) STUDIES ON SPINY AMARANTH (AMARANTHUS SPINOSUS L. INTERFERENCE WITH LETTUCE (LACTUCA SATIVA L.) AS INFLUENCED BY PHOSPHORUS FERTILITY ON HISTOSOLS By JAMES WILLIAM SHREFLER A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1993 To My Parents ACKNOWLEDGEMENTS I wish to express my appreciation to my committee members, Dr. Barry Brecke, Dr. Joan Dusky, Dr. Donn Shilling, Dr. Bill Stall, and Dr. Daniel Colvin for their guidance and support during the course of my studies at the University of Florida. I also am greatly indebted to the faculty at the Everglades Research and Education Center at Belle Glade for valuable assistance and encouragement they provided me. The companionship and assistance of the weed science graduate students and staff and the Everglades Research and Education Center staff is appreciated and will long be remembered. My deepest appreciation goes to my wife, Carmen, for her support and understanding. 111 TABLE OF CONTENTS ACKNOWLEDGEMENTS iii ABSTRACT V CHAPTERS 1 INTRODUCTION 1 LITERATURE REVIEW 2 4 Interference and Competition 4 Factors Influencing Competition 10 Factors for which Plants Compete 12 3 SPINY AMARANTH INTERFERENCE IN CRISPHEAD LETTUCE AS INFLUENCED BY PHOSPHORUS FERTILIZER APPLICATION METHOD 17 Introduction 17 Materials and Methods 24 Results and Discussion 30 4 SPINY AMARANTH Amaranthus spinosus L.) COMPETITION ( WITH LETTUCE (Lactuca sativa L. AS INFLUENCED BY ) PHOSPHORUS FERTILITY OF MUCK SOIL 74 Introduction 74 Materials and Methods 86 Results and Discussion 95 5 SUMMARY AND CONCLUSIONS 185 APPENDICES A CHAPTER THREE MICRONUTRIENT DATA 191 B CHAPTER FOUR TABLES 198 LITERATURE CITED 205 BIOGRAPHICAL SKETCH 213 IV Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy STUDIES ON SPINY AMARANTH (AMARANTHUS SPINOSUS L.) INTERFERENCE WITH LETTUCE (LACTUCA SATIVA L.) AS INFLUENCED BY PHOSPHORUS FERTILITY ON HISTOSOLS By James William Shrefler May, 1993 Cochair: Dr. B.J. Brecke Cochair: Dr. J.A. Dusky Major Department: Agronomy Department Studies were conducted to determine how spiny amaranth Amaranthus spinosus L.) interference with lettuce Lactuca ( ( sativa L.) grown on histosols would be influenced by soil phosphorus (P) fertility and P application method. Additive techniques were used in 3 field studies (spring 1991, fall 1991 and spring 1992) to test for the effects P application method (banded versus broadcast) weed density and duration of , interference on lettuce yields. Phosphorus application by either method increased lettuce yields ca. 100% over controls not receiving P. Spiny amaranth biomass was less responsive to P. Duration of interference reduced lettuce yields in a quadratic fashion with broadcast P application in spring 1991 and 1992. With mid- to full-season interference, lettuce yields were reduced more with 4 weeds per 2.3 m than 1. Lettuce tissue P concentrations explained the yield response to P fertilization; P being least with no added P, intermediate with banded P and highest with broadcast P. Lettuce yield loss due to weed interference was not explained by nutritional status. Replacement techniques were used in 3 greenhouse experiments to study the effect of P fertility on competition between lettuce and spiny amaranth during the first 4 weeks of growth. Monocultures and 1:1 mixtures were used at total densities ranging from 2 to 32 plants per 113 cm2 . Competition was assessed based on analyses of individual plant weight, relative yields, relative crowding coefficients (RCC) and relative mixture response. Competitive interactions varied with experiments. When monoculture growth of the two species was comparable, lettuce was more competitive than spiny amaranth in mixture at all but the lowest P fertility level. When spiny amaranth growth in monoculture was 2 to 4 times greater than that of lettuce, the weed was the dominant competitor. However, relative yield analysis suggested that the competitive ability of lettuce was improved by increased P fertility. Competitive interactions were density dependent. As measured by the RCC, the intensity of interspecific competition increased with density; this density effect being species dependent. However, there were no interactions between density and P fertility in the analysis of interspecific competition. vi CHAPTER 1 INTRODUCTION During the period between 1986 and 1991, lettuce Lactuca sativa L.) produced in Florida had an annual ( average value of more than 38 million dollars (Freie and Young, 1992) Greater than 90 percent of this production . occurred on Everglades histosols. Most of the remainder was grown on histosols in the central region of the state. Weed control is important in the production of quality lettuce (Ryder, 1979) On Florida muck soils, available . weed control strategies are limited. For gramineous weeds, postemergence herbicides are available (Stall and Dusky, 1992) Broadleaf weeds, however, are an important weed . problem on these soils (Dusky et al., 1988). Nonselective weed control between the crop rows can be obtained with a shielded application of paraquat (1, l'-dimethyl-4 ,4 '- bipyridinium) However, weeds in the crop row remain . uncontrolled with this measure. Soil applied herbicides are available for broadleaf weed control in lettuce on mineral soils; however, these are not recommended for use on muck soils (Dusky and Stall, 1992). Thiobencarb (S-[(4- chlorophenyl)methyl]diethylcarbamothioate) is one herbicide that can be used on these soils for weed control in lettuce . . 2 (Dusky et al. 1988) Its herbicidal activity at a given use . rate was found to be less on histosols than on mineral soil (Braverman, Locasio, Dusky and Hornsby, 1990) This was . attributed to greater soil adsorption and decreased mobility of the herbicide in the organic soil compared to the mineral soil (Braverman, Dusky, Locasio and Hornsby, 1990) However, thiobencarb efficacy is dependent upon environmental conditions (temperature and moisture) and there is a relatively small safety margin for lettuce. Due to the lack of options, weed control in lettuce grown on muck soils is highly dependent on cultivation and hoeing. Hoeing reguires a high labor input. Hoeing also results in damage to lettuce plants (Dusky and Stall, 1990) Information concerning the effect weed infestations have on a crop facilitates the decision making process of when to apply control measures (Thill et al., 1991). Such information might help to minimize labor costs and to reduce crop damage that would result from excessive hoeing. Such information for lettuce is scarce. Crop mineral nutrition is important in the production of quality lettuce (Ryder, 1979) Relatively large amounts . of phosphorus (P) fertilizer are required to obtain a lettuce crop of good quality and yield on high organic matter soils (Sanchez and Burdine, 1988) Current . environmental and economic issues, however, compel growers to reduce fertilizer P use (Alvarez and Sanchez, 1991; 3 Sanchez et al., 1990). One promising approach to reduced fertilizer P application for lettuce is the use of a banded application (Sanchez et al., 1990). One objective of this investigation was to characterize the effect of interference by spiny amaranth Amaranthus ( spinosus L.), an important broadleaf weed species, on lettuce. Spiny amaranth was chosen for these studies because of its ubiguitous occurrence throughout the lettuce growing areas of Florida and because of the difficulty of controlling it in lettuce. A second objective was to determine how P fertilization practices would influence the effect of the weed on the crop. In following with these objectives, two series of studies were conducted. These studies are presented in chapters III and IV. Chapter III of this investigation concerns field studies which were conducted to determine how density and duration of spiny amaranth interference affects lettuce yields. These factors were examined at several fertilizer P application options. Chapter IV of this investigation presents studies on competition between lettuce and spiny amaranth during early growth. Competition is assessed in these studies under varied levels of P fertilizer amendment of muck soil. Several methods of analyzing the competitiveness of one species upon another are discussed. CHAPTER 2 LITERATURE REVIEW Interference and Competition It has been stated that weed control measures "focus directly or indirectly on improving the competitive ability of crops with regard to weeds" (Spitters and Van Den Berg, 1982, p. 137). This is an example of how the term competition is commonly used to refer to the overall effect that weeds have on crop growth due to interactions between plants growing in close proximity to one another. Losses in crop yield or quality from interactions among weeds and crops form the basis of modern weed science (Radosevich, 1987) Radosevich and Holt (1984) discussed the existence . of ten possible interactions, previously published by another author, that may occur between plants. These interactions have to do with the influence a plant might have on the environment of its neighbors and are collectively termed interference. Three of the interaction types, competition, amensualism (allelopathy) and parasitism are of a negative nature. These are also of particular importance to crop production. Competition refers to mutually adverse effects of organisms utilizing a resource