soil test P (17), with greater effectiveness indicating more rapid change in soil test P per
unit of fertilizer P applied (poorer buffering), and greater long term risk of P loss.
The objective of this study was to determine how repeated N-based applications of
organic fertilizer sources to established turfgrass affected soil test P and P saturation in
native soil and a sand-based rootzone mixture under field conditions.
FERTILIZER APPLICATIONS
AND MEASUREMENTS
For this study, fertilizers were applied on
an N basis, using natural organic and synthetic fertilizer sources on perennial ryegrass
plots on two rootzone media over 3 years
(July 2008-June 2011). Soil samples from
the plots were analyzed to determine
changes in P availability in each treatment
area after three years of applications. Application rates of the fertilizers were based on
their N content for the original experimental design; therefore, P levels were not
www.stma.org
Table 2. Annual nitrogen (N) and phosphorous (P2O5) application rates for soil and sand root zones.
equalized among treatments.
Perennial ryegrass was grown on both a
Puyallup fine sandy loam native soil
(coarse-loamy over sandy, isotic over mixed,
mesic Fluventic Haploxerolls) and a USGA
sand/peat 90/10% rootzone mixture in the
Puyallup Valley of western Washington,
south of Seattle. The plots on the native soil
were maintained at 62.5 mm as a home
lawn and the plots on the sand/peat mixture were maintained at 12.5 mm as a golf
course fairway. All grass clippings were returned to the plots. The experimental design for each site was a randomized
complete block with five fertilizer treatments and four replications. Plot size was
1.5 m by 3 m.
Each plot was fertilized with one of five
treatments. The treatments included two
natural organic fertilizer sources at a 1× and
a 1.5 × N rate and a synthetic slow-release
product at a 1× N rate. The target annual N
SportsTurf 11
