Soil advice for dairy farmers to improve forage

Dairy farmers are being urged to dig a hole every month to get to know their soils and unlock the potential for healthy, nutrient-dense forage.

Josephine Scamell, independent adviser for Ground Level Nutrition, said it was important to look at soils on a regular basis.

Speaking at the Soil Association’s Soil Symposium earlier this month, Mrs Scamell urged farmers to consider three things; physical soil structure, soil mineral balance and biological content of the soil.

“Physically aerate the soil, use minerals to maintain an open structure and avoid killing earthworms with untreated slurry,” she said.

Farmers need to really closely evaluate soils to look at earthworm populations and levels of compaction. “Earthworms need to be recognised as an effective and free soil service as they can aid fertilisation and turn over 4t/acre a year of soil, creating valuable drainage burrows as they go,” she said.

Sampling advice

Digging down to a spade’s depth and removing a block of soil can give farmers a clearer idea of their soil structure throughout the year. Examining to further depths may be needed if there is a plough pan or compaction present.

“About one cubic foot should be dug out from a representative area of the field, not near a pond or a track. The block should allow the farmer to see the turf on top, the level of compaction and about 9 inches of topsoil,” explained Mrs Scamell.

What to look for

1 Roots

First pull the turf apart to see how strong the side roots are. It shouldn’t be hugely matted as the roots need space to grow and breathe. Root matting is caused by the accumulation of dead organic matter and needs oxygen to degrade.

Compaction reduces the amount of oxygen in soils and leads to preservation of this material. It may require physical aeration to aid degradation.

2 Temperature

Next evaluate the soil temperature compared with the ambient temperature. You are looking to see if it is cold, wet and compacted or preferably open, moist and with a crumb structure.

Phosphate is often severely compromised in compacted soil and the main way to release it is physical aeration.

3 Smell

Smell it. It should have a pleasant compost smell, not something resembling a dank, rancid fishpond.

4 Worms

Look for earthworms. In healthy soil there should be about 25 active, deeply coloured worms of varying sizes in a cubic foot. If they are tightly bundled this indicates stress. If they are dead, one cause may be from slurry application.

But worse still, their death may adversely affect many other soil micro-organisms throughout the food chain.

5 Colour

Soil colour varies greatly depending on rock type and soil type, but generally darker is better, as it means an increased soil organic matter content.

6 Sample

Taking a soil sample for analysis will highlight any problems with the mineral balance and trace elements of the soil, which should be tackled with help from an adviser.

Low levels of calcium and poor liming are common problems. When pH is below 6 the soil is likely to require liming at about 1t/acre.

Liming can be done at any convenient time when the soil will cope with heavy machinery passing over it.

Applying lime in autumn gives it the whole winter to get worked in before grass is grazed. If you apply lime in early spring, it needs about six weeks to get fully worked in, but this can depend on weather conditions.

When pH is 6.5 or above, the soil may still be short of calcium, it just might not be as obvious. In this case, checking the full soil analysis for the cation-exchange capacity will tell you if calcium is at a good level.

Aeration methods

Regular aeration enhances everything else you do during soil management. It creates a 10-20% improvement in nitrogen release, improving the efficiency of soil nutrient use, explained Mrs Scamell.

She suggested the following aeration methods:

1. Slit aeration (vertically cutting lateral roots to a depth of 15-20cm) stimulates healthy new root growth and helps to oxygenate the soil without undercutting the deeper roots, encouraging further growth. This should be done in either spring or autumn, avoiding soil conditions that are too wet or dry.

2. Deep flatlift aeration (18-inch flat tines) gets underneath the plough pan which can be 20-25cm deep to lift and break it up below the topsoil. This should be done when soils are dry – usually in early autumn after a dry summer.

3. Mole ploughing makes a deep drain hole, which is particularly useful on heavy clay as it produces a drainage channel through the winter and if done correctly has a lasting effect. This can be done in autumn when the soil is dry.

Farmers can use the results of their hole digging and soil analysis to create a nutrient management plan.


Mrs Scamell stressed any problems are unlikely to be fully rectified within 12 months, so she recommended a three-year plan to correct any imbalance in the physical, mineral and biological soil properties.

“Using biotreated slurry or composted farmyard manure during the growing season is the most beneficial way to increase soil nutrients and forage yields,” she said.

Biotreatment of slurry minimises the noxious toxic elements and converts them into bioavailable nutrients, transforming it from a detrimental to truly enhancing nutrient source. It typically results in a 30% enhancement of bionutrient levels, and a nutritious, palatable, high-quality forage, she said.

As winter approaches, Mrs Scamell advised farmers to finish slit aeration if it’s not too wet. It’s the perfect time for soil sampling as the soil has had a chance to rest, so check calcium and pH levels in preparation for liming, she said.

“This is also the best opportunity for farmers to think ahead to 2014, to get analysis done on problem fields, to plan ahead and order any products needed before starting again in February.”