DEVELOPMENT OF A RAPID NUTRIENT TEST KIT FOR HORTICULTURAL SUBSTRATES
The 1:1.5 water extract laboratory method for horticultural substrates developed by Sonneveld et al. in Holland for horticultural substrates was adapted as a rapid nutrient test kit for grower use. Horticultural substrates used for this investigation included peat, pumice, bark and sawdust in various combinations and containing 5 levels of NH4-N, NO3-N, P and K for each substrate. These substrates were extracted either for 15 minutes using an orbital shaker or for 2 minutes by vigorous shaking by hand, and the extracts analysed for N, P and K using standard autoanalyzer (AA) methods. There was a high correlation between the machine and the hand extraction with the amounts extracted being similar. The NO3-N value determined in the extract using Merck nitrate strips was well correlated with the AA method although it tended to underestimate the value. NH4-N, P and K by visual methods gave satisfactory results in relation to AA methods. Test carried out by 5 independent operators using a commercial test kit based on this research gave very satisfactory results on 3 samples bearing in mind that for horticultural substrates frequent analysis is the norm; therefore the degree of accuracy required is less than for conventional test of field soils. This test kit can be easily adapted for rock wool and for hydroponics culture.
Prasad, M. and Spiers, T.M. (1989). DEVELOPMENT OF A RAPID NUTRIENT TEST KIT FOR HORTICULTURAL SUBSTRATES. Acta Hortic. 238, 75-82