Resin coatings are very effective in controlling the availability of N from applied urea in moist soil. In leaching studies, 94% of the noncoated urea was recovered in 1 day, compared to a 49% recovery of the N from coated urea (13.2% resin) in 4 weeks of intermittent leaching.Release rates are controlled by the thickness of the coating and the temperature of the medium. Coatings averaging 13.2% resin markedly decreased release of urea, compared to coatings of 9.0% resin. In the range beween 5 to 35C, increased release of urea accompanied increases in temperature. After 4 weeks of incubation and intermittent leaching totaling 20 inches of water, 25 and 67% of the added N were leached from soil at 5 and 35C, respectively. Increasing the temperature 10C was approximately equivalent to doubling the release time within a 16-week period. Increasing the temperature increases expansion of the capsule and the surface area through which diffusion must take place. This effect is probably supplemental to the effect of temperature on the diffusion phenomena per se. Approximately 99% of the capsules were recovered intact after incubation for 16 weeks at four temperatures between 5 and 35C.
Small scale yield studies, germination tests, controlled plantings, and packaging often require the counting of large numbers of seeds. The system described in this paper uses a photosensitive detector and a vacuum pickup to count individual seeds and gives a direct digital readout. The count rate is limited only by how quickly the seeds can be fed through the counting tube without clogging it or having them touch each other. This greatly speeds seed counting, eliminates operator error, and reduces operator fatigue.
With the addition of a relatively simple predetermining circuit, a fixed number of seeds may be counted and a control function can be exercised. This capability is immediately applicable to packaging or repetitious batching of seeds. Zero error for any given number of seeds is attainable if the seeds are fed through the count tube carefully because of the completely digital nature of the circuit.
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