Understanding Soil Fertility and Why It's Important

Soil isn't dirt, it's a living, breathing ecosystem that sustains life on the planet. Among the many attributes of soil, fertility is one of the most critical ones for agriculture, gardening, and food production overall. An understanding of soil fertility and why it's important can enlighten farmers, gardeners, and policymakers to make informed decisions for a sustainable future.

What is Soil Fertility?

Soil fertility is the soil's ability to provide required nutrients to plants in adequate amounts and proper proportions for normal growth. Fertile soil encourages plant growth by furnishing nutrients like nitrogen (N), phosphorus (P), potassium (K), calcium, magnesium, and trace minerals. It also has a balanced pH, adequate water-holding capacity, and a vibrant population of microorganisms.

Major Components of Soil Fertility

1. Nutrient Availability

·         Fertile soil contains the proper balance of macro and micronutrients for plant growth.

·         Nutrients are in a plant-available form.

2. Soil Organic Matter

·         Organic matter raises soil structure, water-holding capacity, and microbial activity.

·         Decomposed plant and animal residue (humus) builds soil fertility and longevity.

3. Soil pH Balance

·         Soil pH affects the solubility and availability of nutrients.

·         Most crops grow well in a slightly acidic to neutral pH (6.0 – 7.5).

4. Soil Texture and Structure

·         Physical composition (sand, silt, clay) affects drainage, aeration, and root penetration.

·         Well-structured soil ensures efficient delivery of water and nutrients to plant roots.

5. Biological Activity

·         Earthworms, fungi, and bacteria participate in the decomposition of organic matter and nutrient cycling.

·         Healthy microbial activity promotes plant health and disease resistance.

Why is Soil Fertility Important?

1. Increases Agricultural Productivity

·         Fertile soil increases crop yields and ensures a constant food supply.

·         It reduces the application of artificial fertilizers, which are harmful to the environment.

2. Promotes Environmental Sustainability

·         Healthy soil reduces erosion, increases water retention, and acts as a carbon sink.

·         It promotes biodiversity and maintains a balanced ecosystem.

3. Economic Advantages

·         Fertile land maintains farmers' livelihoods and national economies.

·         Improved yields and healthier crops mean better revenue and food security.

4. Fights Climate Change

·         Fertile soil sequesters carbon and reduces greenhouse gas emissions.

·         Cover cropping and composting make soil resilient to extreme weather.

Strategies to Improve and Maintain Soil Fertility

1.      Crop Rotation and Cover Cropping

·         Prevents nutrient depletion and breaks pest cycles.

·         Adds nitrogen and organic matter to the soil.

2.      Composting and Organic Amendments

·         Naturally returns nutrients to the soil.

·         Improves soil texture and fertility over time.

3.      Reduced Tillage

·         Maintains soil structure and microbial life.

·         Minimizes erosion and maintains organic matter.

4 Adequate Irrigation and Drainage

·         Provides nutrients without waterlogging the roots.

·         Keeps moisture levels in balance.

Soil fertility is the foundation of sustainable agriculture and food security. In understanding and nurturing the soil beneath our feet, we not only improve crop production but also protect the environment and future generations. Whether you are a farmer, home gardener, or simply someone who cares about the planet, taking steps to preserve and improve soil fertility is one that we all have an obligation to do.

 

Understanding Soil Fertility and Why It's Important

PROCESSES INVOLVED AND HOW TO MAKE A SOIL PROFILE PIT

Pit method of soil profile pit

Dig a soil pit approximately 1 meter deep or until an impenetrable layer is reached and as big around as is necessary to easily observe all of the soil horizons from the bottom to the top of the pit which is approximately 1.5 x 1.5 m wide. In some situations, people may be able to perform the soil characterization measurements at a site where the soil profile has already been exposed through human or natural action such as a road cut or the side of a ravine. In these instances, teachers need to make sure that the site is safe for individuals and there is no objection to them scraping the surface soil away to expose a fresh soil face.

• Digging is much easier when the soil is moist. If possible, plan digging shortly after a rain.
• As soil is removed from the pit, place it carefully in piles representing each of the natural layers as they occur in the profile.
• The removed soil can be put on a tarp or other type of plastic sheet to make cleaning up the site easier.
• Cover piles of removed soil with plastic to prevent them from eroding away.
• Contact a local soil scientist or other professional who may be willing to assist you in digging a pit and help to describe the characteristics of the soil profile.
• When finished with the soil characterization measurements, the horizons need to be replaced into the soil pit in reverse order.

Defining the soil characterization site

• Give the site a name or number. Then record it on the soil characterization sheet.
• Determine and record the location of the pit
• Describe the area including the slope and aspect of the soil pit area.
• Describe and record the cover type of the site, e.g., bare soil, rocks, grass, shrubs, trees, or other.
• Describe and record the type of parent material from which the soil was formed at the site such as soil bedrock, organic material, construction material, marine, lake, stream, wind, glaciers, volcanoes, loose materials on slope moved by gravity, or other.
• Describe and record the land use at the site such as urban, agricultural, recreation, wilderness, or other.

Procedures involved

• Use a trowel to scrape a few centimeters of soil off of the profile to expose a fresh soil face.
• Determine whether the soil profile is moist, wet, or dry. If the soil profile is dry, moisten it with the spray mist bottle.
• Start at the top of the profile and observe the characteristics of the soil moving towards the bottom of the profile. Mark each layer at the top and bottom of each horizon. Be sure there is a consensus regarding the definition of the layer boundaries.
• Look carefully at the soil profile for distinguishing characteristics such as color, texture, shapes, roots, rocks, small dark nodules, worms, small animals, insects, and worm channels. These observations will help to define the horizons.
• Measure the top and bottom depth of each horizon beginning at the top of the profile. Start with the meter stick or tape measure at 0 cm at the top of the profile. Note the depths at which each horizon starts and ends.
• Record the top and bottom depth of each horizon.

Soil structure

This is the shape that soils take based on physical and chemical properties. Each individual lump of soil structure is called a ped. Look at a sample of undisturbed soil from each layer of your pit and examine the soil structure. Structure refers to the natural shape of groups of soil particles or aggregates (peds) in the soil.

UTILIZATION OF TOOLS AND THE TECHNIQUES INVOLVE IN BUILDING UP SOIL

Where feasible, bulky organic amendments may be added to supply both organic matter and plant nutrients. It is particularly useful to account for nutrients where organic fertilizers and amendments are utilized. Start with a soil test and a nutrient analysis of the material you are applying. Knowing the amount of nutrients needed to supply the crop to be grown guides the amount of amendment applied and can lead to significant reductions in fertilizer purchase. The nutrient composition of organic materials can be variable, which is all the more reason to determine the amount you have with appropriate testing. In addition to containing the major plant nutrients, organic fertilizers can supply many essential micronutrients. Proper calibration of the spreading equipment is also important to ensure accurate application rates of it.

Reduce tillage

While tillage has become common to many production systems, its effects on the soil can be counter-productive. Tillage smoothes the soil surface and reduces natural soil aggregation and earthworm channels. Porosity and water infiltration are decreased following most tillage operations. Plow pans may develop in many situations. Tilled soils have much higher erosion rates than soils left covered with crop residue.

Minimize synthetic nitrogen fertilizer use

Animal manure is a good way to add both carbon and nitrogen to the soil. When nitrogen fertilizer is used, try to do it at a time when a heavy crop residue is going onto the soil, too. For example, a rotation of corn, beans, and wheat would do well with nitrogen added after the corn residue was rolled down or lightly tilled in. Spring planted soybeans would require no nitrogen. A small amount of nitrogen could be applied in the fall for the wheat. Following the wheat crop, a legume winter-annual cover crop could be planted. In the spring, when the cover crop is taken out, nitrogen rates for the corn would be reduced to account for the nitrogen in the legume. The addition of legume residue would also be adding carbon. Avoid continual hay crops accompanied by high nitrogen fertilization. The continual removal of hay accompanied by high nitrogen speeds the decomposition of soil organic matter.

Animal manure

Manure is an excellent soil amendment which provides both organic matter and nutrients. Typical rates for dairy manure would be 10 to 30 tons per acre or 4,000 to 11,000 gallons of liquid for corn. At these rates the crop would get between 50 and 150 pounds of available nitrogen per acre. Additionally, lots of carbon would be added to the soil which could result in no loss of soil organic matter.

However, a common problem with using manure as a crop nutrient source is that application rates are usually based on the nitrogen needs of the crop. Because some manure often has about as much phosphorus as they do nitrogen, this often leads to buildup of soil phosphorus. A classic example is chicken litter applied to crops that require high nitrogen levels, such as pasture grasses and corn. Broiler litter, for example, contains approximately 50 pounds of nitrogen and phosphorus and about 40 pounds of potassium per ton. A common fertilizer application for established fescue pasture would be about 50 pounds of nitrogen and 30 – 40 pounds of phosphorus per acre. If a ton of poultry litter were applied to supply the nitrogen needs of the fescue, an over-application of phosphorus would result. Several years of litter application can build soil phosphorus up to excessive levels.

Compost

Composting farm manure and other organic materials is an excellent way to stabilize their nutrient content. A significant portion of raw-manure nutrients are in unstable, soluble forms. Such unstable forms are more likely to run off if surface applied, or to leach if tilled into the soil. Therefore compost is not a good source of readily available plant nutrients like manures are. Compost releases its nutrients slowly, thereby minimizing losses. Quality compost contains more humus than its raw components because primary decomposition has occurred during the composting process. It also does not contribute the sticky gums and waxes those aggregate soil particles together as much as does raw manure because these substances are also released during the primary decomposition phase.

Composting also reduces the bulk of raw organic materials–especially manures which often have a high moisture content. However, while less bulky and easier to handle, composts can be expensive to buy. On-farm composting cuts costs dramatically compared with buying compost.

Cover crops and green manures

Many types of plants can be grown as cover crops. Some of the more common ones include: rye, buckwheat, hairy vetch, crimson clover, subterranean clover, red clover, sweet clover, cowpeas, millet, and forage sorghums and so on. Each of these plants has advantages over the others and their area of adaptability. Cover crops can maintain or increase soil organic matter if they are allowed to grow long enough to produce high herbage. All too often, people get in a hurry and take out a good cover crop just a week or two before it has reached its full potential. Hairy vetch or crimson clover can yield up to 2.5 tons per acre if allowed to go to 25% bloom stage.

When small grains such as rye are used as cover crops and allowed to reach the flowering stage, additional nitrogen may be required to help offset the nitrogen tie-up caused from the high carbon addition of the rye residue. The same would be true of any high carbon amendment such as sawdust or wheat straw. Cover crops also suppress weeds, help break pest cycles, and through their pollen and nectar provide food sources for beneficial insects and honeybees. They can also cycle other soil nutrients making them available to subsequent crops as the green manure decomposes.

Humates

Humates and humic acid derivatives are a diverse family of products, generally obtained from various forms of oxidized coal. Coal-derived humus is essentially the same as humus extracts from soil but there has been reluctance in some circles to accept it as a worthwhile soil additive. In part, this stems from a belief that only humus derived from recently decayed organic matter is beneficial. It is also true that the production and recycling of organic matter in the soil cannot be replaced by coal-derived humus. However, while sugars, gums, waxes and similar materials derived from fresh organic-matter decay play a vital role in both soil microbiology and structure, they are not humus. Only a small portion of the organic matter added to the soil will ever be converted to humus.

ASSESSMENT OF SOIL HEALTH AND THE BIOLOGICAL ACTIVITIES ON THE FARM SURROUNDING

In a situation such as this, a basic soil audit is the first and sometimes the only monitoring tool used to assess changes in the soil. Unfortunately, the standard soil test done to determine nutrient levels which are P, K, Ca, Mg, and so on, do provide no information on soil biology and physical properties. A better appreciation of these biological and physical soil properties, and how they affect soil management and productivity, has resulted in the adoption of several new soil health assessment techniques which are discussed below.

The USDA soil quality test kit

The USDA soil quality Institute provides a soil quality test kit guide. The kit was designed for field use. Components necessary to build a kit include many items commonly available such as pop bottles, flat bladed knives, a garden trowel, and plastic wrap. Also necessary to do the tests is some equipment usually not locally available such as hypodermic needles, latex tubing, a soil thermometer, an electrical conductivity meter, filter paper, and an EC calibration standard. The kit allows the measurement of water infiltration, water holding capacity, bulk density, pH, soil nitrate, salt concentration, aggregate stability, earthworm numbers, and respiration.

Early warning monitoring for crop lands

The monitoring guide contains a set of soil health indicators that are measurable in the crop land. No fancy equipment is needed to make the assessments described in this monitoring guide. In fact, all the equipment is cheap and locally available on almost any farm. Simple measurements can help determine the health of crop lands in terms of the effectiveness of the nutrient cycle, water cycle, and the diversity of some soil organisms. Some of the assessments you can make using this guide are living organisms, aggregation, water infiltration, ground cover, and earthworms.

Direct assessment of the farm soil health

Some quick ways to identify a healthy soil include feeling it and smelling it. Grab a handful and take a whiff. Does it have an earthy smell? Is it a loose, crumbly soil with some earthworms present? Look at the surface and see if it is crusted, which tells something about tillage practices used, organic matter, and structure. Pushing a soil probe down to 12 inches, lift out some soil and feel its texture. If a plow pan were present it would have been felt with the probe. Turn over a shovelful of soil to look for earthworms and smell for actinomycetes, which are microorganisms that help compost and stabilize decaying organic matter. Their activity leaves a fresh earthy smell in the soil. There are two more easy observations which are to count the number of soil organisms in a square foot of surface crop residue and to pour a pint of water on the soil and record the time it takes to sink in.

A simple erosion test in the farm

This test demonstrates the value of ground cover. Tape a white piece of paper near the end of a 3-foot-long stick. Hold the stick in one hand so as to have the paper end within 1 inch of a bare soil surface. Now pour a pint of water onto the bare soil within 2-3 inches of the white paper and observe the soil accumulation on the white paper. Tape another piece of white paper to the stick and repeat the operation, this time over soil with 100% ground cover, and observe the accumulation of soil on the paper. Compare the two pieces of paper. This simple test shows how effective ground cover can be at preventing soil particles from detaching from the soil surface.

Detachment of soil particles occurs when falling rain water collides with bare ground. After enough water builds up on the soil surface, following detachment, overland water flow transports suspended soil down slope. Suspended soil in the runoff water abrades and detaches additional soil particles as the water travels overland. Preventing detachment is the most effective point of erosion control due to the fact that it keeps the soil in place. Other erosion control practices which seek to slow soil particle transport and cause soil to be deposited before it reaches the stream are less effective at preventing erosion.