AGRONOMY 375 Exam II Key November 2, 2018

Transcription

1 1 AGRONOMY 375 Exam II Key November 2, pts 1. a) Latitude, previous crop residue, and soil drainage all influence soil temperature, which is critical in determining early season corn crop growth rate. Any one or a combination of northern latitude, heavy crop residue and poor soil drainage could result in cool conditions would slow crop growth and lower yield potential. 3 pts. b) An example would be Coulter planted (no-till) corn at a northern Indiana location where the soil is poorly drained, corn is following high yield corn (so here is heavy non-fragile surface residue), and there is an early planting date in an unusually cool spring. 3 pts. c) Possible management in this case would include improvement in soil drainage, rotate corn after soybeans to lessen surface residue at planting or use zone (strip) tillage and/or row residue removal in the fall. One may also use starter fertilizer at plant (or zone placement of P and K fertilizer if zone tillage is used) to provide greater access to applied P and K where roots are restricted in growth. As they die and decompose in winter and spring fall-seeded deep-rooted cover crops such as tillage radish or turnip will encourage quicker soil drying and warming 6 pts. 2. (Three answers.) a) Reduced yield b) Decreased height c) Delayed maturity d) Tabled (horizontal) roots e) Visible nutrient deficiency symptoms f) Heightened drought stress g) Increased sensitivity to herbicide injury h) Slowed infiltration of water (surface ponding, evidence of poor drainage such as mottled color or slow crop residue decomposition) i) Increased soil bulk density (e.g. as indicated by greater resistance to a soil probe) and decreased soil structure as the result of an external force j) Surface crusting (shallow compaction resulting from heavy rainfall) k) Seedling lateral roots restricted to seed slot (sidewall compaction) 6 pts. 3. (Three answers.) a) Provide adequate drainage (improve and maintain surface and subsurface drainage). b) Stay off of wet fields. c) Reduce primary and secondary tillage where possible. d) Use lighter equipment or improved flotation tires or tracks on field equipment. e) Maintain pneumatic tires on field equipment at the low end of recommended inflation. f) Use low PSI tires (e.g. Kevlar sidewall radials) on the drive wheels of pneumatically-tired tractors and combines g) Unload at field ends, unload partial combine grain tanks when soils moist. h) Include well-planned cover crop use strategies in the crop management system. i) Include small grains and/or forages in crop rotation. j) Target deep vertical tillage on compacted zones in fields in dry years. k) Natural freeze-thaw cycles will lessen shallow compaction over extended time. l) Natural shrink-swell (seasonal dry / wet cycling), natural earthworm activity, and root growth will lessen deep compaction over time in soils where primary tillage has been reduced or eliminated. m) Controlled traffic patterns for field equipment (RTK autosteer).

2 6 pts 4. Mottling of gray interspersed with rust color in the top 13 to 18 inches of a soil profile indicates poor drainage critically-high in the root zone. An economic response to improved subsurface drainage and/or management targeted to lessen the negative impact of poor drainage (e.g. choice of tillage/planting systems) is likely. The gray color is evidence of prolonged water-logged (low oxygen) conditions which result in the reduced (gray) form of Iron. Soil with a predominantly bright rust color indicates the presence of better drained (oxygen available) conditions since the Iron is present in the oxidized (rustcolored) form. 10 pts 5. (Five Answers) a) Shallow rooting and poor root uptake of mineral nutrition b) Increased soil compaction potential c) Delayed planting d) Delayed harvest e) Late-season drought stress f) Non-uniform herbicide incorporation g) Potential delay in field access for post-emergence herbicide application h) Greater N losses to denitrification 4 pts 6. a) Typical depth of subsurface tile placement is generally 30 to 48 inches so drainage can be effective through the likely full depth of the corn root zone. In some instances tile may be placed as shallow as 24 inches, particularly when the design includes very narrow lateral spacing and/or the potential to use the tile system for water level control and sub irrigation. 4 pts b) Lateral spacing varies with soil conditions and drainage goals (closer in slowly permeable soils) but may be as wide as 80 to 100 feet in older systems. New subsurface tile installations of today are generally spaced no wider than 50 to 60 feet and may be as close as 25 feet. 4 pts 7. GPS technology allows the option to install subsurface tile on contour patterns not possible with traditional land survey tools (optical and laser) which required a straight line of sight to maintain the intended grade while installing tile. Contour installation produces a more efficient drainage pattern in sloping topography. 6 pts 8. (Two answers) a) Grassed waterways. b) Shallow non-permanent drainage ways. c) Including cover crops, winter annual crops (e.g. wheat) and perennials (e.g. alfalfa) in rotation to enhance and protect soil structure. d) Conservation and reduced tillage systems. e) Contour cropping. f) Surface ditches (high water table management). g) Land forming (terraces or shallow cut and fill or shallow cut waterway) h) WASCOB installation (Water and Sediment Control Basin) i) Surface inlets to subsurface tile. j) Cover crops to increase infiltration rate 2

3 3 7 pts. 9. Examples Of Cultural Weed Control Factors (One Answer) Crop Rotation (e.g include perennial, winter annual, summer annual crops) Row Width (narrow row spacing results in more rapid leaf canopy closure) Plant Population (higher population may increase the rate of leaf canopy closure) Crop Residue Management (e.g. remove from row area and consolidate between rows) Cover Crops (e.g. cereal rye) to suppress weeds 8 pts. 10. (Four Answers) a) Use full labeled rates of herbicides. b) Rotate or combine (either concurrent or sequential) herbicide modes/sites of action (no more than two consecutive applications of one mode/site of action). d) Use integrated approach to weed control (cultural, mechanical, and chemical). e) Scout for and remove herbicide resistant weeds before they can produce seed. f) Clean field equipment (e.g. tillage implements, combine) before transporting from field to field when resistant weeds are present. g) Rotate crops (e.g differing life cycles e.g. summer annual, fall-seeded winter annual, perennial and/or plant types e.g. grass, broadleaf). h) Use weed free seed. 8 pts. 11. At 38 ppm, the P1 Soil Test Level is in the drawdown range of 31 to 40 ppm so a drawdown rate is recommended. Full Maintenance would be (210 Bu/Acre) (0.37 Lbs P 2 O 5 /Bu) = 77.7 Lbs P 2 O 5 /Acre The Drawdown Rate is 77.7 Lbs P 2 O 5 / acre - [(77.7 Lbs P 2 O 5 / acre) X (38 ppm - 30 ppm))] = = 10 = Lbs P 2 O 5 / acre 3 pts = Lbs / Acre pts. 12. a) Annual K 2 O (pounds per acre): At CEC = 14, the Critical Level is calculated as follows [ (2.5) (14) ] = = 110 ppm At 120 ppm the K soil test is in the maintenance range of 110 through 140 ppm so a full maintenance rate of K 2 O is recommended. Full Maintenance is [(210 Bu / acre)(0.27 Lbs. K 2 O / Bu)] + 20 = 76.7 Lbs. K 2 O/ acre 3 pts. b) Total annual pounds per acre K 2 O per acre / 0.60 = Lbs per acre

4 8 pts. 13. (Four Answers) a) Amount of mineralized N available from the soil (lower economic optimum applied N rate where greater mineralized N available from soil O.M). b) Relative cost of N vs. value of corn per bushel (economic optimum applied N rate goes up as N cost goes down and/or the value of corn per bushel goes up). c) Total average amount and distribution of precipitation during the growing season (potentially higher economic optimum applied N rate where total growing season precipitation is greater and N loss potential is higher, or where growth conditions are favored by sufficient but not excess rainfall). Annual precipitation varies widely by longitude across the US Corn Belt and sometimes even within a field. N management components of integrated precision crop management software utilize real-time georeferenced weather data to inform N management decision making. d) Soil temperature-influencing factors significantly affect potential N loss. For example, cooler temperatures at northern latitudes may result in less N loss (less nitrification and subsequent denitrification) and therefore lower economic optimum N rates. Real time temperature measurements are used along with temperature to inform N management in integrated crop management software. e) Levels of other yield influencing limitations (greater economic optimum applied N rate where other yield influencing factors are less limiting e.g. P and K fertility, compaction, soil water holding capacity). f) Soil drainage and water holding capacity characteristics For example, N loss is greater on poorly drained soils where N loss to denitrification is greater so more N may be required to reach economic optimum, and/or poor drainage may limit root growth and weaken crop response to applied N. Conversely, Soils with high water holding capacity and good drainage may require higher N rates to support higher yield potential in such a favorable environment. g) Genetic differences in N uptake patterns, total N requirements and comparative relative maturity among corn hybrids. Hybrids differ in total N requirement. For example, N use efficient hybrids may require less total N per bushel. Short season hybrids may require less total N than a higher-yielding full season hybrid. The timing of N uptake (VE to V6, V6 to VT, VT to R6) also varies among corn hybrids. Integrated crop management software may utilize hybrid-specific information to adjust N recommendations concerning rate and timing. h) Timing (e.g. fall, spring pre-plant, starter, sidedress, split early plus late sidedress), form (e.g. Anhydrous Ammonia, UAN solution, Urea, livestock waste), and means of application (e.g. injected, incorporated, surface applied with Y drops, surface broadcast) may affect N rate. i) Use of nitrification inhibitor such as N-Serve or Instinct may allow for a reduction in N rate depending on N form, timing of N application and the level of environmental risk for N loss. j) Crop rotation (previous crop legumes, N fixing cover crops, N trap crops will allow lower rates of additional applied N) k) Soil CEC. High CEC soils generally have higher % O.M. and therefore produce more mineralized N. High CEC soils also retain ammonium N resulting in less loss to leaching. 4

5 5 l) Soil ph influencs soil microbial activity and thereby mineralization, nitrification and denitrification. n) Soil compaction can result in slow infiltration of water and saturated soils which promote N loss to denitrification. o) Soil texture. Coarse soils have low CEC and high permeability which result in greater N loss to leaching. 5 pts. BONUS An Herbicide Resistant Weed survives the proper application of an herbicide at a rate that would normally be lethal to non-resistant plants and produces viable seeds producing plants that inherit resistance to that herbicide.