Kroulík M., Hůla J., Rybka A., Honzík I. (2016): Pneumatic conveying characteristics of seeds in a vertical ascending airstream. Res. Agr. Eng., 62: 56-63.Pneumatic conveying characteristics were measured in vertical tubes for seeds of selected varieties of cereals, wide-row crops, oil crops, legumes and catch crops. The measured values were used for graphical representation of variation curves for the chosen groups of seeds. The values of the critical air velocity for seeds (velocity of seed lift) were computed. Statistical significance of differences in the mean values of critical velocities of tested seeds was determined. The critical velocity of cereal seeds ranged from 8.03 to 10.54 m/s. Among the crops grown in wide rows the highest critical velocity of seeds was found out in maize (13.29 m/s), the lowest in sunflower seeds (8.38 m/s). In oil crop seeds, the lowest critical velocity was recorded in poppy (4.67 m/s), which was the lowest value of all seed samples of the tested crops. The highest value of the critical velocity was measured in pea seeds (14.85 m/s).Keywords: sowing machines; aerodynamic properties of seeds; variation curves Aerodynamic properties of seeds represent the behaviour of seeds in airstream. They are mainly related to seed properties (weight, shape, surface), and also to the condition of the air environment -airflow evenness (Srivastava et al. 2006). The knowledge of aerodynamic properties of grains is applied to the design of grain cleaning and sorting systems as well as to the construction of the pneumatic sowing mechanism of seed drills.The seeds placed in a central hopper of the seed drill are sliding by gravity and by help of an opener to a vane turnstile that delivers them fluently to the airstream from the fan. The seeds are then conveyed by the airstream pressure usually in a vertical direction upwards to a distribution head and then horizontally or obliquely through delivery tubes to drill coulters.The vertical delivery of seeds upwards is a limiting feature for the appropriate function of the sowing mechanism; it is possible only when the volume flow rate of air (m 3 /s) and its velocity (m/s) are chosen in such a way that the airstream will convey the seeds evenly. This air velocity should be higher than so called critical velocity of seeds (velocity of seed lift) and should include a reserve for the potential increased mass flow of seeds associated with the required change in specific seeding rate. The upper limit of the air velocity is a requirement to avoid seed damage in the course of its conveyance.It follows from the experiments conducted in the past (Neubauer et al. 1986;Páltik et al. 2003) that the air velocity (v a ) in the vertical duct should be chosen in the range: 56
Evaluation of new technologies using guidance systems is very important and can help producers with choosing the right equipment for their applications. Without using satellite navigation during field operations, there is a tendency for passes to overlap. That results in waste of fuel and pesticides, longer working times and also environmental damage. When utilising satellite guidance for field operations, there is a close connection with controlled traffic farming (CTF) as well. CTF is currently a quite quickly developing farming system based on fixed layout of machinery passes across a field. Tracks precisely set out for a machine's tyres in the field could be a tool for minimising soil compaction risk which is another threat to the environment. The purpose of this paper was to evaluate the accuracy of currently available guidance systems for agricultural machines. Real passto-pass errors (omissions and overlaps) in a field were measured. Consequently, comparison between observed guidance systems was made regarding final working accuracy. Further, intensity of machinery passes, percentage of wheeled area and repeated passes in fields were monitored. These measurements were made in fields under real operating conditions using a conventional tillage system with ploughing and also a conservation tillage system, both systems with randomly organized traffic. Finally, the same parameters were monitored in fields where fixed machinery tracks were used for all operations and passes but only under a conservation tillage system. Pass-to-pass accuracy was measured for the evaluation of different guidance systems. Size of missed areas or overlaps was evaluated statistically. Concerning intensity of machinery passes and total field area affected by machinery passes, the following facts were found out. The experiments with randomized traffic showed a significant difference of the parameters mentioned above between a conventional tillage system with ploughing and a conservation tillage system. Wheeled area was 86 and 64%, respectively which proves benefits of conservation tillage. The experiments with a fixed track system showed that the total run-over area by machinery tyres decreased even more (up to 31%) in comparison to randomized traffic in a field (only fields under conservation tillage system were monitored and evaluated).The following statements based on our results can be made. The navigation and therefore possibility for better accuracy of machinery passes in fields together with permanent machinery tracks utilization could help with soil condition improvement and also energy savings which would result from that. The CTF system will help with further development of a system for soil compaction protection which is currently a real necessity.
Soil infiltration capacity is one of the key factors in the soil protection against unfavourable effects of water erosion. The purpose of its measuring was to compare and evaluate the changes of the soil physical properties and of water infiltration into soil caused by different intensity of soil cultivation at two individual sites. The ploughing (PL), shallow tillage (ST), and direct drilling (NT) effects on the soil physical properties, water infiltration into soil, and soil surface coverage with the crop residua under the soil condition loamy Haplic in soil. The variant with ploughing showed water saturation in the top layer, the variants with reduced tillage were characterised by vertical macropores and crack effects with the water drain into deeper layers. Ploughing proved its advantage for the short-term rainfall retention. Similar results were also brought in the evaluation on the plot with clay soil (Klapý). The loosening effect was evident during coloured water infiltration in the period of snow thawing. The loosed soil layer showed a significantly higher soil water holding capacity as compared with variants with reduced soil tillage. The result showed major differences in the water infiltration rate into soil and different characters of water infiltration into soil at different soil tillage.
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