Evaluation of a New Sunn Hemp (Crotalaria juncea L.) Cultivar in Alabama by Jessica Michelle Massey A thesis submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Master of Science Auburn, Alabama December 13, 2010 Copyright 2010 by Jessica Michelle Massey Approved by Kipling Balkcom, Chair, Affiliate Assistant Professor, Research Agronomist, USDA-ARS NSDL Jorge Mosjidis, Professor Agronomy and Soils Andrew Price, Affiliate Assistant Professor, Plant Physiologist, USDA-ARS NSDL Stephen Enloe, Assistant Professor, Extension Invasive Plant Specialist Abstract The southeastern region of the U.S. is often characterized by soils with low innate fertility exacerbated by a history of tillage. Nitrogen (N) is an important and limiting soil nutrient applied to fields to maximize crop yields. As the cost of N supplying fertilizers continues to increase, alternative sources of N are sought. Prior to the advent of artificially derived fertilizers in the last century, leguminous cover crops were a commonly used N source. Southeastern rotations may have a period of time in fields where the land is unutilized after summer harvest and before winter plantings. Sunn hemp (Crotalaria juncea L.) is a tropical legume able to produce large quantities of biomass within a short window of time. However, due to limited areas of seed production within the U.S., sunn hemp is difficult to acquire at an affordable price. Recent breeding efforts at Auburn University have produced ‘Selection PBU’, a sunn hemp cultivar able to produce viable seed in the temperate southeastern U.S. Prior to introducing a new plant to the area, a prudent move is to assess the weediness of the non-native. Therefore, an objective of this thesis was to perform a weed risk assessment of ‘Selection PBU’ before southeastern introduction. Secondarily, it was desirable to study cultural practices that maximize the N producing abilities of ‘Selection PBU’. Further objectives of the thesis were to determine optimum planting dates and seeding rates and determine the effect of N from ‘Selection PBU’ on rye (Secale cereale L.) and wheat (Triticum aestivum L.), winter crops commonly grown in the southeastern U.S. To address the first objective, a comprehensive literature review was performed and the Pheloung (1995) weed risk assessment system determined ‘Selection PBU’ to ii be acceptable as an introduction for southeastern fields. Two separate field studies were conducted to fulfill the next two objectives. In the first study, two fields in Shorter, AL had two planting dates after cash crop harvest and four seeding rates sown. Results showed planting ‘Selection PBU’ early maximized biomass production and N contribution to rye. During times of adequate precipitation, moderate ‘Selection PBU’ seeding rates produced as well as higher seeding rates. A second field study was conducted at Headland, AL and Bella Mina, AL. In this study, ‘Selection PBU’ increased wheat grain yield in two of the five growing seasons. Furthermore, N fertilizer application provided augmentation in wheat grain yields. Results from this thesis study indicate the possibility of ‘Selection PBU’ utilization to provide soil improvement in southeastern crop rotations. iii Acknowledgements This work is dedicated to Ruby J. Massey, grandmother of the author. The author would like to take this opportunity to express deep gratitude to all of her committee members for their patient guidance and assistance over the past few years. She sincerely appreciates all of the help received during this time from staff and student workers at the USDA Soil Dynamics Laboratory, AU Agronomy and Soil Department, E.V. Smith Research and Extension Center (REC), Wiregrass REC, and Tennessee Valley REC. Last, but certainly not least, the author is deeply thankful for the family and friends that provided support and motivation along the way. iv Table of Contents Abstract ........................................................................................................................................... ii Acknowledgements ........................................................................................................................ iv List of Tables ............................................................................................................................... vii I. Introduction ..................................................................................................................................1 Conservation Tillage ............................................................................................................1 Cover Crops .........................................................................................................................1 Sunn Hemp...........................................................................................................................3 Sunn Hemp in Field Rotations .............................................................................................7 Experimental Objectives ......................................................................................................8 References ..........................................................................................................................10 II. A Weed Risk Assessment of Sunn Hemp in Southeastern United States .................................16 Abstract ..............................................................................................................................16 Introduction ........................................................................................................................16 Weed Risk Assessment ......................................................................................................19 Discussion ..........................................................................................................................26 Conclusions ........................................................................................................................29 References ..........................................................................................................................30 v III. ‘Selection PBU’ Sunn Hemp Biomass and Nitrogen Production Across Planting Dates and Seeding Rates .....................................................................................................................43 Abstract ..............................................................................................................................43 Introduction ........................................................................................................................44 Materials and Methods .......................................................................................................47 Results and Discussion ......................................................................................................50 Conclusions ........................................................................................................................57 Acknowledgements ............................................................................................................58 References ..........................................................................................................................59 IV. Wheat Nitrogen Requirements Following Sunn Hemp in Alabama .......................................73 Abstract ..............................................................................................................................73 Introduction ........................................................................................................................74 Materials and Methods .......................................................................................................76 Results and Discussion ......................................................................................................79 Conclusions ........................................................................................................................84 Acknowledgements ............................................................................................................84 References ..........................................................................................................................85 V. Conclusions .............................................................................................................................100 vi List of Tables Table 1.01 Results for Pheloung (1995) weed risk assessment of sunn hemp ........................39 Table 1.02 Frequency of sunn hemp weed aspect classification based on Pheloung (1995) weed risk assessment .............................................................................................40 Table 1.03 Results for Pheloung (1995) weed risk assessment of sunn hemp cultivar ‘Selection PBU’ .....................................................................................................41 Table 1.04 Partitioning species by Pheloung (1995) weed risk assessment score and survey classification ..........................................................................................................42 Table 2.01 Sunn hemp field calendars for 2007 and 2008 at the Plant Breeding Unit of the E.V. Smith Research and Extension Center in Shorter, AL ..................................64 Table 2.02 Average monthly precipitation with growing degree days of sunn hemp at the Plant