Soil

What is Soil?

Soils are complex mixtures of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things. It forms at the surface of land – it is the “skin of the earth.” Soil is capable of supporting plant life and is vital to life on earth.

Soil, as formally defined in the Soil Science Society of America Glossary of Soil Science Terms, is:

1. The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
2. The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time.

So then, what is dirt? Dirt is what gets on our clothes or under our fingernails. It is soil that is out of place in our world – whether tracked inside by shoes or on our clothes. Dirt is also soil that has lost the characteristics that give it the ability to support life – it is “dead.”

Soil performs many critical functions in almost any ecosystem (whether a farm, forest, prairie, marsh, or suburban watershed). There are seven general roles that soils play:

1. Soils serve as media for growth of all kinds of plants.
2. Soils modify the atmosphere by emitting and absorbing gases (carbon dioxide, methane, water vapor, and the like) and dust.
3. Soils provide habitat for animals that live in the soil (such as groundhogs and mice) to organisms (such as bacteria and fungi), that account for most of the living things on Earth.
4. Soils absorb, hold, release, alter, and purify most of the water in terrestrial systems.
5. Soils process recycled nutrients, including carbon, so that living things can use them over and over again.
6. Soils serve as engineering media for construction of foundations, roadbeds, dams and buildings, and preserve or destroy artifacts of human endeavors.
7.  Soils act as a living filter to clean water before it moves into an aquifer.

Soil Profile

There are different types of soil, each with its own set of characteristics. Dig down deep into any soil, and you’ll see that it is made of layers, or horizons (O, A, E, B, C, R). Put the horizons together, and they form a soil profile. Like a biography, each profile tells a story about the life of a soil. Most soils have three major horizons (A, B, C) and some have an organic horizon (O).

The horizons are:

O – (humus or organic) Mostly organic matter such as decomposing leaves. The O horizon is thin in some soils, thick in others, and not present at all in others.
A - (topsoil) Mostly minerals from parent material with organic matter incorporated. A good material for plants and other organisms to live.
E – (eluviated) Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials – missing in some soils but often found in older soils and forest soils.
B – (subsoil) Rich in minerals that leached (moved down) from the A or E horizons and accumulated here.
C – (parent material) The deposit at Earth’s surface from which the soil developed.
R – (bedrock) A mass of rock such as granite, basalt, quartzite, limestone or sandstone that forms the parent material for some soils – if the bedrock is close enough to the surface to weather. This is not soil and is located under the C horizon.

Value of Soil

Social issues and soil quality

Nutrient cycling, water regulation, and other soil functions are normal process occurring in all ecosystems. From these functions come many benefits to humans, such as food production, water quality, and flood control, which have value economically or in improved quality of life. People can increase or decrease the value of soil benefits because land management choices affect soil functions. Thus, it is important to understand what benefits we derive from soil and their value so we can appreciate the importance of managing land in a way that maintains soil functions.

What are the social benefits of soil?

People tend to emphasize benefits with the most direct, private economic value. In rural areas, this is usually plant growth especially as  crops and rangeland, but also a recreation areas. In urban/suburban areas, the most direct economic benefits of soil relate to structural support for buildings, roads, and parking. Landscaping, gardening and parklands may also be valued economically.

Those are all on-site, short-term benefits. That is, the landowner who decides how to manage the soil also reaps the benefits (and costs) of those management decisions. In contrast, many important benefits are long-term or go beyond the land being managed. The landholders who make the management choices and pay the costs of managing land may not be the same people who are affected by the landholders decisions. Society should discuss the value of these off-site benefits and to what extent the land owner or society should pay to maintain these soil functions.

Public, off-site benefits of soil relate to the following resource issues:

Water quality of streams, lakes, oceans, and groundwater

Air quality, especially particulates

Greenhouses gases, including carbon dioxide, methane, and nitrous oxide

Biodiversity

Water flow and flood control

Sustainability and land productivity

Aesthetics

Summary of soil benefits

Soil Function	Benefit of Value to Humans
	On-site	Off-site
Nutrient cycling	Delivery of nutrients to plants Carbon storage improves a variety of soil functions	Enhances water and air quality Storage of N and C can reduce greenhouse gas emissions
Maintaining biodiversity and habitat	Supports the growth of crops, range land plants, and tress May increase resistance and resilience to stress  Reduces pesticide resistance	Helps maintain genetic diversity Supports wild species and reduces extinction rates Improves aesthetics of landscape
Water relations	Provides erosion control Allows on-site water recharge of streams and ponds Makes water available for plants and animals	Provides flood and sedimentation control Groundwater recharge
Filtering and buffering	Can maintain salts, metal and micronutrient levels within range tolerable to plants and animals	Improves water and air quality
Physical stability and support	Acts as a medium for plant growth  Supports buildings and roads	Nutrient Stores archaeological items Stores garbage
Multiple functions	Sustains productivity	Maintains or improves air and/or water quality

Conservation Agriculture in the Philippines

What is Conservation Agriculture (CA)

CA is a set of soil management practices that minimize the disruption of the soil's structure, composition and natural biodiversity. Despite high variability in the types of crops grown and specific management regimes, all forms of conservation agriculture share three core principles. These include:

• maintenance of permanent or semi-permanent soil cover (using either a previous crop residue or specifically growing a cover crop for this purpose);
• minimum soil disturbance through tillage (just enough to get the seed into the ground) ;
• regular crop rotations to help combat the various biotic constraints;

CA also uses or promotes where possible or needed various management practices listed below:

• utilization of green manures/cover crops (GMCC's) to produce the residue cover;
• no burning of crop residues;
• integrated disease and pest management;
• controlled/limited human and mechanical traffic over agricultural soils.

When these CA practices are used by farmers one of the major environmental benefits is reduction in fossil fuel use and greenhouse gas (GHG) emissions. But they also reduce the power/energy needs of farmers who use manual or animal powered systems.

Other Important Definitions

Conservation agriculture is largely the product of the collective efforts of a number of previous agricultural movements, including no-till agriculture, agroforestry, green manures/cover crops, direct planting/seeding, integrated pest management, and conservation tillage among many others. Yet CA is distinct from each of these so-called agricultural packages, even as it draws upon many of their core principles. This is because CA uses many of the available technologies in unison, resulting in something many believe to be much greater than the "sum of its parts."

The following terms are often confused with conservation agriculture:

• No-till (NT)/ Zero till (ZT)
  NT and ZT are technical components used in conservation agriculture that simply involve the absence of tillage/plowing operations on the soil. Crops are planted directly into a seedbed not tilled after harvesting the previous crop. Not everyone utilizing no-till technologies adopts other important components of CA. One major difference is that NT or ZT do not necessarily leave residue mulch. Some recent research data suggests this is vital, since without the residue mulch many of the benefits of CA are lost or decreased in value.

• Conservation tillage/ Minimum tillage/ Reduced tillage
  These are tillage operations that leave at least 30% of the soil surface covered by plant residues in order to increase water infiltration and cut down on soil erosion and runoff. Conservation tillage is an intermediate form of CA since it keeps some soil cover as residue from the previous crop. But some tillage is usually done. It developed as a management system after the “Dust Bowl” of the 1930’s in the Mid-West areas of the USA. It was found to reduce erosion by protecting the soil surface from wind and rain.

• Direct planting, direct drilling, plantio direto and siembra directa 
  These are terms used for ZT in other countries like Australia and South America. They use special equipment (e.g. NT drill) to plant seeds directly into crop residues left on the soil surface without preparing a seedbed beforehand.

• Direct seeding
  This term is usually associated with growing a rice crop like any other cereal crop without producing seedlings that are then transplanted into the main field. However, it can also be called NT or ZT if the seed are drilled without tillage.
  
  
• Organic farming
  Organic agriculture does not permit the use of synthetic chemicals to produce plant and animal products, relying instead on the management of soil organic matter (SOM) and biological processes. In some parts of the world, farms must be inspected and certified before their food products can be sold as organic, indicating that no synthetic chemicals were used in producing them. But organic farming uses the principles of CA to some extent and one objective similar to CA is to maintain and improve soil health. Unlike organic farming, CA does allow farmers to apply synthetic chemical fertilizers, fungicides, pesticides and herbicides. Many farmers rely on using these to control weed and pest problems, particularly during the early transition years. As soil physical, chemical and biological health improves over time; the use of agrichemicals can be significantly reduced or, in some cases, phased out entirely. 

CA is often used synonymously with ZT that is also believed to require heavy implements and large tractors. However, CA can be used by farmers with large or small holdings as follows:

• Manual systems can include practices that build hills (eg. The traditional Iroquois Indian “Three Sisters” system) or basins (W.African Zai system) or use hand held planters (jabbar planters or matracas) or planting sticks to get seed into the ground without tilling the soil.
• Animal traction systems can be as simple as making a furrow for placement of seed and micro-placement of nutrients to planters that can place seed and fertilizer even when residues are present.
• Tractor power systems range from low horsepower, two wheel tractor systems to large, high horsepower 4-wheel or more models. They can be low cost no-till seeders manufactured by local artisans building on existing seed drills or expensive machinery developed by large tractor implement companies.

Farmers who do not own tractors can also avail of the tractor powered systems through use of hiring or service providers, a common system for plowing in many developing countries.