Browsing by Subject "Lotsize"

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    Inhomogenität in Getreidesaatgutpartien : Ursachen und Konsequenzen für die Saatgutprobenahme
    (2009) Schmohl, Sven; Kruse, Michael
    The objective of this research was to quantify inhomogeneity and evaluate its formation in cereal seed lots. The results were used to compile proposals for a better in seed sampling schemes and to give recommendations to avoid inhomogeneity formation during seed processing. For this purpose, the extent and structure of the variation in the seed quality criteria, purity, other seed count, germination, thousand seed mass and size grading were determined within seed lots as well as their change during seed processing. Commercial seed lots of oat, wheat and barley were sampled from the delivery point to the bagging of the lots. All primary samples, in total 1944, were analyzed separately. The evaluation of the inhomogeneity was done by either an H-test or a R-test according to the ISTA rules. Additionally, for each seed quality criteria at each station of seed processing the results of the primary samples were analysed by means of regression analyses to detect systematic gradients. From a total of 57 stations, 56 showed significant inhomogeneity in at least one seed quality criteria. There were significant differences between the seed quality criteria and the crop species in terms of composition as well as extent of inhomogeneity. In the unprocessed seed lots the proportion of stations with significant inhomogeneity were between 14 and 100 % for thousand seed mass, 33 and 100 % for germination, 50 and 100 % for size grading, 57 and 100 % for purity and between 0 and 75 % for other seed count. After cleaning, the proportion of stations with significant inhomogeneity were between 17 and 55 % for size grading, 14 and 100 % for thousand seed mass, 0 and 43 % for purity and between 50 - 67 % for germination. During the seed processing the initially stochastic dispersion of the seed quality criteria size grading and purity at the delivery point were increasingly replaced by systematic gradients. In case of thousand seed mass, systematic gradients were already present at the delivery point. However, the determination of the observed gradients increased during the processing. In the processed seed lots the seed quality criteria thousand seed mass and purity with 74 % and 72 % respectively showed most frequently systematic gradients at the sampling stations, followed by seed grading with 59 % and germination with 29 %. Other seed count showed rarely systematic gradients with less than 5 % of the stations. In the processed seed lots the systematic gradients entailed inhomogeneity in up to 100 % of the stations for germination, in up to 60 % for thousand seed mass and in up to 33 % for size grading and purity. In the case of other seed count the systematic gradients did not cause inhomogeneity, however for the most part because the lots were almost free from other seeds. The main reasons for the formation of gradients, and thus for the formation of inhomogeneity, are segregation effects in combination with core flow during filling and discharging silos. Additionally, in the case of the germination the mechanical load of the seeds during the processing is an important factor for the formation of inhomogeneity. Therefore, besides the use of suitable conveying devices and the limitation of lot size, the use of suitable silos in respect to the prevention of core flow and the evasion of unnecessary interim storage are important steps for the avoidance of inhomogeneity. The frequent occurrence of systematic gradients in processed and unprocessed seed lots recommends a systematic or stratified sampling scheme. In case of systematic sampling the primary samples are drawn in constant time intervals. In case of stratified sampling the primary samples have to be drawn within constant periods of time, whereas the time within the intervals is at random. These sampling schemes and the random sampling scheme were evaluated in computer simulations in terms of their accuracy and efficiency. The simulations were using the data collected from the cereal seed lots. The systematic and the stratified sampling of only 10 primary samples results in the same accuracy of the submitted sample as 30 primary samples collected at random according to the present ISTA rules. In case of interference between the systematic and stratified sampling scheme and the systematic gradients, a further decrease of the number of primary samples could lead to a strong impair of the accuracy of the submitted sample. Therefore in terms of these sampling schemes a further reduction of sampling intensity is not advisable. On the basis of the results obtained from commercial seed lots produced in one seed processing plant of one enterprise, inhomogeneity and its causes in cereal seed lots could be studied in detail. From the experimental data of commercial seeds lots conclusions for the further improvement of sampling procedures could be compiled.