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Haifa Blog

22Jul2018
Every plant gets the same amount of water and food

Commercial crop production requires even growth of plants. To achieve this, water and nutrients must be distributed homogeneously. Unfortunately, we see considerable  differences between the drippers along the line, sometimes even between two neighboring drippers. 

Just increasing the irrigation rate will ensure that all plants get enough water, but now some plants will be irrigated in excess.

More water also means higher fertilization rates, sometimes to a level that risk the plants. We know that almost all the ammonium in the feeding solution is absorb by the plant. Potassium uptake also increases as its concentration in the solution rises.

 

More ammonium = reduced pH

Ammonium fertilization reduces the pH of the growing medium. Down to pH level of 5.2, this reduction improves the availability of phosphorus, manganese and other nutrients for plants uptake.  When the pH declines below 5.2, the growing medium might decompose, particularly where rockwool is used.

If distribution of water and nutrients is uneven, plants that get less water and ammonium are also exposed to higher pH, and consequently lower availability of phosphorus and manganese. If the pH level is 6.5 or higher, these nutrients are likely to  in case the pH is above 6,5  both elements shall be deposit in the system and not available form insoluble precipitates, thus becoming unavailable for plant uptake.

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More potassium = calcium deficiency

If there’s more potassium given to the plant the plant prefer the uptake off potassium and at the same time the uptake of calcium decrease. Calcium is very important for strong cell walls and higher uptake off calcium helps to avoid blossom end-rot and sensitivity for fungus

Based on this information we know that the difference between plants can be big if the amount of water supplied to the plants is not the same to all plants. This means that cleaning the dripping system only when changing the plants is not enough. Best is to keep the system clean during the growing season. There two ways to do this.

When the plant receives high potassium levels, it absorbs more potassium instead of other essential nutrients, mainly calcium. Calcium is responsible for the strength of cell walls. It helps preventing Blossom End Rot (BER) and blocking fungal attacks.

Summarising the above, non-uniform distribution of irrigation water might result in considerable difference between the growth conditions of each particular plant, leading to uneven development. To avoid this unwanted situation, it is advisable to keep all the components of the drip system clean throughout the season. Occasional cleaning when replacing plants is definitely not enough.

 

Cleaning with hydrogen peroxide 

There are two common ways to keep the drip system clean, namely hydrogen peroxide products and polyphosphates.

Hydrogen peroxide oxidizes organic particles in the water. When the system is already contaminated, the first step to be taken is washing with hydrogen peroxide products. Figure 1 shows how the organic particles connect to the mineral deposit in the drippers, where the water and the temperature allow them to thrive…and block the drippers.

 

Figure 1

Figure 1

 

Hydrogen peroxide products are available in various formulations. The stabilized products give the best results. In general, dosage of 25 ppm in the tank, giving 10 ppm in the dripper, is recommended. Use test strips to check and tune the dosages if necessary.

 

 

Products based on polyphosphates

Polyphosphates dismantle mineral deposits containing calcium, sulphate, iron and phosphate. Addition of polyphosphates to the drip system returns these elements to the solution, making them available for plant uptake. In contaminated system, add 30.9 mg/ltr P in the form of polyphosphate. When the system is clean, use 15.5 mg/ltr P in the form of polyphosphate. The rest of the phosphorus needed for the crop's nutrition can be given in the form of orthophosphate (e.g. MAP or MKP).

 Polyphosphate products are available in different formulations that may be classified into three groups:  

1) Polyphosphates containing potassium and in some cases also nitrogen. The pH of these products is very high pH, so you'll need to add extra acid to the nutritional solution.

2) Polyphosphates containing sodium. Although featuring neutral pH, these products are not recommended for continuous use, because of the adverse effects of the sodium.

3) Polyphosphate products with potassium and nitrogen that feature a neutral pH. These products require no addition of acid, so they are safe and convenient for use.

Picture: Ronald Valke

 

Summary

  • It’s very important that all drippers emit same amounts of water
  • If the system is contaminated, do the following
    1. Treat with stabilised hydrogen peroxide product for two weeks
    2. Then, treat high dosages of polyphosphate (30.9 mg/ltr P)
    3. When the system is clean, reduce the polyphosphate dosages (15.5 mg/ltr P)
  • Use polyphosphate with neutral pH and no sodium

If polyphosphates are used routinely, there is no need to clean the system when replacing plants

 

 

 

Ronald Valke

Haifa North West Europe BVBA | Sales Manager


This article was published in the Finish magazine "Tradgardsnytt"

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