fertigation methods

Root Zone Monitoring

It is well known that to get good root growth, avoid disease problems, to avoid the waste of water and fertilizer and to steer the crop to optimize quality and yield, root zone conditions must be tightly controlled. This means that irrigation quantity, frequency, EC and pH must be tightly controlled and frequently adjusted to achieve ideal root conditions. The media must be allowed to dry down a little overnight and to wet up quickly in the morning. Then the run-off must be controlled to avoid excessive EC build up in the media whilst at the same time keeping media moisture level satisfactory. So how do you know if your watering settings are achieving the desired goal? Without any monitoring of the root zone this is just guess work.

Manual monitoring

Buckets can be placed at strategic points in the greenhouse to catch samples of both irrigation water and run-off. These are emptied each morning and measurements of EC, pH and depth are taken at each bucket a few times per day. A check must be made at each run-off bucket at 10:30 or 11:00am to ensure run-off has started. Run-off EC should be measured early afternoon to ensure that sufficient flushing is occurring to bring this down to the target level. The moisture level in the slabs or pots should also be measured a few times per day using a hand held moisture meter. Note that when doing this it is difficult to get comparative readings as it will depend exactly where the probes are inserted and how much pressure is exerted on the media. If inserted multiple times in the same place the media can become loose and give a lower reading but if compressed the air will be expelled and it will read much too high.

Automatic data logging

The MINDER system from Autogrow provides a superior solution as the moisture probe is embedded in the media and left. This provides better comparative readings from one day to the next. The MINDER measures the irrigation quantity (from one dripper) together with the irrigation EC and pH. It measures the moisture level and temperature in the media and also the run-off quantity, EC and pH. This allows the run-off ratio to be calculated and displayed as a graph along with EC’s, pH’s, media moisture and temperature. This gives a very complete picture of conditions in the root zone and allows fine tuning of the fertigation system. By selecting to view, say, 7 days data on one screen, trends are easily identified and the sophisticated alarm system allows alarms to be set so that if run-off is achieved by, perhaps, 11:00 am an alarm will be sounded.

In addition to the root zone parameters, a solar sensor may be added measuring Joules/cm2. Irrigation theory says that for every J/cm2 of sunlight received, around 3ml of water should be applied per m2. The system can calculate this ratio, display it graphically and alarm if the condition is not met.

Jeff Broad

Autogrow Systems Ltd