Exam III

Key

December 11, 2002

100 points possible

 

4 pts.     1.              The threshold is 2 larvae per 7 inch soil cube (dry sample).

 

4 pts.        2.           Tabular value for yield loss at 1 borer per plant and at the early whorl stage (extended leaf height 20 inches) is 6.6%

 

                                (175)(.80)(.066)(.75)($2.00/bushel)  =                  $13.86 Preventable dollar loss per acre

                                                                                                                                -  10.00 Cost of treatment per acre

                                           Treat                                                                            ($ 3.86 Net gain per acre if treated

 

 

8 pts.        3. a) Milk line positioned one-half way between the kernel crown and tip (kernels sampled from mid-                                             ear).

 

                       b) Silks first visible without dissection of the ear shoot.

 

                      c) V6

 

                      d) V 17

 

8 pts.      4.  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.      5.   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.        6. 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.        7. 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.        8. a)   40 + [(1.75) (90 Bu/Acre - 50)]  = 110 Total Lbs. N/Acre

 

                                      - N Applied At Seeding   -    15

                                                                                                95 Lbs. N  topdressed in spring

 

                      b)  (0.63 Lbs. P2O5/Bu) (90 Bu/Acre) = 56.7  Lbs. P2O5 / Acre

 

                      c)  [(.37 Lbs. K20 / Bu) ( 90 Bu/Acre)] + 20 = 53.3 Lbs. K20 / Acre

 

6 pts.        9.           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.

 

6 pts.      10.   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.      11.           (50 Bu/Acre) (0.80 Lbs. P2O5/Bu)  =  40 Lbs. P2O5/Acre

 

                                [(50 Bu/Acre) (1.40 Lbs. K2O/Bu)] + 20  =  90 Lbs. K2O/Acre

 

5 pts.      12.           Leghemoglobin is the pink to red substance which supplies  oxygen at a regulated level sufficient to support respiration in the root  nodule system  but insufficient to disrupt the nitrogenase enzyme which is responsible for nitrogen fixation.

 

6 pts.      13.   a) Indeterminate plants continue to grow vegetatively for a time after flowering and pod initiation has begun (up to 6 weeks).  In contrast, Determinate plants flower over a relatively brief period. As a result, Indeterminate plants are generally taller than determinate plants of comparable maturity.

 

                        b) Indeterminate plants have a maximum of one to three small pods at the uppermost node while Determinate plants have a terminal raceme or cluster of pods. Indeterminate plants continue vegetative growth while flowering progresses up the main stem, hence the uppermost pods are developmentally younger and smaller. Because of the more nearly-uniform flowering pattern of Determinate soybeans, pod number and size are more nearly uniform from top to bottom on the plant.

 

5 pts.      14.   a) Increases                  

                        b) Increases  

                       c) Increases

                       d) Decrease

                       e) Decreases
10 pts.    15.  a) V1 = First trifoliolate leaf unfolded with margins no longer touching (this is the uppermost leaf which may be so described).

 

                        b) R3 = A pod > or equal to 3/16 inch  (5mm) long at one of the top four fully developed main stem 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.      16. a) 6 seeds per foot of row.            Approximately 104,544 seeds per acre

 

                        b) 2 seeds per foot of row.          Approximately 174,240 seeds per acre

 

                      c) 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.

 

5 pts. BONUS  The advantage for narrow rows (vs. wide rows) is greatest at later planting dates such as with double cropping as delayed planting means fewer days for vegetative growth (photoperiod determines flowering date) and a more compact plant results. These compact plants need to be in very close row orientation in order to effectively capture as much light as possible during R4-R7 (seed development). Leaf canopy closure must be accomplished by the time of flowering and early pod fill  in order to optimize light use with respect to yield potential.