Hort Science Online: Important plant health measures when considering reducing peat or going peat fr

Optimising Plant Nutrition in Peat Free and Reduced Peat Growing Media Andrew Wilson Technical Manager ICL Professional Horticulture

Reducing Peat in Growing Media

• When changing your growing media it is important to understand the new mixes and adapt nursery processes to make the most of the new media.

Optimising Plant Growth and Nutrition in Peat Free and Reduced Peat Growing Media

Peat alternatives and their What are the current peat alternatives properties Bark  

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By-product of timber industry Not composted, but must be matured (to avoid nitrogen drawdown) Used for structure and air in the substrate

Woodfibre   

Related to nutrition  

Low water holding capacity Slight N-fixation

Low bulk density (cheaper in transport); High air capacity Safe in use: Low risk of Contamination Consistent product

Green compost      

Related to nutrition  

Lower water holding capacity N-Fixation

High bulk density Good water holding Cheaper than peat High nutrient content Variable product Risk of contamination

Coir (Coconut fibre)    

Related to nutrition   

High Bulk density; Risk of high EC levels; N-dynamic, unknown mineralisation

Low bulk density Good water retention and air capacity; Good handling characteristics; Quality variable from Sri Lanka

Related to nutrition   

Lower water holding capacity; High pH possible!

Possible salinity effects!

Peat Free – factors to consider

1.

2.

3.

4.

5.

Beneficial effects; Available nitrogen; pH and Calcium in the substrate; Compaction (slumping) Irrigation

Optimising Plant growth and Nutrition in Peat Free and Reduced Peat Growing Media

1. Beneficial Effects

Peat alternatives, when used correctly, have significant benefits:    

Good rooting, because of high AFP (Air filled porocity) ; Good drainage of water; Good re-wetting ; Low weight (except green compost)

Optimising Plant Growth and Nutrition in Peat Free and Reduced Peat Growing Media

2. Available Nitrogen

Peat alternatives generally require additional Nitrogen due to:  Lower buffering capacity meaning nutrients are more easily leached;  Lower water holding capacity with more frequent watering;  Nitrogen lockup from woody materials

Optimising Plant growth and Nutrition in Peat Free and Reduced Peat Growing Media

1. Available Nitrogen 100% Peat

70% Peat + 30% Woodfibre (With equal nutrition)

 Add extra nitrogen, to compensate N-fixation, during entire culture (not only first 6 weeks)!;  Also be aware of effects of low nitrogen in the other peat substitutes  Ensure bark is fully matured

Supplementary Nitrogen Nitrogen is usually added as Calcium nitrate , very soluble & leachable : After extensive testing , ICL have developed 3 new Nitrogen products to give longer term nitrogen release and reduce leaching.

70% Peat + 30% Woodfibre No extra N added

Supplementary Nitrogen products for peat reduced growing media

Use these products alongside your standard Osmocote or water soluble

Supplementary Nitrogen Recommendations for peat reduced growing media

3. pH of the Growing Media is influenced by:  Composition of growing media

> Peat alternatives have a higher pH and a lower pH buffering capacity to resist changes;

 Dolomitic Lime incorporation to raise pH of the growing media adds Calcium and Magnesium;

> Peat Free growing media needs only 1 third of the Lime rate adding less Calcium and Magnesium

 Feeding program during culture

> Choice of Nitrogen source can raise or lower pH; eg Ammonium Nitrogen can lower pH

 Irrigation

> Composition of the water, but also amount added per cycle > Level of bicarbonates (HCO3) in the water Optimising Plant growth and Nutrition in Peat Free and Reduced Peat Growing Media

4. Possible Slumping with peat substitutes During potting

…after +/- 1 month 100% peat:

100 %peat

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‘Heavy’ substrate;

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Good possibilities for liming and buffering

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Ensure a good air content in the pot!

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Ensure water is evenly distributed in the media ,

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Avoid completely drying out

When a substitute with low bulk density is added (= lots of air):  

70% peat + 30% substitute (example: bark, woodfibre, coir) Optimising Plant growth and Nutrition in Peat Free and Reduced Peat Growing Media

 

Don’t apply too much pressure when filling pots (then the air is ‘gone’)!

Ensure ‘matured’ components and reduce slumping Be aware of dilution-effects! (less substrate and hence fertilizer per pot than planned) Mixes of several peat substitutes reduces slumping

5. Irrigation 

Different compositions of the growing media require different methods of irrigation.

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Get used to the ‘new requirements’ of irrigation in your pots, when you make changes.

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Less water-holding capacity means quicker drying out

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Aim for even moisture in the rootzone

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The plant always needs water for the absorption and transport of nutrients!

Optimising Plant growth and Nutrition in Peat Free and Reduced Peat Growing Media

Irrigation peaks

Equal moisture

Optimum moisture in the root- zone, is crucial for root-development!

Irrigation Tips  Add extra wetting agent, such as H2Gro to maximise irrigation efficiency and save water;  Use shorter more frequent irrigation cycles;  Monitor pot moisture levels to manage irrigation effectively  Media may appear dry on the surface but still be moist in the pot

Optimising Plant growth and Nutrition in Peat Free and Reduced Peat Growing Media

Solutions to Peat reduced challenges Possible challenges for growers, regarding nutrition in peat-reduced substrates:  Changes in substrate = changes in culture!  Different way of irrigation: Keep control of your pot-moisture!

Solutions

For applications in Advice from ICL substrates

Specialists

Wetting Agent

 Different pot temperatures (than with 100% peat)  Extra Nitrogen needed to compensate ‘N-fixation’;  Less peat = less space for liming!  Less peat = less buffer-capacity for pH  Apply the correct rate of fertilizer

CONCEPTS

Things to remember when growing in peat reduced and peat free 1. Adapt irrigation to reflect the potentially lower water holding capacity of peat free substrates 2. Extra nitrogen will be required to compensate for nitrogen lock up with the peat free growing medium, particularly if containing wood based products 3. Peat Free materials generally have a much lower buffering capacity than peat growing media, meaning nutrients are easily leached 4. Peat free growing media require less lime to correct the pH and provides less calcium and magnesium which needs to supplementing in other ways 5. Before growing in peat free growing media it is important to review the nutrition of the mixes. Your ICL Technical Area Sales Manager will give specific advice

Optimising Plant growth and Nutrition in Peat Free and Reduced Peat Growing Media

Thank You Optimising Plant growth and Nutrition in Peat Free and Reduced Peat Growing Media