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This dissertation has been microfilmed exactly as received 66-13~715 WHITNEY~ Arthur Sheldon~ 1933- NITROGEN FIXATION BY THREE TROPICAL FORAGE LEGUMES AND THE UTILIZATION OF LEGUME-FIXED NITROGEN BY THEIR ASSOCI­ ATED GRASSES. University of Hawaii~ Ph.D.~ 1966 Agriculture~ plant culture University Microfilms, Inc., Ann Arbor, Michigan NITROOEN FIXATION BY TIlREE TROPICAL FORAGE LEGUMES AND TIlE UTILIZATION OF LEGUME-FIXED NITRCX3EN BY TIlEIR ASSOCIATED GRASSES A TIlESIS SUBMITTED TO TIlE GRADUATE SQIOOL OF THE UNIVERSITY OF HAWAII IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR TIlE DEGREE OF DOCTOR OF PHILOSOPHY IN SOIL SCIENCE JANUARY 1966 By Arthur Sheldon Whitney Thesis Committee: Yoshinori Kanehiro, Chairman Bruce J. Cooil Robert L. Fox Leslie D. Swindale Goro Uehara ii PREFACE The subject matter discussed'on the following pages is one that has challenged the writer for a number of years, and has been the object of much enquiry by him in Asia as well as nearer home. He is deeply grateful for the financial assistance provided by the East-West Center during his residence at the University of Hawaii, and to the personnel of the Hawaii Agricultural Experiment Station who made facilities and materials available for his research program. Thanks are especially due Dr. G. Donald Sherman for his assistance during the planning and ini­ tiating of this investigation. iii ABSTRACT Three tropical legumes, Desmodium intortum, Desmodium~ and Centrosema pubescens, were grown alone and in combination with napier grass (Pennisetum purpureum) and pangola grass (Digitaria decumbens) in fresh volcanic cinders under continuously moist climate on the Island of Hawaii. Q. intortum gave high yields of both dry matter (ca. 17,000 pounds per acre) and nitrogen (ca. 300 pounds per acre) in a 12-month period, and transferred small but significant amounts of nitrogen to its associated grasses. D. canum yields were low under these conditions, and the nitrogen yields of grasses associated with this legume were depressed. f. pubescens in pure stand was intermediate in yield of dry matter, but equalled!L. intortum in nitrogen yield. However, when com­ bined with grasses, the dry matter and N yields of this legume were reduced by one-half. Transfer of nitrogen to the grasses by f. pubescens was noted only when a 6-month growing period was allowed. The total fixation of nitrogen from the atmosphere during the test period averaged 340 pounds per acre for Q. intortum, 82 pounds per acre for Q. canum, and 156 pounds per acre for f. pUbescens. Of the total nitrogen fixed by Q. intortum, 5% or less was transferred to the associated grasses; but with f. pUbescens, transfer amounted to 11% of the nitrogen fixed in one instance. Transfer due to the release of nitrogen from roots of these legumes was evaluated by circulating nutrient solution through the root systems of plants growing in cinders in the glasshouse. The roots equilibrated with only trace amounts of solution nitrogen, but marked increases in the levels of ammonium and amino nitrogen occurred immediately after iv defoliation. When the root systems of nitrogen-starved pangola plants were included in the perfusion systems, significant transfer of nitro­ gen occurred from the more vigorous legume plants', especially following defoliation. Of the nitrogen mobilized in the legume roots in the 3­ week period after defoliation, the proportions transferred ranged from slightly over 1% for g. canum to 9% for the more vigorous Q. intortum plant. Transfer of nitrogen through the leaching of nitrogen from legume leaves was studied by shaking intact leaves of varying ages in distilled water. The amounts extracted were small, between 0.4% and 0.7% of the total leaf nitrogen. Extractable amino nitrogen tended to be relatively high in rapidly expanding leaves, yellowing leaves, and shaded leaves. Leaf fall accounted for significant nitrogen losses from Q. intor­ !Ym and ~. pubescens in situations where leaf senescence equalled the rate of production of new leaves. Under these conditions, the dead leaves from these legumes supplied nitrogen equivalent to over 1.2 pounds per acre per week. This pathway could thus account for appreciable transfer if long growing periods were allowed. The combined action of these three pathways provides an adequate explanation for the nitrogen transfer observed in the field. A number of ways in which transfer by these means would be affected by manage­ ment and by soil and weather conditions are discussed. v TABLE OF COOTENTS PREFACE.................................... ii ABSTRACT ••••••••••••••••••••••••••••••••••••••••••••••••••••••••.• iii LIST OF TABLES ••••••••••••••••••• 0 ••••••••••••••••••••••••••••••• vi ... LIST OF ILLUSTRATIOOS •••••••••••••••••••••••••••••••••••••••••••• • VJ.1J. INTRODUCTIOO ...................................................... 1 REVIEW OF LITERATURE ••••••••••••••••••.••••••••••••••••••••••••••• 3 SMALL PLOT EXPERIMENT Materials and Methods • ••••••••••••••••••••• e.•••••••••••••••• 16 Results ..................................................... 25 ROOT PERFUSIOO EXPERIMfNT Materials and Methods · - . 62 Results •••••••••••••••••••••••••••••••••• oo ••••••••• ~.e ••••• 70 LEAF NITROOfN EXPERIMENT Materials and Methods • ••••••••••••••••• lit •••••••••••••••••••• 81 Results ..................................................... 82 DISCUSS100 ........................................................ 91 SUMMARY AND CCNCLUSlOOS ........................................... 103 APPENDIX •••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 108 LITERATURE CITED .................................................. 109 vi LIST OF TABLES TABLE I. TOTAL DRY MATTER YIELDS FOR GRASSES, LEGUMES, AND MIXTURES ••••••••••••••••••••••••••••••••••••••••••••• 30 TABLE II. DRY MATTER YIELDS OF LEGUMES, ALCNE AND IN ASSOCIATION WITH GRASSES ••••••••••••••••••••••••••••••••••••••••• 34 TABLE III. DRY MATTER YIELDS OF GRASSES, ALONE AND IN ASSOCIATlOO WITH LEGUMES •••••••••••••••••••••••••••••••••••••• •• 35 TABLE IV. ANALYSIS OF VARIANCE OF DRY MATTER YIELDS •••••••••••• 36 TABLE V. DRY MATTER PRODUCTlOO PER WEEK BY lWO GRASSES AND THREE LEGUMES •••••••••••••••••••••••••••••••••••••••• 39 TABLE VI. PERCa-JTAGE OF NITROGEN IN TOP GROWTH OF GRASSES AND LEGUMES ••••••••••••••••••••••••••••••••••••••••••••••• 40 TABLE VII. TOTAL NITROGffi YIELDS FOR GRASSES, LEGUMES, AND MIXTURES ••••••••••••••••••••••••••••••••••••••••••••• 43 TABLE VIII. NITROGa-J YIELDS OF LEGUMES, ALOOE AND IN ASSOCIATION WITH GRASSES ••••••••••••••••••••••••••••••••••••••••• 44 TABLE IX. NITROG~ YIELDS OF GRASSES, ALOO E AND IN ASSOCIATIOO WITH LEGUMES ••••••••••••••••••••••••••••••••••••••••• 46 TABLE X. ANALYSIS OF VARIANCE OF NITROGa-J YIELDS •••••••••••••• 47 TABLE XI. NITROGEN YIELD PER WEEK BY THREE LEGUMES, AVERAGE OF THREE TREATMa-JTS ••••••••••••••••••••••••••••••••••••• 48 TABLE XII. RATIOS OF ROOT NI TOP N FOR GRASS AND LEGUME SPECIES •• 50 TABLE XIII. NITROGa-J ())NTAINED IN THE ROOTS OF GRASSES AND LEGUMES 52 TABLE XIV. NITROGffi ())NTAINED ~ THE ROOTS OF GRASSES, LEGUMES, AND MIXTURES ••••••••••••••••••••••••••••••••••••••••• 53 TABLE XV. LEGUME CONTRIBUTION TO TOTAL N YIELDS •••••••••••••••• 55 TABLE XVI. LEGUME N ())NTRIBUTION PER WEEK TO YIELDS OF TOP GROWTH ••••••••••••••••••••••••••••••••••••••••••••••• 56 TABLE XVII. LEGUME N COO'TRIBUTION REFLECTED IN THE TOTAL ROOT N LEVELS •••••••••••••••••••••••••••••••••••••••••••••• 56 TABLE XVIII. NITROGa-J RELEASED TO PEROOLATE IN CERTAIN LEGUME PLOTS •••••••••••••••••••••••••••••••••••••••••••••••• 60 vii TABLE IXX. LEGUME AND GRASS YIELDS FROM PERFUSED GINDER CULTURE IN lHE GLASSHOUSE •••~.................................71 TABLE XX. NITROGEN CXlNSTlTUENTS EXTRACTED FROM DIFFERENT SERIES OF LEAF SAMPLES ••••••••••••••••••.••••••••••••••••••• 89 TABLE XXI. ESTIMATED TRANSFER OF NITROGEN FROM LEGUMES TO ASSO­ CIATED GRASSES BY THREE DIFFERENT PATHWAYS ••••••••••••IOI viii LIST OF ILLUSTRATIONS FIGURE 1. LAYOUT FOR LEGUME-NITROGEN EXPERIMENT, WAIAKEA, HAWAII •• 17 FIGURE 2. ROOT SAMPLING CYLINDER FOR SMALL PLOTS ••••••••••••••••• 21 FIGURE 3. NAPIER ROOTS PROLIFERATING IN AND AROUND CENTRO NODULES •••••••••••••••••••••••••••••••••••••••••••••••• 26 FIGURE 4. DRY MATTER YIELDS PER ACRE OF GRASSES, LEGUMES, AND MIXTURES •••••••••••••••••••••••••• So •••••••••••••••••• •• 31 FIGURE 5. NITROOEN YIELDS PER ACRE OF GRASSES, LEGUMES, AND MIXTURES ••••••••••••••••••••••••••••••••••••••••••••••• 42 FIGURE 6. DIAGRAM OF PERFUSION SUBSYSTEM •••••••••••••••••••••••• 63 FIGURE 7. LEGUME ROOTS IN APRIL •••••••••••••••••••••••••••••••••• 73 FIGURE 8. LEGUME ROOTS IN JULy ••••••••••••••••••••••••••••••••••• 74 FIGURE 9. NITROGEN LEVELS IN SOLUTIOOS AFTER PERFUSING LEGUME ROOTS •••••••••••••••••• •• ••••••••••••••••••••••••••• •• 76 FIGURE 10. VIEW OF GRASSES GROWN IN SERIES WITH LEGUMES. CCN- CLUSIOO OF FIRST THREE WEEK PERIOD ••••••••••••••••••••• 78 FIGURE H. VIEW OF GRASSES GROvtJ IN SERIES WITH LEGUMES. CCN- CLUSIOO OF SECOND THREE WEEK PERIOD •••••••••••••••••••• 79 FIGURE 12. TOTAL NITROGEN AND EXTRACTABLE NITROGEN IN KAIMI LEAVES OF DIFFERENT AGES •••••••••••••••••••••••••••••••• 83 FIGURE 13. TOTAL NITROGEN AND EXTRACTABLE NITROGEN IN CENTRO LEAVES OF DIFFERENT AGES ••••••••••••••••••••••••••••••• 84 FIGURE 14. TOTAL NITROGEN AND EXTRACTABLE NITROGEN IN INTORTUM LEAVES OF DIFFERENT AGES ••••••••••••••••••••••••••••••• 85 FIGURE 15. TOTAL NITROGEN AND EXTRACTABLE NITROGEN IN LEAVES OF THREE LEGUME SPECIES ••••••••••••••••••••••••••••••••••• 87 FIGURE 16.

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