The treatment applied to seeds is typically an antimicrobial or fungicidal chemical coating or dressing. By applying fungicides, for example, it is possible to provide effective protection from many seed and soil-borne plant pathogens, guarding against seed rots and blights that occur during storage or after planting. Similarly, the application of insecticides help to fight pests that strike early in the season when seedlings are most vulnerable.
Beyond the battle against disease and insects, some seed treatment also improves planting characteristics. For instance, the addition of thin, water-permeable polymers in the film coating process aids the flow of seed when sowing to improve planting uniformity.
Seed treatment can even improve yield and quality. By way of example, the use of microbial inoculants helps to improve nitrogen fixation in legumes. This process is beneficial as nitrogen is an essential element of life, and nitrogen availability often limits crop yields. In addition, the application of chemical regulators can improve the plant’s ability to tolerate stress-inducing weather conditions in the early stages of growth.
This strategy is environmentally friendly as it eliminates the need to blanket-spray crops in the ground. There is also a cost advantage. Many treated seeds, such as soya bean, are only good for that planting season, so seeds that remain unsown will then require incineration, a process that costs approximately twice that of producing the seed.
Seed treatments may be applied commercially by the seed industry, or in some cases “on farm”. Major seed merchants treat seed in bulk at specially designed plants. Bulk coatings are stored in large tanks and pumped to the coating machine “pots” as they are required.
On farm treatments take place just prior to sowing, typically using portable seed coating machines driven to farms at planting time. Weighed seed enters a cone, whereupon a PLC drives the pump to dispense the right amount of chemical into the coating drum. Seeds receive spray on the way into the drum or within the drum itself. With the right pump it is possible to apply all treatments - including diluting agents, dyes, polymers or other pelleting and coating substances - subsequently and/or at different times and intensities.
Pumps face several challenges in seed treatment applications. Polymer, for instance, is difficult to handle for many pump types, as are pigment-based colours/dyes due to their abrasiveness. The US Environmental Protection Agency (EPA) requires seeds coated with any form of chemical or biological treatment to use differentiating colours, which helps with identification.
As part of the evaluation process, seed treatment machine manufacturers must decide what benefits are most desirable, both for themselves and end-users. Typically, selection depends on the ability to deliver production cost savings, high productivity and high seed yield, while minimising downtime and maintenance requirements. Against all of these criteria, a peristaltic pump will easily outperform comparable progressive cavity or diaphragm pumps in terms of both flow precision and reliability, according to pump supplier Watson Marlow Fluid Technology Group.
It says that peristaltic pumps are simple to install and quick to maintain. Not only can peristaltic pumps run dry, but the fluid only contacts the bore of the hose or tube, making abrasive fluids such as pigments, easy to handle. Furthermore, varying viscosities of the chemical treatments have no effect on flow accuracy, so chemical overshoot is never likely to be a problem. Because chemicals are contained within the pump’s fluid path, there is no risk to operators when cleaning or maintenance is required.
Seed treatment represents significant global business for Watson-Marlow Fluid Technology Group (WMFTG). For low-pressure feed pump applications, Watson-Marlow Qdos, as well as its 500 and 600 series tube pumps, prove popular, while for higher flow/viscosity transfer, Bredel hose pumps are favoured.