I recently was reading through the “Proceedings of the First International Turfgrass Research Conference” (1969) and I ran across something that I wish could say shocked me, but unfortunately at this point it did not. “Fertilizer Trials at Bingley” (Escritt and Legg) was the title of the chapter and it was a group of long-term studies examining the impacts of ammonium sulfate as a primary nitrogen (N) fertilizer and in combination with lime and various organic and mineral fertilizer sources. I will not bore you with the trial details as you can find them for yourself, but I would like to highlight a few quotes from the authors in the results section that I found quite interesting. The findings from this trial seem to have been repeated time after time in the turfgrass literature I have read. I can’t help but contemplate the question “Is ammonium sulfate the best nitrogen source, in conjunction with an acidic pH, the best protocol for all turfgrass systems?”. With long-term use of ammonium sulfate and an acidic pH, the outcomes seem to favor everything we hold important in the industry regardless of the type of system (putting greens, lawns, athletic fields etc.) being managed.
Trial A (1928-1968)
“Sulfate of ammonia and other ammonium salts contributed to soil acidity, discouraged annual meadow grass (Poa annua), diseases, weeds and earthworms, and produced firm, dry surface conditions.”
Trial B (1937-1963)
“Sulfate of ammonia kept out weeds and worms and F. nivale1, but reduced soil pH, available phosphate and moisture retention.”
“Lime increased weeds, worms, soil moisture, pH and available phosphate…”
Trial C (1939-1960)
“With increase of soil pH there was marked incidence of weeds…”
Trial D (1939-1960)
“All the organic materials produced a soft (easily damaged) turf which became weedy.”
Trial E (1948-1969)
“The best playing surface (firm and dry in wet weather and weed-free), has been produced by the sulphate of ammonia/superphosphate treatment, especially when the pH has not been allowed to drop too far.”
Trial F (1948-1969)
“Combinations of sulphate of ammonia and one of the other nitrogenous fertilizers avoid the extreme effects of either on its own” – comparing the effects of dried blood meal and sulphate of ammonia at spring vs fall applications.
Trial G (1931-1967)
“Sulphate of ammonia had a considerable effect in producing a fine weed-free Festuca/Agrostis sward from the original mixed pasture turf but turf treated with nitro-chalk, nitrate of soda, or dried blood was decidedly weedy and calcium cynamide increased the weed population considerably.”
Trial H (1959-1968)
“The other slow release nitrogenous materials used have also been disappointing.” – in reference to organic fertilizer materials and urea formaldehyde (UF) used in the study vs. sulphate of ammonia.
Take Home Message
This trial demonstrated that habitual use of ammonium sulfate as the primary N source lead to increased turfgrass quality and demonstrably less weed and disease competition. Several other long-term fertilizer trials that contain ammonium sulphate as the N source have shown to have similar results. The soil pH acidification effect should be monitored as aluminum (Al) toxicity can become an issue that compromises turfgrass quality on native soils. Keeping the soil pH above 5.5 essentially negates this effect. But, modified sand based roots zones that contain only small amounts of clay particles can be driven below 5.5 and still produce outstanding turfgrass.
Where I see this most useful is in the establishment of new turfgrass surfaces or for fairly young surfaces whose Poa annua contamination is about 10-15% or less. Maintaining an acidic soil pH with the use of ammonium sulphate will likely select for the proliferation of desirable species and select for a population decrease of undesirable species (ie: Poa annua and other weeds). For those who may have existing stands that are comprised of mostly Poa annua, I am not sure if this protocol is best, but it may be worth a shot!
- Fungal pathogen of fusarium ↩︎
