Desktop review of Polyacrylamide use in the Australian cotton industry

[Executive Summary]: Polyacrylamide, commonly known as PAM, is a long-chain hydrocarbon of high molecular weight, synthesized from natural gas for a range of industrial and environmental use. In Agriculture, PAM and other polymers have been historically used as a soil conditioner similar to gypsum and lime. The purpose of this review is to establish the extent to which PAM is useful in agricultural application, particularly within the cotton industry in Australia and identify knowledge gaps and make key recommendations for future research, development and extension. Australian and International agricultural and environmental research reviewed in Section 1 shows that anionic PAM of high molecular weight of food grade quality is possibly the best PAM formulation for land and water application because of its high solubility and purity which is capable of providing substantial benefit at extremely low concentration. High purity of PAM ensures that it contains very little impurities (particularly acrylamide, AMD units from which PAM is synthesized) which could be toxic to aquatic organisms and human. Single dose application of anionic PAM at low concentration (in the range of 1-10 ppm) with irrigation water can cause over 50% reduction in runoff and sediment loss. Other associated benefits with this type of application include reduced transport of nutrients, pesticides, weed seeds, pathogens via runoff and sediment, with little off-site impacts. Due to the need for low application rate, PAM application is economically attractive although repeated applications are necessary to derive full, long term benefit. Despite some indication that PAM degrades over time, information on the breakdown products is limited to AMD only. There is also little knowledge available currently that demonstrates how to remove PAM once it is applied to land. The usage of PAM is significant in the Australian cotton industry with the potential peak usage of one in five of all Australian cotton fields being treated with PAM for various reasons per season. One of the main reasons for using PAM in cotton fields is to reduce irrigation-induced erosion and increase infiltration in soils with low infiltration. However, the commercial application of PAM has produced inconsistent results affecting further use. The reasons for these inconsistent results are due to a lack of understanding of the scientific and technical requirements for successful PAM application and amelioration. For example, when PAM is applied as a liquid in the irrigation water, its benefits are highly sensitive to dosage rate, water quality and soil type. It is difficult for a cotton grower to control PAM dosage as there is a lack of adequate information on the volume of water that is being delivered to the field. The efficiency of PAM application is further affected as there is not enough information readily available on the quality of irrigation water and soil condition. It may be useful to use other strategies to manage soil erosion and/or address infiltration constraints in cotton fields, but there is no best practice yet identified for cotton to combine traditional methods with application of PAM to produce beneficial, long term results. As growers’ capability in monitoring of water application rates improve over time, some improvements in PAM application efficiency are expected. However research, extension and education about the practical application of PAM for cotton growers would be highly desirable. Using PAM to mitigate seepage and evaporation from dams and channels is an emerging and challenging opportunity that is being currently investigated by growers, PAM suppliers and researchers. However, the scientific basis of using PAM to reduce evaporation and seepage is not known as well as for evaporation control and hence, its practical application remains difficult. A collective effort is needed to better understand this area of opportunity. Supporting research, development and extension in this area would of great strategic advantage for the cotton industry.