Knowledge Is Power. So Why Test for Less?

Sometimes the cheapest answer is not the one that costs the least.

Written by: Steve Holloway — Technical Manager, SFS

A basic soil test can tell you quite a lot. The problem is that it can also make you think you know more than you do.

P, K, Mg and pH are useful figures, and for some decisions they may be enough. But once the question changes from “what are my indices?” to “why is this field behaving like this?”, the gaps in that basic picture start to matter. A field can look perfectly respectable on the standard numbers and still not perform as expected, which usually means there is more going on than those four figures were ever intended to explain.

That is where a wider analysis earns its place. Looking at calcium, sulphur, trace elements, CEC, organic matter, carbon, texture and base saturation gives more context around what is happening in the soil. None of those things is a magic answer on its own, but together they can help explain relationships that a basic nutrient index simply cannot show. Just as importantly, more information does not automatically mean more things need correcting. Sometimes it confirms that something is already where it should be, or helps rule out an assumption before money is spent chasing it.

SFS has taken that wider view for a long time. Base Saturation Cation Ratio, or BSCR, has been questioned and criticised over the years, but SFS has used it since the 1990s as another way of understanding the balance of exchangeable cations in the soil. What is interesting now is seeing that sort of thinking becoming more widely available through mainstream soil analysis, including laboratories such as Lancrop. Perhaps some ideas simply take time to move from being challenged to being considered useful.

That does not suddenly make the basic test wrong, and it does not mean every soil sample needs every analysis available. It just means the questions being asked of soil testing have moved on. If the aim is only to check the basics, then the basics may be enough. If the aim is to understand why a soil is behaving the way it is, then having more of the picture starts to look rather useful.

That is the bit I have never quite understood. A lot of money can be spent above ground on seed, fertiliser, crop protection, cultivations, fuel and machinery, all depending on the soil underneath doing its job. Against that, the difference between a basic analysis and one that gives a much broader picture is relatively small.

Saving a few pounds on the soil test can look sensible when you are looking at the invoice for the test itself. It can look rather different when the next decision involves hundreds or thousands of pounds worth of inputs. If the cheaper test leaves an important part of the picture unseen, was it really the cheaper option in the end?

A broader analysis still needs interpretation. A laboratory result cannot know the history of the field, how it has been cultivated, what the crop has looked like or whether the sample genuinely represents the area being discussed. But the more useful information there is at the start, the more there is to work with when those pieces are put together.

That is really what soil testing should give you: enough information to make the next decision with some confidence, rather than simply enough numbers to satisfy a requirement. There will always be situations where the basic test is perfectly adequate, but where the aim is to understand more about the soil, deliberately choosing to know less can be an expensive place to start.

Knowledge is power, but in this case it may also save a fair bit of guesswork.