Physical Conditions

In a general sense, we can describe soil management practices and evaluations as being either physical or chemical. The main thing one would be looking for in a field evaluation would be the physical condition of the soil through the profile (vertical depth). Problem areas may show evidence of a clay layer, a hardpan (perhaps natural or a plowpan), abrupt changes in soil texture from one horizon to another, a gravel layer, or even a water table. All of these factors can vary tremendously within a given field and can affect crop growth and productivity. Physical conditions in the soil, for the most part, are not easily altered (i.e. changing soil texture or horizon organization), but they can impact the way in which we manage these areas in terms of tillage, cultivation, and/or irrigation practices. The presence of a hardpan or plowpan can be dealt with to some extent by the use of deep tillage (i.e. ripping). High water tables may require the use of some drainage techniques. The depth at which gravel, compaction, or free water layers occur can indicate to us the general depth to which roots will grow. For example, as shown in Figure 1A,

Figure 1. (A) A soil profile with a sandy loam surface underlain by a course gravel layer at approximately 18 inches, and (B) an open soil profile with a slight gradient in textures to a depth of four feet.

if a coarse gravel or compacted layer were detected about 18 inches below the surface, this would be a good indication that our effective rooting zone would be limited to this depth as well. So instead of having a full soil profile of four feet available for rooting (water holding capacity and nutrient availability), as shown in Figure 1B, we would only be working with about 18 inches. The bottom line in this respect is "if you don't know what your soils look like below the surface, it may be worthwhile to go find out". This could be useful in addressing some of the problems common to fields or parts of fields.

Chemical Conditions

The other aspect of soil evaluation that is important is that of the chemical condition. Soils are very active chemically and they can differ a great deal in terms of chemical conditions present. The soil chemical environment is very important in that it determines the composition of the soil solution within which the roots live and function, which directly impacts plant nutrition. Physiologically, plant nutrition is clearly recognized as a fundamental aspect of a healthy, vigorous, and productive cotton plant. Accordingly, soil testing has become an integral part of modern agriculture and certainly for cotton production. In developing an assessment of soil chemical conditions or a soil fertility evaluation, it is probably worthwhile to review some basic aspects of making a soil fertility program functional and profitable. This would be true if we were dealing just with problem areas or with entire fields.

As an example, soil pH conditions alone (the degree of acidity or basicity that is present) can have a strong impact on nutrient availability, root growth, and overall plant health. In some portions of the cotton belt (particularly in the Southeast), acid subsoils can reduce or prevent root growth, which can limit the depth of the soil profile utilized by the plant and have a similar end result as the gravel layer described in Figure 1A. This condition may not be detected by augering through the soil and visually inspecting it, but it would be readily apparent if soil samples were collected at regular depth intervals and subjected to a simple pH analyis.