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University of Minnesota
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Methods for Experiment 042 -

Light Penetration

Two light measurements were taken in each of the five 1m X 10cm strips in each of the 37 old fields.

Light Penetration Measurements Methods

At each of the five sampling locations in each field, light intensity above the vegetation and at the soil surface was measured in duplicate using a Lambda Instrument PAR cosine collector.

Sampling for E042

Thirty seven old fields were surveyed for above and below ground biomass, soil nitrogen and light penetration. These fields include the ones used in experiment 14 (see E014), field D and 13 succession strips. In the succession strips, samples were taken through each strip every 15m. In the old fields from E014, except fields A, B and C, samples were parallel to the transect lines of E014. The clip strips were halfway up the transects, with 2 outside the transects and 3 in between the transect lines, making 5 strips per field. In fields A, B, C and D, samples were taken from control macroplots (E004). Five sample strips were taken from each field. In field A (29), two sample strips were taken from plots 1 and 6 and 1 strip from plot 9. In field B (22), two samples were taken from plots 2 and 3 and 1 strip from plot 5. In field C (69), three strips were taken from plot 3 and two strips from plot 5. In field D (94), two samples were taken from plots 1 and 4 and 1 strip from plot 5. Five strips, 1m x 10cm, were clipped in each field for above ground biomass. This was sorted to grasses and forbs. Three root cores, down to 30cm, were taken from each of the five strips in each of the 37 fields. These cores were rinsed, dried and weighed. Two light measurements and one pooled (3 cores, down 10cm deep) soil nitrogen sample (for available and total N) were taken per strip.

Thirty five abundant species of known successional status were harvested from the field (usually 15 individuals per species), including roots contained in a core 20cm x 30 cm, dried, sorted to stem, leaf, and root, and weighed. Root cores were taken from microplots in fields A, B, C and D (E001), all treatments. This was an estimate of root biomass.

Three additional 10 cm deep by 2.5 cm diameter soil cores per strip were pooled and mixed, with 20 g placed in 50 mL of 2 mol/L KCl to obtain extractable nitrate. The remainder of the soil was used for moisture determination and for total soil nitrogen analysis. Leaf, stem, and root tissue and litter from each field were ground and analyzed for total nitrogen content. Total nitrogen of tissue and soil were obtained by potassium persulfate digestion, with the resulting nitrate measured using a Technicon II autoanalyzer. Nitrate in the soil extracts was also determined on the autoanalyzer, and is reported as milligrams of N03-N per gram of dry soil.