Agronomy 375 Exam Archive
Exam 2 Key Spring 1996

1. Plant the female rows first and then follow with the male rows after 40 GDD have passed. This should coordinate pollen release with silking.
2. Plant the female and male rows at the same time but flame or mow the male rows while the plants are young (less than V6) sufficiently (based on past experience) to delay the male parent's developmental rate by about 40 GDD.

In addition, crop management practices (e.g. soil fertility management, plant population, planting date, weed control, etc.) had not been developed as a system which was sufficiently productive to gain the full expression of single cross hybrid yield potential.

1. Plant population.
2. Planting date.
3. Tillage system (e.g. no-till or conventional).
4. Soil fertility levels (P and K)
5. Nitrogen rate and timing of application.
6. Soil type, slope, and water holding capacity.

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 planting date has been delayed be wet Spring weather.

1. (7 pts.) 110 + [1.36 (175 - 100)] - 30 = 182 Lbs N/Acre

   182 Lbs N/Acre
   - 10 Lbs N/Acre starter at planting
   172 Lbs N/Acre as side dressed N
   

2. (2 pts.) 172 / .82 = 209.8 Lbs. NH3 per acre

1. (2 pts.) (175 Bu/Acre) (0.37 Lbs P2O5/Bu) = 64.75 Lbs P2O5/Acre
2. (2 pts.) Critical Level for P1 soil test is 15 ppm for corn.
3. (2 pts.) (15 - 10 ppm) ( 5 pounds ) = 25 pounds P2O5 /Acre
4. (1 pt.) 64.75 + 25 = 89.75 Lbs P2O5/Acre
5. (2 pts.) 89.75/0.46 = 195.11 Lbs 0-46-0/Acre

1. (2 pts.) [(175 Bu/Acre) (0.27 Lbs K2O/Bu)] + 20 = 67.25 Lbs K2O/Acre
2. (2 pts.) 75 + (2.5 X 15) = 112.5 ppm exchangeable K
3. (2 pts.) (112.5 - 100) [ 1 + ( 0.05 X 15)] = 21.9 Lbs K2O/Acre
4. (1 pt.) 67.25 + 21.9 = 89.15 Lbs K2O/Acre
5. (2 pts.) 89.15 / 0.60 = 148.6 Lbs K2O/Acre

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).

1. (4 pts.) Average seed to seed spacing is 35 / 5 = 7 inches.

   (1 seed / 8 in.) ( 12 in. / ft.) (17,424 ft. / acre) = 26,136 seeds/ acre

2. (4 pts.)

   x	x2
   4 - 8 = 4	16	Sum of squares of differences / r - 1 = 30 / 4 = 7.5 = S2
   11 - 8 = 3	9
   7 - 8 = 1	1
   10 - 8 = 2	4	S = 2.74 inches
   8 - 8 = 0	0

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

   2.74 - 2.0 = 0.74 inches of standard deviation greater than 2.

   ( 0.74 ) (3 bushels yield penalty per inch standard deviation greater than 2) = 2.2 bushels per acre

1. (3 pts.) During July, August and September or until the appropriate economic threshold was exceeded or beetles are no longer present. During this interval, the adults (beetles) are laying the eggs which will hatch in the soil as next year's (1996) larvae. Scouting in July, August, and September of the preceding year allows an estimate of the root feeding pressure expected from larvae in the next year.
2. (3 pts.) An average of 0.8 adult beetles per plant.

To calculate the preventable dollar loss for comparison with treatment cost;

(175 bushels) (0.50 infested) (0.75 control) (0.044 yield loss) ($3.00 per bushel) = $8.66 / acre preventable dollar loss.

This compares with a treatment cost of $11 / acre, so treatment is not well advised.

BONUS (5 pts.) Part I.

1. Greater light penetration into leaf canopy exposing more total leaf area.
2. Greater exposure of both upper and lower leaf surfaces.
3. Lower leaf temperature which results in less transpiration and greater water use efficiency.
4. Greater tolerance to high plant population.

Part II. PSNT is most reliable on high organic matter (particularly on muck) soils or where high rates of manure have been applied as this technique predicts how much N is being released through mineralization from organic sources.