In yesterday's mail I received a big package containing the International Turfgrass Society Research Journal Volume 12, which stretches to 848 pages, and that is before the subject and author indices! This book contains the papers presented at the International Turfgrass Society Conference held this month at Beijing.

I didn't attend – various other travel in the past month saw me fly on Boeing 787, 777, 767, 747, and 737s, as well as bullet trains, rapid trains, express trains, and local trains, along with innumerable ferries, buses, taxis, and private vehicles, so I was not anxious to travel any more – but the contents of the journal have left me ensorcelled, and I will share some of my favorite articles here over the next few weeks.

The paper I was most excited to read was this one, Influence of Phosphorus and Nitrogen on Annual Bluegrass Encroachment in a Creeping Bentgrass Putting Green, by Raley et al. Some of the highlights, which I will quote from the paper:

Changes in annual bluegrass cover due to P treatment were detected on all evaluation dates. Annual bluegrass cover always increased, relative to the pre-treatment population, in plots treated with P versus those in which no P was applied.

Increased levels of P in the current study had no effect on clipping yield

Tissue P concentrations above those found in the [no P applied] treatment tended to show greater annual bluegrass cover

Results of this study demonstrate that annual bluegrass encoachment into a newly established creeping bentgrass putting green can be curtailed by withholding P fertilizer such that soil P concentrations and P uptake are below levels that foster the competitive ability of annual bluegrass.

After 2 years of treatments, soil Mehlich 3 phosphorus concentrations were positively correlated with changes in annual bluegrass cover; treatments producing concentrations ≥ 13 ppm had greater annual bluegrass cover than those measuring < 13 ppm.

An annual bluegrass plant

Kreuser et al. found a similar level of soil P to be adequate for creeping bentgrass, and the MLSN guideline level of 21 ppm, developed using a robust method to evaluate thousands of soil samples from good-performing turfgrass sites, is similar to the 13 ppm threshhold identified by Raley et al. 

This is another indication that conventional guidelines (usually in the range of 45 to 75 ppm, more than 3x the MLSN guideline) are targeting a higher level of soil P than is necessary.

For more about this, see:

How much phosphorus does grass require?

Fertilizer and Weeds at Park Grass

How much potassium does grass require?