MONITORING NUTRIENTS & SALT
Leaching Studies

We are sometimes asked whether FullStop can be used in a 'regulatory' role to ensure there is no leaching of nitrate below the root zone of a crop. The answer is no and yes.

The answer is 'no' because FullStop has a minimum sensitivity at which it can detect a wetting front. If the soil is drier than a suction of 2 to 3 kPa, but some water is still draining, the FullStop will not be activated. Moreover, wetting fronts get weaker as they move deeper into the soil. The deeper a FullStop is placed, the greater the chance that a wetting front will be missed.

The answer is ‘yes’ in the sense that there is no easy way to do leaching studies, so the FullStop might be a good way to start. To quantify the amount of nitrate moving past the root zone you need to know both the rate that water is moving downwards and the concentration of nitrate in the water. Several tools can give the concentration of nitrate, but measuring the rate that water is moving downwards is very difficult indeed.

FullStops were not designed to show how much water or nutrient is leached. It is a management tool that tells the irrigator how deep a strong wetting front moved and the composition of that water. The rapid feedback allows timely decisions to be made so that the possibility of water and nutrient leaching can be reduced.