Why Soils are Important

942783176_083c95a60c_b.jpgIt is easy to understate the importance of soil. It seems benign. It seems inert. But the ground beneath our feet is literally teaming with life – most of it too small for us to see or register as important. But all of it IS important and vital to our human life systems. Soil provides the anchor to plant roots. It holds water and nutrients. It is home to micro-organisms and so much more.

When we think of soil, we often think of the physical properties of the soil. How big are the particle sizes? Sand is the biggest, silt is a medium size, and clay is the smallest. We think about the water holding capacity. Clay soils have a lot more surface area of the individual particles and so therefore can hold a lot more water than sandy soils. We think of availability of nutrients and soil structure as indicators of healthy soil. But it is these last two that offer a huge level of complexity that we rarely think about.

Nutrient availability

Whenever a soil is lacking in available nutrient for the given crop it is easy to consider adding an amendment. If the soil is low in nitrogen, then just add some ammonium nitrate and you are good to go. While this method offers a quick (and needed) solution to the immediate nutrient deficiency, it doesn’t take into consideration the complex biology of bacteria, nematodes, fungi and other microbes in the soil that play a role in nutrient cycling. In theory, with enough organic matter present in the soil and the right microbes in the soil, nutrients like nitrogen should be readily available for whatever crop or plants are currently growing.

38362547684_a5e3746e8a_b.jpgSoil structure

Soil structure shows up when soil clumps together and creates peds. These peds allow for cracks and spaces in the soil for water to permeate down and more easily get absorbed. Soil structure can take years and years to form and can easily be destroyed through mechanical cultivation. What causes soils to form these peds? It is largely due to the network of BIOLOGY in the soil. Plant roots send off tiny root hairs that can hold some of the bigger pieces of soil together. Fungi and their mycelium can act as little webs and nets that bind to the plant root hairs and bind to smaller pieces of soil. And proteins excreted from things like protists and other micro-organisms can act like glue that binds individual soil particles together. This inter-connectivity of many different organisms to create soil structure shows the need to pay attention to biology.

Functions of soil

  1. 6230526315_bc10fdf6da_b.jpgWe consider soil to have six major functions. First and foremost, soil is used for food and biomass production. Eleven percent of the globe’s land surface is used in annual crop production with up to 36% of land suitable for some kind of agriculture (livestock or crop). This land grows our food crops, it raises livestock, and it produces biomass like lumber for houses and paper, cotton for clothes, and biomass for fuel like ethanol. The soil is the anchor for the plant roots.
    • Consider that U.S. agriculture produces about 500 million tons of crop residue annually, most of which contributes to maintaining soil organic matter. Plans to use crop residues for bioenergy production could deprive agroecosystems of important inputs for future soil productivity, potentially upsetting existing agroecosystem balances.
  2. An essential function of soil is the storage, filtering and transformation services that it provides. Soil filters water removing harmful micro-organisms, chemicals, and other pollutants to make for clean and safe drinking water. We have created some artificial processes to clean water for drinking, but soil is still the most important filter for us. Soil can also store our garbage (landfills), it can store excess water (think of heavy rains and the soil absorbing that liquid), it can store carbon (living and nonliving matter in the soil store carbon that would otherwise be released in the air). Removing fossil fuels from the soil and burning them and releasing them into the air has shifted the balance and been a primary cause of global climate change. Soils can also facilitate environmental interactions to transform things. For example, bacteria that live in the soil transform atmospheric nitrogen into plant available nitrogen.
    • Wetlands and the soil in the wetlands deliver a wide range of ecosystem services that contribute to human well-being, such as fish and fiber, water supply, water purification, climate regulation, flood regulation, coastal protection, recreational opportunities, and, increasingly, tourism. Despite these important benefits, the degradation and loss of wetlands is more rapid than that of other ecosystems.
    • Consider that through natural processes, such as soil adsorption, chemical filtration and nutrient cycling, the Catskill Watershed provides New York City with clean water at a cost of $1-1.5 billion, much less than the $6-8 billion one-time cost of constructing a water filtration plant plus the $300 million estimated annual operations and maintenance cost.
    • Covering just 6% of Earth’s land surface, wetlands (including marshes, peat bogs, swamps, river deltas, mangroves, tundra, lagoons and river floodplains) currently store up to 20% (850 billion tons) of terrestrial carbon, a CO2 equivalent comparable to the carbon content of today’s atmosphere.
  3. 303107524_94683698cf_b.jpgAnother function of soil is as a biological habitat and gene pool. Soil provides the habitat for seeds to germinate and grow. It provides everything they needs like water, warmth, nutrients, etc. Soil provides habitat for a myriad of animals like worms, moles and insects, but also bacteria, protists, and fungi as well. All of these creatures come into contact with each other and can interact. The insects can mate and produce offspring. The bacteria can divide and reproduce. And sometimes when they do, they evolve and two species can share a little bit of DNA. One success story of this is when a sweet potato absorbed some DNA from a bacteria. This horizontal gene transfer can make the plant resistant to diseases.Consider that there are more living individual organisms in a tablespoon of soil than there are people on the earth.
    • Almost all of the antibiotics we take to help us fight infections were obtained from soil microorganisms.
  4. Functionally, soils are also a source of raw materials. For much of modern human history, ceramic dishes made from clay were the primary tableware. Only in very recent years have we started using more glass, plastic, and one-time-use dishes (styrofoam). Soil can also be the source of countless minerals through mining processes. Soil can also be used for bricks and other materials in building houses.
  5. 5186540530_98ebc01950_b.jpgSoils can also play a functional role in our physical and cultural heritage. Around the world soils have  been shaped for things like effigy mounds potentially for religious ceremonies, burial ceremonies, or other purposes. Soils also protect our cultural past. Artifacts that get covered up by soils can be protected from the elements creating a bookmark and window into our past and heritage.
  6. Finally, soils can serve as a functional platform for us to build our structures on. Whether it is houses, highways, skyscrapers, or football fields, we need a base of soil to provide the stability to build on. Even things like bridges over water, still go down to the soil at the bottom of the river or lake to rest on.

So, could we live without soil?

Sure, we could produce food through things like hydroponics and aeroponics. But without soil we couldn’t produce the amount of food that we need to sustain human life for all seven-plus billion of us. Sure, we have figured out other ways to filter water and store garbage. But our water filter systems haven’t been scaled up to do what soil does naturally. And garbage management systems like burning garbage has other negative environmental repercussions. Without soil countless organisms like moles, worms, bacteria, and fungi would be without a home. Most of those creatures are uniquely adapted to live in soil. Without soil we wouldn’t have the raw materials we need or the base to build our structures. In short, the answer is no. We couldn’t live without soil.

Soil is easy to overlook and some may even call it dirt. But soils are important for many reasons and as farmers and agriculturalists we can protect and improve soils for the betterment of all.

-Will

Nutrient Cycling in the Environment

general cycling

“The nation that destroys its soil destroys itself.” This quote by Franklin D. Roosevelt simply explains the importance of managing soil quality. This becomes extremely applicable to farmers who are trying to maximize crop production, which can be achieved by maximizing the productivity of their ground. Fields contain much more than just dirt. They’re a complex ecosystem that contains a large amount of diversity when it comes to chemical and biological composition. One major factor in soil’s productivity when related to crop production is the nutrients found in soil. Some nutrients come from organic materials that are naturally occurring, while others are added to the soils because they are deficient. This process becomes a bit complicated when talking about specific nutrient cycling. This post will showcase how nutrients move throughout the environment while shining a light on the importance of managing soil nutrients. 

How do nutrients cycle in the soil?

Nitrogen (N)

Nitrogen is a macronutrient required by all plants, and is especially correlated with high yields in corn and soybean production. But first here’s a little bit about the basics of nitrogen in a cropping system! 

  1. Nitrogen gas (N2) is abundant in the air, however it cannot be taken up by plants. The plant available forms of nitrogen is nitrate (NO3) and ammonium (NH4+). 
  2. Nitrate is mobile in the soil profile. Due to this molecule’s negative charge, it repels from negatively charged soil particles and is easily lost to leaching and soil runoff. 
  3. Plants use nitrogen to synthesize amino acids, proteins, and chlorophyll. Ammonium is the easier form of nitrogen to use because it requires less energy in the reduction process. 
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This diagram helps to visualize each process in the nitrogen cycle. Photo from wikiwand.

Now that we understand the importance of nitrogen in crop fields, here’s how it cycles and moves around in the environment! Nin the atmosphere goes through ammonification to become NH4+, which occurs due to nitrogen-fixing bacteria found in the soil. Legume roots have a symbiotic relationship with these bacteria, which adds plant available N to a field. Once in the ammonium molecule, nitrifying bacteria changes NH4to nitrites (NO2) and then nitrates (NO3). From this point, the molecules can either be taken up by plants, processed back to N2 through denitrifying bacteria, or leached with water. If the soil’s natural amounts of nitrogen is insufficient for a specific crop, the producer can apply fertilizers to a field.  It’s important to remember that these processes are constantly changing the chemical makeup of a soil, and that severe weather events could deplete the soil of many plant-available forms of nitrogen. 

Phosphorus (P)

Phosphorus is another essential macronutrient that’s found in phospholipids, lipids, and the backbone of DNA.

  1. Crop grain contains a large amount of phytic acid, which is primarily comprised of phosphorus molecules. 
  2. Phosphate is the plant available for of phosphorus, and the two most common forms of P are HPO4-2 and H2PO4
P cycle

This diagram helps to depict and simplify the chemical changes that occur in the phosphorus cycle. Photo from soilmanagementindia.

Unlike nitrogen, phosphorus’s most abundant form is a solid found in the ground. Organic P is created over an extremely long period of time with plant residue, hummus, and microbial biomass. Organic P is turned into a plant usable form through mineralization, and the reverse reaction is called immobilization. Once phosphorus is available and held in solution it can become unavailable by reacting with clay and various mineral surfaces or by binding with cations such as calcium, iron, and aluminum. Phosphorus held in solution is susceptible to leaching, much like nitrogen is. It’s important to know that the main P inputs into ecosystems are derived from fertilizers and plant residue. 

Potassium (K)

Potassium is a macronutrient that’s required for protein and starch synthesis, acid neutralization, enzyme activation, as well as water regulation in plants. 

  1. Plant available potassium is K+. Some soils can contain a lot of potassium, but not in the cation form. 
  2. If a plant is deficient in potassium, it can exhibit stunting, necrosis, lodging, and an overall reduction in yield. 
K cycle.jpg

This photo showcases the major steps and processes in the potassium cycle. Photo from nutrien-eKonomics.


Potassium starts as a primary mineral such as mica. After years and years of weathering, it changes into a nonexchangeable form. K cations change between nonexchangeable and exchangeable molecules through release and fixation. Once K is in an exchangeable form, it changes into a plant available form through desorption. K in solution is able to be leached, but is much less susceptible than nitrates. In terms of mobility within the soil profile, potassium is immobile. This is because a large percentage of soil K is nonexchangeable, due to its location and attraction to soil minerals. The main inputs of potassium into systems is through fertilizer and plant residues. 

How are these cycles manageable? 

Since these cycles are constant and on-going, it’s crucial for producers to maintain a knowledge of the nutrient levels within their fields and which areas are the most susceptible to losing nutrients faster than others. One way to measure nutrients is to test the plant’s vegetative matter for chemical composition. While these results are helpful and accurate, it doesn’t necessarily provide information for the available forms within the soil. This is where soil testing comes into play! Soil tests can be used to qualitatively measure nutrient levels precisely, which helps to give producers recommendations on management practices in the future years. 

Hopefully this opened your eyes a little to the vast possibilities within soil science, as well as provided a better understanding of some prominent nutrients that cycle through ecosystems!

~Rosie

Why do they do that? Anhydrous

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Early in the spring and late in the fall it is common to see tractors pulling large white tanks across bare farm fields. So, what are these strange white tanks? What’s in them and why is it applied to fields?

They are anhydrous tanks filled with anhydrous ammonia (NH3) – one of the most efficient and widely used sources of nitrogen fertilizer for agricultural crops like as corn and wheat.

Nitrogen is one of the 17 essential elements required for plant growth. Nitrogen is most commonly found in the atmosphere making up approximately 78% of the air that we breathe. But in the air it is in the form of N2 which is not available to plants to use. Nitrogen is part of chlorophyll which makes plants green and allows them to use sunlight to produce sugars (food) from oxygen and carbon dioxide through photosynthesis. Nitrogen supports strong vegetative plant growth, which is vital for good fruit and seed development.

Plants use nitrogen by absorbing either nitrate (NO3) or ammonium (NH4) ions through their roots. Soybeans and other legume plants can convert atmospheric nitrogen into a usable form because of nitrogen fixing bacteria on their root nodules. Other plants, like corn, need to have an ample supply of available nitrogen in the soil. Farmers can add nitrogen to fields in the form of livestock manure, granular urea, liquid nitrogen (UAN solution), and anhydrous ammonia.

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When making environmentally and economically sustainable decisions about fertilizers, farmers consider the 4Rs best management practices. This helps them select the right fertilizer source and apply it at the right rate, right time, and right placement in the soil.

Anhydrous ammonia is often a preferred nitrogen source for many reasons. It is more concentrated than other forms of nitrogen, containing 82% nitrogen. It is readily available, because it is used in the manufacturing process of other nitrogen fertilizers. It can be applied long before the crop is planted. It is usually the most economical option as well.

Farmers store and transport anhydrous ammonia in liquid form in pressurized tanks. Using an anhydrous applicator pulled by a tractor, the high-pressure liquid converts to a liquid-gas mixture as the pressure drops while traveling from the tank to the knife outlet on the applicator. The knife slices the soil and injects the fertilizer 6 to 8 inches into the soil.

Once in the ground, the ammonia (NH3) ions react with moisture in the soil and convert to ammonium (NH4). Ammonium ions are very stable in the soil. They carry a positive charge and are bonded to negatively charged soil particles like clay and organic matter. These ammonium ions can be taken in by plants and used directly in proteins. Over time, the ammonium converts to nitrate (NO3) which is the form of nitrogen most used by plants for growth and development. Nitrate does not bond to soil like ammonium does and could leach out of the soil and into waterways. Nitrogen fertilizer stabilizers are often added to anhydrous ammonia before application to slow the conversion of ammonium to nitrate, thus helping to reduce nitrogen loss from leaching.

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Because of the stability of anhydrous ammonia (and converting to ammonium) it can be applied in the fall with less potential to leach, volatilize, or to be lost in water runoff than other nitrogen fertilizers. Cooler soil temperatures help keep the ammonium ion stable and so farmers try to apply it in the fall after the soil temperature drops below 50°F. If applied in the spring, it is best to apply it at least 3-5 days before planting to avoid damaging seeds and emerging roots.

Good nitrogen management is critical for growing healthy plants, good yields, and a profitable farm business. Farmers consider crop nutrient requirements, results of soil tests, soil conditions, weather, cost, time, and equipment available before choosing a fertilizer program that is the best fit for their operation.

-Cindy