Proportion of NH4-N in mineral N extracted (expressed as %) from Elkton .... Maryland using cover crop treatments of rye, forage radish, rape, and a no-cover.
ABSTRACT
Title of Document:
Nitrogen Mineralization from Brassica Cover Crops Amy Elizabeth Kremen, Master of Science, 2006
Directed By:
Professor Ray Weil, Department of Environmental Science and Technology
The potential of forage radish (Raphanus sativus L.), rape (Brassica napus L.), and rye (Secale cereale L.) cover crops to capture residual nitrogen and then provide early season N to subsequent main crops via mineralization from their residues was compared. At four field experiments established in Maryland (2003-2005), N uptake by radish and rape equaled or exceeded that by rye. No differences in soil inorganic N due to cover crop type were observed during spring 2004. In spring 2005, greatest N release from forage radish residues (March-May) was followed by that from rape residues (May-June). Brassica decay significantly increased growth of immature corn and soybean plants. In a 48-day incubation study comparing N mineralization in fine and coarse textured soils from Brassica and rye root or shoot residues, N mineralization was greatest from forage radish and rape shoots. Compared with rye, the Brassica cover crops showed environmental and agronomic promise.
NITROGEN MINERALIZATION FROM BRASSICA COVER CROPS
By Amy Elizabeth Kremen
Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Master of Science 2006
Advisory Committee: Professor Raymond Weil, Chair Professor Frank Coale Dr. Kim Kroll Dr. Andrew Clark
© Copyright by Amy Elizabeth Kremen 2006
Acknowledgements Thanks to: Dr. Weil for the opportunity to be his student; farmers for providing inspiration, my committee for their guidance; UMD-REC farm managers for their patience and assistance; Stan Schlosnagle for cheerfully sharing his lab expertise; the Weil student group, for giving me a chance to laugh every day; and to my husband Boz Wing and my parents Judith and Jeffrey Kremen, for their encouragement and support throughout this experience.
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Table of Contents Acknowledgements ___________________________________________________ ii Table of Contents ____________________________________________________ iii List of Tables_________________________________________________________v List of Figures _______________________________________________________ vi Chapter 1: Introduction _______________________________________________ 1 Background and problem definition _______________________________________________ 1 Justification for research________________________________________________________ 1 General research approach ______________________________________________________ 2 General research objectives and hypotheses _________________________________________ 3
Chapter 2: Literature review ___________________________________________ 5 Introduction__________________________________________________________________ 5 Nitrogen uptake capacity of rye, rape and forage radish in fall __________________________ 6 Nitrogen retention by rye, rape and forage radish through winter and early spring __________ 11 Spring N release dynamics of rye, rape, and forage radish and effects on main crops ________ 13 Summary of N cycling by the Brassicas and rye and discussion of research gaps. __________ 17
Chapter 3: Nitrogen Uptake and Release by Brassica Cover Crops ____________ 20 Abstract ______________________________________________________________ 20 Introduction ___________________________________________________________ 21 Materials and Methods __________________________________________________ 23 2003/4 (Experiment 1). ________________________________________________________ 23 2004/5 (Experiment 2). ________________________________________________________ 26 Site-specific information_______________________________________________________ 29 Plant sampling and analysis ____________________________________________________ 32 Soil sampling and analysis _____________________________________________________ 33 Statistical analysis____________________________________________________________ 36
Results________________________________________________________________ 37 __________________________________________________________________________ 54
Discussion _____________________________________________________________ 56 Conclusion ____________________________________________________________ 60
Chapter 4: Mineralization of C and N from forage radish, rape, and rye cover crop residues incubated in fine-and coarse-textured soils.________________________ 62 Abstract ______________________________________________________________ 62 Introduction ___________________________________________________________ 63 Materials and methods __________________________________________________ 65 Soils ______________________________________________________________________ 65 Plant materials ______________________________________________________________ 65 Incubation set-up ____________________________________________________________ 66 Analytic determinations _______________________________________________________ 67 Calculation of results _________________________________________________________ 69
Results________________________________________________________________ 70 Carbon and nitrogen composition of materials used in the incubation ____________________ 70
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Visual and olfactory observations________________________________________________ 73 Mineralized C and two-pool kinetic parameters _____________________________________ 73
Discussion _____________________________________________________________ 84 Plant loading rates____________________________________________________________ 84 Carbon respiration ___________________________________________________________ 84 Model modification___________________________________________________________ 86 Nitrogen mineralization and immobilization dynamics _______________________________ 89 Comparing C and N mineralization dynamics ______________________________________ 92
Conclusion ____________________________________________________________ 94
Conclusions________________________________________________________ 96 Appendix A: Comparison of tillage method on spring N mineralization from cover crop residues. ______________________________________________________ 97 Appendix B: Carbon and N mineralization from rye roots incubated in Cedartown loamy sand. _______________________________________________________ 102 Appendix C: Sample SAS codes _______________________________________ 105 References ________________________________________________________ 106
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List of Tables Table 3.1. Description of field sites, soils, and cover crop seeding dates. _______ 24 Table 3.2. Selected soil properties for the four experimental locations.__________ 25 Table 3.3. Cover crop biomass and soil sampling dates______________________34 Table 3.4. Cover crop biomass and N uptake, Fall 2003 and Spring 2004________39 Table 3.5. Cover crop biomass and N uptake, Fall 2004 and Spring 2005________40 Table 3.6. Dry matter and N content of 2-week old soybean seedlings (Expt. 1) and V6 corn shoots (Expt. 2). _____________________________________________ 55 Table 4.1. Characteristics of C and N in plants and soils. ____________________ 72 Table 4.2. Milligrams of N mineralized per g of N added with residue† on selected days. _____________________________________________________________ 79 Table 4.3. Calculation of final (day 48)-initial (day 0) mineral N_______________83 Table 4.4. Labile and recalcitrant pool equation parameters for measured CO2 data, as generated or inferred by having constant pool rates and allowing pool size to vary. __________________________________________________________________ 88 Table A1. Comparing the effects of tillage on N response by immature corn plants. _________________________________________________________________ 101
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List of Figures Fig. 3.1. Cumulative daily (—) and cumulative long-term monthly average (—) precipitation, monthly means of daily temperatures during the study (z) and longterm (20 years) monthly average temperature ({), 01 Aug 2003 to 30 June 2004 at BARC (A),CMREC (B), LESREC (C), and WREC (D). LESREC cumulative daily precipitation values include irrigation. ___________________________________ 27 Fig. 3.2. Cumulative daily and cumulative long-term monthly average precipitation, and monthly mean temperature (during the study and long-term average). Refer to Fig. 1 for symbol legend. _____________________________________________ 28 Fig. 3.3. Expt. 1: Ammonium (filled symbols) and nitrate (unfilled symbols) at 0-15 cm (A,B) and 15-30 cm (C,D) depths at BARC. Abbreviations of FR and NC refer to the forage radish and no cover control treatments, respectively. Vertical bars are average SEM. ______________________________________________________ 43 Fig. 3.4. Expt. 1: Ammonium (filled symbols) and nitrate (unfilled symbols) at 0-15 cm (A,B) and 15-30 cm (C,D) depths at CMREC. Refer to Fig. 3.3 for symbols. Vertical bars are average SEM. ________________________________________ 44 Fig. 3.5. Expt. 1: Ammonium (filled symbols) and nitrate (unfilled symbols) at 0-15 cm (A,B) and 15-30 cm (C,D) depths at LESREC. “FR+Rye” in the symbol legend refers to the forage radish plus rye mixture treatment. Vertical bars are average SEM. __________________________________________________________________ 45 Fig. 3.6. Expt. 1: Ammonium (filled symbols) and nitrate (unfilled symbols) at 0-15 cm (A,B) and 15-30 cm (C,D) depths at WREC. Refer to Fig. 3.5 for symbols. Vertical bars are average SEM. ________________________________________ 46 Fig. 3.7. Expt. 1: Soil mineral nitrogen (0-30 cm) at BARC (A) CMREC (B), LESREC (C) and WREC (D). Vertical bars are average SEM. Mean values with the same undercase letter are not statistically different at (P
