Acid Theory 
A greenkeeping practice which was carried out during the 1920s and early 1930s in the UK and elsewhere, and which was based on the routine application of ammonium sulphate and sulphate of iron to golf and bowling greens.
It had been established earlier in the 1900s that turf fertilisers for a fescue and bentgrass sward should provide an adequate amount of acid soil reacting nitrogen, with a very limited supplies of phosphates and potash; this helped to produce firm and dry surfaces.
Published research, in 1925, from the USA showed that weed free plots of Agrostis tenuis could result from monthly applications of sulphate of ammonia or ammonium phosphate; this also reduced surface earthworm activity.
This approach does, however, underlie a significant element of the Basic Principles of Greenkeeping.
Preventing and controlling certain weeds with certain acidifying fertilisers can be beneficial, however, excessive use proved the downfall of this continued practice.
Excessive application of these acidifying fertilisers
• without consideration being given to the impact this would have on a fine turf sward,
• without adjustments being made to prevent extreme acidity arising, and
• combined with not carrying out other appropriate maintenance practices, resulted in the practice being effectively abandoned by many greenkeepers. This was, arguably, primarily due to poor education and understanding of the wider consequences at the time.
Monitoring and assessment of any turf grass situation will provide useful information on which a turf manager is better informed so as to make the necessary and correct adjustments to any fertiliser programme; this was clearly lacking at the time.
Correct application of what is termed the acid theory has been shown to be the most appropriate regime in many situations, however, this must not be taken as being the only approach to take and will depend upon soil and construction type, as well as the predominant desirable grass species.
For example, if creeping bentgrass is to be maintained on a golf green then less acidic soil conditions will be desired, and a different fertiliser and maintenance programme will be required. This approach would also be inappropriate for dwarf perennial ryegrass dominated surfaces in fine turf surfaces which require a much less acidic (~ pH 6.0 – 7.0) soil for optimum performance.
References and further reading:
• Beale, R. (1924) ‘Lawns for Sport’
• Clouston, D. (1939) 2nd Edn, ‘The Acid Theory or the Effect of Sulphate of Ammonia on Turf’, in ‘The establishment and care of fine turf for Lawns and Sports Grounds’, pp31-34
• Levy, E.B. (1949), ‘Theory and Practice underlying the establishment and maintenance of greens’, in ‘Construction, renovation and care of the bowling green’, (New Zealand Greenkeeping Research Committee), pp10 -35
• Sutton, M.A.F. (1950), 2nd Edn. ‘Golf Courses: Design, Construction and Upkeep’
• Dawson, R.B. (1959) ‘Fertilizers and their Practical use’, in Practical Lawn Craft and Management of Sports Turf, 5th Edn, pp111-124
• Goss, R.L., Brauen, S.E. & Orton, S.P. (1975) ‘The effects of N,P,K and S on Poa annua L. in Bentgrass Putting Green Turf’, in The Journal of the Sports Turf Research Institute, 1975, Vol. 51, 74-82.
• Isaac, S.P. & Canaway, P.M. (1987) 'The mineral nutrition of Festuca-Agrostis golf greens: a review', in The Journal of the Sports Turf Research Institute, 1987, Vol.63, 9- 27.
• Lawson, D.M. (1999), ‘Phosphate and potassium nutrition of Agrostis spp. And Festuca spp. Turf growing on sandy loam. I. Turf ground cover and Poa annua ingress’, in The Journal of Turfgrass Science (incorporating the Journal of the Sports Turf Research Institute) Vol.75 (1999), 45-54.
• Lawson, D.M. (1999) ‘Phosphate and potassium nutrition of Agrostis spp. And Festuca spp. Turf growing on sandy loam. II. Leaf and soil phosphorus and potassium content’, in The Journal of Turfgrass Science (incorporating the Journal of the Sports Turf Research Institute) Vol.75 (1999), 55-65.
• Lawson, D.M. (2000) ‘The effect of nitrogen source, lime application and phosphate application on the quality of Festuca rubra-Agrostis tenuis turf growing on a sand-dominated rootzone’, in The Journal of Turfgrass Science (incorporating the Journal of the Sports Turf Research Institute) Vol.76 (2000), 12-23.