Getting to know the soils in your area

As explained in Chapter 1, it's difficult to make any useful generalizations about the soils of the tropics and subtropics. Soil-forming factors like climate, parent rock, time, topography, vegetation, and management interact in countless patterns. It's not unusual to find two or more soils on one small farm that vary markedly in texture, depth, slope, and other important features.

Here are the best ways of getting to know your area's soil's:

• Visit with farmers and walk through their fields with them. They're the ones most intimately involved with the land and can provide a wealth of useful information on local soils, their behavior, and productivity.

• Arrange for a soils field tour of your area with an agronomist or extension agent.

• Consult soil survey reports or other soil studies on your area. Soil specialists have devised several taxonomy systems to classify soils, first into orders and groups made up of hundreds of soils, progressing down to a very specific series consisting of several closely related soils that share many similar Profile features. (A soil profile is a vertical slice of soil that includes the topsoil, subsoil, and some of the parent material below.) Of the several taxonomy systems, the one developed in the 1970's by the the USDA in cooperation with other countries has become the most widely used. The terms oxisol and ultisol used in Chapter 1 refer to two soil orders in in this system that comprise hundreds of soils formed under tropical and subtropical conditions. (However, not all warm climate soils belong to these two groups, as explained in Chapter 1.)

NOTE: When reading a soil survey report, don't be intimidated by the technicalities and fancy terms. What's most important to farmers and extension workers is how a soil behaves when farmed - not what order or series it belongs to.

HOW TO EVALUATE A SOIL AND DIAGNOSE PHYSICAL PROBLEMS

Using a shovel and a homemade device to measure slope, it's fairly easy to evaluate the 6 major physical characteristics that determine a soil's behavior and management needs:

• TEXTURE

• DRAINAGE

• TILTH

• DEPTH

• WATER-HOLDING CAPACITY

• SLOPE

Let's cover them one at a time. But wait a minute, we haven't said anything about SOIL COLOR - where does it fit in?