Soil: plant relationships of species-rich Molinia i caerulea dominated communities of the Culm ! I I I I I Measures, North Devon, with special reference given to phosphorus cycling by M. Jane Goodwin ,I '' A thesis submitted to the University of Plymouth in panial fulfJ.lment for the degree of , DOCTOR OF PHILOSOPHY Seale-Hayne Faculty of Agriculture, Food:and Land Use In collaboration with Institute of Grassland and Environmental Research September 1995 Copyright Statement This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyrig)tt rests with the author and that no.quotation from the thesis and no information derived from it may be published without the author's prior written consent. 'I ii Abstract Soil:plant relationships of species-rich Molinia caerulea dominated communities of the Culm Measures, North Devon, with special reference given to phosphorus cycling. Margaret Jane Goodwin A semi-natural community known locally as Culm grassland in Devon and N. E. Cornwall is under threat from agricultural improvement, abandonment and inappropriate management In the last fifty years 87% of the original area has been lost. Funher loss may be prevented by ~ examination of the factors that influence the plant community and how they may be manipulated by management. Thus the research described in this thesis addressed the soil conditions and the plant communities, with particular reference to phosphorus cycling. In 1992 a preliminary characterisation of soil nutrient and water conditions, and species composition was conducted on a pristine Culm grassland, an improved grassland and a formerly abandoned Culm grassland. A significant elevation in soil extractable phosphorus was found in mid-April in response to fertiliser applications on the improved grassland. Similarities with previous research and an absence of a similar pattern in mineral nitrogen prompted a detailed investigation of phosphorus dynamics in 1993. A better indication of plant 'available' P was found by removing soil solution directly using novel methods of centrifuging and suction cups. Environmental conditions were highly influential. Low concentrations of P in suction cup solutions on Culm grassland indicated that Culm species may remove P at very low concentrations. An investigation of the above-ground biomass found that the uptake of P was highest in M. caerulea. M. Caerulea also influenced the return of P to the soil via organic matter through the production and subsequent breakdown of large quantities of litter. Additions of P to turfs caused a perturbation by enhancing the uptake of P by M. caerulea and increasing P fixation. The data was employed to produce a schematic model of the Culm grassland which identified input and outputs, storage compartments and transfers within the P cycle. · This contributed towards making management recommendations for a range of Culm grassland communities which may be maintained, improved or recreated iii List of contents List of tables ix List of figures xi List of plates xii Acknowledgments xw Author's declaration xiv Chapter One. Introduction 1 1.1 Introduction 1 1.2 History of semi-natural grassland in Britain 2 1.3 Semi-natural grassland in South West England 5 1.4 Soil:Plant relationships : a review 11 1.4.1 Introduction 11 1.4.2 Factors controlling soil nutrient availability 12 1.4.2 a Chemical factors 12 1.4.2 a i General 12 1.4.2 a ti Soil phosphorus availability 16 1.4.2 b Physical factors 19 1.4.3 Modification of soil nutrient availability 22 1.4.3 a Increase in nutrient availability 22 1.4.3 b Manipulation of nutrient availability by management 23 1.4.3 c Relationship between nutrient availability and species composition 25 1.4.3 c i Strategies employed to adapt to nutrient-poor environments 25 1.4.3 c ti Influence of nutrient availability on species composition 26 1.4.4 Monitoring nutrient availability 27 1.4.4 a Extraction from the soil 28 1.5.4 b Plant nutrient content 30 1.6 Research objectives 33 1.7 Summary 35 Chapter Two. Experimental design and methods 36 2.1 Introduction 36 2.2 Experimental design 36 2.2.1 Site selection 36 2.2.2 Site description 38 2.2.2 a Femhills Moor (Culm grassland) 38 iv List or Contents Continued 2.2.2 b Staddon Moor (Culm grassland) 39 2.2.2 c Staddon Moor (Improved grassland) 39 2.2.3 Plot design 40 2.3 Experimental strategy 47 2.3.1 General sampling strategy 47 2.3.2 Soil conditions . 48 2.3.2 a Soil physical conditions 48 2.3.2 b Soil nutrient conditions 49 2.3.2 c Statistical analysis 49 2.3.3 Plant communities 51 2.3.3 a Botanical surveys 51 2.3.3 b Plant production 51 2.3.3 c Statistical analysis 52 2.4 Methods 53 2.4.1 Soil physical conditions 53 2.4.1 a Soil water content 53 2.4.1 b Soil matric potential 54 2.4.1 c Water table fluctuation 54 2.4.1 d Bulk density 55 2.4.1 e Organic matter by loss-on-ignition 55 2.4.2 Soil nutrient conditions 56 2.4.2 a Chemical extraction of nutrients 56 2.4.2 b Extraction of soil solution 58 2.4.2 b i Suction cups 58 2.4.2 b ii Centrifuging 59 2.4.3 Plant communities 59 2.4.3 a Botanical surveys 59 2.4.3 b Plant community production 59 2.5 Summary 60 Chapter Three. Characterisation or the Culm grassland environment 61 3.1 Introduction 61 3.2 Meteorological conditions 61 3.3 Soil physical conditions 62 3.4 Soil nutrient conditions 67 4.4.1~ ~ 4.4.2 Phosphate-phosphorus 69 4.4.3 Nitrate and ammonium-nitrogen 71 V List of Contents continued 4.4.4 Potassium 74 4.4.5 Calcium and magnesium 74 3.5 Plant communities 17 3.5.1 Staddon improved 77 3.5.2 Culm grassland 79 3.6 Summary 82 Chapter Four. The availability of soil phosphorus in the Culm grassland system 84 4.1 Introduction 84 4.2 Experimental design 86 4.2.1 Evaluation of techniques 86 4.2.1 a Sodium bicarbonate extraction 86 4.2.1 b Centrifuging 87 4.2.1 c Suction cup 89 4.2.1 d Analysis of soil solutions 90 4.2.2 Sampling regime 91 4.3 Results and discussion 92 4.3.1 Sodium bicarbonate extraction 92 4.3.2 Centrifuging 96 4.3.3 Suction cup 101 4.4 Summary 104 Chapter Five. Variation of plant production with season and vegetation community 106 5.1 Introduction 106 5.2 Experimental design 108 5.2.1 Field procedure 108 5.2.1 a Uninterupted growth on Staddon Grazing 108 5.2.1 b Repeated defoliation and regrowth on Staddon Grazing and Staddon 109 Improved 5.2.2 Laboratory procedure 109 5.3 Dry matter yield Ill 5.3.1 Seasonal variation of Staddon Grazing (Uninterupted growth) Ill 5.3.1 a Standing crop 111 5.3.1 b Live material Ill 5.3.1 c Dead material 112 vi List or Contents Continued 5.3.2 Effect of repeated defoliation 113 5.3.2 a Staddon Grazing 113 5.3.2 b Staddon Improved 113 5.4 Phosphorus content in plant tissue 119 5.4.1 Seasonal variation of Staddon Grazing (Uninterupted growth) 119 5.4.1 a Standing crop 119 5.4.1 b Live material 119 5.4.1 c Dead material 120 5.4.2 Effect of repeated defoliation 121 5.4.2 a Staddon Grazing 121 5.4.2 b Staddon Improved 121 5.5 Yield of phosphorus in dry matter 117 5.5.1 Seasonal variation of Staddon Grazing (Uninterupted growth) 126 5.5.1 a Standing crop 126 5.5.1 b Live material 126 5.5.1 c Dead material 126 5.5.2 Effect of repeated defoliation 127 5.5.2 a Staddon Grazing 127 5.5.2 b Staddon Improved 127 5.6 Summary 132 Chapter Six. Response or Culm grassland to nutrient additions 134 6.1 Introduction 134 6.2 Soil phosphorus fixation capacity 135 6.2.1 Background of experiment 135 6.2.2 Experimental procedure 136 6.2.3 Results and discussion 137 6.3 Experimental design of turf experiment 138 6.4 Results and discussion 141 6.4.1 Soil response to phosphorus additions 141 6.4.1 a Pin soil solution 141 6.4.1 b Air-dry soil extractable P 142 6.4.2 Response of the vegetation to phosphorus additions 143 6.4.2 a Dry matter production 143 6.4.2 b Phosphorus content of plant material 144 6.4.2 c Phosphorus content of biomass removed from the turfs 144 6.5 Summary 147 vii List of Contents continued Chapter Seven. Strategies for phosphorus management in the Culm grassland system 149 7.1 Introduction 149 7.2 A review of environmental conditions 150 7.2.1 Characterisation of the Cu1m grassland environment 150 7 .2.2 The availability of phosphorus in the Cu1m grassland system 151 7.2.3 Variation of plant production with season and vegetation community 153 7.3 Phosphorus cycling within the Culm grassland system 157 7.3.1 Inputs and outputs 157 7.3.2 Storage compartments 158 7.3.3 Transfers and manipulation by management 160 7 .3.4 Comparisons of P cycling in other systems 167 7.4 Development of management strategies to manipulate Culm grassland soil conditions 169 7.4.1 Introduction 169 7.4.2 Maintenance of Culm grassland communities 170 7.4.2 a Plateau sites 170 7 .4.2 b Valley sites 172 7.4.31mprovement of Culm grassland communities 174 7.4.3 a Absence of management 174 7.4.3 b Inappropriate management 175 7 .4.4 Recreation of Culm grassland 176 Chapter Eight.