Park Grass experiment video
Baker Street Botany

"I noticed something crazy"

Jason Haines shared an interesting report about clover (or actually, the lack of it) on tees at Pender Harbour GC in Canada.

I noticed something crazy. All the clover on the tees had disappeared ... until 2005 we would spot spray these areas with Killex [2-4-D, MCPP, Dicamba] but haven't applied any type of herbicide since then. Today I could only find one small patch less than 1 m2 on my tee boxes. Crazy!

So what the heck happened to the clover? ... I was not trying to rid the tees of clover in any way. This was an indirect consequence of something that I did ...

Since 2012 I have really only applied nitrogen and wetting agents to the tees. This combined with the lack of liming has, in my opinion, led to the disappearance of the clover ... and the tees have never been better in the 13 years I have been here. Just nitrogen, wetting agents, and some aeration every now and again. No "weeds." Super quick divot recovery. As close to perfect as I can expect.

I was pleased and pleasantly surprised to find that this result had happened so quickly at Pender Harbour, and it reminded me of the results at the Park Grass experiment in 1857 and 1858, as reported by John Bennet Lawes and Henry Gilbert in their Report of Experiments with different Manures [fertilizers] on Permanent Meadow Land in 1859. 


Different species growing on plots at the Park Grass experiment in 2006 as a result of different fertilizer and liming treatments; the plot in the foreground has received ammonium sulfate applications since 1856. Clover does not grow in this plot, but grasses do.

At Park Grass, the differential fertilizer treatments were applied to the meadow for the first time in 1856. The experiment continues to this day The purpose at the start was to evaluate the effect of fertilizer treatments on hay yield and nutritive value of the hay. But what they noticed, almost immediately, was something unexpected (very similar to that "crazy" disappearance of clover at Pender Harbour). Remember, this is what they noticed immediately, at the very start of the experiment:

Perhaps the most remarkable and interesting of the effects of the different descriptions [types] of manure [fertilizer], upon the complex herbage of which the experimental meadow was composed, was the very varying degree in which they respectively developed the different kinds of plants ... the experimental ground looked almost as much as if it were devoted to trials with different seeds as with different manures [fertilizers].

In the second year of the experiment, 1857, and again in 1858, the proportion of different plant species were measured in the different plots immediately after cutting the field. They reported the 1858 results as I quote below – note that I have changed the word manure to fertilizer for clarity in modern usage.

Perennial red clover [Trifolium pratense] amounted to little more than 1 per cent. of the total produce on the unfertilized land, but to nearly 18 per cent. of that grown by mineral fertilizers alone. Not any of it was found in the produce by either ammoniacal salts alone, or ammoniacal salts in conjunction with mineral fertilizers. There was little more than 1½ per cent. of it in the produce by farmyard manure alone, and less than ½ per cent. in that by farmyard manure and ammoniacal salts.

That is, in the second year of the experiment, there was 18 times more clover where mineral fertilizers were supplied in the absence of nitrogen. Adding ammonium sulfate, or ammonium sulfate with other minerals, eliminated the clover.

At the same rate of N, but applied in the nitrate form, and with P, K, and Mg added as well, many "weeds" including clover grow along with the grasses.

The implications of this for turf managers are pretty obvious. Fertilizer applications have an effect on what grasses and weeds will grow. Judicious selection of fertilizer can help to reduce weed populations. Herbicide use can be reduced or eliminated in some situations by adjusting the fertilizer applications. For more on this, see:

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