Be in the market for good soil

By MANDY JOHN | Central Texas Edition

Dr. Mark McFarland, left, shakes the hand of meeting participant, Curtis Holman, from Copperas Cove. McFarland was a presenter at the Texas Certified Farmers Market's annual meeting, which took place Feb. 8 in College Station. -- Photo by Mandy John

February 20, 2003 -- At the Texas Certified Farmers Market's annual meeting, which took place Feb. 8 in College Station, Dr. Mark McFarland discussed the importance of soil quality. McFarland, who is an associate professor and soil fertility specialist with Texas A&M University, explained the importance of keeping soil healthy and protecting it from the outside elements.

"The definition of soil quality is the ability of the soil to produce at a certain rate," stated McFarland. "The physical, chemical, and biological properties all relate to soil quality."

He said what a farmer has based on soil texture all relates back to the old saying of "what you have is what you get." This could mean having sand, silt, or clay on your land.

"Both sand and silt are made up of rounded particles, while clay is flat. This means, in relation to the number of particles available, that clay is going to cover more area in general than sand or silt."

McFarland talked about soil structure and how individual soil particles are arranged or grouped into aggregates, otherwise referred to as small clods.

"Soil structure affects the pore space of the soil based on the number and the size of the particles, water infiltration and movement, air movement into and through the soil, and root penetration. Soil structure can be grouped into four types of aggregates: granular, prismatic, blocky, and platy."

He said the factors that influence structure are environment, chemistry, organic matter, and management.

The effects of soil reaction on plant growth include:

• Nutrient availability,

• Solubility of toxic substances,

• Effects on soil micro-organisms, and

• Direct effect of pH on root cells.

"When you look at the pH, it goes from zero to 14. When you are reading a soil pH, it should be no less than three and no more than nine. One of the things that affects the pH is nutrient availability, such as the phosphorus availability.

"You should look at the solubility level and you should know what the pH range is for each individual plant. The smaller the grind is, the faster the reaction when you are working on adjusting the pH level."

McFarland explained the cation (a positively charged ion) exchange capacity as the nutrient supplying power of soil in the soil water. These charges can attract to positive nutrients. This can cause organic matter to hold in nutrient charges. "The positive and negative charges are like a magnet. The unlikes attract and the likes repel.

"Environmental issues also have to be considered when dealing with nutrients."

He said there are a lot of benefits of soil organic matter. "Some of the benefits are it improves the soil structure, it allows water to hold to capacity, it's a pH buffer, it's a food supply for soil microbes, and it's a plant nutrient source.

McFarland said that soil testing is the key to nutrient management. "A soil test is a chemical extraction that provides an index to estimate the nutrient supplying power of a soil. It identifies the degree of deficiency or sufficiency of a nutrient. You need to have a soil test taken every one or two years and it's critical to have a good soil test taken."