The great herd on the Arkansas [River] through which I passed ……. was, from my own observation, not less than 25 miles wide, and from reports of hunters and others it was about five days in passing a given point, or not less than 50 miles deep. From the top of Pawnee Rock I could see from 6 to 10 miles in almost every direction. This whole vast space was covered with buffalo, looking at a distance like one compact mass, the visual angle not permitting the ground to be seen. I have seen such a sight a great number of times, but never on so large a scale. -from “The Extermination of the American Bison” written by William T Hornaday in 1889.
The term ‘mob grazing’ means keeping large numbers of cattle on a small area of land and moving them frequently. The land then enjoys long periods of rest before the cattle return. It is mimicking how huge herds of wandering bison or wildebeest or caribou used to move through an area, trampling and grazing all around them before they departed, literally, for pastures new, leaving the grasses to grow, mature and reproduce once more.
Grass plants have evolved over millions of years under such grazing regimes and it is only during the past few hundred years that we have started using enclosures and fields, exposing the grasses to completely different grazing pressures, involving constant grazing and re-grazing of the immature plants. Grasses and other forage plants are poorly adapted to such treatments and consequently productivity is much reduced.
By emulating the huge herds of yesteryear, mob grazing encourages the grass plants to complete their full lifecycle, improving overall capture of sunlight and hence improving the land’s productivity. Additionally, mob grazed cattle trample significant quantities of forage onto the soil surface, feeding the microorganisms and other soil life and increasing the soil organic matter.
A happy side effect of allowing grasses to grow to maturity is that cattle are much healthier. They too have adapted to eat large amounts of bulky forage material with a good combination of fiber, protein and energy. The sheen on their coats and the firmness of their dung, coupled with the growth rates and overall health of their calves is testament to the benefits of mob grazing more mature pastures.
Incorporating cattle into an arable rotation offers real financial benefits. Soils become more fertile and, if the right mixture of forage is grown for grazing, significant savings in nitrogenous and other fertilizers can be made. The friability of soils also improves and both its water holding capacity (useful in a drought situation) and the rate of water infiltration (useful during periods of heavy rainfall) are greatly improved. The bottom line is that cattle in the rotation can improve your bottom line! Profitability is enhanced and the environment is much improved too.
The basic premise of mob grazing is one of high stocking densities – huge numbers of cattle bunched into tight groups – which are moved frequently with the aid of electric fences, trampling into the soil as much forage as they graze. The pasture land is then left, untouched, until it is fully recovered, giving opportunities for a whole host of plant species, that would otherwise be grazed out or out-competed, to establish in the sward.
Mob grazing simulates the vast herds of bison that used to migrate across the American plains, or the millions of wildebeest that still sweep over the African savannah, or the famous European auroch herds that grazed their way across our own continent thousands of years ago. The grass plant evolved alongside such migrations, adapting and specialising to a life cycle that included short, intense periods of grazing and trampling followed by long rest periods. I realised that it is only in the last few hundred years that grasses have been managed differently and that such management is detrimental to the long term productivity of our grasslands.
To understand exactly why mob grazing works, it is important to break down the process into its component parts. Firstly, the long recovery time between grazings allows the plant to establish a healthy root system. The roots grow deeper into the soil, bringing up hidden nutrients and making the plant more drought-hardy. Carbohydrates are also stored in the root and provide the energy vital to feed the new regrowth post-grazing. The long recovery time also leads to high volumes of above ground forage, a mixture of leaf, seed and stem.
The high stocking density means up to 50% of the plant is trampled to the ground by the animals. Cattle turned into a fully mature pasture graze the lush tops of the plants, eating seedheads and upper leaves full of energy and protein. The tougher, lower stems aretrodden onto the soil surface and these stalks act both as a mulch and as a food source for the soil microorganisms, building new soil in the process.
The cattle only eat the best parts of the plant before being moved onto a new area of ground, and this is why performance doesn’t suffer – they are not forced to eat the poorer stems et cetera – and their dung is tight and firm, reflecting the balanced diet they are getting.
As the organic matter rises and the soil becomes more fertile, the land grows more forage and stocking rates – the total carrying capacity of the land – increase. Neil Dennis, a Canadian farmer, improved his stocking rate fourfold. As he pithily observed, he’d gained the equivalent of another three farms at no extra cost, and is now harvesting and selling sunlight (in the form of beef) much more efficiently than under a set-stocked regime.
Another notable feature of mob grazing is that the permanent pastures don’t appear to become worn out. Conventional reseeding is unheard of, and both grasslands and their underlying soils are healthier than ever before. As practitioners regularly point out, it is farming in nature’s image, mimicking what has happened naturally for millions of years.
The Mob-Grazed Grass Plant
Grasses have been on earth for a very long time. Archaeologists believe the earliest grass pollens date back some 65 million years. It is one of the most successful plant species on the globe, with grass plains covering much of the temperate regions of our planet. It provides a food source to millions of animals, both wild and domesticated, as well as forming the bulk of the human diet.
In the last five or six million years, the grass plant has evolved in conjunction with the great grazing herds of the plains and is perfectly adapted to periodic defoliation and subsequent rest periods. A key adaptation is the location of the growing point on a grass plant, which is found in the crown of the plant, at or just above the soil surface. This protects it from potential damage by large grazing animals and allows it to regrow quickly once the herds move on.
Another feature of the grass plant is the ability to store carbohydrates in its roots. As a plant is defoliated, it uses these root energy reserves to create new leaves (which grow from the protected growing point). These leaves in turn capture energy from the sun through photosynthesis which both replenishes the root reserves and is used for respiration and reproduction by the plant.
Different species of grass differ in the timing of their growth through the year, but all follow a broadly similar growing pattern. Upon awakening from winter dormancy, they start to produce new vegetative leaves and tillers from their growing points. These leaves are like mini solar panels, all helping to intercept the sunlight that streams down to earth, converting it into chemically stored energy. Growth during this phase is rapid.
After a while, the plant has sufficient energy-capturing leaves to allow it to enter into its reproductive phase. At this point, it starts to grow reproductive tillers, bearing the familiar stem and seed heads. Vegetative growth slows down as the plant puts much of its energy into the reproductive phase. At the end of this phase, annual plants senesce and die, whereas perennial grass plants enter a brief stage of slow growth before a secondary vegetative growth stage begins at the back-end of the year.
Traditionally, livestock farmers graze plants during the vegetative stage, stopping the grass from throwing up reproductive stems and restarting the cycle.
However, many of the mob graziers I met believe grass plants become exhausted over time if they are not allowed occasionally to complete their natural life cycle – necessitating reseeding and other costly remedial work. They emphasized that a plant was only fully mature when it had completed its reproductive stage. This means that the recovery phase – the period when animals are kept away from the plant – can be anything up to 100 days or longer, depending on climate, rainfall, time of year, latitude etc.
They are not averse to grazing a plant before it reaches maturity but they believe firmly that occasionally the grass plant has to be allowed to follow through all the phases of its lifecycle to remain healthy. As they regularly pointed out, grasses have evolved under a system of rapid and extreme defoliation followed by many months of uninterrupted growth and grow best under such systems.
An interesting result of allowing the plant to reach maturity is the vast quantities of forage that are produced per hectare. Some of the warm-season, or C4 grasses I saw in North America stood higher than the cows, at over six feet tall and even here in the UK, stems of between four and five feet are achievable.
Equally interesting is the claim that underground roots mirror the above ground forage. The picture (pg 8) shows an experiment in the US where bunchgrasses were defoliated at different heights, demonstrating quite clearly this phenomenon. Allowing plants to mature fully results in the formation of large, complex and deep root systems. These are able to extract vital minerals from lower down in the soil strata, they are better able to reach water supplies during a drought and, when they die off, they leave huge amounts of valuable organic matter in the earth.
The huge amounts of above ground forage also capture large quantities of sunlight. As farmers, it is important to remember that this is what we are in the business of doing. We are selling sunlight (in the form of meat, milk, grains, etc.) to the rest of the world. The more efficiently we can capture the sun’s energy, (which freely streams down to earth every day) the more people we will feed and the more money we will make!
The seed heads on a grass plant are also full of carbohydrate and hence concentrated bundles of energy – admittedly not as plump as cultivated wheat or barley grains, but nevertheless they are extremely nutritious. Mob grazed cows, turned in to a mature pasture, strip the seed heads off the plant with relish. It’s like self-feeding grain to the cattle out in the field!
Finally, allowing grass plants to reach maturity and set seed means the pasture effectively renews itself each year. A significant number of the grass seeds will be shed onto the ground. Some will fail to germinate and will decompose (feeding the soil biota), some will be eaten before they reach the soil, but a significant number each year will land on the soil or on a cowpat and will germinate, constantly refreshing and reseeding the pasture, for free!
The huge amounts of both above- and below-ground organic matter produced when a grass plant is allowed to reach full maturity is a valuable source of energy and nutrients for soil organisms. A healthy, living soil contains billions of bacteria, fungi, nematodes, arthropods and protozoa.
Humus is a catch-all term often used to describe much of the soil organic matter. In its truest sense, it is an incredibly stable carbon compound which has amazing properties. It has many negatively charged sites within its molecular structure and these negative charges ‘hold on’ to the positively charged plant nutrients (eg nitrogen, phosphorus, potassium and other important trace elements). It has huge water holding capacity, acting like a sponge and thus both allows heavy rainfall to penetrate the earth (rather than flowing away into streams and rivers) and then holds on to the moisture, making it available to be used by the plants during periods of low rainfall and drought.
Another, recently discovered, substance is glomalin. It is critically important to the formation of good soil structure, being a type of ‘glue-like’ substance which holds soil particles together in peds and clods. It is believed to be exuded by the mycorrhizal fungi which live in a symbiotic relationship with healthy roots. Glomalin also makes us realize how little we know about the earth beneath our feet: despite the key role it plays, glomalin was only discovered by soil scientists in the mid-1990s. How many more key ‘players’ in the make-up of our soils are still waiting to be found?
The ratio of bacteria to fungi varied according to the land use. For example, heavily cultivated arable soils growing large amounts of annual monocultures will be predominantly bacteria-dominated. Conversely, undisturbed woodland soils with high levels of lignified material falling onto the soil surface will be populated by huge amounts of fungi and very few bacteria.
Permanent grassland sits somewhere in the middle, tending to have a balance of both bacteria and fungi in its soils. In a bacteria-dominated soil, annual weeds thrive. In a fungal soil, perennial woody shrubs do best. This allows us, as land managers, to study the weed species growing in our swards and fields to determine what is out of balance. In theory, if we get closer to the desirable ratios for grasslands, then desirable grass species will thrive and less desirable ‘weed’ species will not!
The Benefits of Organic Matter
Using mob grazing to build organic matter in your soils can have a dramatic effect both on the appearance and the productivity of your land. I have already referred to the capacity soil organic matter has for holding onto nutrients, making them more available for the growing plants. I have also mentioned the way organic matter improves the structure of the soil, ‘glueing’ particles together which not only improves water infiltration but also reduces soil erosion. In addition, this well-structured, high organic matter-containing soil has a much greater water holding capacity than soils with poor levels of organic matter – 1g of carbon can hold between 4g and 5g of water. This slows down the speed that rains pass through and over the soils, improving the water cycle and making more water available to the plant for longer during times of drought.
On Gabe Brown’s farm in North Dakota, where he has been mob grazing and growing cocktail cover crops for over fifteen years, I was handed a steel rod, some 1.2m long and with a small handle on top. Gabe asked me to try to push it into the ground. To my amazement, the rod slid into the ground like a knife into butter, all the way to the handle. Gabe explained that this was because his soils had excellent structure to great depths as a result of his focus on soil improvement and adoption of all available techniques to enhance his soils.
On Menoken Farms, also in North Dakota, Jay Fuhrer showed me the effect of combining mob grazing and cocktail cover crop mixtures to build organic matter, and the changes were equally dramatic. Grey sands were converted into a dark, rich, friable soil within just a few years.
Perhaps the most visually dramatic changes I saw, partly due to the scale of the change and the fact that it was a work in progress, was on Phil and Jill Jerde’s ranch in South Dakota. The Jerde family farm a huge herd of buffalo, using holistically planned mob grazing to utilize the grass efficiently and improve the ranch soils. The results, in an otherwise dry and sparse high prairie, were nothing short of amazing. Vegetation was starting to appear in the natural draws, or valleys, in the landscape and more productive forage plants were starting to colonize this newly fertile soil.
The water cycle was starting to function again. The infrequent rainfall was no longer running off the land and being lost, but instead was being absorbed and slowly seeping through the soil profile.
There were hundreds of draws and valleys on the Jerde ranch that were showing signs of being transformed. Those on lower land were much further advanced, with the green, lush forage starting to spread high up the sides of the draws. Draws much higher up were only just starting to show signs of improvement, with small, isolated patches of more productive grasses and other plants growing in the base of the draw.
The beauty of this is that as more grasses are produced, there is more organic matter available to be trampled into the soil. This further improves soil fertility and water holding capacity and so the rate of improvement increases still further.
The improvements were most clearly visible when standing alongside the boundary fence on the Jerde’s ranch, comparing their grassland with that of their neighbours. The improvements were tangible and were all a result of improving the soil organic matter content.