University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Agronomy & Horticulture -- Faculty Publications Agronomy and Horticulture Department 1996 Applications of an Ecophysiological Model for Irrigated Rice (Oryza sativa)- Echinochloa Competition John L. Lindquist University of Nebraska-Lincoln, [email protected] Martin Kropff University of Minnesota Follow this and additional works at: https://digitalcommons.unl.edu/agronomyfacpub Part of the Plant Sciences Commons Lindquist, John L. and Kropff, Martin, "Applications of an Ecophysiological Model for Irrigated Rice (Oryza sativa)- Echinochloa Competition" (1996). Agronomy & Horticulture -- Faculty Publications. 617. https://digitalcommons.unl.edu/agronomyfacpub/617 This Article is brought to you for free and open access by the Agronomy and Horticulture Department at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Agronomy & Horticulture -- Faculty Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Weed Science Society of America Applications of an Ecophysiological Model for Irrigated Rice (Oryza sativa)-Echinochloa Competition Author(s): John L. Lindquist and Martin J. Kropff Reviewed work(s): Source: Weed Science, Vol. 44, No. 1 (Jan. - Mar., 1996), pp. 52-56 Published by: Weed Science Society of America and Allen Press Stable URL: http://www.jstor.org/stable/4045782 . Accessed: 14/09/2012 10:47 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Weed Science Society of America and Allen Press are collaborating with JSTOR to digitize, preserve and extend access to Weed Science. http://www.jstor.org Weed Science, 1996. Volume44:52-56 Applications of an Ecophysiological Model for Irrigated Rice (Oryzasativa)- Echinochloa Competition1 JOHN L. LINDQUISTand MARTINJ. KROPFF2 Abstract.A simulationmodel of rice-barnyardgrasscompeti- yield loss. These empiricalrelationships show considerablevari- tion for light was used for two managementapplications. ation among years and locations (1, 21), presumably due to First,simulations using 47 weatherdata sets fromfour loca- variationin weatherand otherenvironmental factors. A number tions in Asia were conductedto evaluate the influenceof of simulationmodels have recently been developed to quantita- weathervariation on single year economicthreshold densi- tively describemechanisms of inter-plantcompetition based on ties of barnyardgrass.Second, rapid leaf areaexpansion and fundamentalplant physiology (6, 12, 16, 20, 22, 23). These leaf area index were evaluated as potential indicatorsof ecophysiologicalmodels may be utilized to evaluatethe relative improved rice competitiveness and tolerance to barn- importanceof weather,year, and location variabilityin weed- yardgrass.Influence of weather variation on single year crop interferencerelationships. economicthresholds was small under the assumptionthat Improved cultivar competitiveness and tolerance to weeds competitionwas for light only. Increasingearly leaf area have been suggested as methods of reducingthe negative influ- expansionrate reducedsimulated barnyardgrass seed pro- ence of weeds on crop yield (2, 5, 9). Improvedrice competitive- ductionand increasedsingle year economicthresholds, sug- ness may benefit managementby reducing weed reproductive gestingthat the use of competitiverice cultivarsmay reduce output. Because fewer seeds are produced, the influence of the needfor chemicalweed control. The model predicted that barnyardgrasson rice yields in subsequent years should be rice leaf area index 70 to 75 d after planting was a good reduced. Improved tolerance to weeds aids management by indicator of early leaf area expansion rate. Nomencla- reducingthe impact of each weed on crop yield, resultingin an ture: Barnyardgrass,Echinochloa crus-galli (L.) Beauv.,#3 increase in the numberof bamyardgrassplants needed to cause ECHCG;rice, Oryzasativa L. 'IR72.' economic damage(i.e., economic thresholdweed density would Additionalindex words.Economic threshold, integrated weed increase). Ecophysiological models may be used to generate management,weed ecology,IPM, weed-cropinterference, hypotheses regarding which plant characteristicsconfer im- ECHCG. proved competitivenessor tolerancein crops. An ecophysiologicalmodel (INTERCOM)was developedfor INTRODUCTION rice-barnyardgrasscompetition for light in well-fertilizedhigh- yielding irrigatedrice ecosystems (12). Kropffet al. (17) evalu- Worldrice productionmust be increasedby as much as 67% ated INTERCOMperformance using data from an experiment to feed the projectedhuman population in 2025 (8). Weed com- with irrigateddirect seeded rice and barnyardgrass.Dry matter petition reduces currentrice productionby an estimated 25% production, leaf area development, and yield were simulated (18). Echinochloa species are among the most severe weeds in accuratelyfor all treatments.Further tests of model performance irrigatedrice cropsand most rice producersrely on handweeding were made using eight data sets collected over a wide range of for control. Owing to high costs or lack of available labor and environments.Direct seeded or transplantedrice yield loss re- herbicides, a need for alternativeweed managementstrategies sultingfrom barnyardgrass interference was predictedaccurately exists. Integrationof culturalweed managementpractices may by the model (92%of variationaccounted for) over a wide range be utilized effectively in many rice growing areas.Development of competitionsituations (14). of appropriatecultural practices requiresa quantitativeunder- In this study,INTERCOM was used to examine two applica- standingof weed-cropinterference relationships and factorsthat tions for an integratedweed managementprogram. Objectives alterthem (13). were to evaluatethe influenceof weathervariation and improved Empirical weed-crop interferencemodels (e.g., 4, 15) are early leaf areagrowth rate on simulatedrice-barnyardgrass com- commonlyused to quantifycompetitive relationships and predict petition and on single year economic threshold densities of barnyardgrass. 1Receivedfor publicationMarch 22, 1994, andin revisedform May 23, 1995. 2FormerGrad. Res. Asst., Dep. Agron.Plant Gen., Univ. Minnesota,St. Paul, MN 55108 and Systems Agron., InternationalRice ResearchInstitute, P.O. Box 933, 1099, Manila, The Philippines. Present address of authors:Dep. Agron., MATERIALSAND METHODS Univ. Nebraska,Lincoln NE 68583-0915; Dep. Theor.Prod. Ecol., Wag. Agric. Univ., Bomsesteeg 65, 6708 PD Wageningen,Netherlands and the Institutefor Model overview.Details of INTERCOMstructure have been Agrobiologicaland Soil FertilityResearch, P.O. Box 14,6700 AA, Wageningen, describedelsewhere (12). Requiredmodel inputs include daily Netherlands. weather data (maximum and minimum temperature,global ra- 3Lettersfollowing this symbol are WSSA-approvedcomputer code from Composite List of Weeds, Revised 1989. Available from WSSA, 1508 West diation, and rainfall), site latitude, plant density, planting date, UniversityAve., Champaign,IL 61821-3133. and a numberof species-specific parameters. 52 WEED SCIENCE The model simulates competition for light, based upon the Table1. Weatherdata bases used in rice-bamyardgrasscompetition simulations. profile of absorbedphotosynthetically active radiation(PAR)4 in Julian the canopy and the photosynthesis-lightabsorption response Years date of curveof individualleaves. The quantityof PARabsorbed by each Locationof station available planting species is a functionof the amountand distributionof photosyn- Beijing, China 1980 to 1988 145 theticarea (leaves, stems,reproductive organs) within the canopy KhonKaen,Thailand 1975 to 1988 45 and the light extinction coefficient. The photosynthesis-light Aduturai,India 1980 to 1992 45 Los Banos, Philippines 1980 to 1990 45 response curve is defined using a saturationfunction with the maximumvalue determinedby the nitrogencontent of leaves. Forboth rice andbarnyardgrass distribution of photosynthetic area within the canopy is assumed to be parabolicwith a peak stants).A coefficient estimateand its standarderror may be used area at 50% of plant height. This assumption is supportedby to determineET stochasticallyand provide information about the the data of Noda et al. (19). Height growth of each species variabilityof weed threshold levels. The estimate of I and its occurs independentlyof species interactionand is simulatedas standarderror obtained from fitting Cousens' equation to the an empirical function of accumulated growing degree days simulateddata in Figure 1 were used to evaluatethe influence of (GDD)4. weather variabilityon single year economic thresholdpopula- Gross CO2assimilation is integratedover canopy height. Net tions of bamyardgrass.Values of I are assumed to be normally CO2assimilation is determinedby subtractingmaintenance and distributed and therefore may be randomly generated using growthrespiration from gross CO2assimilation. Daily drymatter the Box-Muller algorithm(10). This method was used to gener- growthincrease is calculatedfrom net CO2assimilation