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Gypsum Blocks

Measuring Principle

Gypsum Blocks or G-Blocks are an evolution in design. They provide quick response and true sensitivity to conditions where moisture remains relatively high. All G-Blocks are wetted and checked for speed of response and ability to maintain overall consistency from block to block prior to shipping. The design of electrode spacing ensures a sensitive response to changing moisture conditions below 2 bars of matric suction with overall operating range to 10 bars of matric suction. G-Blocks provide significant improvements over any competitive or older style blocks.

Optimise water usage

There are several methods to optimise water use with G-Blocks. The first, and easiest, is the "Limits Method". This simple, but effective, method requires that you determine the limits to which you want water to migrate. Plant maturity, rooting depth, rooting patterns and the system of irrigation will help you to determine these limits. Older and less effective irrigation, such as flood or furrow, will have a broader range of water limits; shallow rooting and precision applicators will have a narrower limit band. The G-Blocks are placed at the minimum water level (minimum refill point) and at the maximum water depth (maximum refill point) for irrigation cycles. Frequently another G-Block is placed at a depth past the maximum refill point to ensure irrigation water does not exceed the set minimum-maximum limits.

The second method is the "Matrix/Segmental Method" which is simply an extension of the "Limits Method". By placing additional G-Blocks between the minimum-maximum limits, you are able to more accurately monitor subsurface moisture due to root uptake, evaporation, and the water release characteristics of different soil types. This added information can be used to more accurately determine the precise level required for partial recharges.

Manually reading G-blocks

G-blocks are often read manually with a hand held reader. The reader is small, light weight, battery powered and has a digital readout.

Typically a number of G-blocks (3 or more) will be buried in the soil at different depths across several sites depending upon the size of the farm or experiment. Each G-block has two bare wires which are left protruding from the soil surface. These wires are clipped onto the hand held reader terminals and then the read button is pressed to immediately display the current soil tension. The reading is manually recorded in a notebook, the wires unclipped and then moved to the next G-block.

Logging G-blocks

The most common method of reading G-blocks is by automatically recording the data using a datalogger. The advantage of using a datalogger is savings in time, labour and guaranteed frequency of collection of the soil tension data. However, not all dataloggers can read G-blocks because of the need for AC excitation of the sensor.

The ICT smart logger can read G-blocks as it uses a smart interface that can accept between 1 and 4 G-block sensors. The smart interface, incorporates a micro-controller that remembers all the calibration and sensor details making it a smart sensor that no longer requires any programming. Used in this manner G-blocks become truly plug & play allowing the user to focus on data interpretation rather than difficult time consuming setup procedures.