Chemistry of plug production Neil Bragg Product Development Director Bulrush Horticulture Ltd

Issues to consider: Physical size of the plug unit Water quality Chemical properties of ingredients Practical fertigation Monitoring for quality,

Different size of plug units 350’s to 28’s – volume of units Tray Vol mls 350 4.7 230 7.5 40 87.5 28 285

Water quality and the issues surrounding: Most important characteristic: ALKALINITY –degree of temporary hardness, Soft water – rainwater collection – 10-120ppm Alkalinity Issues Calcium and Magnesium supplies Medium Hard water 120 -220 ppm Alkalinity May be worth ‘softening’ water via acid injection Choice of acids, Nitric and for lower levels of hardness citric acid Hard water – 220-330 ppm Alkalinity Acid treatment needed to release Calcium and Magnesium, avoid Increasing pH and hence lock-up of elements such as Iron (Fe).

Chemical properties of ingredients: Ref: Technical monograph: Growing media laboratory methods, ADAS 2016 – ISBN: 978-1-5262-0393-9 Moving towards new materials we need an understanding of things such as the CEC of materials:

Issues of moving away from peat pH control in relation to spp: Petunia vs Geranium Supply of Calcium and Magnesium Other sources, Gypsum & Epsom salts Leaching potential CP095 Fellowship work Water holding capacity Ease of filling plug trays

Feeding to achieve optimal growth: Koranski – favoured the stages of growth approach For ageratum Stage 1, 2-3 days fertiliser 50ppm Stage 2, 7 days fertiliser 50ppm Stage 3, 14 days fertiliser 150ppm

Example taken from Plug and transplant production – Styer & Koranski

Issue of achieving the N inputs Feed containing 150mg/l N How much is actually applied per watering? Might be 5mls – Equivalent to : 0.75 mg N applied??????? Once or twice a week???

Monitoring of substrates in plugs Squeeze tests Saturated paste Lab 2:1 extraction Probes Interpreting values- building the picture