organic matter

Sampling Design:

 A total of 120 litterfall baskets were distributed among the 3 study sites.  In the Sevilleta's Cerro Montoso site, 30 baskets were placed under juniper trees, and 30 were placed under pinyon trees.  At the Bosque del Apache site, 30 baskets were placed in 3 transect lines of 10 baskets each, at 10 meter intervals, through the cottonwood forest.  At the Magdalena Mountain site, 30 baskets were placed in 3 transect lines of 10 baskets each, at 10 meter intervals (as in the Bosque site).

Sample Unit:

Each basket was considered a sample unit. 

Frequency of Sampling:

During the same times as arthropod pitfall collections (several times/year)

Sample Size:

120 baskets total.  Each basket was a rubber basin with a small (5 mm) hole drilled in the bottom to allow rainwater and snowmelt to drain out. Basket dimensions were circular, with a diameter of 41.5 cm at the top rim, tapering inward to a diameter of 35 cm at the basket bottom.  The basket height was 12.5 cm.

Measurement Techniques:

Litterfall baskets were place under tree canopies to catch falling leaves, twigs, and reproductive parts.  In the Bosque del Apache and Magdalena Mountain sites, the baskets were placed systematically in 3 transect lines through the forest (which generally had a closed canopy).  In the Pinyon-Juniper site on SNWR, the baskets were placed under individual trees (basket locations were halfway between the trunk and the edge of the canopy) due to the patchiness of tree locations. Hence, the results for this site are for a "per tree" basis, and should be scaled up to reflect different tree densities in various Pinyon-Juniper sites.

Litterfall samples were collected by placing all litter into plastic zip-lock bags, marking each bag with the basket tag number, and taking the bags back to the laboratory. If samples were wet from rain/snowfall, the sample bags were opened and allowed to air-dry for several days.  Litter was then sorted by category (leaf, twig, reproductive part, or "miscellaneous" if the part could not be recognized) and by species.  The sorted litter was then oven dried at 60 degrees Centigrade for one week, and weighed on a Mettler top-loading balance.

Experimental Design:  

Setting up each location: 1989 through 1991:

The design of this decomposition study includes placement of three (3) primary litter-types (black grama, juniper, and indian rice grass) at seven (7) locations. Litter of each species was collected after senescence in the fall. The grasses were clipped from standing plants before the litter was on the ground. All material that was not produced during the previous growing season was discarded.  All reproductive parts were discarded. If there was any doubt about whether or not the material was produced that growing season, it was discarded. Juniper was collected from trees with senescent material or that had recently died and were still on the branch. Juniper litter consisted of only that material that still had bracts (woody stems without bracts were discarded). Pinyon was collected from trees that still retained senescent needles by shaking and capturing on a cloth or plastic sheet.  Branches of 4-wing saltbush were trimmed from bushes in October when material looked senescent and leaves were picked from the branches and air-dried. Creosote leaves were attempted to be collected by spreading sheets on the ground; however, litterfall is very episodic and not enough material could be collected. Thus, creosote was collected by cutting live plants and drying in a forced-air oven at 60 °C; then the freshly dried leaves were removed from the branch and any reproductive parts (seeds) were discarded. Yucca was collected by cutting leaves from a recently dead yucca plant. Cottonwood leaves were collected in plastic trays as they fell and before the fresh litter was rained on. Arizona fescue, douglas fir, ponderosa pine and aspen were collected by others and we do not know what methods were used.  All litters were sorted and damaged material or reproductive parts were discarded. Unless previously dried, litter was air-dried in the laboratory. Litter bags consisted of coated fiberglass window screen material cut into 12 by 7.5 sheets, which were folded in half and two of the edges folded over and stapled. Litter was inserted through the unstapled edge, which then was folded over and stapled. Each bag initially contained 5.00 g (4.95-5.05 g) of air-dried material. For each litter type, a total of 34 bags were prepared for placement at each location. All the litter bags of one species for an individual location were placed in a separate bag and the bag was sealed for transport the field.

At each location and for each species, the experimental design included placement of enough litter bags for three replicate bags per collection date; one collection at the time of placement, eight collections over a two year period, and 7 additional bags to allow for some mortality of bags (34 bags total per location).

When the litter bags were placed at each location, the location was marked with fence posts as a warning. Each location was identified by a color-coded marker. The color-coded markers for each location are as follows: location (1)=plain, (2)=tan, (3)=green, (4)=orange, (5)=orange/green, (6)=tan/green, (7)=green/tan, (8)=green/orange, and (9)=tan/orange.

Litter bags were placed on bare soil between plants at all times. Each litter bag was anchored by inserting a 16 penny nail through diagonal corners of the bag and into the ground.  Decomposition bags with creosote, blue grama, yucca (tethered, not bagged), and four-wing saltbush all were placed at the deep well location (location 2); and cottonwood at the Bosque del Apache (location 8).

In the fall of 1990, only 5 litter types (black grama, blue grama, juniper, creosote, and Indian ricegrass) were collected for placement in Feb. of 1991. Blue grama litter was only placed       at Deep Well, while the four other litter types were place at 4 locations (#2, 7, 10, 11). Litter was collected as described in the previous year and bags were placed on bare soil at each location.

In February of 1999, the Rio Salado and Red Tank sites did not get new litter bag placements; instead the new locations at Blue Springs and 5 points were established and the 4 common litter types were placed at these locations along with Deep Well and Cerro Montoso.

Sample Collection Methods:

For each individual location collection, three replicate bags are placed in zip-lock bags and are identified by species, field location, collector initials, and date of collection. A general maintenance survey of each location is done at this time by the collector(s). At the time of placement, three bags of each species were collected and placed into a gallon-sized zip-loc bag for transport to the lab. This method insured that each replicate was handled the same way with bouncing during transport and sample handling consistent for all samples. These three samples taken at the time of placement determine the starting (incubation in the field time 0) replicate litters. For each collection date, 28 gallon-size zip-lock bags were be needed.

Sample Analysis Methods:

Overview: 

Handling of the field samples involves three phases: (1) initial cleaning and oven-dry weight; (2) grinding and ash correction; and (3) chemical analyses. Once in the laboratory, field samples will come in with 3 replications/plant type in a bag labelled with the site, plant material, and collection date. In Phase 1, the samples are cleaned, oven dried at 60° C for a minimum of 24 hours, and oven-dry weight recorded. The  samples are then transferred to coin envelopes, ground on the Tecator grinder, and stored back in the coin envelope. In Phase 2, ground plant material is then used for ash-free weight determinations. In Phase 3, the remaining ground plant litter is used for chemical analyses.

Phase 1. 

WEIGHING 

1.  A zip-loc bag with field samples  is selected to begin weighing out. One mesh bag is selected and  this sample was arbitrarily assigned as a replicate number and Sample ID number. Any foreign material was removed from the outside of the bag, such as: differen plant material, mud, ROCKS, etc, making sure to lift up the side folds to release any trapped rocks.  The weighed and labelled weigh boat was placed on a sheet of paper and the contents of the bag were emptied into the weigh boat. This was repeated for all samples and the samples were placed in the oven. 

2.  Samples were dried for a minimum of 24 hours at 60° C. Samples were weighed and weights were recorded in the record book.  Samples were then placed into a coin envelope labelled with the collection date, site number, plant type, and Sample ID number.

GRINDING 

Plant material was ground in order to perform ash-free weight corrections and chemical  analyses. The only plant material needed to be ground using liquid N were: pinyon, juniper and creosote. All others were ground warm.

Phase 2. 

ASH-FREE WEIGHT CORRECTION METHOD 

Methods 1989 through 1991: 

ASH THE EMPTY CRUCIBLES: Line up a sufficient quantity (about 40) of the tall, narrow, numbered porcelain crucibles. Wipe them out with a Kimwipe. Load them into the muffle furnace making sure not to touch the oven sides or each other. Use the shelf to fit them all in. Close the muffle furnace. Turn on the exhaust fan. Turn the controller to 5.0, and turn the timer to 2 hours. After about 1.5 - 1.75 hours, check to verify that the temperature has or will reached 500 °C.  If it hasn't, add additional time to the controller. When it does hit 500 °C, it is hot enough and ready to shut off. Let cool, closed, overnight. The next day the crucibles can be removed and stored in a desiccator.

DRY THE GROUND MATERIAL: The ground material in their envelopes  was placed in a 60 °C oven for 24 hours prior to weighing out for ashing. When the crucibles are thoroughly cooled, weigh the empty crucible and then place out approximately 1 gram using the analytical balance (BE SURE TO MIX THE SAMPLE WELL BECAUSE PARTICLES TEND TO SEPARATE DURING STORAGE AND HANDLING) of ground material into the crucible, and then record the filled crucible weight on the data charts in the front of this book. Remember to weigh and include a blank (empty) crucible with each run.

ASH THE WEIGHED SAMPLE:  Using tongs, load the crucibles into the muffle furnace, making sure not to touch the oven sides or each other. Use the shelf to fit them all in. Close the muffle furnace. Turn on the exhaust fan. Turn the controller to 5.0, and turn the timer to 2 hours. After about 1.5 - 1.75 hours, check to verify that the temperature has reached 500 °C. If it hasn't, add an extra 15 minutes to the timing. When it does hit 500°C, and the timer has turned off the furnace, turn the controller to 2.0, and the timer to 2 hours. Let cool, closed, overnight.

WEIGH THE ASHED SAMPLES: Using tongs, remove the crucibles to a desiccator. When they are thoroughly cooled, use the same analytical balance and record the filled crucible weight on the data charts in the front of this book. Remember to weigh and include the blank (empty) crucible from each run. Dump out the ashed sample into the garbage, wiping the crucible with a Kimwipe if necessary. The crucibles are now ready to be filled again and fired. 

Methods after 1991: 

Ashing methods were changed in 1991 when the use of porcelain crucibles was replaced by use of disposable aluminum boats. All methods stayed the same EXCEPT: The disposable aluminum boats did not need to be 'tared' or fired before use. The clean boats were taken directly from the package and placed into use. To identify the boat, the SAMPLE ID # was 'written' (etched indented with a pencil-pen) on the bottom of the boat. The boat weight was recorded and the sample (WITH MIXING!) was added (about 1 gram). The rest of the procedures remained the same. If the muffle furnace was allowed to exceed 550 °C, the aluminum boats would melt and significant changes in their weight could occur. Blank boats are run with each operation to insure no significant loss-gain during firing.

Analytical Methods Used:

Kjeldahl Nitrogen and Phosphorus by Technicon Industrial Method No. 369-75A (Revised 8/21/75) Digestion and sample preparation for the analysis of total kjeldahl nitrogen and/or phosphorus in food and agricultural products using the technicon BD-20 Block digestor and Technicon Industrial Method 334-74A (revised 8/21/75) Individual/simultaneous determination on nitrogen and phosphorus in BD acid digests.

Percent Nitrogen and Percent Carbon were determined by High Temperature combustion, the resulting gases were eluted on a gas chromatography column and detected by thermal conductivity and integrated to yield carbon and nitrogen content.  Analyses were performed on a ThermoQuest CE Instruments NC2100 Elemental Analyzer, ThermoQuest Italia S.p.A., Rodano, Italy.