Water and watering – don’t underestimate their importance!
by Jon Harris, Horticentre
We all know how important adequate supplies of good quality water are for optimum crop production but when did you last have your water tested?
An indication of maximum desirable source-water component levels is contained in the table below:
|
Component |
Maximum desirable (ppm) |
|
Nitrogen |
5 |
|
Phosphorus |
5 |
|
Potassium |
5 |
|
Calcium |
120 |
|
Magnesium |
25 |
|
Chloride |
100 |
|
Sulphate |
200 |
|
Bicarbonate |
60 |
|
Sodium |
30 |
|
Iron |
5 |
|
Boron |
0.5 |
|
Zinc |
0.5 |
|
Manganese |
1.0 |
|
Copper |
0.2 |
|
Molybdenum |
0.02 |
|
Fluoride |
1 |
|
pH |
7.5 |
|
E.C. |
1 |
Apart from the requirement for quality water, there is also a very important need to understand whether we are delivering too little, too much or just the right amount of water to our crops.
What are the consequences?
Too little water (apart from the obvious direct plant stress and wilting) will encourage fertiliser salt accumulation and a worsening situation over time.
Too much water can result in saturated media/soil with low oxygen levels resulting in root tissue death. Dead root tissue is the perfect entry site for root disease pathogens such as Phytophthora and Pythium!
How do we know whether we are under or over-watering?
We do not want to see wilting to determine under-watering nor do we want to see plant death to conclude over-watering! Long before we see these dramatic results, the plants have suffered greatly and sometimes irrecoverable yield loss has already occurred.
The more-sophisticated operations will have solarimeters or light-joule counters that ‘integrate’ light and irrigation in an effort to match plant activity with water requirement. They will also usually have water-content meters and/or weigh-scales to monitor irrigation scheduling. Less sophisticated operations do not have these tools but can utilise manual monitoring of representative bags or slabs. They can do this by regularly measuring irrigation volumes being applied and also drain volumes leaving the substrate. A number of factors need to be considered when determining optimum irrigation strategies – substrate, crop type, stage of growth, weather conditions, dripper capacity etc etc. Irrigation start and stop times also need to be considered carefully (remember the golden rule: transpiration then irrigation).
Please talk to your Horticentre representative for assistance with this subject.
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