We are still working on this page so please be patient!!
The key to managing soil and other growing media is maintaining a good structure with a high proportion of air filled pores, without restricting water supply.
There are various factors at play in maintaining this balance. The following definitions will help to understand these factors.
Saturation point - the maximum amount of water a soil can hold. This depends on total porosity - it rarely occurs as air gets trapped in the soil even during flooding.
Air Filled Porosity - The % by volume of air held in a previously saturated soil or growing medium when gravitational drainage has ceased at field capacity.
Field capacity - the amount of water remaining in a previously saturated soil after gravitational water is lost
Temporary wilting point - the point at which plants wilt during the day but can still recover at night. This happens when water loss exceeds water uptake.
Permanent wilting point - where plants wilt but do not regain turgor overnight because the roots can no longer extract water.
Soil moisture deficit - the amount of water required to return a soil to field capacity.
Available water content - the amount of water available to plants ina soil - between field capacity and permanent wilting point.
The above are affected by soil texture, structure, organic matter content and the amount of water added through irrigation and precipitation.
Irrigation techniques to maintain moisture levels in soil
Ebb and flow system - or flood and drain system, is used in commercial hydroponic growing systems. Plants are grown in an inert media in a grow tray. The ebb and flow system floods the grow tray with nutrients in a solution and then drains the excess back into a reservoir with a submerged pump on a timer. The media is then allowed to dry out before being flooded again. This short dry period forces the roots to grow in search of water, establishing a healthy root system for optimum nutrient uptake. Other benefits of this system are that it is low cost, compact and easy to build. They are highly efficient as it is all automated, and nutrients are recycled through the system so there is little waste. There are downsides to this system however in that it is:-
Dependent on electricity and a pump
Expanded systems are more complicated to build
Unstable pH and nutrient levels of the recycled solution
Need to watch for algae and pathogens in the open growing container
Getting the cycle timing right can be challenging
Overhead sprinklers
For use in polytunnels and glasshouses, overhead sprinkler systems are one the most versatile irrigation systems. They consist of a upvc pipe held up with straining wire, with attached sprinkler heads suspended at regular intervals over the growing area. They can be connected to a mains water supply and run on a timer for automated early morning watering and ensure an even distribution of water over the whole area. The downsides to this is that there can be some wastage of water due to drift and there may be a high operating cost.
Porous pipe
Made from recyled rubber, porous pipe or ‘soaker hose’ is often used in garden borders as it is flexible an easy to bend around corners and fit to shape. 16mm pipe is used for the borders and a smaller 6mm pipe can be used for plant pots and hanging baskets. Ideally a pressure regulator would link a tap to the soaker hose as high pressures can cause the pipe to split. Soaker hose is impractical over a large area due to its erratic drip pattern. As water travels along the hose water flow and pressure decreases until there is nothing left at the end of the hose. Porous pipe can only be used for lengths no longer than 20-30m and no more than 50m in total for an irrigation zone.
Drip irrigation
Drip line irrigation is an advanced method of drip irrigation. It has pressure compensating drip emitters fitted every 33cm along its length. This means that flow requirements can be calculated to ensure efficient watering with minimum waste. They are easy to install and can be used effectively in larger areas, with runs up to 150m possible in one irrigation zone. The main drawback with this system is its initial expense, but with a lifespan of up to 20 years this may be worth the outlay.
Water balance sheet
P=E+Q Precipitaiton = Evapotranspiration + streamflow - where there are no changes in storage
A water balance chart compares the total water supplied to the site, the actual water consumed within all the water end uses in the site, and the total water leaving the site. This will help to identify areas of significant water usage and problem areas, including leaks and uncontrolled losses.
Drainage techniques to improve soil aeration
Good aeration is vital for growing plants. On wet soils it may be necessary to install drainage in order to improve growing conditions. In order to identify areas of poor drainage you can :-
After it has rained look for puddling on the surface of the soil. This may be due to compacted soil, groundwater from a spring or a broken irrigation pipe. In these situations drainage may not be necessary.
Dig a hole 50cm deep and fill it with water. Cover the hole to prevent rain entering and monitor how long it takes for the water to drain away. If it doesn't drain within a day you might want to consider installing drainage.
Often drainage issues can be solved without installing underground drainage. If an area has become compacted it may be just a case of digging or rotavating to break up the compacted layer and adding lots of organic matter to improve soil structure. See soil cultivation