Crop Science Study Guide 

What is microfauna?

Amish Lecture 

Amish

∙ A two-year study was conducted involving researchers from U of A and Purdue ∙ The study was conducted in Elkhart ad LaGrange counties in Indiana ∙ The study involved sampling soils of 12 Amish farms and 12 “English” farms o Soil physical and biological properties

Microorganisms

∙ Decompose natural and man-made compounds

∙ Build organic matter by transformations that create and stabilize humus ∙ Improve soil structure

∙ Change form and availability of nutrients

∙ Sequester nutrients, thereby preventing loss from ecosystem

∙ Fix N from the atmosphere (bacteria)

∙ Feed on pathogens and pests

∙ Vital compounds of food web of which all life depends, including plants  

Microfauna

∙ Alter litter decomposition rates

∙ Recycle nutrients (may provide 25-75% of N taken up by crops) ∙ Control bacterial and fungal growth rates and community composition  ∙ Inhibit disease-causing organisms

What is the importance of Mendel and genetics?

∙ Cause commercially important diseases o many plants  

Protozoa

∙ A thousand to a hundred thousand protozoans per gram of soil ∙ Mainly in the surface soil  

∙ Consume bacteria

∙ 3 free-living groups  

o Flagellates

o Amoebae

o Cilates

Nematodes

∙ Ten to a thousand grams of nematodes per soil  

∙ Mainly in the surface soil  

∙ Include microbial consumers

∙ 5 trophic groups  

Expectations or healthy soils

∙ The microbial biomass retains nutrients in labile, but organic form. They are the agents of  decomposition  

∙ Increased diversity and a complex food web (diversity of grazers) are important in order to  facilitate decomposition ad nutrient release

∙ Nutrients should be in available forms, but retained, and there should be enough, but not  excessive nutrients

What are the three free-living

Vegetation grows worst in sterile soil. It grows better in soil with bacteria and it grows best in soil with  bacteria and nematodes.  

Cover Crop Lecture Don't forget about the age old question of iatra study guide

Experiment hypothesis: a combination of winter legume cover crops and summer legume intercrops  (planted along with winter corn) would supply all or part of the N needs of a growing corn crop  

Experimental Design We also discuss several other topics like mcdb osu

∙ Australian winter peas would be planted each fall

∙ These peas would be moved and incorporated into the soil before corn planting the following  spring  

∙ Corn was planted in May along with intercropped cowpeas

∙ Cover crops and intercrops would decompose and when they did, they would contribute  mineralized N to the soil, which would support corn growth  

The treatments

∙ Cover cropped winter peas Don't forget about the age old question of ∙ Why are other countries more interested?

o Half the yield was planted to winter peas and the other half was left fallow ∙ Companion cropped cowpeas

In Summary

∙ Legume winter cover crops show promise in NW Arkansas of providing all or part of corn’s N  needs

∙ Applied N is about 40% of the corn grower’s budget

∙ Legume inter-cropping with cow peas may have reduced yield rom competition  ∙ Winter pea cover crops can remove a lot of moisture from soil prior to corn planting  

Fun fact: 400 million pounds of poultry litter in the Illinois River annually  

Week 10 Lecture: Mendel and Genetics 

Mendel and Genetics 

∙ Principles of heredity and genetics were discovered 145 years ago, by Gregor Mendel; an  Austrian monk We also discuss several other topics like socialized power occurs when power is directed at helping oneself as a way of achieving one's own selfish ends.
Don't forget about the age old question of this system of government gives all key powers to the national government

∙ The importance of discovery not realized until the twentieth century  

∙ Low budget research featuring garden peas

∙ Studied inheritance of seven traits  

o Seed color: yellow vs. green

o Seed shape: smooth vs. wrinkled

∙ This set fives four possibilities for appearance

o Yellow/smooth

o Yellow/wrinkled

o Green/smooth

o Green wrinkled

Structure of a pea flower 

The anther contains the pollen grains, where the male gametes are produced

Formation of a pea flower 

∙ Ovule contains the megaspore

∙ Meiosis produces four haploid nuclei (megaspore)

∙ Three nuclei degenerate

∙ Anthers contain microspore mother cells

∙ Meiosis produces four haploid cells (microspores)

∙ Each microscope develops into a pollen grain

Don't forget about the age old question of biology 1107 uconn

Genetics Terminology 

∙ Progeny: offspring of particular parents

∙ Hybrid: when a progeny results from crossing different parents

∙ F1, F2, F3

Mendel’s Experiments 

∙ 2 parents

∙ 1 trait (seed color) with two expressions: yellow and green

∙ 3 generation: F1, F2, and F3

∙ Observations:

o Yellow seeded parent produced yellow-seeded progeny when self-pollinated o The same thing occurred when green-seeded plants were self-pollinated

∙ His conclusions:

o Color trait was not produced of the environment, but of heredity, since both green and  yellow seeded plants’ environments were identical

Mendel’s Experiments 

∙ How can color trait passed from parent to progeny  

∙ Mendel referred to this control as “heredity factor” (genes)

∙ Mendel knew that both egg and sperm nuclei must carry a gene because egg and sperm are all  that is contributed by each parent  

∙ Meiosis diagram, chromosome pair (one in both the egg and the sperm) goes through meiosis ∙ YY and yy = all Yy (all yellow)

∙ Yy and Yy = 3 yellow and 1 green  

∙ Yy and YY = all yellow

∙ Yy and yy = 2 yellow and 2 green  

∙ What is the color of the F1? Yellow

∙ Don’t the yellow and green colors blend? No  

∙ Reason? Yellow is a dominant trait and green is a recessive trait

∙ Phenotype: visible or measurable plant traits (color, height, yield, disease resistance) ∙ Genotype is the genetic make-up (genes involved)

∙ Phenotype = genotype x environment (P = G x E)

∙ Mendel also discovered the fact that genes in mating population segregate and recombine in a  random but predictable fashion with certain mathematical probabilities  

Mendellian Genestics

∙ Year 1: The true yellow and true green parents were crossed

o F1 hybrids were all yellow

∙ Year 2: The F1 hybrids (all yellow) were crossed:

o F1 hybrid x yellow parent

▪ Progeny: all yellow

o F1 hybrid x F1 hybrid

▪ Progeny: 3 yellow, 1 green

o F1 hybrid x green parent

▪ Progeny: 2,2?

∙ By observing the phenotypic color ratios of this cross and others, Mendel was able to deduce  the nature of inheritance

∙ Mendel gave upper case letters to dominant traits (YY, yellow parent) and lower case letters to  recessive traits (yy, green parent)

∙ Mendel started with numeric ratios and worked backwards

Week 12 Lecture: Crop Pests and Their Control 

Crop Pests and their Control 

∙ Pests (weeds, insects, and pathogens) have posed a serious threat to crop production since the  beginnings of recorded history

o Ancient Egypt was plagued by worms, locusts, rats, and birds

o Historic records show enormous crop damage  

Pests and Modern Crop Damaging Weeds 

∙ A weed is simply a plant growing where it is unwanted

∙ Example: Downy brome grass in the Pacific NW is considered a weed by wheat growers.  Livestock producers in the same are consider it a valuable forage

Weeds 

∙ What is the relationship between weed density and crop yield and profitability? o Competition between sugar beets and Kochia

▪ Sugar beets (t/a) decrease as the number of Kochia plants (weeds per 100 ft.  row) increase

o Competition between corn and giant foxtail  

∙ Weeds also lower crop yields through allelopathy  

o Allelopathy is the chemical interaction of plants

o One plant species (e.g., foxtail) secretes a chemical substance into the soil that retards  the growth of another species (corn)

o Other problems with weeds

▪ Crop seed becomes contaminated with weed seed

▪ Serves as host or refuge for crop diseases and insects

▪ Can poison livestock  

▪ Expensive to control  

▪ Can reduce property value  

∙ Two major factors support weed growth

o Vast number of seed per plant  

▪ In redroot pigweed, as many as 117,000 seeds per plant

o Persistence in soil  

▪ Seed of many species remain viable for decades

▪ In one experiment, seed from 36 species viable after 38 years

Insects 

∙ Chewing mouth parts: feed directly on leaves, stems and roots, eg boll weevil (cotton insect) o Feed on young leaves but prefer squares (young buds)

o Female lays eggs in squares, young emerge and continue feeding

o Can be as many as eight generation of boll weevils during one growing season  o Losses to crops: in excess of $100 million

o Bool weevil eradication plan

∙ Piercing/sucking mouth parts: puncture plants and feed on internal cell sap o Puncture wounds – site of disease entry

o Injects toxins in to plants

o Aphids – penetrate phloem and suck out photosynthate

∙ Stored grain insects: as much as 50% of harvested crop has been lost due to insects in the  tropics

o Eggs laid on grass

∙ Insect life cycles:

o Complete metamorphosis – egg, larva, pupa, adult (corn rootworm)

o Incomplete metamorphosis – egg, nymph, adult (grasshopper)  

o Aphids – small grain and Russian wheat

Pest Control Methods 

∙ Some plants have a natural genetic resistance to pests

∙ This is allowed them to survive unaided by humans in their wild-type environments ∙ This natural resistance is called host plant resistance and is a desirable alternative

Host plant resistance 

∙ Nonpreference

o Chemical or anatomical characteristics that limit the ability of pests to fed or lay eggs on  plant, eg smooth leaf cotton causes cotton bullworm to lay eggs less successfully  because they can be dislodged by wind

∙ Antibiosis

o Anatomical or chemical characteristics that reduce survival, reproduction, or  development of pests, eg, hooked leaf hairs on field beans prevent insects  

Pest Control Methods 

∙ Tolerance

o Some plants have the ability to withstand attack of insects and pathogens or  compeittion from weeds without high yield loss, eg corn can replace roots damaged by  rootworms

∙ Escape

o Involves plants that mature so rapidly that they can outgrow pest populations, eg early maturing cotton varieties  

∙ Cultural Control – managing of the crop environment to control pests

o Tillage

▪ Tillage is the mechanical stirring of the soil

▪ Tillage of the soil can disrupt insect life cycles, eg grasshopper egg pods exposed  to air cause them to dry out

▪ Tillage for weed control:

∙ Burial of annual weed seed

∙ Disruption of weed roots

∙ Cutting weeds below the soil surface  

∙ Crop rotations

o Growing same crop year after year allows weed population to build; rotating crop  species from year to year prevents this

o Corn rootworm eggs laid in the fall of the year will have a difficult time of next year’s  crop soybean  

∙ Planting and harvesting dates

o Dates can be adjusted to avoid expected pest problems

o Planting corn early in Arkansas (April) will often allow crop to mature before insect  population peak in July/August  

o Chemical control – pesticides  

▪ Herbicides for weed control

▪ Insecticides for insects

▪ Fungicides for control of fungal pathogens

▪ Nematicides for control of nematodes

▪ Miticides for control of mites

▪ General terminology

∙ Selectivity is the ability of a pesticide to kill one species while leaving other species unharmed  o Not all insects are harmful, eg pollinating bees

o Certain insect species keep harmful species in check, and if they are killed, population  become out-of-balance  

o Selectivity in herbicides

▪ Plants feature metabolic and anatomical differences

▪ These can be exploited for control purposes

∙ Broadleaf weeds in grass crops and vice versa

∙ Annual vs. perennials

∙ C3 and C4 metabolism (herbicides altered in plant to lethal or nonlethal  forms)

∙ Even grass weeds can be selected out of grass crops and broadleaf  

weeds out of broadleaf crops  

∙ Mode of action:

o Refers to the behavior of a pesticide

o Herbicide mode of action involves the following

▪ Commonly absorbed by roots and leaves

▪ Can be translocated from leaves through phloem and roots through xylem ▪ Kills or retards growth by  

∙ Disruption of cell membrane  

∙ Interference with cell division  

∙ Interference with chlorophyll synthesis

∙ Disruption of photosynthesis, respiration  

∙ Enzyme activity or DNA synthesis  

∙ Biological control

o Control of a pest by its natural enemies

o Use of a modified pest organisms or characteristics to destroy and eliminate reproductive characteristics of target pest

▪ Examples

∙ Plants

∙ Insects  

Week 13 Lecture: Tillage Systems 

Rotary hoeing to break soil crust or control small weed seedlings

Row weed cultivating to control weeds in the middle.

Tillage Systems

∙ Consideration involved in the seeding process

∙ Seed size

∙ Smaller seed need to be planted at shallower depth

∙ Planting depth – later than optimum planting dates may result in increased seedling rates ∙ Moisture content – a dry seedbed may require more than a farmer plant deeper, “plant to  moisture”

∙ April 2 – 16 is the perfect time to plant

∙ If you wait until later, like May, the yield gets lower and lower