Science Into Practice - Irrigation needs of substrates

This project developed and tested irrigation schedules for reduced, peat-free and industry standard growing media to help cut water use while maintaining or improving crop quality.

Three species (Ribes sanguineum 'Koja', Escallonia rubra 'Crimson Spire' and Sidalcea oregana 'Party Girl') were selected because all are moderately resistant to drying out. They were grown in three substrates: 25 per cent bark, 75 per cent peat (Sinclair, "standard peat-based"); 25 per cent wood fibre, 25 per cent bark, 50 per cent peat (Bulrush "reduced peat"); and composted green waste and bark (Vital Earth "peat-free").

Work in the first year found the optimum water content and irrigation "setpoints" for each substrate. Irrigation schedules for each crop in each mix were developed and used for two full seasons while crop growth and quality was measured.

Schedules that reduced or eliminated "run-through" were drawn up for each of the irrigation systems and growing media. Scheduling was achieved using moisture probes in representative pots that triggered irrigation when the moisture content fell to a pre-set level.

The quality of plants was similar regardless of which substrate they were grown in. To maintain the optimum moisture content, irrigation was applied more frequently to plants growing in the peat-free substrate. Automated scheduling prevented over-irrigation.

The approaches developed could be used to identify optimum substrate moisture contents for most crops and growing media.

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