Phosphorus Fertilization in Turf – Turfgrass Science at Purdue University

Phosphorus Fertilization in Turf

Phosphorus (P) fertilization of turf is being questioned nationally for two reasons. Phosphorus fertilization almost never induces a visual turfgrass response and deficiency symptoms are rarely seen, thus calling into question the need for P fertilization. Secondly, higher levels of P contribute to algal blooms and decrease water quality of ponds, lakes, and streams. Since phosphorus is extremely immobile in the soil, elevated P levels in bodies of water likely result from P moving on eroding soil particles, which would be expected in agricultural fields or on newly planted lawns. However, there is some question if P enters surface water in other unexpected ways. A number of research projects across the country are currently examining phosphorus fate in turf, but it will be a few more years before definitive results can be expected. Until we definitely know fate of P applied to turf, it is best to be conservative with our P fertilization. Following are our current Best Management Practices for phosphorus:

1) Never dump clippings into a water bodies or storm drains (clippings contain 1-2% P by dry weight). Avoid dumping tree leaves into water bodies or storm drains for the same reason.
2) Avoid spreading fertilizer onto impermeable areas like walks, drives, and cart paths, and then sweep or blow fertilizer off these areas back into the turf./p> 
3) Avoid spreading fertilizer into water bodies, leaving an untreated buffer strip. The steeper the slope and thinner the turf, the wider the buffer strip should be.
4) Phosphorus is important in seed and sod beds to hasten establishment, decreasing weed invasions and future pesticide use. Therefore, apply 1.0 to 1.5 lbs P2O5 at the time of sodding or near germination of seed (See Table 1 for specifics). Note: P is listed as %P2O5 by weight on the fertilizer label.
5) Soil test every 2 to 3 years to determine P requirements. Realize that many IN soils have adequate P already and/or multiple of years of P fertilization may have built up levels to adequate. Table 1 can serve as a guideline for interpreting soil tests (these are more conservative than our earlier recommendations). As a general rule of thumb, it takes approximately 0.5 lb P2O5/1000 ft2/yr to maintain soil test P levels where grass clippings are returned and 1.0 P2O5/1000 ft2/yr per year to maintain soil test P levels where grass clippings are collected.

Table 1. Purdue University ‘s 2005 phosphorus recommendations for newly planted turf and for annual fertilization of established turf.

Soil test values
sod or seed 
(lb. P2O5/1000 ft2)
(lb. P2O5/1000 ft2/yr)

lbs P/A

0 – 13
0 – 25
13 – 25
26 – 50

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