Global Journal of Agricultural Innovation, Research & Development, 2016, 3, 1-9 1 E-ISSN: 2409-9813/16 © 2016 Avanti Publishers Derivation of a Cropping System Transfer Function for Weed Management: Part 2 – Microwave Weed Management Graham Brodie * Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Nalinga Rd. Dookie, Victoria, 3647, Australia Abstract: System behaviour is described by transfer functions, which relate the system’s output to one or more input parameters. This paper derives the transfer function for crop yield potential as a function of applied microwave energy for control of weeds. The resulting transfer function reveals that microwave weed control and soil treatment can increase normalized crop yield potential above the ideal weed free potential. It also revealed that there was an ongoing yield advantage associated with a once off microwave soil treatment to deplete the weed seed bank. Keywords: System analysis, weeds, microwave, herbicide resistance, crop ecology. 1. INTRODUCTION Good weed management is based on controlling the viable weed seed bank in the soil. A study by Chauhan et al. [1] found that in a no-till cropping systems, approximately 65% of the viable weed seed bank is found in the top 1cm of soil and 90% of the viable seed bank is in the top 5cm of soil [2]. Burnside et al. [3] reported that viable weed seeds in the soil can be reduced by 95% after five years of consistent herbicide management; however, Kremer [4] pointed out that in spite of achieving good weed control over several years, weed infestations will recur quickly in succeeding years if intensive weed management is discontinued or interrupted. These efforts to deplete the soil seed bank are also hindered by the growing list of herbicide-resistant weed biotypes. Herbicide resistance in many weed species is becoming wide spread [5] and multiple herbicide resistances in several weed species has been widely reported [6]. Some studies have demonstrated that competition from weeds can reduce the expected yield of crops by between 35% and 55% [7, 8]. In time, herbicide resistant weeds may ultimately result in more significant yield reductions and grain contamination. The International Agency for Research on Cancer (IARC), which is part of the World Health Organisation (WHO), has concluded that glyphosate is probably carcinogenic to humans [9]. This announcement has generated considerable debate in the media concerning the use of herbicides. Other authors have *Address correspondence to this author at the Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Nalinga Rd. Dookie, Victoria, 3647, Australia; Tel: +61 3 5833 9273; Fax: +61 3 5833 9201; E-mail: grahamb@unimelb.edu.au also highlighted the potential hazard to human health of exposure to herbicides and pesticides [10-15]. Interest in the effects of high frequency electromagnetic waves on biological materials dates back to the late 19 th century [16], while interest in the effect of high frequency waves on plant material began in the 1920s [16]. Many of the earlier experiments on plant material focused on the effect of radio frequencies (RF) on seeds [16]. In many cases, short exposure resulted in increased germination and vigour of the emerging seedlings [17-19]; however, long exposure usually resulted in seed and plant death [16, 20]. Davis et al. [21, 22] were among the first to study the lethal effect of microwave heating on seeds. They treated seeds, with and without any soil, in a microwave oven and showed that seed damage was mostly influenced by a combination of seed moisture content and the energy absorbed per seed. Other findings from this study suggested that both the specific mass and specific volume of the seeds were strongly related to a seed’s susceptibility to damage by microwave fields [22]. These finding may be associated with the radar cross section [23] of the seeds, with larger seeds intercepting more microwave energy. In a theoretical argument, based on the dielectric and density properties of seeds and soils, Nelson [24] demonstrated that using microwaves to selectively heat seeds in the soil “cannot be expected.” He concluded that seed susceptibility to damage from microwave treatment is a purely thermal effect, resulting from soil heating and thermal conduction into the seeds. Nelson’s final conclusion was that microwave soil treatment was unviable because of its high energy requirements; however these studies ignored the effects of herbicide resistant weeds on crop yields.