NUTRIENT LEVELS AND THE GROWTH OF LETTUCE IN BLOCKING COMPOST

Peat blocks, prepared from growing media with a high content of sedge peat, are widely used for the production of young lettuce plants in the U.K. Storage of blocking media containing the slow release nitrogen fertiliser ureaformaldehyde resulted in large increases in the conductivity of calcium sulphate extracts of such media and high nitrate nitrogen accumulation.
Calcium and magnesium concentrations also rose during storage due to dissolution of dolonitic limestone in the medium.
Some of these cations probably replaced potassium ions on exchange sites in the sedge peat, causing a rise in potassium concentrations in water extracts of media.
Sulphate and phosphorus concentrations remained relatively constant in storage.

Growth of lettuce was poorer in blocks of stored media than in blocks of newly prepared media, but not greatly so.
Growth may have been much worse if plants had been raised under less favourable growing conditions eg. low temperature, low block moisture content.

The wet nature of sedge peat, and hence of blocking media, provides suitable conditions for both chemical and microbial degradation of slow release fertilisers.
If the latter are used as nutrient sources, then blocking media should not be stored for long periods.

Symposium on Substrates in Horticulture other than Soils In Situ

C.P. Turner, W.R. Carlile

https://doi.org/10.17660/ActaHortic.1982.126.26