Food And Soils

Modern Agriculture Effects:

Let's consider the principles of modern industrial agriculture and some of the impacts on the environment. Today large scale conventional agriculture as practices many countries, violates some of the laws and principles of ecology. The first thing that agriculture does, all agriculture does, is an annual disturbance. You come in and you plow the field and you turnover the soil. You're halting succession. Naturally plants go through maybe smaller to larger and from annuals to perennials and maybe from grasses to woody species, to trees. In large industrial agriculture, there's typically the removal of organic material that could be allowed to decompose and return nutrients to the soil.

A great deal of energy goes into growing, irrigating, fertilizing, harvesting, transporting, processing, and preparing food. That's not only happening on a commercial large scale agricultural farm, but there is a lot of that going on and possibly more of it because the large scale farm is using pesticides, fertilizers, that are coming from fossil fuels.

When considering any kind of agricultural method it's valuable to know the energy subsidy, which is the energy that is required for each calorie of food produced. So for example, when growing corn there might be four calories of fossil fuel energy expended to yield one calorie of corn. The energy subsidy for conventionally grown corn, we say is four calories.

That's for the tractors and the irrigation and the fertilizer and the pesticide and all the energy inputs, all the fossil fuel energy inputs that go into growing that corn. Small scale agriculture has a lower energy subsidy than industrial large scale agriculture. Beef has a higher energy subsidy than chicken or pork. Meat and poultry have a higher energy subsidy than plant based crops like lettuce or tomatoes for example. So each different food item and the way it's grown all factor into a given energy subsidy. Some energy intensive costs to agriculture that are most notable are as we said the production of fertilizers, which require large amounts of fossil fuel. Shipping food especially if it's transported by airplane, especially if the food must be kept refrigerated or frozen, all the shipping costs add to the energy subsidy.

Pumping water if there's a lot of irrigation that's going to involve using electricity. Coming from the grid, it's probably coming from fossil fuels. Irrigation, if not done properly, can lead to water logging. That occurs when soils remain wet or underwater for prolonged periods of time. Water logging impairs root growth, because roots can't get enough oxygen. Water logging also leads to anaerobic respiration in the soil and the release of potent greenhouse gases, both nitrous oxide and methane, potentially released from organic waterlogged soils. Another thing that happens with irrigation is salinization.

Salinization occurs when small amounts of salts in the irrigation water become highly concentrated on the soil surfaces through evaporation. So the water evaporates as pure H20 and the salts get left behind. And at some point those salts can reach toxic levels in the soils and impede plant growth. Intensive irrigation can also reduce the availability of water for other purposes. In commercial agriculture, typically uses monocultures. Large, even-spaced rows with one species that leads to minimal biodiversity. A biodiversity of one, that's quite small. It has improved agricultural productivity. It allows large areas of land to be planted, treated, and harvested all at the same time. But monocropping makes crops more vulnerable to pest invasions. A large expanse of the single crop species represents a vast food supply for a pest that specializes on that one crop. 

Monocropping can lead to more soil erosion than intercropping mixing different species of crops. Since  monocropping can lead to more soil erosion than intercropping mixing different species of crops. Since a large area is harvested all at the same time, a large expanse of soil will remain uncovered and unprotected for an extended period of time. Which could lead to water or wind corrosion of the soil. Mechanization is something going on in a great amount in large scale industrial agriculture. Fields must be plowed, planted, irrigated, weeded, protected from pests, harvested and then prepared for the next season.

Modern Agriculture Alternatives:

Given all the adverse consequences of large-scale industrial agriculture, a number of people in the United States and elsewhere in the world have looked at other forms of agriculture, organic agriculture, sustainable agriculture. Let's talk about them. 

Organic agriculture aspires to work with natural systems rather than dominate them. Some of the goals are to enhance biodiversity in the fields, keep as much organic matter and as many nutrients in the soil and on the farm as possible, maintain the soil by increasing the soil mass, the biological activity of organisms in the soil, and beneficial chemical properties of the soil. Organic agriculture avoids the use of synthetic fertilizers and synthetic pesticides. It tries to reduce as many adverse environmental effects of agriculture as possible. Organic agriculture still utilizes fossil fuels and mechanization. Organic agriculture still plows the soil. Organic agriculture can still be detrimental to the environment. Organically grown foods are often sold at a premium price, at least in some countries, and that is sometimes an advantage for the grower.

Sustainable agriculture that allow us to say that they are definitely more favorable and more desirable for the natural environment. Sustainable agriculture fulfills the need for food and fiber while enhancing the quality the soil, minimizing the use of non-renewable resources, and allowing economic viability for the farmer. So sustainable farming has even perhaps a broader-reaching set of goals than organic farming. A farmer practicing sustainable method wants to be able to continue agriculture on a given piece of land indefinitely.

Inter-cropping is when two or more crop species are planted in the same field at the same time to promote a synergistic interaction between them, so for example, corn and peas. Corn requires much nitrogen from the soils. And peas are a legume that fix nitrogen, or the microorganisms associated with the pea plants fix nitrogen in the soil. So growing those two plants together benefits each. Crop rotation is rotating the crop species in a field from one season to another. So using the same example, you might plant peas for one year in a field and there's a buildup of nitrogen. And then in the next year, you plant corn in that same location, and the corn makes use of that nitrogen that's been accumulating in the soil.

Agroforestry is intercropping trees with vegetables or other crops. So agroforestry is another kind of sustainable agriculture. The trees can act as a windbreak that catch soil that might have otherwise blown or washed away. And the trees can also be a crop themselves, say if you had fruit trees or if you cut down the tree and used the biomass for burning, for example.

Contour plowing is plowing and harvesting parallel to the topographic contours of the land. It helps prevent erosion by water, while still allowing for the practical advantages of plowing. So you try to keep as much of your land more or less level, and then step down to the next contour.

No-till agriculture is when farmers do not till their fields, leaving crop residues in the field between seasons. It's done in some sustainable agricultural practices. It prevents soil degradation, for intact roots hold the soil in place, reducing erosion. It reduces CO2 emissions because intact soil undergoes less oxidation; however, sometimes farmers need to use an herbicide to keep some of the undesirable species from overtaking the crop species. So that becomes a problem with no-till agriculture.

Genetically modified crop or genetically modified organism, which is often abbreviated as GMO. Genetically modified refers to a process in which a gene with a desirable trait from one organism is inserted into another organism. Genetically modified crops and livestock offer the possibility of greater yields and food quality. They do so by breeding strains of plants or animals that are resistant to drought or disease or perhaps cold temperatures. This increases productivity, maybe extends the growing season, and decreases the need for pesticides. GMOs are banned by the European Union but are abundantly used in the United States. In commercially grown crops in the United States, perhaps 85% to 90% of corn and soybeans and some of the other species that are commonly grown are GMO crops. GMOs appear to be safe for human consumption, although we can't say that for certain. And there do seem to be some concerns about few food allergies in some people.

There are some legitimate concerns that GMOs will breed with native plant or animal species and then escape to wild populations. We also need to consider the demand for land and water in different forms of agriculture. Modern industrial agriculture uses a large amount of land area. This use of land can lead to habitat fragmentation and halt succession of an entire landscape.

The maximum sustainable yield of a renewable resource is the maximum amount that can be harvested without compromising the future viability of that resource. So if we want to consider soil as a resource, we want to grow food in a sustainable way that doesn't compromise the ability of that soil to support food in the future. We might also consider that when we're talking about a wild population, the maximum harvest that can be removed from a population and can be replaced by that population. So we can consider that when we take trees down from a forest. We cut down trees. We don't want to cut down so many trees that we're removing nutrients, that we're eroding the soil, that we're preventing the regrowth of that forest.

The Soil Resource:

Soils are a membrane that cover much of the terrestrial surface on Earth. And they're made up of organic materials and mineral materials. Soils provide a variety of ecosystem services, such as supporting plant life and purifying water. The availability of Earth's resources was largely determined when the Earth was formed. Nearly all of the elements found on Earth today are as old as the planet itself. These elements still cycle through the Earth and through its ecosystems. It takes hundreds to thousands of years for soils to form.

Soil Forming Factors:

Soil is a dynamic mixture of both mineral and organic material. The mineral materials come from the weathering of rocks below the soil, or glacial till. Organic material comes from decomposing leaves, sticks, branches falling from above. A poorly developed soil, which we often call a young soil, tends to have less organic material than a more developed or mature soil. There are five factors that determine the properties of soils. These are called the soil-forming factors.

Parent material is one of the soil-forming factors. Parent material is the rock material from which the inorganic components of a soil are derived. Different soil types arise from different parent material.

Climate is the long-term accumulation of weather events, such as temperature and rainfall, in a given environment. And climate is an important soil-forming factor. Climate will have large effects on soil formation in some cases. For example, soils do not develop rapidly in very cold temperatures due to slow decomposition of organic matter and lack of movement, for example, when the soil is frozen.

Topography is another soil-forming factor. Topography is the surface slope and arrangement of a landscape. Soils that form on steep slopes are subject to erosion or sometimes more drastic material movements, such as landslides. Soils that form at the bottom of steep slopes are constantly accumulating material from higher elevations, making them quite deep.

Organisms, another important soil-forming factor  important soil-forming factor. Plants remove nutrients from soil and release elements and organic acids that speed the chemical weathering of soils and the rocks below the soils. Animals that tunnel and borough can, for example, mix soil, distributing mineral and organic material uniformly throughout a particular horizon. Termites and earthworms are other examples of organisms that influence soil, sometimes in drastic ways. And humans are organisms that impact soil.

Time is the last soil-forming factor. Soils require time to develop. As soils age, they develop a variety of characteristics, such as greater depth, different kinds of organic matter concentrations, and so on.

Horizons:

As soils form, they develop characteristic layers, or horizons. The composition of these different horizons depends largely on the soil-forming factors that we just described.

The O horizon, also called the organic horizon, is a layer of organic material, such as leaves, needles, and twigs, all in various stages of decomposition. The O horizon is most pronounced in forest soils and some grasslands.

The A horizon is present in soils that are naturally or artificially mixed. Also known as topsoil, the A horizon is a zone of organic material and mineral material that have been mixed together by earthworms, by a plow, or by some other means.

The E horizon is a zone of leaching or eluviation that forms under the O horizon, or less often under the A horizon. When present, it always appears above the B horizon, and it's only found in forests. Iron, aluminum, and dissolved organic acids from the overlying horizons are transported through and removed from the E horizon and then deposited in the B horizon.

The B horizon is commonly known as subsoil and is composed primarily of mineral material with much smaller amounts of organic material. If there are nutrients in the soil, they will be present in the B horizon.

The C horizon is the least weathered soil horizon, and it's very similar to the underlying parent material. If you want to know if a soil will produce a large crop yield or produce healthy trees, you can examine soil texture and soil chemical properties.

The texture of a soil is determined by the percentages of sand, silt, and clay it contains. To compare soil types, we can plot the percentages of sand, silt, and clay on something called a soil texture chart, a triangle-shaped diagram used in identifying and comparing soil types. Sand particles, the largest of the three components, pack together loosely, allowing for more water to pass through in a sandy soil. Clay particles, the smallest of the three components, pack together tightly, making it difficult for roots to penetrate the soil and for water to pass through the soil. The best agricultural soil is a mixture of sand, silt, and clay, allowing for balanced water drainage and nutrient retention. A loam is 40% sand, 40% silt, and 20% clay. And in many cases, that is the ideal agricultural soil.

Cation exchange capacity is the ability of a particular soil to adsorb and release cations. Cations are positively charged ions. Clays, one of the components of soil, have negatively charged outer surfaces. And the positively charged cations are attracted to the negatively charged outer surfaces of clays. The CEC of a soil is largely dependent on the amount and types of clay particles that are present. Soils with higher CECs may have more cations present in the soil, meaning they are better able to retain nutrients in the soil and release these nutrients to plants.

Base saturation is another important chemical property to understand. Base saturation is the proportion of soil bases to soil acids, expressed as a percentage. The soil bases are calcium, magnesium, potassium, and sodium. The first three of these are essential for plant growth. The soil acids are aluminum and hydrogen and are detrimental to plant growth. So the base saturation is the ratio of soil bases to the sum of soil bases and soil acids. And typically, this is expressed as a percent. Thus, when growing crops or trees, soils with high CEC and good base saturation are most likely to promote high productivity.

A diverse group of organisms inhabit soils and play vital roles in the cycling of materials in soil. 80% to 90% of life in soils is fungi, bacteria, and protozoan. Other organisms may include rodents, earthworms, slugs, snails, and insects. Soil degradation and erosion is also important to consider.

Soil degradation is the loss of some or all of the ability of soils to support plant growth. One of the main causes of soil degradation is soil erosion.

Soil erosion is caused by the disturbance of topsoil, followed by water or wind removing the top layers of soil. Topsoil can be disturbed by removing vegetation, plowing, or soil compaction. Another form of soil degradation is nutrient depletion. Soils can be depleted of its nutrients by intensive agriculture and excessive irrigation.