December 13, 2000
100 points possible
8 pts.††††††† 1. a) 40 to 45 %
††††††††††††††††††††† †b) Silks first visible without dissection of the ear shoot.
††††††††††††††††††††† c) V6
††††††††††††††††††††† d) V 17
8 pts.††† 2.† Soybeans are the more drought tolerant crop.
††††††††††††††††††††††† a) Soybeans sustain their photosynthetic rate under a more negative leaf water potential ††††††††††††† (e.g. down to - 11 bars vs. down to -4 bars for corn).
††††††††††††††††††††††† b) Soybeans flower over a much longer period (e.g. as long as 4 to 6 weeks for Soybeans vs. approximately 1 week for Corn). Soybeans are therefore able to compensate for stress during one part of flowering by retaining a higher percentage of flowers, pods, and seeds at times of lower stress.
††††††††††††††††††††††† c) Soybeans produce a much larger number of flowers than will ever be realized as pods).
††††††††††††††††† d) Soybeans are a self-pollinating crop and are therefore less vulnerable to drought stress than corn which is open-pollinated.
10 pts.†††† 3.†† Excessive rainfall in the springtime often restricts planting at a critical time.† However, this Spring maximum provides a useful recharge of the soil's water holding capacity.† Mid-season days (e.g. July, August) are generally quite dry and may result in drought stress during the critical period of pollination.† Fall precipitation may delay harvest.
††††††††††††††††††††††† Mid-season clear skies may result in stress during pollination but they also contribute the abundant, uninterrupted solar radiation necessary to produce the high corn yields typical of the U.S. Midwest.
††††††††††††††††††††††† Low temperatures early and late may restrict season length and therefore yield potential.† Extreme high temperatures mid-season may result in stress during the critical pollination period.† However, corn is a tropical grass species and grows most rapidly at high temperatures if it is well-watered.
4 pts.††††††† 4. a) Seed within 2 weeks after the Hessian Fly Free date for a given location.
††††††††††††††††††††† b) The range of Hessian Fly Free Dates for Indiana is† September 22 in the North through October 9 in the South.
6 pts.†††††† 5. a) 25 to 30 plants/square foot
††††††††††††††††††††† b) 144 in.2/ 6 in. = 24† inches of row length/square foot
††††††††††††††††††††† c) (2 heads per plant) X† (20 plants per square foot) X (1.6) = 64 bushels per acre
6 pts.†††††† 6. a)†† 40 + [(1.75) (85 Bu/Acre - 50)]† = 101 Total Lbs. N/Acre
††††††††††††††††††††††††††††††††††††† - N Applied At Seeding†† -††† 20
††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† ††††††††††††††† 81 Lbs. N† topdressed in spring
††††††††††††† ††††† † b)† (0.63 Lbs. P2O5/Bu) (85 Bu/Acre) = 53.6† Lbs. P2O5 / Acre
††††††††††††††††††††† c)† [(.37 Lbs. K20 / Bu) ( 85 Bu/Acre)] + 20 = 51.5 Lbs. K20 / Acre
6 pts.†††††† 7.†††††††††† As dormancy is broken, while tillering (prior to jointing)
††††††††††††††††††††††††††††††† a)† N available when needed for growth as it begins in the Spring.
††††††††††††††††††††††††††††††† b)† Least foliar burn potential as exposure is limited to the first leaves.
††††††††††††††††††††††††††††††† c) Avoids stem breakage as only leaf tissue is exposed.
††††††††††††††††††††††††††††††† d)† Maximum ability to compensate for damage done by wheel traffic or through leaf burn as tillering and leaf development continue until jointing.
3 pts.†††††† 8.†† Uniform stand establishment for this Winter annual crop generally suppresses Summer annual weed pressure and is generally sufficient as the primary weed control method. (Fall seedbed preparation has also generally contributed to weed suppression.)
††††††††††††††††††††††† Post emergence herbicide application is rarely† necessary as a rescue. Such applications are generally targeted at perennials or at annuals which are growing in areas of thin wheat stand establishment.
6 pts.†††††† 9.†††††††††† (60 Bu/Acre) (0.80 Lbs. P2O5/Bu)† =† 48 Lbs. P2O5/Acre
††††††††††††††††††††††††††††††† [(60 Bu/Acre) (1.40 Lbs. K2O/Bu)] + 20† =† 104 Lbs. K2O/Acre
5 pts.†††† 10.†††††††††† As a legume,† soybean plants derive most of the nitrogen they require through the process of symbiotic nitrogen fixation carried out by Rhizobium japonicum bacteria which infect soybean roots to produce nodules.† Root nodules provide an environment conducive to the nitrogenase mediated reduction of atmospheric nitrogen to a form available for plant use. Symbiosis exists as the bacteria (bacteroids) are provided with a carbon energy source by the host plant roots.
3 pts.†††† 11.†† a) Group II soybeans will flower sooner as they will flower in response to a slightly longer photoperiod than will the group III variety (group II would normally be adapted to a slightly more northern latitude than would the group III variety).
3 pts.††††††††††††† b) Since the group II variety flowers first, its vegetative growth will be stopped relatively earlier than will that of the group III variety. As a result, the group II variety will be slightly shorter at maturity than the group III variety in this setting.
5 pts.†††† 12.†† a) Increases††††† b) Increases††††† c) Increases††††† d) Decrease††††† e) Decreases
7 pts.†††† 13.†† The yield advantage for narrow rows (vs. wide rows) is greater at more northern latitudes since the relatively - shorter growing season length at northern latitudes means adapted varieties have fewer days for vegetative growth before flowering than adapted varieties at more southern latitudes. Plants at the northern latitudes will generally then be more compact and should be in drill rows to maximize light capture during R4-R7 (seed development) and thereby optimize yield potential.
10 pts.†† 14.†† a) V1 = The leaflets at the second true leaf node (the first trifoliolate leaf node)† no longer have their leaf margins touching and define the uppermost node with this characteristic.
††††††††††††††††††††††† b) R2 = A flower at one of the two uppermost developed nodes.
††††††††††††††††††††††† c) R4 = A pod > or equal to 3/4 inch (2 cm) long at one of the top four fully developed main stem nodes.
††††††††††††††††††††††† d) R5 = A seed > or equal to 1/8 inch† (3mm) long in a pod at one of the top four fully developed main stem nodes.
††††††††††††††††††††††† e) R6 = A green seed which fills the seed cavity in a pod at one of the top four fully developed main stem nodes.
6 pts.†††† 15. a) 2 seeds per foot of row.
††††††††††††††††††††††††††† Approximately 174,240 seeds per acre
††††††††††††††††††††† b) Soybeans planted in drill rows are much more likely to have difficulty emerging uniformly through a crust since there are only approximately 2 seeds per foot of row length in such a system. In 30 inch row spacing, 6 seeds per foot or row† germinate and emerge resulting in a fissure over the row, effectively helping each other through the crust and increasing† the uniformity with which the crop will emerge. Only two emerging plants per foot of drill row will have a much more difficult time emerging uniformly through the crust.
2 pts.††††† 16.† a) Plant no later than 90 days prior to the first frost date for your location.
2 pts.†††††††††††† b)†† Donít plant if soil is not sufficiently moist to initiate germination† (or at least adequate rainfall is imminent).
5 pts. BONUS The yield advantage for narrow rows (vs. wide rows) is greater at more northern latitudes since the relatively - shorter growing season length at northern latitudes means adapted varieties have fewer days for vegetative growth before flowering than adapted varieties at more southern latitudes. Plants at the northern latitudes will generally then be more compact and should be in drill rows to maximize light capture during R4-R7 (seed development) and thereby optimize yield potential.