Acid Theory 
This is the term used to describe a greenkeeping practice that was especially carried out during the 1920s and 1930s in the UK and elsewhere, and which was based on the routine fertiliser applications of ammonium sulphate and/or ammonium phosphate, and in some cases along with 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 limited supplies of phosphates and potash; this approach also helped to produce firm and dry surfaces.
Published research, in the mid 1920s showed that weed free plots of Agrostis tenuis could be maintained (mostly in that condition) with monthly applications of sulphate of ammonia or ammonium phosphate; this also reduced surface earthworm activity. Where the turf also contained weeds then the reduction of weeds might be more difficult than where the turf is initially free from weeds.
This approach does, however, underlie a significant element of the Basic Principles of Greenkeeping, which is to focus on conditions which are more suitable for a fescue-bent sward rather than turfgrasses in general, with this also including the undesirable annual meadow grass.
Preventing and controlling certain weeds with certain acidifying fertilisers can be beneficial, however, excessive adherence to this acid theory resulted in sward thinning, reduced soil biological activity (for example less beneficial micro-organisms), an increase in thatch build-up, and a less resilient sward in hot and dry weathers, resulting in a significant reduction in turf quality.
With the development and introduction of selective herbicides in the 1940s, there was no longer the need to try and control weeds through the acid theory, or similar practices, so the misapplication of this theory along with the new weed control products saw its downfall and abandonment by many greenkeepers.
• not enough consideration was given to the longer-term impact this would have on a fine turf sward where used continuously, in particular the overuse of ammonium sulphate is most undesirable,
• no, or limited, adjustments were made to prevent extreme acidity arising,
• an inadequate undertaking of other appropriate maintenance practices, for example a suitable top-dressing (made with compost) to ensure a desirable sward was maintained.
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.
Correct application, or maybe better termed adaptation, 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 (about pH 6.0 – 7.0) soil for optimum performance.
In conclusion, the acid theory, where appropriately applied and managed can contribute to the production of good fescue-bent greens, however, where misapplied and managed will lead to significant deterioration of playing conditions.
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.
• Reed, F.J. (1950), ‘Lawns and Plying Fields’, Faber, 137-138.