Maintaining a correct soil moisture level is an important aspect of gardening. Most gardeners know too little moisture in the soil will adversely affect plant health, but excessive watering is just as detrimental. Overwatering can flush vital nutrients beyond the reach of plant roots, prohibit proper root growth, promote plant disease and waste water and money. Learning how to measure the moisture level in soil will help to establish a proper irrigation schedule for your gardens.
The gravimetric method measures the moisture level in soil by comparing an unaltered soil sample against a dried soil sample from the same area. The method used several soil samples are taken from various points throughout an area. It is important to take these samples from points that represent the average soil level. Mix the soil samples together and weigh a 25-g sample of the mix. Weigh and dry it either in the microwave or oven, and checked the weight for changes every five minutes. When the weight no longer changes, this indicates that all the moisture has been removed from the sample. Using a chart that lists the bulk density and wilting point of five different soil types, you can determine the average available water in the soil.
Soil Moisture Blocks
This method works by measuring the amount of electricity conducted through the soil. Since water conducts electricity, the more electrical current present, the higher the moisture content in the soil. Two types of blocks are available for this method: gypsum blocks and granular matrix sensors. The block is buried in the soil, ensuring optimum block-to-soil contact. Complete contact with the soil is important, which is why this method works best for loose soil types. The blocks absorb water from the soil and the moisture levels are shown on an attached data logger or a portable, hand-held meter.
Feel and Appearance
The feel and appearance method is, by far, the least accurate method for measuring moisture in soil, but it requires no additional equipment and is suitable for hobby gardeners that don't need exact data. This method teaches gardeners how different soil types should feel and look with varying moisture levels. For all soil types, a handful of soil, squeezed tightly, that leaves a moist outline on the palm of your hand indicates 100 percent water capacity. This is excessive moisture in the soil, as the desirable moisture level is of 40 to 60 percent. Soil with proper moisture levels should appear dry or slightly crumbly. When squeezed in the hand, coarse and moderately-coarse soil types, such as sand or sandy loam, should not form a ball that sticks together when the pressure is released. Medium to fine soils, such as loam or clay, form a ball that holds when released.