THE TRANSPORT OF MINERAL AND ORGANIC MATTER INTO THE SOIL PROFILE BY LUMBRICUS RUBELLUS HOFFMEISTER by HUBERT J. TIMMENGA Landbouwkundig Ingenieur, Wageningen, 1981 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in Soil Science THE FACULTY OF GRADUATE STUDIES Department of Soil Science We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA 13 September 1987 © HUBERT J. TIMMENGA, 1987 k 6 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) ABSTRACT The biology and ecology of the earthworm Lumbricus rubellus Hoffmeister, 1843, and its effects on the turn-over of organic matter and soil are not well known. To gather this information, the ingestion and egestion rates were measured using a litterbag technique and the transport of organic matter was quantified with a newly developed method, using soil columns to which 14C labelled plant material was added. The feeding habits of the worm were positively influenced by temperature in wet soils (> -15m of water) and were negatively influenced in dry soil (< -15. m of water). The total egestion rate changed from 0.3 g.g-'.day"1 at 5 °C to 1.0 g.g~1.day~1 at 20° C in moist soil (- 5 m of water). The egestion rate at medium range temperatures, 10 and 15° C, was less affected by drought stress than at 5 and 20 °C. The egestion rate of carbon was a more stable parameter than the total egestion rate, and ranged from approximately 20 mg.g-1.day"1 at 5 °C, to 50 mg.g-1.day_1 at 20 °C. The moisture and temperature effects were apparent in the Q10 of the total egestion rate and of the egestion rate of carbon. The Q10 ranged from 1.66 in wet soils to 3.27 in dry soils in the 5-15 °C interval and from 1.98 to 0.32 in the 10-20 °C range. For the egestion rate of carbon, the Q10 i i ranged from 1.92 to 3.21 and from 1.28 to 0.47, respectively. The body water content of the worm varied considerably with the soil water potential, and reached a maximum level of 5.5 kg.kg"1 (dwt) between -15 metres of water and -30 metres of water. When under drought stress, worms stopped ingesting large quantities of soil, switched to a diet high in organic matter and lowered their activity. In the 1"C column experiment, the total cast production was significantly related to depth. L. rubellus produced 15 % of the cast on the surface of the soil, 46 % in the 0-5 cm layer, 22 % in the 5-10 cm layer and 16 % in the 10-15 cm layer. Independent calculations from a) the uptake of 1ftC labelled carbon in earthworms, b) removal of litter from the surface and c) 1"C label recovered from cast, showed that the worms ingested 78-82 % of the offered organic matter as shoot litter and 18-22 % as root litter. 1"C originating from shoot and root litter was recovered in casts throughout the profile, indicating that the worms mixed food from all layers. iii The total egestion rate found in the column experiment was 5.2 times higher than was found in the litterbag technique under comparable conditions (2.34 vs 0.45 g.g"1.day"1). The egestion rate of carbon was similar in both techniques (37.1 vs. 46.1 mg.g~1.day~ 1 , 10 °C). In preliminary litterbag trials, it was found that L. rubellus egested 15.5 mg.g~1.day~1 of carbon (5 °C) for each of four food types offered. The 5 °C temperature trial of the litterbag technique, showed a similar amount of carbon egested. It was concluded that the worm needed a constant amount of carbon to provide nutrients and energy, of which a part or all may originate from ingested microorganisms. Based on the distribution of cast in the profile and the feeding strategies of L. rubellus, it was concluded that this earthworm cannot be classified as an epigeic worm. A new strategy class was proposed: eurygeic worms, earthworms living in the litter-soil interface, mixing organic matter into the profile and mineral soil into the litter layer. Based on the literature and results from the present study, a computer model was developed to simulate the longterm effects of earthworms on an agricultural soil system. Simulations of the mixing of soil and organic matter in a limited-till agricultural system, showed that earthworms iv negatively affected the accumulation rate of surface litter and positively affected the organic matter content of the mineral soil. The model can be used to predict the trends in organic matter in soils, important in soil conservation, mine reclamation and reforestation. v TABLE OF CONTENT ABSTRACT ii TABLE OF CONTENT V1 LIST OF TABLES X LIST OF FIGURES xii LIST OF ABBREVIATIONS xiii LIST OF SPECIES NAMES xiv ACKNOWLEDGEMENTS xv I. INTRODUCTION 1 II. LITERATURE REVIEW 5 A. THE ROLE OF EARTHWORMS IN THE TURN-OVER OF ORGANIC MATTER AND SOIL 5 1. Ecological strategies and classificaton of earthworms 5 2. Earthworm food 9 3. Impact of earthworms on the soil system 14 a. Effects of earthworms on soil structure and fertility 14 b. Effects of earthworms on infiltrability 14 c. The mixing of organic matter into the profile 15 d. Surface cast production 17 e. Parameters affecting the cast production of earthworms 18 B. LUMBRICUS RUBELLUS HOFFMEISTER, 1843 21 1 . Distribution 21 2. Reproduction 24 3. Food sources and eating habits 24 4. Respiration 25 5. Egestion and soil turn-over 25 6. Ecological classification and strategies 26 III. THE EFFECTS OF SOIL MOISTURE AND SOIL TEMPERATURE ON THE EGESTION AND INGESTION RATES OF LUMBRICUS RUBELLUS HOFFMEI STER 28 A. MATERIALS AND METHODS 28 1 . Introduction 28 2. Site description 28 3. Field data collection 29 vi . 4. Earthworms used in the experiments 30 5. Sample collection 30 6. Litterbag technique 31 7. Water content of the worm 35 8. Chemical analysis 36 9. Calculations and Statistics 36 B. RESULTS AND DISCUSSION 36 1 . Litterbag technique 36 2. Calculations and statistics 37 a. The grouping of the moisture and temperature levels 37 b. Calculation of the ingestion rates 37 c. Statistical analysis 37 d. Curve fitting 39 3. Egestion rates of soil and organic matter 39 4. Egestion rate of carbon 43 5. Q10 values of the activity of earthworms 45 6. Faecal organic matter 47 7. Faecal water content 49 8. Ingestion rates 50 9. Worm size 55 10. Soil temperature and soil moisture in the field 55 11. Comparison of ingestion and egestion rates to literature data 56 12. Drought-survival strategies of Lumbricus rube 11 us 59 a. The water content of earthworms ... 59 b. Feeding behavior of the worm as related to the body water content 63 13. Testing of assumption 67 IV. THE TRANSPORT OF ORGANIC MATTER INTO THE SOIL PROFILE BY LUMBRICUS RUBELLUS 68 A. MATERIALS AND METHODS 68 1 . Introduction 68 2. Animals used in the column experiment 68 3. Soils used in the column experiment .... 69 4. Clover used in the column experiment ... 69 a. Production of clover 69 b. Radiolabelling of clover 70 5. Experimental Set-up 71 6. Experimental design and statistics 73 a. Experimental design 73 b. Statistics 74 vii 7. Sample preparation 74 8. Chemical Analysis 75 B. RESULTS AND DISCUSSION 76 1 . Production of clover 76 1 2. *C02 fumigation of the clover 76 3. Observations on materials and techniques used in the column experiment 77 a. Micro-arthropods in the soil 77 b. Plant material 78 c. Experimental temperature and soil moisture content 78 d. Diffusion method for carbon analysis 79 4. Airflow above the columns 79 5. Soil water potentials in the columns... 80 6. Recovery of 1"C activity from the samples 80 a. Specific activity of the recovered materials 80 b. Total activity of recovered materials 83 c. 14C activity recovered from the bulk soil 83 7. Respiration and decomposition 85 a. Respiration 85 b. Weight loss of clover material .... 88 8. Recovery of casts from the soil columns 89 a. Description of the burrows 89 b. Description of casts 91 9. Distribution of casts 91 10. Egestion rates 93 1 1 . Organic matter 95 a. Distribution of organic carbon in the cast 95 b. 1WC activity in casts as related to depth 97 c. Calculation of the use of added organic matter by the earthworms 98 12. Testing of assumption 100 EARTHWORM SIMULATION MODELS 101 A. SIMULATION MODELS DESCRIBING THE DYNAMICS OF SOIL MIXING BY EARTHWORMS 101 1 . Introduction 101 2. Published earthworm models 101 3. "MIXER", a new conceptual model describing earthworm activity in soil systems 104 a. Introduction 104 viii b. Soil layers in the model 105 c. Population dynamics 105 d. Earthworm food 107 e. Cast production 109 f. Flow-diagram for MIXER 109 B. F-MIXER, A SIMULATION MODEL FOR SOIL MIXING BY EARTHWORMS 111 1.