 6.5, so that the lime application will maintain soil pH for a number of years. Where soils have a risk of having high molybdenum content, it is advised not to raise the soil pH above 6.2 to reduce the risk of copper deficiency.

“The release of nutrients from the soil and the response to applied fertilisers will be reduced where the soil pH is low (or high). In the case of P, soils with low pH will tend to lock up P and make it unavailable.

“Applying additional P fertilisers in this case is poor value for money for two reasons, as firstly, the low pH means that the potential of the soil to release P is not fully realised, and secondly, the availability of the P fertiliser applied will be reduced.

“There is no point applying additional fertiliser to soils where the underlying problem is soil pH or fertility. Therefore, correcting and maintaining the soil pH should be first consideration in soil fertility management.

“Last year Grassland Agro co-ordinated the analysis of soil samples on an extensive number of farms across Northern Ireland,” confirmed Campbell Hume.

“Analysis of this type allows us to get the balance correct between the inherent levels of soil fertility plus the interaction of organic manures and bagged fertilisers in order to maximise crop yields.”

Campbell made these comments while visiting the Coleraine dairy farm of Norman, Nancy and Nathaniel McCollum. The family milk 280 pedigree Holstein cows and incorporate crops of grass, winter wheat, spring wheat and forage maize into the rotation practises followed on the farm.

“We normally soil test one third of the fields on the farm annually,” Campbell continued.

“This is the time of year when farmers should consider soil testing, particularly from a grassland point of view. Soil test results examined over the last week or so, confirm large offtakes of potash and phosphate from both grazing and silage areas last year. This reflects the almost perfect grass growing conditions that existed for most of 2014, resulting in excellent dry matter yields. These nutrient losses from the soil must be replaced over the coming weeks, in order to ensure maximum crop responses in 2015.”

A commitment to regular soil testing and agreeing bespoke fertiliser programmes also pays dividends for cereal and vegetable growers. A case in point is Eglantine Farms on the outskirts of Lisburn in Co Antrim. The Sloan family grow potatoes, carrots and a combination of winter and spring cereals with the core objective of maximising yield through the attainment of optimal soil fertility.

“We have worked with the team at Eglantine Farms for the past number of years,” Roland confirmed.

“Soil test results are the basis on which all fertiliser recommendations are made. Farmyard manure and slurry are available courtesy of the dairy farm. And we strive to make optimal use of these inputs.”

John Sloan, Eglantine Farms, is of the opinion that a good Soil Nutrition and Fertiliser Plan is an integral part of achieving consistently good yields with his farming enterprise.

Grassland Agro Manager for Northern Ireland Noel McCarey has told Farming Life that current regulations require that phosphate should only be applied where there is a proven crop requirement. It is therefore vital that there should be regular soil samples taken at least every four years.

Although there are a myriad of regulatory reasons for soil sampling Noel believes we should soil sample in order to achieve maximum efficiency of our chemical and organic inputs, thus achieving optimum yields for whatever crop is grown on the farm.

“Our main focus in Grassland Agro is to maintain or improve soil fertility and nutrient status. Healthy soils and matching crop offtake requirements lead to healthy plants and healthy yields and healthy profits for our customers.

“We have been involved in Northern Ireland for over 2 decades in soil science, and now have a team of qualified advisors dedicated to providing soil nutrient management planning solutions.”

 Noel added that Grassland Agro provides a range of soil sample packages ranging from the most basic (basic includes pH, P, K, Mg, Calcium, Sodium and estimated CEC) to the complete soil health package. A complete package is a measure of your soil health based on the chemical physical and biological results of soil sample. Included in the complete package is Soil Organic Matter, a measure of Microbial Activity in soil, Levels of the major macro and micro elements in soil and Textural Classification.