Soil testing of horticultural substrates (iii) Evaluation of 1: 1.5 water extract and Olsen's extract for phosphorus

1981 
Abstract The 1: 1.5 water extraction and Olsen extraction of horticultural substrates for P were evaluated using P uptake as the criterion. Three crops, tomato, chrysanthemum (2 trials) and verbena (2 trials) were grown in a number of substrates including peat, peat + pumice, bark, peat + sawdust + sand and peat + soil. The number of P application rates varied from 8 for tomatoes to 20–22 for the other two crops. The relationship between both the soil tests and P uptake was quadratic rather than linear, and was generally very good (R2> 0.8 in most cases). Generally the water extractable P gave marginally higher R2 when regressed against P uptake, than Olsen P for most of the non‐soil substrates when each substrate was considered separately. When the substrates were combined for any one trial the relationship deteriorated somewhat as P uptake per unit of soil test was not constant for all materials. This deterioration was more marked in the water extractable P than the Olsen P. When a substrate contained a...
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