The soil beneath our feet is something many of us take for granted yet it is a precious resource that is absolutely crucial for both the future of our planet and the sustainability of our businesses. It is an unusual resource in that, with care and a little supplementation, it can be used again and again for the foreseeable future.
The pioneers of the organic movement recognised that in order to deliver health, farming systems need to build and conserve natural soil fertility through the development of humus. In order to achieve this, farming practice needs to observe and emulate biological cycles of growth and regeneration. It is these observations that underpin the principles and practices of organic farming today.
Despite recognition by organic farmers and growers that soil health is at the heart of successful organic production, best soil management practice on farm is still the exception rather than the rule. There are a number of sources of information that can help but are they really helpful and can they substitute for basic common sense and good observation. This article will examine the role of soil analyses to see if they can really help and are they worth the money that is paid.
The answers to this question will depend on who has been asked but in general most would agree that a good soil for cropping should have good structure, an ability to withstand cultivations and a good reserve of fertility. No soil that is used to produce food can be regarded as being in its natural state but it is possible to emulate natural systems and cycles through a combination of good agricultural practices. So in a sense we can say that the best soils depend on what the grower has to work with in terms of texture, structure, drainage, etc. and critically on how the grower manages the valuable resource to which he or she has been given access.
Before looking specifically at soil analyses it should not be forgotten that there are many other ways in which producers can assess and monitor their soils. Awareness of the soil and its condition should be a continual process and everyone will be doing this often unconsciously. Picking up early warning signs is vital as it can take time to address a problem that has gone undetected for a period of time.
Several of the five basic senses:
This essentially involves taking an undisturbed slice of the topsoil and carefully examining it to determine the gross structure, the texture, aeration, rooting depth and a number of other properties. The test is best carried out when the soil is moist so that compaction problems are obvious. The advantage of this method of visual examination is the consistency of technique. These observations should be used to guide subsequent choices for cultivation and fertilisation. If there are dead layers or compacted horizons in the soil, they should be loosened at the earliest dry weather opportunity using a chisel plough, deep tines or a sub-soiler.
It is possible to gain a lot of information from this test but the main focus is an assessment of the structure of the soil in the profile. A range of actions can be taken to address identified problems but it should be remembered that there is generally no immediate success with the various measures that can be taken – it can take several years before improvements can be seen. It is however well worth the effort as soil structure and soil condition are absolutely fundamental to the productivity of the soil. Compaction at any level within the soil will affect yields whether of vegetables, cereal or grass so it is vital to detect it then apply corrective action.
This is an area that farmers and growers will be most conscious of and is largely based on common sense. If weather and light conditions are favourable crops should be demonstrating good vigour if they are getting what they need from the soil. Colour is another important indicator – an even green colour from top to bottom of a crop plant and across the bed is a sign that things are reasonably optimum. Any variation in colour on a single plant or across the bed should be investigated – this might be a variation in the ‘greenness’ or there might be stress colours such as yellow or red creeping in.
Weeds can be very useful in providing clues about the fertility and condition of the underlying soil. Keep an eye on the vigour of your weeds and if they are struggling be worried. If they are doing well then the underlying conditions are probably good but of course they are then a greater problem. Some weeds can provide specific indications of particular conditions e.g. chickweed and fathen are indicators of good friability and nitrogen content, sorrel is an indicator of acidity and horsetail is linked with poor subsoil drainage.
It will be argued by many that it is important to monitor pH, organic matter and available nutrients on a regular basis. Soil analysis can tell you a lot about the nutrient status of your soil and also about changes over time. It can be particularly useful when taking on a new holding or when adding new land to an existing holding. Soil analysis is not a substitute for the day to day observations and assessments that all growers should be doing – the growing plant is the most important yardstick. The other important thing to remember is that it costs money and it could be money wasted if the results cannot be accurately interpreted.
There is potentially a wide range of different soil analyses ranging from the so-called ‘standard’ type of analysis offered by many laboratories to the very complex analyses offered by companies such as Independent Soil Services and Laverstoke Park. As a general rule the more complex the analysis the more it costs and the more external interpretation is required. It is probably fair to say that they all have their place but it is important to think about why you are commissioning a soil analysis in the first place before making a choice.
‘Standard’ soil analysis generally provides estimates of crop available phosphorus (P), potassium (K) and magnesium (Mg), along with a measurement of the soil pH. The estimate is based on a chemical extraction of available nutrients but it cannot predict precisely what will happen in the field, given the important influences of weather and soil biology on nutrient uptake. This can be a problem for biological systems where much of the nutrient supply at any one time is stored in humus and soil organisms and is therefore not detected through chemical soil analysis. Other factors, such as sampling and laboratory procedures, will also introduce variable results and must be taken into account when interpreting soil test results in order to avoid wrongly predicting deficiencies. There are a number of laboratories offering this type of analysis but probably the most experienced is Eurofins (formerly Direct Laboratories and before that the central ADAS analytical laboratory).
Other more complex analyses are available including the comprehensive analysis based on the Balzer method formerly offered by the Organic Research Centre, Elm Farm. As the name implies it attempts to cover a wider range of soil parameters including clay content, organic matter levels, pH in water and in potassium chloride solution, calcium , phosphorus measured using 3 different extractants to give an assessment of the ratios between different fractions in the soil, potassium, magnesium and 4 micro-nutrients (iron, manganese, copper and zinc). The results of the analyses were always accompanied by a reasonably detailed if slightly formulaic commentary on the results. In recent years the actual analysis had been sub-contracted to NRM Laboratories and it is now offered directly by NRM who have secured the services of a former ORC employee to provide commentary and interpretation.
NRM, from its history as the soil testing laboratory of ICI, based at Jealott’s Hill, has been testing soil for over 40 years. It has been for some years the largest soil testing laboratory in the UK analysing over 50% of the agricultural soil taken for analysis in the UK. Over 200,000 soil samples were analysed in 2007 for pH, P, K and Mg and many thousands more for more detailed analyses. NRM’s customers include most of the Agronomy Groups in the UK as well as agrochemical, lime and fertiliser distributors. The customer base also includes advisory and research establishments.
Another type of complex soil analysis is based on the Albrecht method of soil analysis and is offered by companies such as Independent Soil Services and Glenside Fertility. ISS provide what they claim is the world’s most comprehensive Soil Audit Report and it includes a measurement of the cation exchange capacity (nutrient holding ability of a soil), pH, the labile pool of nutrients, plant available nutrients, nutrients that might be ‘locked up’ and why, total and available trace elements, nutrient ratios, organic matter, humus and biological activity. The audit involves a preliminary meeting to gain an understanding of the farm and subsequent meetings to provide interpretation and remedies.
ISS will also offer what they describe as soil food web assessments but the only licensed Soil Foodweb laboratory in Europe and the UK is based at Laverstoke Park. This means that this laboratory is able to offer proprietary soil health testing developed by Elaine Ingham in the USA. As the name implies the testing offered by this laboratory is much more focused on the biological activity of the soil and the components that contribute to the overall picture. The assessments can include total and active bacteria, total and active fungi, protozoa, nematodes, mycorrhizal colonisation, leaf organisms, E. coli, etc. They can also carry out nutrient analysis but the focus is on the biological health of the soil.
All the companies that offer soil analyses will provide guidance on how and when samples should be taken. Sampling should aim to be representative of the area to be evaluated so up to 25 sub samples might be taken and mixed and a final sample of 200-400 grams taken from the mix. It is absolutely vital to use clean equipment, containers, surfaces and bags and to also avoid touching the soil. Spring or autumn are generally considered to be the best time to take samples though late winter is also recommended. Consistency is essential so always take samples at the same time of year, use the same sampling protocol and ensure that the same analytical methods are used if comparisons over time are to be made.
It is clear that there is a wide range of services on offer some of which are really focused on the very complex nature of the soil. This should however sound a warning – the soil is so complex that it is impossible to define with absolute certainty. Account must be taken of the surroundings including prevailing climate, topography, drainage patterns, previous use and inputs, geology, etc. This can all be done and some of the companies will visit the site to carry out a detailed assessment.
On the other hand there is much that the individual can and should be doing ranging from regular spade diagnoses to the day to day observations of crops and weeds that are part and parcel of being a producer that is in tune with the environment. Comparing notes with friends and colleagues can also be extremely useful as a fresh pair of eyes can sometimes help with an important breakthrough in problem-solving.
There is a place for soil analysis and it can be very useful in helping to define the baseline on new land and it can also be a useful check on progress when used on a three year cycle on the same fields. The other area where it comes into its own is when a problem arises that is difficult to assess through local observations and assessments. The choice of analysis might be difficult and it would be easy to understand why the cheaper options might be preferred but once again it might be necessary to bite the more expensive bullet in respect of an intractable problem.
What ever approach is taken it is important to respond to the outcomes of the assessments and/or analyses. It might actually require a significant change to cropping sequences and cultivation methods and this should not be delayed however difficult this might appear. It is important that producers take responsibility for their soils and not let the cropping tail wag the soil health dog if that makes any sense.