REGENERATIVE AGRICULTURE / The Importance of Soil Organic Matter for Soil Fertility and the Health of the Great Barrier Reef

ANDRE LEU

Key Points

• There is a growing movement among cane farmers and graziers to improve soil health
• Soil health is a key component of regenerative agriculture
• The second regenerative cane farming forum is being held in Cairns on February 15-16, 2021 where the focus will be on soil health
• Check out the regen cane farming website: https://www.regencane.com.au and watch the video

Introduction

The Great Barrier Reef (GBR) is facing several major threats. The greatest is from climate change, however the next major threats are from runoff from farming along the catchment.

There have been many studies showing that agricultural runoff is causing numerous problems for the GBR. One of the most significant is the 2017 Scientific Consensus Statement. It was prepared by a multidisciplinary group of scientists with expertise in Great Barrier Reef water quality science and management, with oversight from the Reef Water Quality Independent Science Panel. The report clearly states that the main source of the primary pollutants (nutrients, fine sediments and pesticides) from Great Barrier Reef catchments is from diffuse sources of pollution from agriculture. These pollutants pose a risk to Great Barrier Reef coastal and marine ecosystems.

The consequences of these reports has been regulatory oversight programs for farmers in the GBR catchment. These have led to disputes between farmers, government and scientists with farmers stating the new requirements will lead to production losses and reduced income.

It doesn’t have to be a zero sum game – a trade-off between high yields and a healthy environment. It is possible to achieve both with correctly managed regenerative agricultural systems.

Soil and nutrient loss is expensive for the farmer as well as the environment. It is in everybody’s interest that they stay on farm.

Progressive cane farmers are focusing on soil health to tackle pathogens, reduce costs, improve productivity and to play their part in caring for the reef. The second Regenerative Cane Farming conference is being held in Cairns next month, February 15 – 16, 2021.

Information, master classes and advice can be found on the regen cane farming website https://www.regencane.com.au. The short video provides a great introduction.

Soil Organic Matter Reduces Runoff and Erosion

In last week’s article we looked at the science on how Soil Organic Matter (SOM) can capture and hold more water and build resilience to the increasing weather extremes caused by climate change.

In summary, the more porous structure of soil with good levels of SOM allows rainwater to quickly penetrate resulting in less water loss from run-off and higher levels of water capture. Long term scientific trials showed that soils with good levels of SOM were more resistant to erosion and had less leaching of nutrients.

Soil Organic Matter Improves Nutrient Availability

SOM stores 90 to 95% of the nitrogen in the soil, 15 to 80% of phosphorus and 50 to 20% of sulphur in the soil.  It has many sites that hold minerals and consequently dramatically increases the soil’s Total Exchange Capacity (TEC).  TEC is the measure of the amount of plant available nutrients that the soil can store. Think of it as the fuel tank. The bigger the tank, the further you can drive without refueling.

SOM stores cations, such as calcium, magnesium, potassium and all trace elements. It can store significantly higher amounts of anions (nitrates, sulphur, phosphorous) than clays.  Very importantly SOM prevents nutrients from leaching by holding on to them.

Most Plant Available Nutrients are Stored in the Soil Organic Matter

The majority of minerals that plants can access are stored in SOM. This means that soils with higher levels of SOM have higher levels of plant available nutrients and therefore higher levels of fertility and production.

There is a direct relationship between soil health and SOM. Higher levels of SOM have greater soil microbiomes because an important function of SOM is to feed, host and encourage the soil microbiome – the beneficial soil microorganisms that make minerals such as nitrogen, phosphorous, potassium and trace elements bio-available to our cash crops. Also SOM provides a host for beneficial microorganisms such as Trichoderma sps and penicillin sps which help control disease causing pathogens such as Rhizoctonia, Phytophthora, Amilleria, Pythium, etc.

The Soil Solution

SOM has largely been ignored by industrial agriculture, as it has preferred a hydroponic model of nutrition where plants are directly fed from dissolved mineral ions, mostly sourced from chemical fertilisers. This combination of dissolved mineral ions in the soil water is known as the soil solution. The plants absorb these dissolved minerals when they take up the soil solution into their roots to obtain water. In most agronomy texts this is seen as the only model for plants to absorb nutrients so the role of organic matter in the soil was seen as irrelevant. The trouble with this method is that many of these nutrients leach out, reducing farm fertility and causing problems downstream, such as in the Great Barrier Reef. Because they leach out, they have to be bought and applied every season, which is a substantial cost in farming systems.

Other Ways Plants Absorb Nutrients

Absorbing minerals through the soil solution is not the only method. Research shows that plants also obtain significant levels of nutrients from ion exchange, from absorbing larger organic molecules like chelates and amino acids, from direct symbiosis with micro-organisms, through the action of plant root enzymes and through the stomata in their leaves. Several of these critical areas of plant nutrition are clearly linked to the organic matter cycles in soils. Research shows that in natural ecosystems these other ways that plants absorb nutrients are responsible for a higher percentage of nutrients than the soil solution.

SOM also creates large complex organic molecules that allow minerals ions to adsorb (stick) to them for later use by the crop. This is very important for storing nutrients for later in the crop cycle when plants are fruiting/seeding and have their highest requirements for minerals. It is critical in areas that are inundated with periodic heavy rainfall as these organic carbon molecules prevent the mineral ions from leaching, keeping these nutrients on farm for later use by crops and preventing eutrophication of water catchments. The stable forms of organic matter such as humus and charcoal (biochar) acts as storage banks and buffers for these minerals. Humic, fulvic, ulmic acids and other organic acids such as carbonic and acetic acids from decay of organic matter help make locked up minerals available for use by plants by changing them into forms that plants can use. The term for this is that the minerals are bio-available.

Summary

Increasing soil organic matter is the best way to hold soil and nutrients on farm so that they are used to feed the crop rather than leaching out and damaging aquatic ecosystems such as the Great Barrier Reef. Studies show that farmers and graziers who increase their levels of SOM, use significantly less fertilisers to achieve high yields, thus reducing costs and increasing profitability.

THE NEXT SERIES OF ARTICLES on Regenerative Agriculture will give examples of farming and grazing systems that increase SOM and it’s many other benefits to make farming and grazing more productive and profitable.

ABOUT THE AUTHOR / André Leu is the International Director of Regeneration International, a global NGO that promotes food, farming and land use systems that regenerate and stabilise eco systems, climate systems, the health of the planet and people. He, along with the other founders of Regeneration International, started the world wide regenerative farming movement. André is the Author of the ‘Myths of Safe Pesticides’ and ‘Poisoning our Children’. He is the co-author with Dr Vandana Shiva of ‘Biodiversity, Agroecology, Regenerative Organic Agriculture – Sustainable Solutions for Hunger, Poverty and Climate Change’ . André first came to the Douglas Shire in 1971 and has, with his wife Julia, an organic tropical fruit farm in Lower Daintree.