Roberto Gaitan is the President of the Rio Grande Valley Chapter, Native Plant Society of Texas. The Chapter has recently taken over operations and management of the RGV Native Plant Center on South Padre Island.
Some would say there is no difference between soil and dirt. I would agree except for perhaps the ability to distinguish the static, lifeless view of dirt, while on the other hand, soil contains a dynamic ecosystem full of life and activity. Though I may be tempted to say soil is ‘alive’ it, like dirt, is a collection of lifeless minerals. Minerals that hold the vital nutrients our plants need. These minerals are trapped unless the living micro- and macro-organisms within the soil convert them into an exchangeable form for our plants to use.
The three basic components of dirt are sand, silt and clay. The main difference is their size. Sand is the largest particle at 0.05 ~ 2 mm. Silt is smaller at .002 ~ .05 mm. Clay is the smallest at less than .002 mm. Being minerals, these particles have rough, sharp edges.
The bigger molecules link together but with relatively large gaps between them. This leads to gaps in sand which allows water to flow through quickly. The smaller silt molecules bond closely together with small gaps that allow water to flow slowly.
The tiny clay particles bond tightly with significantly smaller gaps between molecules. Clay will allow water to flow, but at a rate significantly slower than silt. Much of the water in the RGV seemingly lingering in puddles and lawns for days after a shower is likely sitting over a layer of clay.
All of our dirt types are a combination of the three molecules. Sand can feel coarse and is made from either quartz in inland areas or calcium carbonate along the coast. Silt is powdery when dry and slick when wet.
Clay is sticky and will expand and contract with rain and heat.
Regardless of the dirt type, the molecules hold nitrogen, phosphorous, potassium, calcium, iron, magnesium, manganese, sulfur, zinc and others. Without these molecules, plants will not have the nutrients they need to grow, bloom and create seeds.
For a long time, it was believed plants simply collected the nutrients through their roots unaided. But the nutrients were trapped within the dirt molecules.
Today we know that macro-organisms, beetles, pill bugs, earthworms, etc., digest dirt molecules and break them down into small pieces to be further processed by micro-organisms, fungus, bacteria, protozoa, etc. The resulting nutrients are finally in a form plants can absorb, usually with the additional help of micro-organisms like mycorrhizal fungi. This living ecosystem of micro- and macro-organisms transforms dirt into soil.
When this soil ecosystem does not exist, we are forced to use toxic fertilizers to feed the plants. Sometimes we have to resort to chemicals because of an imbalance within the soil. While most nematodes, for example, are beneficial micro-organisms feeding on viruses and other micro-organisms, plant-parasitic nematodes will feed on live plants. Unabated, these bad nematodes can kill the plant.
To promote a healthy soil ecosystem, we must try to feed the soil with natural compost which our macro-organisms will devour to feed the micro-organisms which, in turn, feed our plants. We must try to not disturb the soil more than necessary. The delicate structure of fungi and bacteria takes time to develop but can easily be destroyed. Taking care of our garden must begin with taking care of our soil.
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