soil health

Spotlight – Soil Degradation

One of the most pressing resource related issues around the world is the continual reduction in the percentage of arable land. Currently, 37% of land worldwide is considered agricultural, only 10% is deemed arable, or plowable, and suitable for crop production (World Bank Group, 2015). The shrinking percentage of suitable farm land is a direct result of soil degradation, which is attributed to tillage practices and the use of agrochemicals in intensive agriculture. Overgrazing of rangelands, natural occurrences such as wildfires, and non-agricultural human activities such as road salt applications also contribute to the degradation of soils, making mediation efforts cumbersome. Although the degradation of soils is a multifaceted process with a range of negative effects, effects tend to be closely tied with one another making the process as a whole degenerative.
 

The current intensive agricultural systems in place throughout the world aim to maximize production through increased inputs, such as labor and agrochemicals, while reducing waiting periods between crops. Large-scale annual crop production relies primarily on conventional tillage methods such as the moldboard plow, an implement that cuts a furrow slice of soil (around 8 inches in depth). The furrow slice is lifted, flipped, and dropped back down, inverting the soil profile. Simultaneously, this implement forms a hardpan layer of compacted soil beneath the disturbed portion. Both the inversions and hardpans negatively impact the soil’s structure. A compromised soil structure carries its own concerns and at the same time predicates multiple downstream effects.

A soil’s structure refers to the arrangement of fine soil articles into groups called aggregates. Many soil activities such as water movement, heat transfer, and aeration are directly impacted by the formation and arrangement of aggregates which results from a range of slow biological, physical and chemical processes. Aggregates are delicate and become destroyed in frequently disturbed soils such as those in annual cropping systems. Destruction of aggregates increases the bulk density of a soil. As bulk density increases water infiltration, water holding capacity, aeration, and root penetration decrease, making it more difficult for crops to access resources essential for growth.

The regular application of agrochemicals in cropping systems further diminishes the health of soil. Agrochemicals include herbicides, pesticides, fertilizers, and other soil amendments. One of the main concerns with the addition of these chemicals is their interaction with soil organisms. Soil macro- and microorganisms include bacteria, fungi, and earthworms; all contribute to a healthy plant rhizosphere and provide a range of benefits within cropping systems. These organisms are very sensitive to variation in their environment such as changes in pH, salinity, and the carbon:nitrogen ratio. These inputs represent rapid cyclic environmental shifts to which soil organisms cannot acclimate or adapt to. Instead, the diversity of soil organism diversity is diminished.

Soil organisms play a range of roles in the development and maintenance of a healthy soil profile, which in turn affects the growth and development of crops. Microorganisms such as bacteria fix nitrogen, making the largely inaccessible pool of atmospheric nitrogen available for plant uptake. Fungi, like mycorrhizae, form mutualistic associations with plant roots, extending their network of nutrient and water uptake. Larger organisms such as earthworms help to form soil aggregates by creating macropores and producing worm castings. Many insects also contribute to the formation of soil aggregates as well as help reduce the weed seedbank via predation. Healthy, natural soil systems are engineered by a consortium of organisms and by design are able to provide the needs of plants. However, in some cropping systems, this level of provision is deemed inadequate, prompting the need for agrochemicals and at the same time impacting the functionality of the soil.

Soil degradation is not limited to artificial systems. There are several factors, both natural and human induced, contributing to the percentage of degraded land around the world, outside of agricultural systems. Wild fires, which occur regularly in arid regions, burn vegetation which help to hold soils in place. Climate change, combined with lack of management in fire-prone areas, has dramatically increased the frequency and intensity of these fires, increasing the potential erosion. Mismanagement and overgrazing of rangelands in dry regions also diminishes soil-stabilizing vegetation, creating the same potential for erosion. In more temperate regions, road salt application during the winter months has become cause for concern as these salts become distributed into the ecosystems affecting both soil structure and soil organisms.

The effects of soil degradation are not discrete, often tied to each other in a continuum in which some agricultural practices initiate a predictable sequence of events that ultimately leads to diminished soil health. Conventional tillage methods and the use of agrochemicals seem to be the catalytic events for such series of events in annual cropping systems; affecting soil structure, organic matter content, and the health of soil organisms. These in turn compromise the functionality of soils as the medium for crop growth and development. There is wealth of information on alternative practices that aim to reduce the impact of agriculture on soil health. For more information on soil conservation and alternative agricultural practices please visit the UConn Extension website or contact your local extension office.

Despite the evidence supporting the continual degradation of soils due to agricultural activities, there is little consideration for the viability of suggested remediation practices in regard to the effects on food production, farmers and the agriculture industry as a whole. Reducing tillage and agrochemical input is not a solution for many agricultural systems as some crops simply do not perform well in no till systems, while reduced agrochemical input would greatly compromise crop yields. Considering the importance of agriculture to society at large, farmers, who may be the most hardworking and underpaid individuals in the world, utilize available options to maintain soil health while still maintaining a productive and economically feasible operation.

From the farmers perspective, this is often represented by tradeoffs. Farmers are not ignorant to the concept of soil degradation or the importance of soil health. In fact, they understand the impact of these much better than anyone else. Operations which use agrochemicals and employ conventional tillage methods still take steps to maintain soil health. Many of these cropping systems utilize conservation practices such as the incorporation of cover crops or selection of organic agrochemical alternatives. Elizabeth Creech of NRCS (Natural Resources Conservation Service) wrote an informative piece entitled “The Dollars and Cents of Soil Health: A Farmer’s Perspective” which depicts many of the challenges farmers face when it comes to maintaining soil health. For more information please follow this link: https://www.usda.gov/media/blog/2018/03/12/dollars-and-cents-soil-health-farmers-perspective.

Soil pH – The Master Variable

The UConn Soil Nutrient Analysis Lab tests for and analyzes multiple soil parameters; but none as critical, and as often overlooked, as pH. Soil pH plays a crucial role in the growth of vegetation planted, as well as ground water quality. Before we start talking about soil pH, I think it is a good idea to try to define what exactly pH is, and how it is determined.

When most of us think of pH, a pool probably comes to mind. I remember growing up, watching my mother apply different chemicals to our pool, and impatiently wondering why I had to wait to go swimming. She would tell me that she was adjusting the pH of the water to ensure it was safe to swim in. The basic understanding is that pH is tells us how acidic, neutral, or alkaline something is. To get a little more technical, pH is the measurement of the activity of Hydrogen Ions (H+) in an aqueous solution. The equation for determining and quantifying pH is:

pH = -log10 (aH+)

(aH+= Hydrogen Ion Activity in Moles/L)

We express pH on a logarithmic scale of 0-14, where 0-6 is considered “acidic”, 7 is “neutral”, and 8-14 is “basic”.

soil pH scale
Image from: http://www.edu.pe.ca/gulfshore/Archives/ACIDSBAS/scipage.htm

Mineral soil pH values generally range from 3.0 – 10.0. There are numerous factors that determine soil pH including climate, parent material, weathering, relief, and time. Texture and organic matter content also influence soil pH. Most Connecticut soils are naturally acidic. Nutrient availability is directly influenced by pH with most plants (with some exceptions) thriving at pH values between 6 and 7. A majority of nutrients are available within this range.

Our lab measures pH using an 1:1 soil-to-DI water ratio. The saturated soil paste is mixed, then is analyzed using a glass electrode and a pH meter. We calibrate our meter using 2 solutions with known pH values, 4 and 7. We use these values because we expect most Connecticut soils to fall within this range. Once the initial pH value is obtained, a buffering agent is added. In our lab we use the Modified Mehlich Buffer. A second pH reading is obtained, and from these two values plus crop information, we are able to make limestone and/or sulfur recommendations.

The Buffering Capacity of a soil is the resistance it has to change in pH. Soil buffering is controlled by its Cation-Exchange-Capacity, Aluminum content (in acidic soils), organic matter content, and texture. A soil with a lot of organic matter and clay will have a higher buffering capacity than one with little organic matter that is mostly sandy.

If the soil pH is lower than the target range for a particular plant, limestone would be recommended. Whether you use pelletized, ground or granular limestone, the application rate would be the same. Once the target pH is reached, a maintenance application of 50 lbs/1000 sq ft would be applied every other year to maintain it.

If the soil pH is higher than desired, sulfur recommendations are made. Typically only powdered sulfur is available locally but granular sulfur could be mail ordered. Aluminum sulfate can be substituted for sulfur and used at a higher rate. Check out this listof preferred pH ranges for many common plants.

Monitoring your soil pH is essential to ensure that it is falling within the range best suited for the vegetation you are growing. The Standard Nutrient Analysis performed at our lab gives you a pH value, a buffer pH value, a lime/sulfur recommendation, available micro & macro nutrient levels, and a fertilizer recommendation. For more information on pH, you can contact Dawn or myself (Joe) at the UConn Soil Nutrient Analysis Lab (www.soiltest.uconn.edu). Test, don’t guess!

By Joe C.

Nitrogen – The Fix

corn
Chlorotic corn. Image provided by T. Morris, 2018

Nitrogen is an essential nutrient required for the production and growth of all plants, vegetation, and living organisms. It makes up 78% of our atmosphere; however, that only accounts for 2% of the Nitrogen on our planet. The remaining 98% can be found within the Earth’s lithosphere; the crust and outer mantel. The Nitrogen found within the nonliving and living fractions of soil represents an unimaginably low fraction of a percentage of all the Nitrogen on our planet. That tiny percent of all total Nitrogen found in our soils is what we can interact with to help or hinder plant production.

To be considered an essential nutrient, an element must satisfy certain criteria:

  • Plants cannot complete their life cycles without it.
  • Its role must be specific and defined, with no other element being able to completely substitute for it.
  • It must be directly involved in the nutrition of the plant, meaning that it is a constituent of a metabolic pathway of an essential enzyme.

In plants, Nitrogen is necessary in the formation of amino acids, nucleic acids (DNA and RNA), proteins, chlorophyll, and coenzymes. Nitrogen gives plants their lush, green color while promoting succulent growth and hastens maturity. When plants do not receive adequate Nitrogen, the leaves and tissues develop chlorosis. However, over-application of Nitrogen can cause even more problems, including delayed maturity, higher disease indigence, lower tolerance to environmental stresses, reduced carbohydrate reserves, and poor root development.

Read more….