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University of Minnesota
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Methods for Experiment 024 -

Fertilization Strategy

The experiment uses 3 different nitrogen addition levels and 4 other nutrient additions trying to create different pH levels. Each nitrogen-pH combination is assigned a capital letter.

Treatment CodepH LevelNitrogen Level
A10.0 g/m2
B18.0 g/m2
C125.0 g/m2
D20.0 g/m2
E28.0 g/m2
F225.0 g/m2
G30.0 g/m2
H38.0 g/m2
I325.0 g/m2
J40.0 g/m2
K48.0 g/m2
L425.0 g/m2
 

The nitrogen additions used the "microplot" strategy found in nutradd.doc at the levels noted. pH Level 1 received 62.5 g/m2 S + 250 g/m2 FeSO4. pH Level 2 received no nutrients to adjust the pH level. pH Level 3 received 62.5 g/m2 of Ca(OH)2 in 1984 and 125 g/m2 in 1985. pH Level 4 received 125 g/m2 of Ca(OH)2 in 1984 and 250 g/m2 in 1985. The plots are 16 m2 in area. Irregularities occurred in N level additions in 1985, two plots in the first fertilization received 25.0 g/m2 when those plots had been assigned to 0.0g/m2.

Field Operations: Fertilization

Fertilizer was mixed and spread by hand twice a year, once in early May and once in late June. Each plot got the fertilizer mixture specified by its fertilizer treatment code.

Light Penetration

Light meter readings for E024 were taken in 1987, 1989 and 1990 in the same way as in E001 except gopher mounds were ignored. Light meter readings were taken in the same positions in all plots, regardless of the presence of gopher mounds.

Light Penetration Measurements Methods

From 1982 to 1988, light meter readings were taken using a Li-Cor, Inc. Integrating Quantum/Radiometer/Photometer, model LI-188B. Two people were needed to take light readings with this system. One would hold the control box and record data and the other would hold the light sensor. The batteries would be checked before starting each session. If the batteries were OK, they would proceed to take readings. The sensor was connected to the control box by a relatively short cord, so the two people taking readings were required to stay close together. When taking readings, it was necessary to get a range value for each light value entered. If the integrating time of 1 second was not sufficient, it was increased to 10 seconds. This was also recorded.

In 1989, two new light meters were acquired. These are SF Sunfleck Ceptometers, model SF-40 (40cm probe). They were purchased from Decagon Devices, Inc., P.O. Box 835, Pullman, WA 99163. One person can easily handle a ceptometer alone. This makes is possible for three people to get the readings done more quickly and easily. One person records data while the other two take readings from the plots simultaneously. No range values are needed. To take readings a person needs to select function #1 (PAR readings), position the probe (see below) and press ``A' (read value). More than one reading can be taken and then averaged by pressing a certain sequence of letters (A, A, B, B, A).

Measurements are taken within a 4 hour period, 2 hours on either side of solar noon. (Solar noon is half way between sunrise and sunset; it is not 1200 hours). Solar noon is at 1315 hours, Central Daylight Time. Samples are taken between 1115 hours and 1515 hours. Measurements are not taken when the plot being sampled is shaded. Light readings are done when the sky is clear, whenever possible. If a cloud passes over the plot being sampled, assistants wait for the cloud to pass before taking the readings. If the sky is mostly cloudy, light meter readings are not taken.

Two measurements are taken in each plot. Each measurement consists of one reading above the vegetation and a second reading at ground level. Both values are taken to get the percent of sunlight above the vegetation that reaches ground level. In taking the above vegetation reading, the sensor must be kept level, held high above all vegetation, kept out of the shade (of plants and people) and it must be clean. When taking the below vegetation reading, at ground level, the sensor must be kept level, out of the soil and out of the shade created by people.

In 1991, light meter readings were only taken in E026 and E055. Light profiles were taken using an A-shaped frame made of aluminum. Wires were strung across the frame at 10cm intervals. The frame was placed over the subplot being metered. A reading was taken over the top of the frame, and then at each 10cm level, by placing the light meter across the wires, starting at 90cm above the ground. Readings were taken every 10cm down the frame and again at ground level.
Light Data Transformations:
Light readings are transformed to obtain percent light penetration which represents the percent of light above the vegetation that reaches the ground surface. In cases where the experiment involves shading, another variable is computed to reflect the percent of sun light that reaches above the canopy. This variable is called light available. In the case of absence of artificial shades, the latter is set to 1.

percent light penetration = ( Light below canopy / Light above canopy ).

percent light available = ( Light below shade / Light above shade ).

Treatment layout : trmte24

Field IdentificationExperiment Number Plot Number pH Number Nitrogen Treatment Ammonium Nitrate(34-0-0) addition(g/m2/yr)
B2413516
B2422750
B2434516
B2443750
B245490
B2461516^
 

Vegetation Sampling Methods

E024 was in field B. Plots in this experiment were not sampled on a regular basis. Each time it was sampled, the sample strip was located in a different place.

Documentation on where the strips were located for each year can be found in the vegetation sampling.

Sample size was 0.1m x 3m.

Vegetation Sampling for B024

lip strips are 10cm wide and 3m long.

1987: Clipped 75cm from right side
1989: Clipped 65-75cm from left side

Sampling Problems in B024:

1987: B-24-5 clipped at 75cm from right side
B-24-9 clipped at 60cm from right side
B-24-10 clipped at 75cm from left side
B-24-32 clipped at 125cm from right side
1989: B-24-25 reclipped at 15-25cm from right side