Kropff, M. J.

Rajan, Amarthalingam

Universiti Putra Malaysia Institutional Repository

UPM Research Report 1998: Volume2APPLICATIONS OF CROP-WEED COMPETITIONMODELS FOR OPTIMISING EFFICIENCY OF WEEDMANAGEMENT IN RICE PRODUCTIONA. Rajan and M.J. KropffFaculty of Agriculture,Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor,MalaysiaDepartment of Theoretical Prod.· Ecology,Wageningen Agric. UniversityKeywords: weed-competition models, weed-crop ecol-ogy, model development, model applications.IntroductionSystems approaches in agricultural development have in re-cent years drawn considerable attention. The rationale aswell as the advantages in improving cultural and other man-agement practices through systems analysis, in the context ofsustainable production practices with minimal inputs, havebeen well documented in the literature (Kropff and van Laar,1993). Many crop-weed competition models have been de-veloped for crops such as maize, soybeans, rice, pineapplesand other field crops. Crops vary in their cultural require-ments and competitiveness. Optimising crop growth underdifferent weed scenarios with single and multispecies situa-tions requires a thorough understanding of the complex fac-:tors that determine competitiveness between the interactingspecies. Competitive ability of plants vary depending on ini-.tial seed weight, earliness of emergence, relative growth rate,photosynthetic rate, plant height incremental rate, leaf angle'and water and nitrogen use efficiency. Weed-Crop competi-tion models can be useful as a quantitative tool in under-standing the competitive mechanisms between species, bothunder homogeneous as well as patchy weed distribution oftenencountered in the field. Analysis and identification of pa-rameters that significantly influence competitive ability of,species under various scenarios that maybe readily simulatedcould provide useful information to breeders in their searchfor more efficient plant types. Validated models are also use-ful for predicting crop losses as well as designing improvedcrop management practices.Materials and MethodsTwo field experiments and two tank experiments were ini-tially conducted to collect data on the effects of competitionby barnyardgrass (Echinochloa crus-galli (L.) Beauv. var.crus-galli) on rice (Oryza sativa cv. MR84). Inthe first set,rice was sown at different densities (50, 100, 150 kglha),while in the second set sowing dates of rice for the three den-sities were varied (delayed) in relationto emergence date ofthe weed. Parameters collected include data on growth pa-rameters such as dry matter partitioning, height increments,leaf area development and yield component analysis. Data28from earlier experiments were used for parameterisation andpreliminary validation of the model (Rajan, 1991; Rajan etal. 1995). Additional field experiments also gave informationon weeds dominant in direct-seeded field situations in themajor rice growing areas in Peninsula Malaysia. Hence, dataon characteristics of two other major weeds were also in-cluded for study, i.e. Leptochloa chinenesis and Fimbristylismiliaceae. Additional experiments were subsequently con-ducted to use the data to validate the improved model for ap-plications in plant breeding and under· different weed sce-narios.Results and DiscussionResults of all validation experiments showed that the devel-oped model can accurately simulate and explain yield loss,leaf area development and enhancement or delay' in matura-tion due to differences in crop density effects, weed densityeffects, emergence times, sowing dates, vegetative and re-productive development rates, and temperature effects. Themost sensitive parameters in the model are seedling vigour(or relative growth rate) and height growth parameter. Themodel can be easily adapted for studying competition effectsof other weeds where minimum data sets for the critical vari-ables were available. The ability of the model to identify keytraits with respect to competitive ability makes it a usefultool for designing new crop ideotypes (Bastiaans et al. 1997).ConclusionsThese competition models are available for use by studentsand researchers in the field of crop-weed ecology. The mod-els are useful for training students in ecology. They can beused as quantitative tools by extension specialists for trainingfarmers on impact of weeds on crop loss and recommendingappropriate cultural practices for specific weed situations.ReferencesBastiaans, L., M.J. Kropff, Rajan, A., Kempuchetty, N. and Migo,T.R. 1997. Can simulation models help design rice cultivars thatare more competitive against weeds? Field Crops Research.' 51: .101-lli. 'Kropff, MJ. and Laar, H.H. van. 1993. Modelling crop-weed inter-actions. CAB International, Wallingford and International RiceResearch Institute, Manila. p. 274.Rajan, A. 1991. Simulation of weed interference and yield loss in di-rect-seeded irrigated rice. In: H.H. van Laar et al. (eds.). Casestudies in crop growth simulation, 1990-1991. IRRI (philippines).CABO and TPE, Wageningen (The Netherlands). p. 147-152.Raj~, A .• Singh. S., Ibrahim, Y. and Harun, W.S.W. 1995. Applica-uon of the INTERCOM model in plant breeding - model valida-.tion and effect of early leaf area growth on crop-weed competi-tion in direct-seeded irrigated rice. In: P.K. Aggarwal, R.B. jMatthews, MJ. Kropff and H.H. van Laar. (eels.). Proceedings ofS~ ~pplications Workshop, 18 April - 6 May, 1994. IRRI,(Philippines), DLO-Res. Inst. Agrobiol. and Soil Fertility (TheNetherlands). TPE. WAU (The Netherlands). D. 67-74. .Supported by IRPA Grant 01-02-04-0025

Applications of crop-weed competition models for optimising efficiency of weed management in rice production

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Applications of crop-weed competition models for optimising efficiency of weed management in rice production

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