Improving Plant Growth by Knowing Your Soil.

It is important to understand soil, in order to be a good grower. The first thing to look at is soil texture. This is simply the percentages of sand, silt and clay that make up any soil. The size of the particles is important in how much air and water will be in a soil type. Sand particles (range from 0.05-2mm) are the biggest, so they will encourage soils to drain allowing oxygen to get to the roots. However, without watering the plants, sandy soils can dry out and leave the plant without water, which is crucial for photosynthesis. Clay particles are the smallest, (less than 0.002mm) so water has a hard time moving through clay. Also, clay had a negative charge so water and nutrients that have a positive charge ‘stick’ to clay. This means clay soil’s hold on to water (and nutrients) so they help keep a soil moist. However, clay soil’ can have slow or no drainage which means the soil will become waterlogged (all the pores full of water) and the roots won’t be able to get oxygen and the plant will not grow and will eventually die. The amount of pore space in most soils is usually about around 50% for all mineral soil types. (Porosity – actual volume of spaces between soil particles) The rate that water moves through soils is called permeability. (Permeability – rate through which water moves through soil). It might seem that porosity and permeability are the same, a lot of pores means the water will move quickly. This is not the case. Soil’s that have a lot of clay, have a lot of pores, but they are very small pores, so the permeability of clay soil’s is very slow. Movement of air and water through the soil regulate the growth and type of plants that are able to live there. Therefore the best soil, called a loam, has a percentage of sand and silt and clay that allows for plants to get oxygen and water to the roots.

Summary clay – made up of small particle that fit tightly together = small pores
lots of pore space, but water doesn’t drain well b/c it’s held tightly
sand – large pores, plenty of aeration, dries rapidly and easily loses nutrients
loam – good mix of water holding ability and drainage

Note: A soil with as little as 20% clay will behave as a clayey soil. A soil needs 45% to 60% sand to behave as a sandy soil. In a soil with 20% clay and 80% sand, the soil will behave as a clayey soil

If you have a ‘heavy’ clay soil, you can add sand, if you have a sandy soil, usable clay is not easy to get, but you can add organic matter in the sustainable forms of compost, coco coir, and manure or try adding the mineral vermiculite which will also help soils’ to hold water.

1 comment:

hillbilly said...

if only i had been able to read this years ago! this beautiful explanation of soil/clay/porosity is representative of years of trial/error (learning the hard way). i live on a mountain top in west virginia and there is almost nothing but clay under the lawn everywhere on the propery (maybe a few thousand rocks, too). i struggled with sand and other amendments for 5 growing seasons with poor results - i finally gave up and put in raised beds. had i been aware of this blog earlier, i am quite sure i wouldn't have found myself bumbling around in the clay - thanks Dr. Myers - as always