The Natural Farmer · Summer 2014: Building Soil Carbon

1. Use plants to grow soil carbon. The most economical and effective way

This paper explains how atmospheric carbon is introduced into the soil and how it is stored in stable forms. It identifies the farming techniques that are responsible for the decline in soil carbon and gives alternative practices that do not damage carbon. Increasing soil carbon will ensure good production outcomes and farm profitability. Soil carbon, particularly the stable forms such as humus and glomalin, increases farm profitability by increasing yields, soil fertility, soil moisture retention, aeration, nitrogen fixation, mineral availability, disease suppression, soil tilth and general structure. It is the basis of healthy soil.

Organic agriculture also helps to reduce greenhouse gases by converting atmospheric carbon dioxide (CO2) into soil organic matter. Some forms of conventional agriculture have caused a massive decline in soil organic matter, due to oxidizing organic carbon by incorrect tillage, the overuse of nitrogen fertilizers and from topsoil loss through wind and water erosion. [Read more…]

Closeup of a cover crop cocktail comprised of Sorghum/sudangrass, hybrid pearl millet, cowpeas, soybeans, buckwheat, phacelia, hairy vetch, crimson clover, sunflowers, safflower, Winfred kale, Hunter turnips, brown top millet, persian clover. Photo courtesy Gabe Brown

The farm we’re on today was purchased by my wife’s parents back in 1956. They farmed conventionally — tillage, heavy tillage, half summer fallow, half small grains. They primarily grew spring wheat, oats, barley and, once in a great while, flax. So it was primarily cool-season grasses, half summer fallow, half crops. They also had a small cow/calf herd up until the late ’70s. In 1983 when I finished college, Shelly and I moved onto the place and entered the cow/calf business. Her folks were still operating the grain farming aspect of the operation and we did the cow/calf enterprise. Both my wife and I worked in town. During the late ’80s we started to divide up the pastures a little bit to do some rotational grazing as there were only three pastures on the operation when we arrived. That was our first foray, so to speak, into rotational grazing. [Read more…]

The capacity for appropriately managed soils to sequester atmospheric carbon is enormous. The world’s soils hold around three times as much carbon as the atmosphere and over four times as much carbon as the vegetation. Soil represents the largest carbon sink over which we have control.

When atmospheric carbon is sequestered in topsoil as organic carbon, it brings with it a wealth of environmental, productivity and quality of life benefits. An understanding of the ‘carbon cycle’ and the role of carbon in soils is essential to our understanding of life on earth.
[Read more…]

Over the last twenty plus years of intensive vegetable growing at Tobacco Road Farm, we have constantly sought ways to improve the health and vitality of our crops and soils. Much of the land grows vegetable crops year round so the intensity of production demands very careful soil care. To this end, soil amendments, fertilizers, inoculants, and compost have been carefully selected and applied over the years in no small degree.

Years of tillage, however, had left the field with a soil structure that was lacking. To reduce tillage damage to soil, techniques and tools were introduced: chisel plowing with shallow roto-tilling, permanent wheel tracks, use of sweeps and points for primary tillage, increased use of cover crops, for examples. Even under this minimum tillage difficulties still presented themselves: poor soil structure with low fungal activity, low calcium levels and high nitrogen and potassium in tissue analysis, weeds proliferation — especially galinsoga, excessive soil drying during summer dry periods, along with insect and disease pressure. [Read more…]

The soil foodweb of microflora and microfauna constitutes an underground engine of fundamental significance to plant productivity. Mycorrhizal fungi play a key role in the functioning of this foodweb, drawing down plant sugars derived from photosynthesis and providing much needed energy for the soil ecosystem. Mycorrhizal fungi also improve aggregate stability, enhance soil structure, build stable soil carbon, improve plant water use efficiency and increase the efficiency of utilization of important nutrients like phosphorus, sulphur and nitrogen.

Agricultural research tends to focus on conventionally managed crop and pasture lands where loss of diverse perennial groundcover and/or intensive use of agrochemicals, have dramatically reduced the number and diversity of soil flora and fauna, including beneficial microbes such as mycorrhizal fungi. As a result, the potential contribution of soil biology to agricultural productivity has been greatly underestimated.
[Read more…]

In this paired site comparison, parent material, slope, aspect, rainfall and farming enterprise are the same. Levels of soil carbon in both paddocks were originally the same.

On the Left Hand Side (LHS) is a 0-50 cm soil profile from a paddock in which groundcover has been actively managed (cropped and grazed) to enhance photosynthetic capacity.
[Read more…]

Q: Is it fair to say that carbon is the key ingredient that makes the difference between barren, unhealthy soil and fertile, healthy soil?

A: Yes. The glues and gums that hold soil particles together in the form of aggregates (small lumps) are made from carbon. Aggregation is what gives soil its tilth – making it well-structured, porous and friable. Porosity, in turn, improves the infiltration and storage of water. Carbon derived from plants also provides the energy for the soil biota essential to nutrient availability. Plants give to the soil, rather than take from it, as many people believe. The greatest threat to soil health is bare ground. When soil lies in bare fallow for long periods (eg. between crops) – or if it is over-grazed and has bare patches – it will deteriorate. Around 80-90% of plant nutrient acquisition is microbially mediated. If there’s no energy for the microbes (in the form of carbon) there will be very little nutrient – particularly vital trace elements – for plants. These deficiencies are passed along the food chain to animals and people.
[Read more…]

Wetlands, rivers, oceans, lakes, plants, decaying vegetation (especially in moist environments such as rainforests) – and a wide variety of creatures great and small – from termites to whales, have been producing methane for millions of years. The rumen, for example, evolved as an efficient way of digesting plant material around 90 million years ago.

Ruminants including buffalo, goats, wild sheep, camels, giraffes, reindeer, caribou, antelopes and bison existed in greater numbers prior to the Industrial Revolution than are present today. There would have been an overwhelming accumulation of methane in the atmosphere had not sources and sinks been able to cancel each other over past millennia.
[Read more…]

It is spring planting time, and most farmers are out planting seeds. The process of developing varieties of plant traits is as old as agriculture and farmers have been selecting seed from plants they like and replanting it for generations. They use open pollinated (OP) seed in this process, which in nature creates new varieties by spreading pollen to flowers randomly. When grown in isolation from cross-pollination with different same species, however, OP methods are designed to produce seed offspring very similar to the original parent population. OP seeds will grow ‘true-to-type’ generation after generation. Heirloom seeds are open-pollinated and have been handed down by seed savers for many years.
[Read more…]