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Big farms, “low yields” and extensive farming might not be the setting where we would expect soil health and function to be promoted strongly. Yet, the dry and mixed farming countryside of North Dakota provided us with the setting for a wonderful review of soil, its purpose and function.
Jay Fuhrer is a soil health specialist involved in conservation with the United States Department of Agriculture (USDA). Jay told us that many soils in the US had taken a battering in recent decades from reducing fertility, falling organic matter levels and excessive cultivation, which resulted in problems like the dust bowl and left the soil subject to water erosion.
Soil-related problems have not gone away. There are still serious issues, with water erosion and nutrient and chemical contamination in the US. With the Mississippi and Missouri rivers running through the bulk of central US, it is not surprising that they are picking up nutrients from this intensively farmed region and transferring them to the Gulf, where they produce eutrophic blooms.
Emphasis was placed on soil physical properties to make soils more durable and to enable them to hold the nutrients and water that drive agricultural productivity. Jay was only one of a number of people we met with a similar outlook on soil. And improving soil also had a big environmental benefit.
Natural soil development
Jay told us that the drive to improve soils looked initially at how they were formed. For prairie land in the Dakotas, that was relatively easy. These were Indian regions, where tall prairie grasses dominated the landscape and herds of buffalo roamed through, perhaps twice a year. This knowledge was highly influential in the subsequent actions of scientists and conservationists.
Ultimately, it was about leaving vegetation behind following grazing or cropping. Across this region, pastures or range land tend to only be grazed once or twice and the advice evolved to allow the grasses to grow tall (perhaps about 30in), but only allow animals to graze off the top. This left a lot of vegetation in situ which acted to hold and collect snow over winter and reduce the direct impact of the summer sun on the soil.
For crop farmers, it brought about a change in the way residue is managed. Crops were being no-till drilled, with straw either removed or frequently chopped. As with the grass, the objective was to leave standing residue as much as possible.
Again, this had the benefit of being able to hold snow over winter and allowing the thaw water to penetrate into the soil. This then had the double benefit of reducing flooding and soil erosion risks, while providing more soil moisture to support crop growth.
The theory is easy. The objective was moisture collection, percolation and preservation. It was obvious that they were happy to see the residue from the two or three previous crops when inspecting the current crop. And their drilling machinery was designed to cope. Tall stubbles will always break down in time and then they contribute to the soil ecosystem.
As is the case everywhere, having organic debris on the surface leads to increased biological activity with the associated benefits of carbon sequestration, nutrient recycling and moisture retention – plus stable soil structure and extra productivity.
Shaking soil from a maize plant, Jay pointed out that some soil always clings to the roots. He suggested that this is a plant sugars/glue effect, as well as root hairs. He said that roots are always high in sugars and actually encouraged us to have a chew. He was right. Basically, growing plant roots give off exudates (mainly sugars) which help feed the soil biology. This biology, in turn, mineralises nutrients and builds soil aggregates.
Multiple crops benefit structure
He went on the say that plant glues are hugely important for the stability of soil structure. He indicated that each plant type produces a somewhat different glue, but that together these contribute enormously to the durability of soil structure. And well-structured soils improve trafficability, especially in wet conditions.
The more types of plants that a farmer grows, the stronger will be the resultant soil structure. Perhaps this goes some way to explaining why it is difficult to keep soil structure intact in monocultures, whether that be land under cereals or ryegrass. He hinted that a soil will benefit from having up to 10 different crop types. Whether these substances be direct glues or other substances that are converted to binding products with the help of the biological army is irrelevant – the net effect is a stronger soil.
So rotation must then form part of a sustainable farming system. However, very few farmers anywhere have the option to produce up to 10 commercially economic crops and that is no different in the Dakotas. Advisers there suggest that, where possible, a rotation should include a crop from four categories:
Part of the drive for rotation is to not have the soil bare for any length of time. Other benefits relate to standard husbandry issues. But how can they fit up to 10 different crop types?
The answer is quite simple. The majority of the crop types are provided by a catch crop mix. In this way, they can grow a number of species at the same time. And, depending on the location and farming system, they can opt to plant the catch crop as an additional element of the rotation (a five-year rotation).
Where farms have both crops and animals, the catch crop is frequently used as a source of winter feed. It is common to graze these crops over winter on frozen ground with snow on top. This way, they preserve all of the animal manure in situ on the land and also the urine, as well as any crop material.
The challenge is to help build soil organic matter and the same processes normally build fertility and structure. But this is a slow process and Jay indicated that it normally takes up to 12 years to increase soil organic matter by 1%.
He went on to say that if you continue building, you will eventually hit an equilibrium level. However, with the use of catch crops one can then help to raise the level of this equilibrium.
Rotation and weeds
Another of the benefits reported for rotation was the ability to significantly affect weeds. Seeing cereal fields completely free of wild oats was a welcome sight. Farmers told us that they did have this problem but that it has largely disappeared since they returned to active rotations.
Rotations act on weeds in different ways. The simplest is the alternation of spring and winter planting – favouring some in one year and then favouring others and not favouring the same ones all the time. They also act through the fact that some crops enhance the germination of specific species and if these can be controlled, then weed seed numbers are reduced.
Where a number of crop species are used in a catch or cover crop, there is a greater likelihood that different ones will affect different weed types.
There were very few Roundup Ready crops in that area to help with overall weed control. Indeed, many recognised in advance the inevitable consequence of resistance development following the continued use of any one herbicide.
Soils workshop
Jay Fuhrer operates a mobile workshop for the Natural Resource Conservation Service (NRCS). This is a soils demonstration unit, which he takes all over the US. He conducted a number of simple farm office-type tests which delivered very visual and definite messages.
The first demonstration was a simple soil stability test. He had two soil clods about the size of a lump of coal, which were dried out for the test. Then he had two big clear plastic jars and he made two hanging U-shaped suspension devices made from light steel mesh.
He put one of the clods on each piece of mesh and immersed them into the jars, one into each (see picture one).
Because the soil was dry, most or all of the moisture present was removed. When the soil was immersed in water, the air spaces initially filled with water to push out air bubbles. One of the soil lumps was from a weak continuously tilled soil; the other was from a very well-managed field of prairie grassland.
Shortly after the weak soil was immersed, we could see small particles falling through the mesh and the water became murky. The whole clod disintegrated in about 20 minutes and fell through the mesh. The good soil never lost even one particle in 90 minutes.
The difference is the soil structure and Jay said that it was the various plant glues that were acting to hold the structure in place to resist the consequence of the water.
In a weak and beaten soil, it is common for the aggregates to break easily and clog up the drainage pores. This makes it difficult or impossible for water to get away down into the soil.
Jay used two different tests to demonstrate this and one is shown in picture two. Both tests simulated rainfall coming in on top, but the weak soil sealed to prevent water penetration. The better-structured soil allowed most of the water to pass through and a proportion was retained in the soil.
One of the stated benefits of good soil structure and high soil organic matter is that water can penetrate more freely. Good soils actually hold more water even though percolation is easier.
Another demonstration sprayed artificial rain across intact sods from five differently managed soils. The device enabled Jay to apply a given quantity of intense rainfall (1in) and he could measure the water that came off the top and the water that went through the different sods (see picture three).
The really good soil on the right had little come off the top, but it also had much less go through during the test. The very worn tillage soil (second from left) smeared on top and most of the water came from surface runoff which caried soil with it. Other soils produce intermediary results.
The great benefit of healthy well-structured soils is that they allow water to percolate more easily. And, whether we are in America or Europe, improved percolation slows the surface movement of water to significantly reduce the risk of flooding and soil erosion.
That’s the prize that everyone wants. While percolation is enhanced by better structure and higher organic matter, nutrient leaching risk is also reduced. Jay tested the nitrate content of the water at the end of these tests using test strips.
Given that a healthy soil has high organic matter and biological activity, Jay used a test – the SOLVITA test – to measure this activity. The bugs in the soil must respire and when they do this, they give off heat and carbon dioxide. The test involves placing a soil sample in a sealed container with a test strip to measure CO2 production. The test uses a fresh soil sample and the carbon dioxide released is taken as an indirect measure of the level of life in the soil. This also provides a measure of potential nutrient recycling.
Farm visits
Later that day, Jay took us out to two farms which were practising improved land and soil management. Both farms had crops and grassland and both were benefiting from higher grass and crop output with reduced production cost.
Mike and Becky Small breed Angus cattle with some crops. Having spent some years fighting the uphill battle for farm income, they changed their farming system in 2008. Soil health and environment became a targeted focus for the whole family. Basically generational transfer is now seen as a change of stewardship rather than just land transfer.
The grassland was fenced into mainly 35- to 45-acre paddocks (some bigger) to help grassland utilisation. The soil was naturally sandy, so soil organic matter was a significant focus. Eight years in, the farm is now carrying 320 cows rather than 220. And even with the bigger number, the cows stay out on the land longer, leaving less need for winter feed and less manure to handle. He needs about 120 days of winter feed and much of this is fed on the pastures.
His crops are also benefiting from the improved soil, but when we visited, his oats had been hammered by a hail storm that passed through a few days earlier. The crops grown are oats, alfalfa, maize and mixed crops and they are all fed on the farm. Annual rainfall is around 16in and there can be up to 46in of snow during winter.
On one of the grass farms, owned by Todd McPeak, Jay did a water percolation test in the field. This should be of interest to farmers here practising intensive paddock grazing, as good percolation is key to good utilisation.
Jay drove a piece of 6in aluminium pipe, with a bevelled edge, down about 2in into the ground. He then poured 444ml (the equivalent of 1in of rain) into the pipe. But first he lined the pipe with cling film, so he could remove it instantly to get an accurate measure of the time it took for all the water to percolate.
In this field, it took about 13 seconds for the water to disappear. This was actually the same soil that was used in the test in picture one, which was very stable in water. He then repeated the test a second time with the first inch of water already in the soil. The second inch of water took slightly longer and the two together proved a good indication of the ability of a soil to cope with the extreme rainfall events which can occur in that part of the world.
Todd runs a very impressive cattle operation and good grassland management has given him an additional 75 days of feed per year. Improved soil health increased his hay yield on 75 acres from 155 round bales (660kg/bale) initially to 274 bales in 2015. Given his winter conditions, plus the risk of drought, his aim is to get his feeding days down to four months from 6.5 months per annum. He also explained some of the challenges of out-wintering cattle and keeping water flowing when temperature gets down to -26°C.
This was a very informative day and left all present with an image of what soil is expected to do and how management plays a critical role in the properties that a soil will exhibit.
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