SOIL SCIENCE 109
Midterm Two
Spring 1997




(12 points)
1.   Describe the process of mass flow and the factors which affect the efficacy of this process.







(4 points)
2.   List ions which are most affected by mass flow.







(10 points)
3.   The concentration of nitrate in soil solution varies considerably on a temporal basis. Why is this measurement so variable over time? Would it be wise to make a nitrogen fertilizer recommendation based on this measurement?







(10 points)
4.   Soil potassium is sometimes found to be inadequate in some soils, especially in California. In additon to pH, what factors affect the availability of potassium in soils?







(10 points)
5.   The following soils have these characteristics.

Soil Characteristic

Soil A

Soil B
     

pH

5.7

6.9

% clay

27

8

% Organic Matter

2.1

1.1

Extractable iron oxide %

2.1

0.6

% Calcium

1.2

1.8



(4 points)
(a)    What soil would you expect to have greater phosphorus adsorption?







(5 points)
(b)    Explain why you chose the above answer.







(5 points)
(c)    Through further investigation you find out that soil B is relatively young compared to soil A. What forms of P would you expect to find in soil B compared to soil A?







(10 points)
6.   It was found from previous studies that a soil on your ranch has a certain capacity to mineralize N. Calculate the amount of nitrogen mineralized per hectare during the year given the following:

- soil contains 3 % C

- C to N ratio of the soil is 10

- weight of the top 15 cm soil in a hectare is 1,800,000 kg

- 2 % of the N in the organic matter is mineralized during a year.







Answer the following keeping in mind the above answer.

(10 points)
(a)    You plowed under a winter cover crop (ryegrass) with a C to N ratio of 45. The crop you want to establish requires 140 kg N per hectare per year. Would simply taking the difference between the amount of N mineralized per year and the amount required give you a good estimate of the N required for the present crop? If not why and what processes could affect the fate of the cover crop N?







(10 points)
(b)    In the following year the incorporated winter cover crop (legume) has a C to N ratio of 20. You experience serious flooding three weeks after incorporation that lasts two weeks. Describe the processes and possible fates of the N contained within the cover crop residue.







(10 points)
7.   You find a cheap source of fertilizer N in the form of urea. What are some of the biological processes and practical management considerations you need to know to get maximum N use efficiency in the crops you apply it on.







(10 points)
8.   Two continuous corn crop rotation have received the same amount of P fertilizer as different forms of super phosphate fertilizers for the past 40 years. In addition to removing the grain, the residue has also been removed as silage and fed to dairy cattle on a different farm. Describe a possible reasons for the negative interaction in corn yield from using different forms of super phosphate type fertilizers shown in the following graph.