Managing pastures for soil health. Pasture management

Managing Pastures for Soil Health – Part 1

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As horse owners, we care for large herbivors and, in order to support them with the food they are designed to eat, we must take care of our land. Managing pastures for soil health by making the right land management decisions – ones that will create healthy pastures, and adequate food resources for our horses and for ourselves – is often easier said than done and certainly not something you can buy off the shelf. 

By understanding the ecosystem as a whole and its natural functions, you will be able to make management decisions that support the natural patterns. 

In a previous Equine Permaculture article, we focused on the element water – a crucial ingredient for growing plants. But, without nutrients present in soil, pasture plants won’t survive either. Soil stores nutrients and serves as a medium for growth. It is an anchor for roots and also holds water. Soil contains the air, water and food that provides a suitable place for plants to grow. But, let’s not forget the living organisms in soil – they also play an important role in providing nutrients and water to our plants!

Nature’s inherent complexity can be understood better by describing the four fundamental processes that operate in any ecosystem. These are:

  • Water cycle,
  • Mineral cycle,
  • Solar energy flow, and
  • Community dynamics (the patterns of change and development within communities of living organisms, such as our soil food web).

If you consciously modify any one of these processes, you automatically change all of them in some way because, in reality, they are only different aspects of the same thing.

It helps if you think of them as four different windows through which you can observe the same room – our ecosystem – as it functions.

In this article, we will focus on the ‘room’ that is our pasture and soil.

Window 1: water supply

One of the first fundamental processes we need to be aware of is the water cycle on our pastures.

Without water in our soils, organisms cannot survive and plants won’t grow. This becomes very obvious if you are dealing with compacted soils, which are not uncommon on horse properties!

Have a look at the image on Page 35 (download the pdf version of this article) – The water cycle. It depicts two situations:

  1. On the lefthand side, you see a typical pasture with compaction problems, which causes run-off – the water runs over the top and is not stored in the soil (nor does it seep into underground reservoirs).
  2. On the righthand side with good groundcover, good topsoil and a thriving underground community of organisms, any rainwater that falls is able to penetrate to the deeper soil layers and is slowly filtered to underground reservoirs.

The most important reason to manage our soil is to improve water infiltration. In a previous article (8 Ways to Manage Run-Off and Control Erosion on Horse Properties, which you can read at: http://bit.ly/2gondy5), we discussed how we can improve the water cycle and decompact soils on our horse property.

Window 2: minerals and nutrients

The second fundamental process that we need to consider to improve our soil and pasture health is known as the mineral or nutrient cycle.

There are at least 16 essential chemical elements for plant growth. Carbon, hydrogen and oxygen are obtained in large amounts from air and water, and make up the bulk of plant dry matter in the products of photosynthesis, but usually are not included as ‘nutrient’ elements. Nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, zinc, copper, boron, molybdenum and chlorine are obtained from the soil and required by all plants.

Sodium, silicon and nickel are essential elements for some plant species and, although not required, have positive or beneficial effects on the growth of other species. Cobalt is essential for nitrogen fixation by legumes.

Additional elements, such as selenium and iodine, are not required by plants, but can be important in plant nutrition, because they are essential nutrients for our horses, other animals and ourselves – all of whom consume plants.

Sources of plant nutrients in soil

Plants obtain mineral nutrients through root uptake from the soil solution (or via soil organisms). Sources of these soluble nutrients in soil include:

  • Decomposition of plant residues, animal remains and soil microorganisms,
  • Weathering of soil minerals,
  • Fertiliser applications,
  • Manures, composts, biosolids (sewage sludge), kelp (seaweed) and other organic amendments, such as food processing byproducts,
  • Nitrogen-fixation by legumes,
  • Ground rock products, including lime, rock phosphate and greensand,
  • Inorganic industrial byproducts, such as wood ash or coal ash,
  • Atmospheric deposition, such as nitrogen and sulfate from acid rain, or nitrogen-fixation by lightning discharges, and
  • Deposition of nutrient-rich sediment from erosion and flooding.

Losses of plant nutrients from soil

Mineral nutrients also can be lost from the soil system and become unavailable for plant uptake.

Nutrient losses are not just costly and wasteful, they can be a source of environmental contamination when they reach lakes, rivers and groundwater.

Nutrient losses occur through:

  • Runoff: Loss of dissolved nutrients in water moving across the soil surface.
  • Erosion: Loss of nutrients in or attached to soil particles that are removed from fields by wind or water movement.
  • Leaching: Loss of dissolved nutrients in water that moves down through the soil to groundwater or out of the field through drain lines.
  • Gaseous losses to the atmosphere: Primarily losses of different nitrogen forms through volatilisation and denitrification, which is the conversion of plant-available nitrate-N to N-gases that are unavailable to plants and easily lost from soil.
  • Crop/pasture removal: Plant uptake and removal of nutrients from the field in harvested products.

Therefore, an effective mineral cycle also requires a vegetation-covered and biologically-active soil.

If we look now at the image on the next two pages that is illustrating two soil conditions, we can see when the mineral cycle is effective (right side), many nutrients cycle between living plants and living soil continually.

In contrast, when soil is bare or exposed, and has a low biological activity (left side), nutrients become trapped at various points in the cycle, or are lost to wind and water erosion.

Nutrient cycling is never 100% efficient. There are always some losses or ‘leaks’ from the cycles, even natural ecosystems.

In farming systems, we typically buy minerals (and nutrients) in to get our output, which is either pasture, or is sold as a crop or hay.

In commercial farms, the balance between nutrient inputs and outputs is easily shifted in one direction or the other. Farms typically quantify the balance between inputs and outputs, and set up a nutrient budget.

Nutrient budgets can be determined at different scales – from single fields to whole farms, to landscapes and even broader regional areas. While this all seems very complicated, in short it means we just have to maintain soil fertility – to maximise nutrient cycling and nutrient-use efficiency.

The primary challenges we face in sustaining soil fertility are:

  • Reducing nutrient losses,
  • Maintaining or increasing nutrient storage capacity,
  • Promoting recycling of plant nutrients,
  • Applying additional nutrients in appropriate amounts, and
  • Supporting the development of healthy, vigorous root systems,
  • So, how do we accomplish this? There are many cultural practices that can be used to reach these goals, including:
  • Proper grazing management (rotational systems),
  • Growing cover crops (and crop rotations), such as Winter legume,
  • Handling manure as a valuable nutrient source,
  • Composting and using all available wastes or by-products,
  • Liming to maintain soil pH,
  • Applying supplemental fertilisers (organic, inorganic or chemical based), along with
  • Routine soil testing.

As Permaculture supports the use of organic farming practices, I will continue using this as an example for fertilisation.

Fertilising

Organic agriculture’s approach to fertilising is to feed the soil and let the soil feed the plant. Manure, compost, kelp and other organic fertilisers that supply multiple nutrients are emphasised, but inorganic materials are also important in this process.

Inorganic fertilisers for organic crop production must be from natural rock deposits and cannot be chemically processed.

These can also be used for pastures. They are relatively insoluble, with slow release of plant nutrients (whereas chemically processed inorganics are designed to be more soluble for plants and soils).

Ground minerals, like rock phosphate, especially colloidal or soft rock phosphate, greensand (K, P), gypsum (Ca, S), and limestone (Ca, Mg, pH) are commonly applied. Even less soluble products, like basalt and granite dust (K, Mg, Ca, trace-metal micronutrients) are also used.

Nutrient release from minerals with low solubility depends upon accelerated weathering reactions, which are stimulated by an active population of soil microbes, such as bacteria and fungi.

Living microorganisms themselves are also a major nutrient storage pool, so organic cultural practices to maintain soil fertility are designed to enhance soil biological activity.

Ideally, this microbial population functions both as a ‘sponge’ that soaks up excess nutrients and a nutrient source that releases nutrients when the population turns over, in addition to its role in promoting release of nutrients from minerals and decomposing organic matter. The phrase “feed the soil” refers to the importance of meeting the nutrient needs of these soil organisms and their subsequent roles in meeting the nutrient needs of plants. This brings us to the third window!

Window 3: living organisms – our soil food web

You never feed plants! You feed the soil through a process of breaking down of organic matter with soil organisms, such as earthworms and dung beetles, as well as microbes, bacteria and fungi.

The plant produces food (simple sugars) that is made available at the end of the root tip and in their leaves through the process of photosynthesis.

Plants form associations with soil biology, like bacteria and mycorrhizal fungi, to trade foods. The sugars are the food soil organisms need and will be made available to them in exchange for all essential nutrients, minerals and even water that is delivered through fungi.

Fungi

Let’s look at fungi as an example. When most people think of fungi, they think of mushrooms – and they also think they are plants. A characteristic of plants is they inhale carbon dioxide (CO2) and exhale oxygen (O2). Fungi actually breathe in oxygen (O2) and exhale Co2 like humans.

Fungi survived two mass extinctions – the last of which was 65 million years ago – and the only plants that survived that were the ones that formed association with fungi.

Plants send out chemical signals to fungi that’s says, for example, “I need magnesium” – an element essential to plant growth.

Fungi networks – chains of microscopic mycelium (fungi) strands that have been recorded up to 1–10km long and deep – can search out the required nutrient and deliver it to the plant in exchange for food (namely carbohydrates, such as glucose and sucrose) the fungi needs to survive and thrive.

Bacteria

Nitrogen-fixing bacteria are microorganisms capable of transforming atmospheric nitrogen into fixed nitrogen (inorganic compounds usable by plants).

More than 90% of all nitrogen fixation is effected by these organisms, which thus play an important role in the nitrogen cycle. In soils, we are interested in the symbiotic species, such as the Rhizobium, which is associated with leguminous plants (various members of the pea family and lucerne).

There are other species that are associated with certain types of dicotyledonous plants (flowering plants) or cereal grasses.

The symbiotic nitrogen-fixing bacteria invade the root hairs of host plants, where they multiply and stimulate formation of root nodules, enlargements of plant cells and bacteria in intimate association. Within the nodules, the bacteria convert free nitrogen to ammonia, which the host plant utilises for its development.

To ensure sufficient nodule formation and optimum growth of legumes, such as lucerne, beans, clovers, peas, soybeans, and seeds are usually inoculated with commercial cultures of appropriate Rhizobium species, especially in soils poor or lacking in the required bacterium.

Earthworms

Earthworms can substantially improve the quality and quantity of pasture production. Feeding and burrowing activities increase the cycling of soil nutrients and organic matter, and are beneficial to soil structure.

Earthworms are counted in spadeful’s of soil taken from the top 10cm of a 25cm2 block. Samples should only be collected when soil moisture is high (generally in late Winter or early Spring) as worms will retreat to greater depths when surface drying has commenced. Separate soil carefully to avoid splitting the worms and always count the worms twice to confirm the number.

Less than 10 earthworms per block is considered low, 15 moderate and more than 20 represents an abundant population. When soil is moist, most worms will be found near the surface in the root zone of the pasture.

Dung beetles

Dung beetles also play an important part in our pastures. Not only do they clean up horse poo, they do a great job of nutrient cycling!

Dung beetles feed on manure, use it to provide housing and feed for their young, and improve soil structure and forage growth in the pasture areas.

Adult dung beetles are drawn to manure by odour. Many are species-specific in that they prefer a certain type of animal manure. They will fly up to 16 km in search of just the right dung and can attack dung pats within seconds after they drop.

Some species will even hitch a ride near the tails of animals in anticipation of a deposit. Once drawn by the odour, the adults use the liquid contents of the manure (‘dung slurpie’) for their nourishment. Majority of dung beetles will even bring manure underground in burrows to lay eggs, which means aeration and fertilisation without even doing any work yourself!

They are important enough in manure and nutrient recycling, making them well deserving of the pasture manager’s attention. Thus, in our next article, we will look at farming strategies to support more living organisms in our soils.

Read our article on the amazing dung beetle here

Community dynamics

Bacteria, fungi, earthworms and dung beetles are just a selection of organisms we like to see in our pastures, there will be many other insects and organisms playing a critical role in creating soil, and cycling nutrients and water. We probably haven’t studied them all yet!

It is important to have variety of these organisms in your soils. With a few exceptions, natural communities strive to develop towards ever-greater complexity, and thus, stability.

When we humans start to develop pastures and crops that are monocultures, we reduce the complexity and defy principles of nature, so they only can be maintained by unnatural means – and then only temporarily.

In a low successional community, there are comparatively fewer species present. Amongst those present, it is usual for their populations to fluctuate widely and often very rapidly, due to weed and insect outbreaks for instance. These communities of organisms are usually very unstable and out of balance, as depicted to the left of Image A on the previous page.

On the other hand, in high successional conditions there are many species and, whilst number of individuals within each species tends to be lower, their relationships with each other lead to very stable populations. There is balance, as shown on the righthand side of Image A.

Within nature, succession is generally advance. You can see it as a coiled spring. When compressed, succession is retarded, but when the compressive force is released, the spring rapidly moves upwards towards a higher level.

It is likely you will see rapid changes in succession when you deliberately manage for them. This involves improving soil condition and water cycle, so you create the right environment for organisms to live in and do their job – breaking down organic mater to make more soil and feed plants! This brings us to window four!

Window 4: Energy flow

Blue (water) before green (plants) before black (soil).

We cannot create good soil without organic matter (plants), which needs to be broken down to humus-like material. But in order to grow plants, we need water.

In addition, the organisms that break down these plants require water as well. This means everything in our soil and pasture is dynamic, and energy is transferred from one to the other (never truly lost as we explained in our first part of the Equine Permaculture series). This is referred to as energy flow as shown in Image B on the left page.

Almost all life requires the energy that flows daily from the sun. The basic conversion of this solar energy to a usable form takes place through plant material on land and in water. That is why plants form the base of the energy pyramid depicted in this article.

As the energy passes from plants to whatever eats them and, in turn, eats the eaters of the plants, some energy is lost as heat, but eventually we end up with decay, which is returned to the soil and feeds the plants.

Most people understand this principle, but only a few see how this works to our advantage when we start thinking about pasture health. We need to capture as much solar energy, so we can create more or better soil – this even means utilising plant species that we may label as ‘weeds’.

If you want to improve your soil, you need to use weeds, let them capture this energy and slash the plants to return it to the soil. Once you are building soil, it will be easier to allow for succession with more preferred pasture species.

Summary

The hardest realisation of learning about working with natural systems and improving pasture health is that it’s not something you can buy off the shelf from the local rural supplies, spread it, spray it or water it in.

Soil health will be achieved when we restore the natural balance that allows the interaction of the soil food web as illustrated throughout this article.

Natural systems are a way of thinking – they are the only science recognised by nature. All we have to do is study it and support its natural patterns with the tools and practices available to us, such as:

  • Proper grazing management (rotational systems) to maintain grass cover,
  • De-compacting pastures using deep ripping equipment,
  • Handling manure as a valuable nutrient source, composting and mulching.

All of these techniques will enhance one or more of the fundamental processes discussed and, ultimately, will lead to better pastures and, therefore, better health for your horses!

Read the next part of this two-part series.

 

Mariette van den Berg, PhD, BAppSc (Hons), RAnNutr

Mariette van den Berg has a PhD in Equine Nutrition and Foraging Behaviour, is a RAnNutr equine nutritionist, a Certified Permaculture Designer and a dressage rider. She is the founder of MB Equine Services.

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