Effects of Time and Height of Cut on Rooting Activity of Merion Kentucky Bluegrass as Measured by Radioactive Phosphorus Uptake¹

Abstract

Radioactive phosphorus provides a means by which the depth and lateral extent of ‘Merion’ Kentucky bluegrass (Poa pratensis L.) rooting can be measured over the growing season under field conditions. Each 15.2‐cm (6‐inch) depth increment, irrespective of the height of cut, was found to have 1.5 to 3 times as much root activity as the increment immediately below it. The depth of rooting activity was least in the spring (May) and increased to a maximum in the fall (October). The relative lateral distribution of root activity for both heights of cut was approximately 62, 27, 8, and 2% of the total activity for each 5.1‐cm (2‐inch) lateral strip from the line of injection. The lateral extent was least in the spring and greatest in the fall. Throughout the growing season there was more total root activity with the 4.4‐cm (1 ¾‐inch) cutting height than with the 2.2‐cm (7/8‐inch) cutting height. In comparison to the radioactive phosphorus method, the physical measurement of roots tends to overestimate the importance of the roots above 20.3 to 25.4 cm (8 to 10 inches) and underestimate the importance of the roots below this depth.

Effect of P, K, and Lime on Growth, Composition, and 32P Absorption by Merion Kentucky Bluegrass1

“…Apparently, fewer roots andjor a lower activity of those present contributed to this phenomenon. Less absorption at lower depths has been reported by O'Donnell and Love (10). They found this relationship of uptake and depth to be consistent to 76.2 em.…”

“…Volume, weight, and distribution of roots provide useful information, but none of these measurements necessarily reflect the activity or absorptive capacity of the root system. Tracer techniques with 32 P have been used to measure the absorptive capacity of plants (2,4,10,12,15), and it was concluded that…”

Growth of Scotch Pine Trees in Bluegrass Sod as Affected by Fertilizer Depth, Release Rate, and Season of Application

“…The 30 cm depth placed the fer tilizers within the pine effective soil volume but below the top 15 cm (6 in) of the bluegrass root system. O'Donnell and Love (12) found that this placement re duced bluegrass absorption of fertilizer nutrients from the top 45 cm (18 in) of soil by as much as 690/0. The slowly dissolving, compressed fertilizer resulted in the greatest increase in trunk caliper (Fig.…”

Root Interaction Between Bromus Tectorum and Poa Pratensis: A Three-Dimensional Analysis

“…The root growth for both species in monocultures as reported here agrees closely with other published accounts. Using a radioisotope injected into the soil, O'Donnell and Love (1970) found that P. pratensis is relatively shallow rooted. Roots and rhizomes of 2-yrold plants were within 30 em of the soil surface and had a maximum lateral spread of 20 em.…”