The Absorption of Phosphate and Calcium From Different Depths in Soil by Swards of Perennial Ryegrass

A method for measuring the depth in soil from which plants absorb nutrients is descrihed. Radioactive tracers are injected at different depths and when allowance is made for any variations in the extent to which the added tracer is diluted hy labile ions in the soil at each depth the relative quantities of nutrient taken up from different depths can be calculated. Results obtained with perennial ryegrass swards of contrasting age indicated that the nptake of P and Ca always occurred predominantly from within the top 12.5 cm of soil. Apart from the initial few months of a sward's life, the proportion of both elements absorbed from different depths for a whole growing season varied little with age of sward up to 3 1/2 years. Considerable changes in the relative contrihution of different depths of soil to uptake occurred within a season; the extent of uptake from the surface layers was primarily influenced by variations in soil‐water content and the application of fertilizer to this region.