Agronomy 375 Exam Archive
Exam 2 Key Spring 1997

1. Collect soil samples from representative areas of the field and plant a sensitive species as a bioassay to indicate carryover. The sensitive species should also be planted into a sample of untreated soil to serve as a check. Commercial lab analysis options are also available but the additional cost for such an analysis is generally not justifiable.
2. Go back to the crop species that was planted in the field in the prior year (do not rotate).

   An alternative is to plant a resistant hybrid or variety where such an option is available.

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 silk coordinating).
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.

1. Broaden genetic base (assures at least some genetic diversity as protection against catastrophic loss which could occur where a narrow genetic base is vulnerable to a disease or other damage).
2. Reduce risk of stress at sensitive growth stages by spreading the progression through these stages out over time across different fields.
3. Spread out work load at harvest (optimizes the use of harvest equipment and labor).
4. Optimizes the use of drying, handling, and storage capacity by managing the flow of mature grain into the system.

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.

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.

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.

1. (7 pts.) 110 + [1.36 (177 - 100)] - 30 = 184.72 Lbs N/Acre
2. (2 pts.) 169.72 / .82 = 207 Lbs. NH3 per acre

   184.72 Lbs N/Acre
   -15.00 Lbs N/Acre starter at planting
   169.72 Lbs N/Acre as side dressed N
   

(2 pts.) 65.5/0.46 = 142.4 Lbs 0-46-0/Acre

1. (2 pts.) [(177 Bu/Acre) (0.27 Lbs K2O/Bu)] + 20 = 67.8 Lbs K2O/Acre
2. 2 pts. 67.8 / 0.60 = 113 Lbs K2O/Acre

1. (4 pts.) Average seed to seed spacing is 36 / 5 = 7.2 inches.

   (1 seed / 7.2 in.) ( 12 in. / ft.) (17,424 ft. / acre) = 29,040 seeds/ acre

2. (4 pts.)

   x	x2
   6 - 7.2 = 1.2	1.44	Sum of squares of differences / r - 1 = 78.8 / 4 = 19.7 = S2
   4 - 7.2 = 3.2	10.24
   3 - 7.2 = 4.2	17.64
   14 - 7.2 = 6.8	46.24	S = 4.4 inches
   9 - 7.2 = 1.8	3.24

3. (4 pts.) 3 bu / acre yield penalty for each inch of standard deviation greater than 2.

   4.4 - 2.0 = 2.4 inches of standard deviation greater than 2.

   (2.4) ( 3) = 7.2 bushels per acre as the potential yield penalty.

BONUS (5 pts.)

Adjust ground speed to reach precision goal (faster generally results in less precision)
Repair or replace worn parts
Use uniformly graded seed (uniform size, shape, weight)
Properly align planter attachments (e.g. starter fertilizer coulters)
Do calibration checks periodically in the field
Manage surface residue in the row environment (e.g. trash whippers) where appropriate