Agronomy 375 Exam Archive
Exam 2 Key Fall 1996

1. 1. (5 pts.)

        (300 ft)(60)
      ________________   =  5.1 MPH
      (40 seconds)(88)
      

   2. (6 pts.)

      45 OPM/128 = .35 GPM

      .35 GPM x 5940	       2079
      ____________     =   ________   =  29.12 GPA
      5.1 MPH x 14 in.       71.4
      

2. (5 pts.)
   1. Boom bounce
   2. Uneven tire pressure
   3. Non-level boom
   4. Bent boom
   5. Swinging boom
   6. Spraying through sharp turns
   7. Non-uniform nozzles
   8. Worn or damaged nozzles
   9. Poor materials suspension
   10. Non-uniform ground speed
   11. Faulty pressure gauge
   12. Foaming of tank mixture
   13. Failure to check calibration

3. (5 pts.) PPI herbicides should be uniformly incorporated through a depth of 1 to 3 inches.

4. (5 pts.)
   1. Detassel ear parent (female) rows and specify a single pollen parent in male rows.
   2. Manage the planting dates of ear and pollen parent lines so as to encourage synchrony between them at pollination (tassel and silking coordinated).
   3. Flame one parent line to slow its growth where it is more rapid than its counterpart (synchronize silking and pollen release).
   4. Manage the frequency of ear parent and pollen parent rows to accommodate the productive potential of the pollen parent.
   5. Low altitude aircraft to assist pollen dispersal.
   6. Isolate the seed field.
   7. Remove rogue plants from the parent rows.

5. (5 pts.) Single cross hybrids (Sx) are by far the most common in use as they present the greatest hybrid vigor and the most uniform response to top management.

6. (4 pts.) (120 days) (23.5 GDD per day relative maturity) = 2820 GDD relative maturity.

7. (10 pts.)
   1. Grain yield and profit potential increase as total season length increases to provide greater total interception of solar radiation.
   2. Increased harvest index due to affect of low temperature early (vegetative growth) and high temperature mid- to late season (grain development). Increases harvest index contributes directly to increased yield.
   3. Plant height is reduced due to the low temperature affect on early growth. This results in less potential for lodging and greater tolerance to high plant populations.
   4. Pre-harvest losses are reduced as early-planted corn matures quickly and dries down early in the fall while temperatures are high and relative humidity is low.
   5. Early planting results in a broad choice among alternative hybrids.
   6. Early planting allows replanting with the first-choice hybrids.
   7. Early planting generally results in an avoidance of high temperature and drought stress during pollination.

8. (5 pts.) PSNT may be quite valuable where there is relatively high uncertainty as to the level of plant available N present in the soil just prior to sidedressing. Examples of such situations include;
   1. N applied in the Fall of Spring followed by unusually warm, wet conditions over a prolonged period. Under these conditions there is a high potential for N loss through denitrification and leaching.
   2. On soils with high organic matter levels or on soils which have received heavy applications of livestock waste. Under these conditions significant amounts of N are mineralized from the organic sources but the amount of N made available can be quite variable. PSNT will allow a snapshot in time to determine sidedress needs with greater precision.

9. (8 pts.)
   1. All of these strategies improve the efficiency of N fertilizer use by the crop. Without these precautions, the potential for N loss through leaching and / or denitrification is particularly high for Fall applications because of the extended time that fertilizer nitrogen would be exposed to loss when Fall applied.

      Application of N as ammonia only, allows for maximum security from loss as ammonia reacts with soil moisture to produce ammonium (NH4+), a cation which is held by a soil's exchange sites. Fall N application is not recommended unless a soil has a C.E.C. of at least 10 meq / 100 grams as a means of assuring adequate capacity to retain Fall applied ammonium.

      At temperatures below 50 F (particularly at more northern latitudes where temperatures generally remain low once this threshold is passed), and in the presence of a chemical nitrification inhibitor such as N - Serve, the conversion of ammonium (NH4+) to nitrite (NO2-) (and ultimately to nitrate (NO3-) is slowed sufficiently to lessen the potential for N loss to acceptable levels.

10. (6 pts.)
    1. Cost effective, efficient, least potential for environmental contamination. Side-dressing results in very low levels of loss and maximum N availability to the developing crop.
    2. Allows N rate adjustment as conditions dictate in the spring.
    3. Allows a switch to soybeans where losses are extreme.

11. 1. (7 pts.) 110 + [(1.36) (160 - 100)] - 30 = 161.6 Lbs N/Acre

       161.6 Lbs N/Acre
       - 15 Lbs N/Acre starter at planting
       146.6 Lbs N/Acre as side dressed N
       

    2. (2 pts.) 146.6 / .82 = 178.8 Lbs. NH3 per acre

12. 1. (2 pts.) (160 Bu/Acre) (0.37 Lbs P2O5/Bu) = 59.2 Lbs P2O5/Acre
    2. (2 pts.) Critical Level for P1 soil test is 15 ppm for corn.
    3. (2 pts.) (15 - 12 ppm) ( 5 pounds ) = 15 pounds P2O5 /Acre
    4. (1 pt.) 59.2 + 15 = 74.2 Lbs P2O5/Acre
    5. (2 pts.) 74.2/0.46 = 161.3 Lbs 0-46-0/Acre

13. 1. (2 pts.) [(160 Bu/Acre) (0.27 Lbs K2O/Bu)] + 20 = 63.2 Lbs K2O/Acre
    2. (2 pts.) 75 + (2.5 X 18) = 120 ppm exchangeable K
    3. (2 pts.) (120 - 108) [ 1 + ( 0.05 X 18)] = 22.8 Lbs K2O/Acre
    4. (1 pt.) 63.2 + 22.8 = 86 Lbs K2O/Acre
    5. (2 pts.) 86 / 0.60 = 143.3 Lbs K2O/Acre

14. (4 pts.)
    1. Early planting date (cool soils)
    2. No-till soils with heavy surface residue
    3. Poor soil drainage
    4. Very low soil test (e.g. P1 < 15 ppm or 30 Lbs/acre, K < 75 ppm or 150 Lbs/acre)
    5. Low rates of fertilizer application (especially where soil test levels are relatively low).

15. (5 pts.)
    1. Soil fertility levels (particularly P and K) will vary greatly among managers).
    2. N rate.
    3. Timing of N application (Fall, Pre-plant, Sidedress).
    4. Plant population may be unique.
    5. Planting date has a major impact on overall yield as well as on other factors such as population. On site testing of hybrids will bring out optimal combinations for unique management packages.
    6. Use of N-Serve
    7. Tillage and planting system (e.g. no-till, residue management, etc.)

BONUS (5 pts.) Earlier planting will be likely to decrease overall crop height (less interplant competition) so an increase in plant population would be likely to increase yield potential.