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Soil water stages

Plant available water in bowling greens

The amount of plant available water in bowling greens is determined by the texture and structure of the rootzone soil. In our recent investigation into soil texture in bowls green maintenance we saw how the Particle Size Distribution within the soil (rootzone) can determine the soil’s porosity or air space. Having determined that the ideal rootzone will be 50% space, we then saw how soil porosity is split into two main types, namely Macro Porosity; the large spaces between soil particles responsible for drainage and aeration, and Micro Porosity; the smaller spaces between soil particles that are largely responsible for water and nutrient retention.


We also saw in an earlier article, the need for water to adhere to soil particles in order to stay available to plants. This brings us to a further split in Soil Porosity types. The Micropore space is actually broken down into two types of soil porosity called Micro and Meso Porosity. the word Meso comes from the Greek and roughly translates as middle; so we now have small (micro), medium (meso) and large (macro) pore spaces in the soil to think about.

The Mesopores are where most of the plant available water is held, whilst the very smallest Micropore spaces directly adjacent to the soil particle surfaces, usually hold water too tightly (due to surface tension) for plant roots to extract it.

Stages of Saturation in Bowling Green Soils

Imagine for a moment that your bowling green has just had a thorough soaking due to a heavy thunderstorm. Eventually, there will come a point in the deluge, when the green can take no more and puddles start to appear on the surface. When the rain stops, we will normally see the rootzone go through 3 stages of wetness.

1. Saturation Point

This is when all of the soil pore spaces (macro, meso and micro) are filled to capacity with water. In a well structured soil, this stage will be short lived as gravity will start to pull the water out of the macro pore spaces in the soil. Incidentally, the USGA golf rootzone specification lays down parameters for the speed of drainage from 150mm (6″) to 600mm (24″) per hour. The specification of the rootzone is altered to achieve this depending on the expected precipitation in the location that the green is being built in. Imagine that for a minute; these rootzones can be

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