In contrast, the soil in narrow cores (e.g. 2 cm diameter) might weigh only 50-100 g, which makes them easy to handle and transport. However, the probability of detecting seeds in such small amounts of soil is so very low that that many cores must be sampled for compensation. There are very few studies that compare core sizes for sampling efficiency. Benoit et al . (1989) found that augers with diameters of 1.9, 2.7, and 3.3 cm were not different in estimating the number of Chenopodium album seeds when a similar volume of soil was sampled. Although the largest and smallest of these diameters differ only by a factor of 1.7, the largest and smallest volumes of sampled soil from a single core exhumed by these augers differ by a factor of 3. In other words, three times as many soil cores of 1.9 cm diameter would need to be sampled as cores of 3.3 cm diameter in order to estimate similar seed bank densities. The additional labour involved in taking more cores may not compensate for the ease of using small-diameter cores.
Seed bank researchers must devise protocols that are suitable to their objectives, equipment and labour constraints, and the agricultural system in which they work. Consequently, our goals in this report are to provide guidelines that may help researchers, especially those new to seed bank analyses and to tailor new studies on weed seed banks with a minimum of effort devoted to protocol development. This is not to suggest that new and more efficient protocols should not be devised. Instead, we urge new seed bank researchers not to duplicate and repeat weak protocols that could have been stronger with only slight modifications. These modifications often require no extra labour or expense. In some cases, only the time or type of sampling would need to be altered.
Where N is the estimated number of necessary samples (i.e. 5-cm diameter soil cores) to adequately represent a seed bank, and D represents the desired level of precision. D is defined as the standard error of the mean divided by the mean (SE m / m ). The value of m is divided by 509 to convert the area of a 5-cm diameter core to 1 m 2 . Dessaint et al. (1996) indicated that a D value of 0.3 was a practical level of precision for seed bank studies. We believe that even a precision value of 0.5, which is less precise than 0.3, may be adequate depending upon the goals of the researchers. For instance, perhaps D could be set to 0.4-0.5 for species that are relatively uncommon but easily controlled. In contrast, species that are both common and difficult to manage probably merit D values of 0.2-0.3. Thus, sampling efforts can be conditioned by the required value of the resulting information.
However, also other factors are involved in the choice of diameters of soil-coring devices. The most significant of these is soil texture and soil water content. Wet soils with high percentages of expanding clays are notoriously difficult to remove from sample tubes, especially from small-diameter tubes. Cores with diameters of up to 10 cm should be considered for such soils. Application of non-toxic oils (vegetable oils) to the coring implement helps greatly in preventing clay from sticking to the device. Orifices that are a few millimetres narrower than the diameter of the sampling tube also may aid in preventing the soil from adhering too tightly to the inside of the sample tube. However, these types of coring tools are more likely to compress soils with low bulk densities while the coring tool is being driven into the soil. This compaction of the core confounds reliability of core depths. In contrast, very dry soil can resist penetration by coring implements. In these cases, narrow cores may be more practical than the recommended 5 cm diameter cores. Researchers must be practical and balance multiple factors when choosing sampling equipment.
Fallopia convolulus (L.) Loeve
Seed being sold in Wyoming must be labeled according to the Wyoming Seed Law and Regulations. The seed law requires all seed being sold to be labeled, and the label must include percentages of pure seed, other crop seed, weed seed, inert matter, and germination. A seed test will give the required values.
The Wyoming Seed Analysis Laboratory is funded by the State of Wyoming, and administered by the University of Wyoming to serve the seed testing needs of farmers, private and public seed buyers, seedsmen, the Wyoming Crop Improvement Association, University of Wyoming seed researchers, and the Wyoming Department of Agriculture. The lab is equipped with modern testing equipment necessary to perform tests on all kinds of seeds, and is staffed with one Registered Seed Technologist and three permanent-staff lab assistants. The Rules for Testing Seeds by the Association of Official Seed Analysts (AOSA) are used as the basis for the purity analysis and germination tests performed in the seed lab.
Testing saved seed will give the person using the seed a good understanding of the germination potential of his seed lot, and determine if the seed contains any problem weed seeds, including noxious weed seeds. It is advisable to check for problems before planting. If the seed lot has a low germination percentage, a good stand will not be achieved. If the seed lot has noxious weed seeds, or is contaminated with other crop and weed seeds, it may not be suitable for planting.