This is a guest post by Niels Corfield, soil health, agroforestry and whole farm planning advisor, researcher and advocate.
For graziers and farmers
It’s been a “funny old year” from the wet, water-logged winter-spring to the now, dry spring-summer.
Since we’re in a prolonged dry spell people are watching the sky and “praying” for rain (or at least hoping), I wanted to share some relevant gleanings from visual assessments of soil structure and how they pertain to soil moisture, in these most “drying times”.
To conclude the piece I will attempt to show how these observations could be brought-to-bear on management decisions now, and in the future. With a view to ensuring your soils are “ready for the rain”.
Below are some images of soils under different management. When looking at these images I want you to ask yourself: What can we see here? What is the appearance (the structure of the soil) telling us?
The first and perhaps most important point to make, is, to make a clear distinction between observations and conclusions (or to cited causes). Not that we shouldn’t draw conclusions, simply that there may be multiple reasons for an observed phenomena.
But the first step to understanding a given situation is observation.
Above is an image of a soil under permanent pasture in mid winter.
Q: What do we see in this picture, in terms of the visual appearance of the soil structure?
A: a tale of two (very distinct) layers
So, what, might we say, is the most important difference in the state of these two layers?
1. the upper layer appears darker — it is wet (or well hydrated), and;
2. the lower layer has a lighter appearance — is dry.
If we look a little more closely are there any other aspects of the appearance we can identify?
Well, structure is one of the macro features of soil we can look-to to judge it’s condition and it’s state of “health”.
The two broad categories of soil structure are: aggregated and consolidated.
Consolidated soil is the product of physical bonding, typically, having a uniform and homogenous structure, with angular or blocky sections. An aggregated soil is very different, it’s structure is a result of a biological activity — the secretion of sticky substances — that glue the separate soil particles (sand, silt or clay) into little globs, that have a rounded appearance (they look like mini worm castings). See below for an example of an aggregated soil.
A Closer Look
By getting right-in there we should be able to spot relevant, features or characteristics, not otherwise visible. Let’s look at these two layers separately, and see how they can be characterised in terms of their structure.
The upper layer (or turf layer as we might call it) has a more aggregated structure, we can see this because the particles sizes vary-, they are generally small, have a “crumb”-like structure, and are held apart from one another, in a disordered kind of arrangement. Overall, the structure is: non-uniform, irregular and generally open in nature (this can be seen by the large number of small shadows visible in the image).
This is also where the majority of the roots are concentrated. They are densely distributed and are mostly coated with soil, with some showing signs of “rhizosheaths”.
These are all signs of biological activity (or the bi-products of microbial activity).
The section of soil below the turf layer has a quite different appearance. Rather than shadows everywhere from all the nooks and crannies created by the many discrete soil particles, what can be seen is a fairly solid mass, with distinct faces, broken into large angular sections. Between- and within these sections there are cracks, clearly visible.
Generally, where it does break breakdown into smaller fragments, these are still angular and blocky in nature, rather than rounded.
There are roots present throughout this layer, however they are fairly widely distributed and mostly white in colour — indicating they are “clean” and free of soil. Not a good sign as it means the roots aren’t building lots of aggregates.
These visual cues are all indicative of a physical structure, one where the soil particles are bonded in crystal lattice: highly ordered, tightly packed and densely arranged, having a low porosity.
We can see clear a distinction between these two different soil strata or layers. But what is the significance of these observations?
The land has had ample rain so why isn’t the whole of the soil profile hydrated.
If it were water loss due to evaporation (somewhat unlikely in winter) surely it would be the upper layer that would be dry, either through direct losses or through transpiration from the majority of the roots.
If it were lack of precipitation we should see a proportion of the lower lever showing signs of hydration, yet there is a distinct boundary, exactly where the soil structure changes.
What seems most likely here is that the rain that has fallen on to this soil has been unable to percolate into these lower depths, basically ending up moving laterally, and leaving the land (taking some goodness with it).
Why is this significant? Why should we care?
Well we can can say, that, amongst other things, soil is a water store (a reservoir) that holds water from rains (or snow melt) from which plants can draw-on in dry periods.
Generally, we can say that better aggregation allows more water to enter the soil profile and holds more of that for later in the year. This is shown, in this example, because the upper layer of this soil is well hydrated, and is also well aggregated. As opposed to the bottom which is dry, and has a consolidated structure. We can broadly say that this layer and below will hold (and therefore offer) little water to plants come the growing season.
In a drought this maybe the difference of several weeks of additional growth.
We can also broadly say that a better hydrated soil will have more active microbial populations, and thus more microbial activity, meaning more nutrient release, and therefore: healthier-, more nutritious grass plants. Which means healthier-, better nourished animals, with better weight-gain, higher conception rates and improved meat quality.
So how are we to respond to these observations? What practices or measures can we put in place to address these issues? What might our objectives be, based on what we can see? Where would we want to end up, over what period?
We can say that these observations are generally associated with poor pasture condition. Either through historic management practices or through some issue associated with cultivation, back in the day.
There is no one right response. Every farm is different and you have to work with the constraints you have. However, whatever response you do try, it is important to monitor as you go so you can see if it’s working.
That said, it’s important to note that the image referred to here, is just one sample and as such may not be representative of the whole field.
To get a more accurate picture of the soil condition in a field as a whole, a number of samples should be taken. Or an attempt should be made to return to the same spot each time samples are taken.
Either way, the important point is that samples are representative.
This soil sample has been selected for this piece because it illustrates a point clearly.
With this in mind, we can use the baseline we have from the samples we take, record a measure of topsoil depth typically the upper layer, with more aggregated structure (potentially the turf layer) and look to increase that depth year-on-year. Perhaps using a yearly, or twice-yearly assessment – ideally taken from the same- or close to the same location in that field. The VESS test will also be appropriate for referencing progress/improvements.
Another, more immediate method for measuring success would be forage volume, either with a plate meter or a sward stick. With increasing totals and faster growth rates being valued.
Finally, perhaps the most direct method for assessing water penetration into soils, is the water infiltration rate test. Which is kind of a no-brainer, though that said, it’s really a measure of aggregation — since as aggregation improves, so does infiltration. It couldn’t be more appropriate for this drought July 2018.
Soil Health Principles
Once you’ve decided how you will measure success, the next step is to identify interventions/management practices that can help you achieve your objectives.
These may well be novel practices or represent a change in management, as such there’s some consideration to be made when selecting a specific option. So, what’s useful is to have a criteria against which to make your selection.
One tool for making selections (or at least shortlisting) is the soil health principles (see below). Basically, practices that match more of the soil health principles should be favoured (where practical).
- Living Root — for long as possible, as often as possible
- Covered Soil — with residues or living plants (leaves)
- Minimise Disturbance — tillage/cultivation
- Diversity — in your rotations or mixes
- Feed Soils — organisms need energy (carbon) to live and be active
- Incorporate Animals — ideally using adaptive/planned grazing techniques
- Minimise Use of Chemicals/Synthetics — undoes your good work above
In almost all cases, if improving soil health is your aim, then the main objective is to increase microbial activity, either by feeding the organisms directly or by inducing the grass plants to grow larger and more rapidly (which has the knock-on effect of feeding soil biology also, through exudates).
In general we’re looking to increase residues and residuals, increase trampling and shifting to a lower (or ultra-low) utilisation rate — potentially 10–20%, with 30% being an upper range. Frequent moves and high stock density will facilitate these goals.
Some techniques and frameworks for improving soil health in pasture.
All these practices are routes to increased soil aggregation. And as such their success can be evidenced by this.
Holistic Planned Grazing (HPG)
A tool to deal with the complexity and variables associated with managing grazing systems, and achieve higher goals, like high animal performance, improved pasture growth and better soil.
As they say “proper planning and preparation, prevents….” In this case, the planning means you are generally better prepared for unforeseen circumstances. So when a drought hits- or an extended wet period you should be better able to react and still achieve those goals.
HMG Grazing Charts are downloadable here. Though you may want some support with getting started.
Otherwise there’s a new app PastureMap which takes much of the work out of the process, especially the recording, and on the fly monitoring. As well as this, the support staff are all planned grazers, so they can provide help with the app and the grazing planning.
Grazing technique that can help to get the most out of your pastures in any given year, especially in drought and when grazing “into the shoulders”. Extend the season and improve the bottom line. Especially effective when applied in a holistic planned grazing framework.
High stock densities (and frequent moves) reduces over utilisation of grasses through selective grazing and ensures even
Works best with smaller animals, with larger rumen to frame size ratio — animals bred to perform well on “low quality”, all-grass diets (450–600kg liveweight).
After a grazing event, close attention should be paid to: trampling, litter/bare soil and residuals, especially when beginning in this practice. Percentage bare soil can be recorded using a quadrat, explained here.
In drought, trampled residues keep soil moist, and protect open areas in sward from heat, and loss of structure, potentially facilitating germination of shed seed. Low utilisation rates facilitate rapid regrowth of grass plants by leaving plenty of “solar panels” for photosynthesis.
The pics above show some of the results of high stock density grazing. Evidence of trampling and high residuals is clear. With particular interest being from the moisture retained on the soil surface below litter.
Not visible in this image the fact that many areas of the pasture have been heavily utilised (perhaps 60% or more) and some areas are untouched (as well as being untrampled).
Residuals and trampling could be be increased, while at the same time reducing over utilisation of favoured grasses, by increasing the stock density further, say moving twice per day. In these most drying of times. This should have the effect of improving the speed of regrowth (keeping the pasture growing in this dry weather) while improving the sward composition (by reducing selective grazing of favoured plants).
This technique is typically carried-out in the dormant season, and can be combined with out-wintering.
It’s a good way to keep the manure and urine going on to the field (with reduced need for mucking-out or housing) while adding residues to the field -when forage is insufficient.
Drought situations also present similar conditions. In this case, where grass is running low (or when you want to just leave more residuals) you can put out stored feed. This will have the effect of trampling the residual hay into the soil, which feeds soil organisms and helps to cover soil, in patchy pastures.
Care should be taken to ration the bales offered, to roll out bales (ensuring an even covering — preventing clumpy dense patches that may be slow to breakdown) and to move animals across fodders by: mob grazing, rotational grazing (higher stock densities mean higher residuals).
These are just two possible techniques that have a proven track record in improving soil health, while supporting high numbers of stock. Increasing sward diversity, either with perennial pasture species or annual forages is another route. See examples presented below:
All these techniques can help to improve soil health and with it pasture health, which in drought translates to longer growth into the dry period and in mature systems, continued growth through the “dry season”.
While also facilitating longer out-wintering through better soil structure, that resists poaching, and providing additional available forage in the dormant season.
Convince Yourself: On-Farm Trials
These techniques are all novel, have a degree of nuance to them and of course can be applied alongside existing practice or together.
So, when implementing them there’s a real risk of disruption to the existing operation, and a need to master- or at least road-test these techniques.
For this reason, a period of experimentation is highly indicated.
The most appropriate vehicle for testing novel techniques is on-farm trials.
This could take the form of a “split field” trial – where one half of one field is managed using a new technique and the other half is managed as normal. This is monitored, using a set of tests that can be carried-out across both areas and the results compared. See below for examples.
Some knowledge of variability in soil types is useful. Wherever possible we’re trying to remove variables. So if one part of a field is a different soil type, attempt to split the field through or across that section. So as to have both soil types represented in both treatments.
Side-by-side experiments give the most immediate feedback.
This might start with a single field, perhaps one that is close to the yard – for easy access and monitoring, one that is perhaps average in condition – neither especially good nor bad. Then the two treatments can be compared side-by-side, without the variable of: soil type, aspect etc.
Another option could be to compare different stock densities in one half of the field to the other. For instance: standard rate vs double rate. Then compare: residuals, level of trampling, groundcover and potentially Brix or some soil health tests also. While of course being aware of body condition, fill and overall animal health.
Utilising grazing planning tools, like holistic planned grazing would assist this process. But basically it would mean that on each rotation around the farm when the animals arrived to the test field, the same management would be applied.
At the end of year soil health assessments should indicate success of the trialled technique.
This article is a short expose on the process you might go through to assess underlying (soil health) issues and what steps you might take to address or remedy these issues.
There is always more than one way to skin a cat, and I would be wary of presenting any of this information as gospel. Simply that it starts with what can be observed directly, what that tells us about the health of the soil, how we can measure this, and implementing management changes to address the underlying causes of these issues.
This is particularly pertinent during this drought period as everyone is “running out of grass” (in a year when winter rains were, if anything excessive).
The basic thesis is that a healthy soil with soak up all the rain the winter throws at it, let much of that pass through, slowly — thus eliminating flood pulses — but holding the remainder (interstitially) where it can be accessed by crops and pasture plants for growth into hot dry spells (when they can grow best), giving longer growth with less headaches.
Healthy soils irrigate crops in drought — by capturing & storing rainwater.
If you have any thoughts or questions, get in touch: email@example.com