Soil Conservation – Stopping the Removal of Top Soil

TOPSOIL is disappearing faster than it can be replenished

Amherst, Mass. – A recent study performed by researchers at the University of Massachusetts seems to indicate that topsoil erosion rates are removing soil at an accelerated rate, faster than the ability of natural mechanisms to create new topsoil.

The study reviewed 20 prairies bordering tilled farmland.  Of interest was the delta in height between the tilled farmland and the natural prairie.  Of particular interest was the loss of topsoil presented at the border area between the two land masses.  The prairie soil height above the tilled farmland borders showed a median reduction from prairie height to tilled farmland height of between 0.04 to 0.69 m,  This difference in soil heights at the borders of fields corresponds with a soil erosion rate of between 0.2 – 4.3 mm/yr .  The  median soil erosion rate was calculated to be 1.9 mm per year.  Compared against the USDA established removal rate of 1 mm per year, the actual loss is almost double what the USDA identifies as the maximum soil loss allowed per year.

The study associated the measured soil height difference between a tilled field and prairie along with topographical curvature in predicting topsoil erosion from the beginning of farming (1870’s) to present day.  The median historical erosion rate turned out to be 1.8 mm/yr.  This rate is significantly different from the USDA established loss rate.  The USDA has underestimated the topsoil loss rate which they hold to 1 mm/yr.

The study researchers suggest the discrepancy may be due to the USDA not incorporating tillage erosion into their calculations.  It may be a situation where definitions of erosion are in conflict resulting in confusing, seemingly contradictory, data.

To determine if the current calculated erosion rate was similar to historical erosion rates, the researchers set out to establish erosion rates in soil unaffected by cultivation. To accomplish this analysis researchers looked to undisturbed prairie lands as the best sampling area from which high quality data could be obtained.

The study, appearing in the journal Geology reported the use of Beryllium-10 to determine the soil erosion rate buried deep beneath the prairie in soil that would not have been affected by any farming practices.Data acquisition was accomplished using a boring tool and taking samples at a variety of sites.  Each sample was prepared in the lab and sent off for analysis to establish the number of beryllium-10 atoms present.  Samples were theorized to be from top-soil dated back to approximately 12,000 years.

Beryllium-10 is formed by high energy cosmic rays breaking apart oxygen or nitrogen molecules in the atmosphere.  The atoms then precipitate from the atmosphere into the soil below.  Through the measurement of the beryllium molecules it becomes possible to determine average erosion rates over the span of thousands of years.

The process involves separating quartz crystals from other material in dirt samples.  The quartz is sent off to a lab where the exact number of beryllium atoms can be counted.

To establish erosion rates scientists must take a number of soil samples across a wide area at different depths.  This data is then compared and a map is produced to show the concentrations of beryllium.  From that map assumptions are then made to determine the erosion process and rates of movement.

The calculated erosion rate is reported to be 0.04 mm/yr for pre-agricultural soil.  Modern day erosion rates established by the study seem to be 25 times higher in erosion.  Depending upon where measurements were taken the topsoil erosion rate was 1000 times higher than the natural rate.

In this study the presentation of the methods and the singular reliance upon beryllium-10, its concentrations and distribution within the strata, could be more thoroughly addressed.

The formation of beryllium-10 and deposition in soil is not a constant process and can vary over time. Beryllium-10 (10Be) is a radioactive isotope of beryllium that is formed in the Earth’s atmosphere primarily through the interaction of cosmic rays with nitrogen and oxygen atoms. These cosmic rays, high-energy particles originating from outer space, constantly bombard the Earth’s atmosphere.

Once formed in the atmosphere, beryllium-10 can be deposited onto the Earth’s surface through precipitation or dry deposition. It can then become incorporated into soil through various mechanisms such as rainfall, erosion, and biological activity.

The amount of beryllium-10 in soil is influenced by several factors that can vary over time. These factors include variations in cosmic ray flux, which can be influenced by solar activity, Earth’s magnetic field strength, and atmospheric conditions. Additionally, local factors such as climate, geography, and soil composition can also affect the concentration of beryllium-10 in soil.

A troubling aspect to the study’s base assumption regarding erosion rates of 0.04 mm/yr is the sole reliance on and variability in 10be formation and deposition.

Cosmic ray intensity can vary over time due to several factors:

1. Solar activity: The Sun’s activity, specifically its solar cycle, has a significant impact on cosmic ray intensity. During periods of high solar activity, such as solar maximum, the Sun’s magnetic field is stronger, and it can better deflect cosmic rays away from the inner solar system, resulting in lower cosmic ray intensities. Conversely, during periods of low solar activity, such as solar minimum, the weaker solar magnetic field allows more cosmic rays to reach the Earth, leading to higher intensities.
2. Earth’s Magnetic Field: The Earth’s magnetic field acts as a shield, deflecting and trapping a significant portion of cosmic rays coming from space. However, the intensity of the Earth’s magnetic field is not constant and undergoes changes over time. These variations, which occur on long timescales of thousands of years, can affect the shielding capacity of the magnetic field and consequently influence cosmic ray intensities.
3. Earth’s Atmosphere: The Earth’s atmosphere plays a crucial role in modulating cosmic ray intensities. The atmosphere acts as a shield, with high-energy cosmic rays colliding with atmospheric particles, producing cascades of secondary particles. The interaction of cosmic rays with the atmosphere depends on factors such as altitude, latitude, and atmospheric conditions, which can vary over time. Consequently, cosmic ray intensities can be influenced by changes in these atmospheric parameters.

Combining the variability mentioned above with atmospheric, geophysical, and biological influences, the adoption of 10be as a baseline for measurement seems a bit fragile, particularly when making an assertion of geological activity 12,000 years in the past.  Without strata identification to correlate core samples, the aggregation of 10be in any given area is interesting, but of limited value.  The 10be counts could be representative of significantly different time periods that may represent significantly different atmospheric, geophysical, and biological influencers that could either increase or decrease 10be presence.  Changes to 10be deposition rates could possibly change the formulae outcomes and alter the assumption of 0.04 mm/yr erosion rate.

To compensate for the variability of 10be formation and deposition, the  study might add an additional control to assess the age of the soil at different striations.  The use of OSL (Optically Stimulated Luminescence might add more confidence to the study findings.  Analyzing core samples from similar time periods would provide the correlative element to increase confidence in the process and findings.

OSL dating measures the accumulation of trapped electrons within minerals like quartz and feldspar. When these minerals are exposed to sunlight, they store energy from ionizing radiation in the environment. By analyzing the luminescence signal released when the minerals are stimulated by light, scientists can determine the time since the last exposure to sunlight, indicating the age of the soil.

No need to panic at all!  The study points out that there seems to be no change in soil erosion rates dating back to the dust bowl of the late 1800’s – even with soil erosion practices having been implemented.  However, if the study findings are correct and we are losing soil at a rate greater than the replenishment rate, then it is prudent to explore replenishment and/or erosion abatement practices in agricultural soil-use venues.

There are three types of erosion identified in the study.  They are Wind, Water, and Mechanical.  A fourth type of erosion also exists and it is the leeching (Dissolution) of nutrients in and around soil particles.  This type of erosion is often handled by adding back to soil those essential nutrients through a variety of compounds and distribution methods.  This type of erosion is not addressed in the study and so it is not discussed here.

Wind erosion is an insidious process where fine soil particles are lifted into the air by the wind.  The finer the particle the easier it is to keep it suspended in the wind.  For wind erosion to occur the soil must be dry and the wind must be in direct contact with the soil to lift particles.

Wind erosion is were the wind causes fine soil particulates to become airborne and suspended in an airflow pattern.  The wind keeps the soil particulates airborne until the wind slows down and the particulates fall back to the earth.  This type of erosion is all about wind speed and turbulence.

The greater the speed of the wind the more particulates will be launched into the air and deposited somewhere else.  To reduce this process or erosion one has to interrupt the wind slowing it down.  Great success has been achieved with planting rows of trees at varied intervals in or near a field.  As the trees grow they create larger and larger impediments to the wind causing surface wind turbulence.  This in turn reduces significantly the ability of the wind to suspend soil particulates and redeposit them.

If you have a field consider a few trees to preserve your soil and keep it from eroding away.  Trees also assist in pest control by introducing a barrier that must be overcome in order for a pest to move to another field.

Water erosion operates using the same physics as wind erosion, but it is much more effective with a wider range of particulate sizes.  Water erosion has the ability to move much greater amounts of soil due to water being a semi solid material, and providing greater resistance to soil particles precipitating out during water movement.  Water also has greater mass so it can use higher amounts of kinetic energy to liberate soil particles into the flow.

The most  effective deterrent to water erosion is turbulence.  When water encounters turbulence it slows down.  When water-flow slows down it loses its’ ability to keep particulate matter suspended.  Gravity then pulls soil particulates from the water as sediment.  To slow or halt soil erosion simply introduce barriers that will slow down the flow long enough to let the soil particulates precipitate out of the water.

This can be achieved using bales of straw aligned end-to-end, erecting a sediment fence, changing the slope of the erosion area, introducing a sediment pond with a spillway, or using multiple methods to achieve your goal of slowing down the water.

Mechanical erosion occurs as a result of mechanically moving top soil from one location to another.  This is done as part of field preparation typically.   As the tillers cut through the field surface turning under a winter cover or field stubble from the last harvest.  They mechanically move soil a few inches to the left or right.  As time progresses the action of moving soil during tilling causes high points in the field to flatten moving top soil away.

Addressing mechanical erosion requires the addition of biomass to the flattened areas and can take many years to build the soil back up to acceptable performance levels.  Changing directions during tilling can reduce the mechanical erosion depending on the plow type and field contours.

To make a difference at your home look for areas where erosion may be taking place and implement some of these mitigating strategies to keep your soil at home where it can work to produce healthy plants of your choosing.

Examine areas that you frequent and offer suggestions to those responsible in an effort to reduce soil erosion and re-deposition.