10/7/03 Name ________Answer Key________________

Bio/ENTS 160 Agroecology - Quiz 1

1. Describe two "ecosystem attributes" that differ between a tall grass prairie and an industrial cornfield.

20 points: Here should be a description of two ecosystem attributes (such as species diversity, trophic interactions, productivity, nutrient cycling, etc) and how they differ in a prairie and a cornfield. Note that soil characteristics like soil fertility and susceptibility to erosion are not ecosystem attributes. See your lecture notes from 9/18 and 9/23.

2. a). In terms of plant biology, what is the difference between a macronutrient and a micronutrient?

10 points: Macronutrients and micronutrients are both necessary for plant growth. However, macronutrients (H, C, O, N, P, K, Ca, S, Mg) are needed in large quantities, whereas micronutrients (B, Cl, Cu, Fe, Mn, Mo, Zn) are needed in much smaller amounts.

b). What three macronutrients are most limiting for plant growth in terrestrial environments?

10 points: Nitrogen (N), Phosphorus (P), and Potassium (K) 3. a). Using the soil triangle at right, identify a soil that is 30% sand, and 20% silt. 10 points Type: ______Clay_________________

s of

of

il

ay USDA Soil Classification Triangle

b). How would this soil compare to a loam soil in t

water re 10 points This soil has

ermtention, water drainage and ability to hold

nutrients?

30% sand, 20% silt and 50% clay.

ompared to a loam soil, a clay soil would have: e area

soil particles b/c clay particles are so small); in so

the "Clay" and "Loan" designations do not s

describe the soil texture, i.e., the relative amounts of sand, silt and clay.

C1) better water retention (due to increased surfac

2) poor water drainage (due to smaller pore sizes b/c of lower sand content and higher clay content);3) better nutrient retention (due to more negatively-charged clay particles).

Note that anything about organic matter content. These names only

Agroecology Quiz 1 - Page 2 10/7/03 4. al soil. b). What are the main characteristics of each horizon? 10 points 10 points

I gave partial credit if you described the soil profile of a virgin nonagricultural soil. 5. Define the term "organic matter" and describe two benefits of it in agricultural soils.

10 points: Organic matter is the portion of soil composed of both living organisms and dead organisms at various stages of decomposition. 10 points: There are many benefits of organic matter, including: 1). Improved tilth 2). Improved soil drainage due to the creation of soil aggregates (mineral particles are glued together

with organic matter to make larger particles). 3). Improved nutrient retention due to negatively-charged organic matter (more negatively-charged

than clay) 4). Nutrient reservoir – Nutrients in organic molecules of organic matter are made available

(mineralized) by soil microorganisms. 5). Increases population densities of soil microorganisms 6). Increases biological activity of soil (metabolic activity of soil microorganisms) 7). Reduces soil-borne diseases 8). pH buffering

a). Draw and label the three principal horizons in agricultur

Subsoil

Parent Material

Topsoil Topsoil – this comprises the "furrow slice" and is the result of

homogenizing layers O, A, and perhaps some of E in the virgin soil profile. This topsoil is often much reduced in size compared to the original O and A layers due to soil erosion. This lay is characterized by high organic matter content and high level of biological activity.

Subsoil – the original E, and B layers in the soil profile. This has the regions of maximum leaching and accumulation, meaning that there is likely a higher clay content. Also lower organic matter content and lower biological activity.

Parent Material – This layer is below the subsoil and has many characteristics of the unweathered parent rock. It is loose enough to turn with a shovel, but is also gravelly or rocky (depending on the identity of the parent rock). It is devoid of biological activity.