The role of clover in grassland with particular reference to the use of nitrogenous fertilizer on grass-clover swards

Reid, David (1959) The role of clover in grassland with particular reference to the use of nitrogenous fertilizer on grass-clover swards. PhD thesis, University of Glasgow.

Abstract

A review of the literature on the role of clover in grassland has shown that the greatest agronomic and practical Interest at present centres on the problem of obtaining maximum benefit both from the clover in grass-clover swards, and from fertilizer nitrogen applied to such swards. Two experiments are described in which some of the managerial and botanical factors involved in this problem have been studied. Managerial factors investigated in the first experiment were stage of growth at cutting, closeness of cutting, and dates and rates of fertilizer nitrogen application. The effects of these on yield and contribution of clover from an established sward in which perennial ryegrass predominated were measured. Closeness of cutting was shown to be an important factor controlling clover growth. Clover yields were greater when the herbage was cut 1 inch from ground level than when it was cut 2-21/2 inches from ground level, but continued use of heavy fertilizer nitrogen dressings appeared to reduce this difference. Total herbage yields were also consistently greater under close than under lax-cutting. This effect is tentatively explained with reference to flower-shoot development in the grasses, but the need for further investigation is stressed. The principal factor controlling clover suppression was shown to be the total amount of fertilizer nitrogen applied over the season, clover yields being on average inversely proportional to this. The date on which the first fertilizer nitrogen dressing was applied in the spring also had a controlling influence. Delaying the first dressing until after the first or second cut of the season slightly increased clover yields where a total of 8-12 cwt. 'Nitro-Chalk'/acre (s 139-208 lb. nitrogen) was applied, but had no effect on clover where the total applied was only 4 cwt. (69 1b. nitrogen). At all nitrogen levels total herbage yields were reduced by this delay, but the seasonal distribution of these yields was more uniform than, where the first dressing was applied early in the spring. In the second experiment certain botanical factors were investigated. A study was made of the relative values of S184, S100 and Kersey white clover, their compatability with S23 or S24 ryegrass, S143 or S37 cocksfoot, S48 timothy or S53 meadow fescue and their reaction to increasing rate of fertilizer nitrogen application. Again the principal factor controlling clover suppression was the total amount of fertilizer nitrogen applied over the season. In the first harvest year, however, a total application of 4 cwt, 'Nitro-Chalk'/acre (69 1b. nitrogen) increased the clover yields from S24 ryegrass, S48 timothy and no sown grass mixtures, and only slightly depressed those from S143 and S37 cocksfoot mixtures. This treatment depressed clover yields from all seeds mixtures in the second year; so also did a total application of 10 cwt. 'Nitro-Chalk'/acre (= 174 lb, nitrogen) in both years. Yields from all three clover strains were, on average, equally depressed under each of the fertilizer nitrogen treatments though in the second harvest year S100 was slightly less affected by the light treatment than were S184 or Kersey. In general S100 was superior to Kersey in all except the S143 and S37 cocksfoot mixtures in the first harvest year, but Kersey was equal or superior to S100 in all but the S24 and no sown grass mixtures in the second year; S184 was the poorest yielding strain throughout, but its greater stolon development suggests that it might be more persistent than the other two strains. Clover growth under fertilizer nitrogen treatment varied to a greater extent with the gtrain of grass than with the strain of clover Included in the seeds mixture. Throughout the experiment S53 meadow fescue was the best companion grass for clover, while S143 and S37 cocksfoot were the poorest. It is concluded that under certain conditions maximum benefit can be obtained both from the clover in grass-clover swards and from fertilizer nitrogen applied to such swards. These conditions include the use of seeds mixtures in which meadow fescue predominates; close but not too frequent defoliation of the sward; and application of only moderate amounts of fertilizer nitrogen, or, alternatively, the delay of the first dressing of the season until after the first or second cut, if greater total amounts of nitrogen are applied.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: J Walton
• Keywords: Agronomy, Range management, Soil sciences
• Date of Award: 1959
• Depositing User: Enlighten Team
• Unique ID: glathesis:1959-72595
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 11 Jun 2019 11:06
• Last Modified: 11 Jun 2019 11:06
• URI: https://theses.gla.ac.uk/id/eprint/72595