Is Soil Fertility and Soil Productivity the Same Thing?

Sitting by the camp fire, you hear discussion after discussion about food plots.  Why can two hunters, or let me say land conservationist to be a little more eco-friendly, plant the same products and use similar fertilizers and have different results?

Yes, soil fertility is vital to having a productive soil, but a fertile soil is not going to be necessarily a productive soil.  There are soil-plant relationships that need to be recognized.  Things that control plant growth are temperature, air, water, mechanical support, nutrients, and light.  In part, the soil supplies the plant with all these factors except for the light source.   Each of the factors listed above directly affect plant growth. The soil’s own texture, structure, and depth play a vital role in soil productivity.

The first of many things one has to look at is the soil texture.  Soil type is classified by how much sand, silt, and clay are present in the soil.  If the soil has high sand content then it is simply classified as “sand”.  If it mainly has clay then it is called “clay”.    If there are similar percentages of sand, silt, and clay, then this middle of road soil is called “loam.”  You have variations on the name based on three things, percent of sand, percent of clay, and percent of silt.  There are 12 textural classes for soils: Clay, Sandy Clay, Silty Clay, Clay Loam, Silty Clay Loam, Loam, Sandy Clay Loam, Sandy Loam, Loamy Sand, Sand, Silt Loam, and Silt.  Sand has a coarse particle size and feels gritty when rubbed; it has great filtration and aeration but has low reservoir-like properties of holding water and nutrients.  Clay has a fine partial size and gives soil a sticky feel.  Because of the fine particle size, these soils can easily become compacted.  Silt is of intermediate size; they take on water very slowly, but have greater reservoir like properties of holding the water once absorbed.

The second thing one has to look at is the soil structure.  The soil structure impacts the movement of water, air, and roots within the soil medium.  Good management helps maintain or develop good soil structure.  The best structure is granular and blocky with the soil particles aggregated to prompt movement of water and air.  Structure can be impacted by man and his choices of cultivation techniques and crop production.   For example, intensive cultivation may result in soil compaction which is an artificial soil shrinkage cause by man.  Think about the tire wheels of a tractor or truck going over the same path multiple times, you can physically see and feel the soil becoming like a hard pan.  Yes it is more stable for the rolling stock traffic, but it impedes plant growth.   The more compact the soil is the less likely water will be able to permeate the surface.   Cover crops can facilitate some structural improvement because the root systems strive to penetrate the soil.  Cover crops are best planted on soils that have had mechanical assistance to break through the compaction.

The last thing one has to look at is the soil depth.  You can see the depth by looking at exposed banks or digging test holes.  Soil surveys are usually done at a minimum of five feet unless a natural hardpan is found.  The survey shows the layers of soil types that may be present in the field in question.  Water and root penetration is affected by the different texture of the different layers.  For example water-logging can occur were a sub-soil layer has noticeable increase in clay content.  The water may accumulate above this layer because it just can’t readily permeate the compaction this layer may have.  Effective root depth is a term that basically represents the portion of the soil favorable to root growth; therefore restrictive layers in a soil will impact the effective root depth available for plant growth. Soils that have greater depth with uniform texture throughout are easier to manage.

Since many factors control soil productivity, we not only have to look at the fertilizer we use, but the soil’s own texture, structure and depth to see how some of the components may limit the benefits of fertilizer and impact plant growth.  Simply put: food plot management is more than just disking, fertilizing, and planting.  The productivity of your plot will be determined (in part) by the soils in which you chose to create your food plots.  This could be why the other hunter’s plot may be better than your plot.  Happy planting!!!  -CG