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Sunday, October 3, 2010

Soil Water

Soil water is an important part of the soil. Yes soil. Soil is made up of organic matter, Mineral particles and pore space. Soil water is found in the pore space. Ideally around 50% of the pore space is water when the soil is at field capacity. (More on that to come). The other 50% is air. The air is important because it is needed by the microbes and invertebrates the live in the soil. Oh yeah - that means the soil is alive.

When soil is saturated that means it contains too much water. When the soil is saturated, if you dig a hole in it the hole fills up with water. This water is called gravitational water. This means the water will flow in the soil under gravity. If I say the soil is saturated, you should think - too wet. If soils are gummy, they are probably saturated. Working saturated soils causes compaction. Gravitational water is removed by tile drainage. This is a good thing because the gravitational water uses up all the pore space in the soil and plants cannot grow into it, so the water is unavailable.

When I say the soil is very moist, that means it is probably at or around field capacity. That is the moisture level where tile will no longer remove water. The closer to field capacity the soil is, the easier it is for the plant to take up the water. Moisture still moves when the soil is below field capacity, it just moves more slowly and from areas of higher moisture to areas of lower moisture. Water can move at this point by capillary action. Roots have enough air to function and plants can use the water.

When the soil gets dry, eventually you will see corn leaves rolling during the day. At night, evapotranspiration slows down and the plant can catch up on its water needs. When the plants no longer recover at night, the soil has reached it's wilting coefficient. Rain or irrigation is very critical at this point. The plant will probably not yield to its highest potential even before these symptoms persist. The soil will still look like it has some moisture in it.

A good bit of water is not available to plants because it is held too tightly to the soil particles. To find out moisture content, soil has to be dried 24 hours in a very hot oven. Then it needs to be weighed before it can pick up moisture from the air.

I used Buckman and Brady 7th edition to make sure I did not leave anything out. Yeah, it is old, but these things do not change.

1 comment:

charliemood said...

Hi dave
I can see why folks read your blog!