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Soil and plant nutrient management

John Hibma for Progressive Forage Published on 28 September 2017
Soil nutrient management

Healthy soil is the foundation for all successful agriculture and is made up of an aggregate of four primary components – minerals, organic matter, air and water.

Without these four major components, soil cannot properly fulfill its primary purpose – to provide a medium in which plants may grow and provide sustenance for humans and animals. Soil dynamically recycles nutrients, moving them from soil to plant and plant to soil.

Other nutrients move within the soil itself and still others cycle from the soil into the atmosphere and back again. Those nutrients include carbon, oxygen, nitrogen, water, protein, carbohydrates and minerals.

Besides the recycling of nutrients, soil’s physical characteristics and structure serve to preserve its very integrity through the prevention of erosion, conservation of water and recharging aquifers, each of which impacts the health and productivity of the soil.

Successfully raising crops – whether forages, fruits and vegetables or grains – depends upon the proper management of all nutrients in all aspects of the nutrient cycles. Physical, chemical and biological actions take place during plant growth.

A key factor in attaining sustainable soil and plant nutrient management is understanding that improper agricultural practices will rapidly deplete the soil of nutrients, which ultimately results in negative effects on plant growth and health. As crops are grown and harvested, organic matter and minerals are removed from the soil, and they must be replaced.

Productive and healthy soil is a valuable resource that cannot be wasted or abused. Damaged soil is costly to repair or replace and takes many years to restore.

Due to poor soil management practices, healthy soil is a dwindling resource in many parts of the world. While modern agriculture has dramatically increased the productivity of farmland worldwide, it has also taken its toll on soil health.

And while this article is not intended to criticize modern agriculture, it is noteworthy, however, that the advent of commercial fertilizers and the availability of irrigation technologies along with modern machinery has changed the landscape of agriculture both literally and figuratively.

Heavier machinery has led to soil compaction that prevents roots from reaching deep for water and nutrients. Excessive plowing has broken down the soil structure, leaving it exposed to wind, rain and erosion. In an effort to improve production and profitability on every acre of farmland, agribusiness has become more “reactive” than “proactive” in dealing with problems that develop with farming.

When the soil becomes deficient in nutrients, commercial fertilizers are added. If the soil doesn’t retain moisture, applying more water with irrigation has become the solution. When it becomes too compacted, run a chisel through it. If a disease sets in, apply pesticides.

All of these modern management and farming practices have, in many cases, broken down the soil’s structure, reducing its ability to retain moisture and reducing the organic matter in the soil that’s so very critical to maintaining the beneficial microbes and living organisms.

Much of the effective management of plant and soil nutrients must be focused on preventing what’s already in the soil from being removed or destroyed. Properly structured soil will have the ability to store water and maintain moisture for long periods of time, reducing the need for excessive irrigation and the potential for erosion and leaching of essential nutrients.

However, successful agriculture requires that the soil must give up something. Every crop will remove nutrients from the soil, and a key factor in preventing the depletion of soil quality and health is the rapid restoration of those nutrients.

At the same time, while it’s necessary to maintain optimal nutrient levels and structure, the overapplication or accumulation of commercially sourced nutrients can potentially result in nutrients such as nitrogen or phosphorus escaping into the environment in places where it’s not needed or wanted.

Therefore, effectively managing plant and soil nutrients becomes a balancing act of replacing nutrients before excessive depletion occurs and, at the same time, not overfertilizing a crop when it’s not necessary or after a crop has been harvested.

It’s critical that the soil is not abused with excessive vehicle traffic or left fallow for extended periods of time. Where moisture is lost and soil is left exposed, topsoil may be blown away and microorganisms will die off.

Even though organic matter makes up only a small percentage of soil (1 to 6 percent), organic matter has a profound effect on how well soil functions, stays together and recycles nutrients. Rotating crops and implementing cover crops creates a synergy among microbes in the soil that can accelerate the accumulation of organic matter.

Effective and successful plant and soil nutrient management is an ongoing work in progress for any farmer. It’s not enough to prepare a field, plant a seed and water the crop until harvest time. Plants cannot grow successfully if the soil is depleted of nutrients, no matter how much water is added.

Healthy and productive soil contains millions of species and billions of organisms including bacteria, fungi, algae, insects, earthworms, beetles, ants and more. The vast majority of these organisms cannot be seen with the naked eye. And even though they only make up a fraction of a percent of the total soil mass, they must be there in order for plants to grow.

As crops grow and mature, they must absorb nutrition through the root systems. Water and minerals must be absorbed into the roots at the molecular level. Nutrients such as nitrogen, phosphorus and potassium must be made available in forms that can be absorbed through the roots. Organic matter coming from manure, cover crops and unused plant material provide nutrition for microbes that, in turn, decompose organic matter into molecules small enough to be absorbed through roots.

Water is essential for the growth of crops. Water provides the medium in which the chemical reactions and physical flow of nutrients take place. Yet water is also capable of destroying soils. Once again, organic material in soil is instrumental in absorbing and storing water, and at the same time, allowing water to replenish aquifers and improve water quality.

Soils devoid of organic material will rapidly shed water, which, as it flows, will take with it soluble nutrients, which can pollute the environment when not properly contained.

Much of what makes soil healthy and full of beneficial nutrients is keeping the soil in a condition that is unfavorable to disease-causing pathogens. Controlling weeds and keeping soil well-drained, as well as keeping good soil tilth and fertilization in balance without excessive plowing, will keep the healthy nutrients in and the damaging pathogens out.

Healthy soil should seldom be uncovered and lay fallow. In other words, it should have a crop growing on it as often as possible, even if it’s a temporary pasture. The organisms that make soil healthy must have access to plants in order to survive.

Leaving soil uncovered for extensive periods of time allows the structure of soil to break down. A cover crop that can return nutrients to the soil should immediately follow the harvest of a cash crop. Monocultures should be avoided and crops should be routinely rotated.

Farming is a labor-intensive activity and crops must be aggressively managed to properly survive. At the same time, successful plant and soil nutrient management is a process set in motion and left alone with minimal human interaction. Successful soil and plant nutrient management and healthy soils are actually two sides of the same coin. One cannot happen without the other.  end mark

PHOTO: Effective and successful plant and soil nutrient management is an ongoing work in progress, but we must treat the problem, not the symptom. Photo by Mike Dixon.

John Hibma
  • John Hibma

  • Consulting Ruminant Nutritionist
  • South Windsor, Connecticut
  • Email John Hibma

Highlights of proper soil and plant nutrient management:

  • Build up and maintain high soil organic matter levels.

  • Rotate crops to maintain diversity of microbes and break pest and disease cycles.

  • Use cover crops to sequester nutrients, enhance soil structure, reduce runoff and erosion, and provide microbes with fresh organic matter.

  • Incorporate manures into the soil quickly to reduce nitrogen volatilization and potential loss of nutrients in runoff.

  • Rotate legumes into a field after a crop that has used high levels of nitrogen from previous crops.

  • Maintain soil pH in the optimal range for the most sensitive in the rotation.

  • Regularly test soils for the critical elements: nitrogen, potassium and phosphorus.

  • Avoid soil compaction with high levels of equipment traffic.

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