A study was conducted at 11 locations across Canada to determine if corn hybrids have different corn heat unit (CHU) requirements in different climates. The study included six hybrids, four each in the three years 1977–1979. Differences in the time between planting and emergence were attributable to slow emergence of two hybrids as well as management and weather factors at different locations. Genotypic differences were expressed mainly in the period between emergence and anthesis. At three locations, 198 CHU more were required than at other locations. In the period from anthesis to 45% ear moisture, two hybrids required more CHU than other hybrids. These extra CHU requirements were not related to hybrid rating, i.e., late-maturing hybrids did not require more CHU to complete the ripening phase. In a comparison of growing degree days (GDDi) with bases ranging from 5 to 15 °C, no one thermal unit had sufficient advantage over the CHU system to warrant its adoption in Canada. Further, calendar days were the best for predicting the duration of the period from planting to emergence. The period from emergence to 10% anthesis was least variable of all the stages and could be predicted accurately by any of the methods.Key words: Zea mays, temperature, adaptation, thermal units

. l9j'7. Feeding value for beef steers of corn silage as affected by harvest dates and frost. Can. J. Anim. An experiment was conducted in 3 consecutive yr with corn grown each year on a field from which silage was made of corn harvested at different dates before and after freezing. Yields of green and dry weight were recorded at each harvest.Individual whole plants and ptant parts were evaluated for dry matter (DM), total nitrogen, total available carbohydrates and in vitro digestibility of DM. Animal gains, feed consumption and carcass grades were determined by feeding the silages to yearling Hereford steers and DM digestibility determined with sheep. The total yield and contribution of the ear increased from the first to the second harvestins date. The in vivo digestibility ofDM ofthe silages declined between the second ani final harvests in all years as did animal gain in years I and 3. The This agrees with the observations of Demarquilly (1969) in France and Daynard and Hunter (1915) in Ontario where temperatures would not be expected to be high during the corn maturation period. Cummins (1970)

A mixrure of timothy, o."nrrfl*rfff;.t1ro.r"t, alfalfa and l-;adino clover was seeded on areas of upland and dikeland soil at Nappan, N.S. Over a 3-year period plots were cut at 3-, 4-and 8-week For personal use only. (.1,2;t,6, 8, 9). Plots clipped to a stubble 'height of l% inches always produced greater yields of dry matter than plots clipped to a 3-inch height.Seasonal distribution of yield is generally considered almost equal in importance to actual total yield. The above results may be also observed in Figure 1

Empire, Leo, Viking and Wallace cultivars of birdsfoot trefoil were evaluated in a greenhouse experiment for total forage production, aerial and root growth, in vitro digestibility, cold hardiness, etiolated regrowth and modulation. Plants were harvested at the vegetative stage (four harvests); 10% bloom (three harvests); 50% bloom (two harvests); and maximum growth (one harvest), at two stubble heights, 2.5 and 7.5 cm. Harvesting at the maximum growth stage produced the most dry matter but the lowest digestibility, with the greatest etiolated regrowth and best nodulation. Production at the vegetative stage produced the least forage which was the most digestible. Empire was the most productive cultivar, with a hardiness rating equal to Leo. At the 10 and 50% bloom stages, Wallace equalled this cultivar in production and there was no difference between the four cultivars in forage production when harvested at the vegetative stage. Viking appeared to be the least hardy of the cultivars examined, although it produced more etiolated regrowth than Empire and Wallace but not as much as Leo. This experiment shows that criteria other than total production must be examined in evaluating birdsfoot trefoil cultivars.

Tirrrorhy.performed somewhat bertcr rrran 3;d bro-"gri.trt ti"-Li.r planrine dates and borh responcied bctrer than legumes ro delayed planting. Weed anE bare grourd lTgqnts were grearer with"each so.."ssii-" pia.rii"g-;rt.. By;h; errd of the third harvest y6ar species composition diftJ.e";;;-a;;ibutable to planring dare rvere practicilly eliininated.