Sunday, August 14, 2022

How to do a visual soil assessment on-farm

In the eighth and final piece in our series on soil health tests you can do on farm, the VSA Field Guide is even easier to use – and ease of use was the point from the start.

For our final effort on soil we are going to look at a system that was created in 1999 by a Kiwi, Graham Shepherd, examined and lab-tested by those in Landcare Research and several other New Zealand research organisations, and has since been picked up and raved about by a number of overseas countries, particularly those with a temperate climate.

Shepherd had been asked by regional councils to give an oral paper at their national conference on simple and cheap soil physical indicators of soil quality. The conference loved his demonstrations, but what they really wanted were “gumboot indicators”.  On his way home that night he came up with the idea of showing soil and plant performance in good, moderate and poor condition using three comparative photographs, and Landcare loved it.

What resulted was the “VSA Field Guide”, which contains instructions on how to carry out the various parts of the Visual Soil Assessment, and three comparative photos and tables that are used to score soil and plant indicators for pasture, and similar ones for crops.  In addition, the VSA provides a quick, low-cost method for estimating the potential for nutrient loss into the groundwater and waterways, carbon sequestration and the emission of greenhouse gases.

Given the multiple changes coming up from legislative changes that are imminent, knowing some of these figures sounds like a useful idea.

You will definitely need the book, or know what’s in it, so ask your mates to see if anyone already has a copy or order one online from BioAgriNomics.  Shortened FAO versions for different land use are also available here.

The assessment itself consists of digging two holes (a small one under the fenceline and a larger one in the paddock) and comparing the look of the soil clumps with the photos. Initially the clump required what was called the drop fracture test, but now requires the following, which is quicker:

Remove a sample of topsoil 200mm long by 150mm wide by 200mm deep with a spade. 

First look at the clump for the number of macropores, how dark the colour of the soil is, and whether you can see any orange or grey mottles in it.  Compare with the relevant soil type photos in the book.

Then apply gentle pressure and attempt to loosen the soil with both hands, exposing the soil structure (that is, the natural aggregates and the man-made clods).  Use the force required to break up the sample.  Compare the resulting distribution of structure with the soil structure photos in the book.

Now look at what’s on top, using a Brix meter and a garlic crusher, for example. Assess the sugar content, which will tell you how well those plants are really doing. The sweeter the healthier.

Compare your two soil samples.  This comparison is simply to compare the soil colour. Fill in the score card and muse on your results. The score card now comes in an abbreviated form which, while giving the same answer as the comprehensive scorecard, is much quicker to complete. There is even a Volume 2 of the first edition that gives guidelines for sustainable management if they look moderate or poor.  The VSA is first and foremost a farm management tool.  It’s about repackaging soil science and agronomy into a format that can reach the farm gate and beyond.

Overall, what you have discovered from your investigations underground is going to come in very handy when new rules require you to report on much that you’ve previously not given a whole lot of thought to.  So find that spade, keep it handy, and get digging!

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