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Title:   Author  item
                                            Brazee, Rossitem
                                            BUKOVAC, M - PROFESSOR EMERITUSitem
                                            Zhu, Heping
  Submitted to: Transactions of the ASAE
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 3/10/2004
                                    Publication  Date: 6/30/2004
                                    Citation: Brazee, R.D., Bukovac, M.J., Zhu, H. 2004. Diffusion Model for Plant Cuticular Penetration by Spray-Applied Weak Organic Acid Bioregulator in Presence or Absence of Ammonium Nitrate. Transactions of the ASAE. 47(3):629-635.Interpretive Summary: For agricultural crop management and protection operations, new and better ways are needed to deliver pest-control and bioregulating agents to their sites of action in plants, with minimum adverse effect on the environment. Particularly in the case of systemic agents, which must penetrate plant surfaces to be effective, the plant cuticle with its surface waxes and membrane layers can be a formidable barrier to efficient uptake, depending on the treatment formulation which is usually spray-applied.  In this investigation, a mathematical cuticular penetration model was developed to aid in identifying and quantitatively determining the significance of factors in uptake processes that can be effectively manipulated to accelerate penetration.  The model was tested by comparing its predictions with cuticular-penetration data for naphthalene acetic acid (NAA) growth regulator alone and with ammonium nitrate additive, which accelerates NAA uptake.  The model satisfactorily simulated the penetration processes for both modes of delivery over a typical treatment period of 120 hours, although it tended to over-estimate penetration during the first 10 hours following spray application.  Model simulations also indicated that cuticular sublayers are physically or chemically altered by some additives, possibly confirming mechanisms by which uptake rates can be increased.  Growers and application specialists will ultimately benefit from these results in their crop portection operations.  systemic materials are effective crop management/protection tools, and these results can help secure quicker and more efficient penetration into plants, in turm promoting more timely response and reduced use of crop protection and bioregulating compounds.
                                Technical Abstract: In agricultural crop management and protection, it is necessary to continually seek new and better ways to deliver systemic pest-control and bioregulating agents to their sites of action in plants, with minimum disruption to the environment.  Thus, a goal of the present investigation was development of a plant cuticular penetration model that can aid in identifying and quantifying factors in systemic uptake processes that can be effectively managed to accelerate penetration.  A model was formulated on the basis of diffusion theory using a time-dependent diffusion coefficient and an instantaneous plane source representing a finite-dose application of a solution containing a systemic solute.  A time-dependent, three-layer, apparent diffusion coefficient model was devised in an effort to account for drying of the outer donor layer and possible alteration of the two-layer cuticular membrane by the solution or its additives.  The model was tested by comparing its predictions with cuticular-penetration data for naphthalene acetic acid (NAA) alone and with ammonium nitrate additive, which accelerates NAA uptake.  Data were obtained with a finite-dose diffusion cell in the laboratory.  The model satisfactorily simulated the experimental observations over a time course of 120 hours, other than its tendency to over-estimate penetration during the first 10 hours following application.  The model results also support the idea that epicuticular and possibly cuticular sublayers may be physically or chemically changed by some additives such that uptake rates are increased.


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