WATER-SATURATED EXTRACTS AND THE FATE OF NUTRIENTS IN A DECLINING MAPLE STAND

The soil solution provides the majority of essential nutrients needed for plant growth. Obtaining this solution in situ presents logistic pr oblems and therefore most results are obtained from air-dried soils, e ven though chemical properties of soils can be substantially modified by drying. Water-saturated extracts obtained from dried soils were tes ted for their efficiency to detect the effects of in situ fertilizatio n with P-TSP, K-K2SO4 and Ca-Ca(OH)2 on the Ahe horizon of a maple sta nd. Results obtained with water-saturated extracts on dried soils were compared with those obtained from conventional (exchangeable) extract ion on dried soils and to those obtained from extraction with a soil:w ater ratio of 1:5 on dried soils. A similar experiment comparing water -saturated extracts with the soil:water ratio of 1:5 was carried out u sing soils fertilized in vitro. The effects of fertilization were clea rly evident with saturated extracts when these could be observed by co nventional analysis. Furthermore, the saturated extract indicated pote ntial toxicity of Al in relation to pH. For the same samples, the satu rated extracts were more sensitive than the extracts with a soil:solut ion ratio of 1:5, especially with regard to element ratios not easily expressed by conventional analysis. The originality of this method res ts on a combination of efficient centrifugation with a double bottom c ontainer, the convenience in the utilization of air-dried soils and th e use of near water field capacity as a representative water content.