Soil health is a function of soil physics, chemistry, and biology
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The properties of soil often determine the balance and nature of vegetation, and indirectly, the population of inhabitants that can be supported. The above-ground portion of plants is most generally equally balanced with the sub-soil mass of roots in area. Most of the communicated directions we receive for nurturing plants have focused on water and raw material fertilizers. But today’s operations manager has been exposed to tactical ideas such as no-till, synthetic fertilizers, pest control products, bio solids, and a myriad of bio-stimulants.
Soil must provide an anchoring system for plants, nutrient storage, water reserves and a habitat for biomass that are the cyclers and re-cyclers. This will require a stable soil matrix and balanced porosity. Soil physical specifications must have properties that hold capillary water, gravitational water and will also inherently hold unavailable water (hygroscopic). Soil must also protect water by filtering water to ensure quality. Clay particles and the organic component of soils are the nutrient reservoirs that also make up a component of soil physics.
Soil physical components are described as a balanced mix of sand, silt, and clay. This balanced distribution of particle sizes is the direct influence for water holding, oxygen capacity, and stored nutrient reserves.
Soil physics will provide water infiltration at the soil interface or surface percolation, or movement through soil porosity and finally drainage. As water moves down through soil, air is pulled into large pores for storage. This activity will also remove gasses that can build up and have a negative influence on root activity.
Physical properties of soil must provide for the ability of oxygen, water, and roots to move freely through macro pores. Porosity is divided in two sizes: capillary that are the micro pores that hold water and non-capillary that are the larger macro-pores that will store air and promote rooting.
How important are the physical specifications for soil performance?
Approximately 45% of the dry matter analysis of plants is comprised of oxygen. Almost 88% of all plants examined are dominated by only two of the essential elements: oxygen and carbon. That leaves about 6% for hydrogen and 6% for all the fertilizer elements we sometimes consider the most important.
Deficient physical properties will greatly impact plant rooting performance and limit top growth eventually. Soils without oxygen are described as anaerobic and will alter biology as well as limit root growth and no longer suppress pests. The greatest impact is cell division that will cease, and essential “ions” are no longer being transported in the soil solution. Plants will display symptoms that indicate a need for either fertilizers or water.
Nutrients that have a beneficial direct impact on soil physics are a very short list. Calcium is the most misunderstood nutrient of the 17 essentials due to the impact on soil physics. Calcium simply pushes clay particles apart and creates porosity.
The critical point to remember about Calcium nutrition is that it is “phloem immobile” or needs to move upward through the roots to the upper plant parts. (Marschner, 1983)
It is also noteworthy to remember that calcium is our most insoluble and immobile of all the elements.
Salts including sodium and bicarbonates that will be a component in most all water sources in the Sunbelt, directly impact soil physical properties. Even your favorite organic fertilizer comes with a salt impact. A question we never hear is in reference to salt index of a product such as Urea. Salts and bicarbonates will act as a cementing agent for soil particles and reduce porosity.
Once physical properties are lost, we suffer greater risks from heavy rainfall, salts from irrigation water, surface germination of “misplaced plants” (weeds) and restricted growth response on selected plants.
Soil physical properties will influence chemical performance especially control products. Several studies have indicated that chemical degradation can be slow or disturbed when aerobic (with oxygen) and anaerobic (no oxygen) micro sites are not fully functioning. These micro sites must be in proximity or other failures will occur. Corrective measures are simple if we use frequency as a key component for all cultural practices. A list of beneficial practices is as follows:
Watering properly by frequency and delivery rate. If soils will not accept the water source due to hardness of water or hardpan, simply reduce application times and provide time allowances for a soaking-in cycle between total irrigation events.
Summary
- Apply calcium on a regular basis and rotate sources. Water in thoroughly.
- Monitor “salts” that you control in all products used.
- Manures will have a greater efficiency than conventional composts and municipal waste. Poultry manure will have lower salt risks and reduced inorganic ash content. Compost from site should be first choice.
- Rotate sources of fertilizers, such as use of nitrogen from nitrate, ammoniacal, urea, and protein.
Cultural practices listed above are not complete without assigning a responsibility of stewardship activities, which ask us to increase our knowledge of soils beyond the conventional soil chemical test.
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