previous year's dead

PBB01 Belowground Plot Experiment: Aboveground net primary productivity of tallgrass prairie based on accumulated plant biomass


To address the potential interactive effects of fire, aboveground biomass removal, and nutrient amendments on above- and belowground responses, a long-term field experiment was initiated in 1986 as part of the Konza Prairie Long-Term Ecological Research (LTER) program. The general goals of this experiment are: 1) to document both short- and long-term responses of plants and soils to fire, aboveground biomass removal (a surrogate for grazing in these small plots), and nutrient amendments (additions of N and/or P); and 2) to provide a better understanding of the mechanisms underlying tallgrass prairie responses to fire, aboveground biomass removal and nutrient enrichment. Peak foliage biomass is measured annually in late fall (September to October) on the 64 belowground plots. Effects of burning, mowing and N + P additions on aboveground NPP are measured. Two 0.1m2 quadrats harvested per plot). 2003 was the last year the mowing treatment was implemented.

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To monitor long-term changes in plant production and nutrient balance due to the effect of annual burning (late April-early May), mowing (late June; stopped 2003), and nitrogen (10gN/m2) and phosphorus (1gP/m2) fertilization (late May-early June).


Location of Sampling Stations: HQC.

Frequency of Sampling: Once per year for peak biomass in September to October.

Variables Measured: 1. Plant biomass sorted by grass, forb, woody and p.dead. (PBB011); 2. Total-N and total-P (PBB012)

Methods: Field and lab methods are identical to those for PAB01 except two 0.1m2 quadrats are clipped from each plot. The plant material is dried at 60oC and then separated into grass, forb, woody and p.dead material. The samples are then dried again at 60oC and weighed. Samples are no longer kept for analysis.

Summary of All Changes:

Prior to 1992: only one 0.1m2 quadrat per plot was clipped.
As of 2000: all samples are discarded. Prior to this, all samples were kept and ground to pass a 2 mm screen and acid digested by the Kjedahl procedure and the solution analyzed for total-N and total-P by automated calorimetric analysis. (PBB012)
2002: c.dead no longer separated from live grass.
Before 2004: there was a mowing treatment for half of the plots. Mowed plots were clipped in mid- to late - June before mowing; then mowed to a height of 4 inches. All clippings were removed. The mowed plots were clipped again at time of peak biomass; same date as un-mowed.
June 2004: irrigation cistern collapsed during repairs (located uphill from plots 33-44). Huge flood and rock debris; debris was removed within 2 days of 'damage'.
May 2, 2006: damage to middle section of plot #44 and a small part on east side of #43. There was a bentonite spill during the installation of two seismograph wells on the hill above these plots. An attempt was made to clean up the area. Damaged area was delineated by flags and avoided during clipping for 2 years.
2017: fertilizer treatments have ended.

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Additional information: 

As of 2000, samples are no longer ground and archived for nutrient analysis. Samples from 1987-1993 were analyzed for N and P concentrations, and data are archived as KNZ dataset PBB012. Ground plant samples from 1987-2000 are archived for additional future analyses, as needed.


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