ROW-CENTERED LOG RATIOS AS NUTRIENT INDEXES FOR SATURATED EXTRACTS OFORGANIC SOILS

Composition of soil solution was investigated in the top layer of a Ty pic Mesisol across seven crop sequences. Each sequence started and end ed with carrots (C) and included onions (O), barley (B) and weeded fal low (F) as follows: CCCC, CCBC, CBCC, CCOC, COBC, CBOC and CFFC. The s oil showed adequate pH and electrical conductivity values. Soil soluti on composition was assessed by the saturated soil extraction procedure . The changing levels of nutrients in the saturated soil extracts over seasons, years and crop sequences were analyzed using absolute values of nutrient concentrations, nutrient percentages relative to total so luble salts (the nutrient intensity and balance concept) and row-centr ed log ratios of nutrient concentrations or activities (compositional data analysis). The row-centred log ratio is the log-transformed ratio of a given element to the geometric mean of soluble elements. Nutrien t percentages were highly correlated with row-centred log ratios. The three relative nutrient expressions reduced seasonal variations as com pared with raw nutrient concentrations by incorporating component prop ortions. Concentration of total soluble salts was significantly correl ated (P < 0.01) with concentrations of NO3-N (r = 0.37), P (r = 0.80), K (r = 0.80), Ca (r = 0.96) and Mg (r = 0.92) in saturated soil extra cts. Between-years homoscedasticity as well as reduced skewness and ku rtosis for all nutrients were obtained using row-centred log ratios of ion activities. Other advantages of using row-centred log ratios are discussed.