Healthy soil – healthy crops – healthy livestock – healthy humans

Tuesday 22 May 2012

Eighteen farmers attended the latest meeting of the Burnley and Pendle Farmers group to hear local soil specialist James Bretherton (AgScope) give a most interesting and thought-provoking talk on soil health.

Soil is the most valuable resource on any farm as it forms the basis of all life. Although to most of us soil looks like an inert substance it is actually a living environment and James described it as being equivalent to the rumen in a cow – in order for it to function and remain healthy it must be managed correctly. Soil health is much more than just the pH, N, P and K.

Healthy vs sick soil

If a soil is healthy it will be seen in the quality of the grass – forage grown in a healthy soil will be more palatable and have a higher nutritive value as a result of the nutrients and minerals being taken up more effectively. The grass will grow better to give increased yields and the soils will drain more effectively, which again promotes better growth as drier soils warm up more quickly in the spring. The plants will utilise fertiliser much more effectively and due to better uptake of minerals will provide a more balanced forage for livestock. In comparison sick soils will produce less grass of lower quality and value and with increased growth of weeds.

2t/ha = the extra grass grown in a healthy soil compared to a sick one.

Soil composition

Soil is composed of approximately 46% minerals, 24% water, 24% air and 6% organic matter. Of these fractions organic matter is the most important as it provides nutrients for the plants and also gives the soil flexibility and structure. Without a good proportion of organic matter the soil is very hard and difficult to work with. Air is also an essential component to support the bugs and microbes living in the soil.

It has been calculated that one teaspoon of soil can contain up to a billion different microscopic organisms, of many different species, many of which we know nothing about

Soil is full of bacteria, fungi, mites, insects and worms. The number of worms in a soil is a key indicator of how healthy soil is, and James recommended that by digging a hole in your fields and assessing the number of worms it will tell you an awful lot about the health of your soil. A high worm population will aid in the drainage of soil as they move a lot of soil around, and their excrement also adds nutritive value.

What causes anaerobic soils?

Livestock poaching and intensive machinery use will lead to the formation of a pan below the soil surface where the soil becomes so compacted that water cannot drain through it and plant roots cannot penetrate. Compacted soils also become starved of air below the pan which will effectively suffocate the micro-organisms living there.
Heavy slurry applications will make the soils anaerobic – this is why you often see a lot of seagulls following slurry tankers as they are picking up the worms which come up to the surface to get air.
Over-cultivation of soil – although ploughing can be useful in some situations to break up compacted soils, it also effectively destroys the ‘cities’ that are created by the bugs and organisms living in the soil. It takes a lot of time to rebuild these environments after ploughing.
Some fertilisers can affect the structure of soils – magnesium tends to bind the soils particles together to create a much tighter soil whilst calcium will open the soil up and make it lighter. This must be taken into consideration if you are applying lime as applying mag lime to a soil which is already quite tight will have the effect of making it even harder. The key to this is ensuring that you know what soil structure you have on your farm and this can be discovered by a more detailed soil analysis.

Dig a hole

The best way of assessing how well your soils are functioning is to dig a hole and examine the soil in more detail.

Smell – healthy soils should not smell unpleasant. If they smell sour it is a bad sign and may indicate that the soil is anaerobic with little air in it.
Structure – it will be easy to see whether your soils have a compacted layer and also where this is located in the soil. Livestock poaching tends to results in shallow pans just below the surface, whereas machinery pans tend to be deeper in the soil profile. Compaction can be alleviated by using aerators (shallow pans) or subsoilers (deeper pans).
Worm numbers and types – ideally you want a good mix of different sized worms as these are varying ages and stages of development.
Root growth and mass – good strong plants will have a strong root system which penetrates deep into the soil.

Aerating soils

Aeration of soils is a good way of improving them and provides the following benefits:

Increased air content encourages soil life and helps soils warm up more quickly in the spring which encourages early grass growth.
Improves the nitrogen cycle
Improved phosphate uptake
Improved grass palatability – aeration of sour soils will improve the taste of the grass.
Drainage

Summary

Balance in the soil is key
Soil is a living environment and should be treated as such
Soil health is much more than just N, P and K.
Assess the health and condition of soil by digging a hole