Soil sampling

Deep cores (1 m deep) were taken in each plot in fall 2013. A single core was taken in each plot. Cores were partitioned by depth (0-10 cm, 10-25 cm, 25-50 cm, and 50-100 cm), and the soils analyzed for % carbon, % nitrogen, pH, lime index, phosphorus, potassium, calcium, magnesium, and cation exchange capacity by the MSU and UW Nutrient Labs. In addition, samples were frozen for DNA extraction and microbial community analysis.

Surface soils (15 cm in WI; 20 cm in MI) were taken prior to planting, except for Oregon, where samples were taken in July 2013. Samples were analyzed for % carbon, % nitrogen, pH, lime index, phosphorus, potassium, calcium, magnesium, and cation exchange capacity by the MSU and UW Nutrient Labs. Cores were taken again in fall 2014 at the Wisconsin sites and analyzed in the same way.

In the future (2015-onward), soils will be sampled every 3 years at both sites. Using a push corer (2 cm diameter), take four cores in each split plot (2 cores at each of 2 locations), to a depth of 15 cm. Composite the cores by plot, sieve (mesh 2 mm diameter in WI; 4 mm diameter in MI), air dry, and send to the MSU and UW Nutrient Labs.

Yield

Harvest yields are measured in the fall of each year, starting in 2014. In 2015 and going forward, yields will be recorded separately for each split plot (fertilized and unfertilized). For treatments G5-G7 and G9-G10, harvest yield is determined by weighing the biomass removed during harvest. The G11 treatment is a control; it was not seeded and is not harvested annually. In order to estimate harvest yield, the aboveground biomass within quadrats are is clipped, dried, and weighed. G8 is harvested on a 6-year rotation, and annual productivity will also be estimated using allometric equations.

G8 Yield

Measure the basal tree diameter (mm) at 15 cm above the soil surface on 10 randomly chosen trees in each plot.

G11 Yield

Materials

1. PVC/Wooden Quadrats
2. Paper bags
3. Weighing Balance
4. Drying oven
5. Plant grinder
6. Labels and pens
7. Meter stick
8. Calipers for poplar diameters

Each fertilized and unfertilized microplot will be sub-sampled 3 times. Place quadrats (2m x 0.5 m) within the plot according to Table 1 (MI-South, WI-South, WI-Central, and WI-North), Table 2 (MI-Central), or Table 3 (MI-North). The different tables account for differences in plot size and orientation among sites. Clip all plants within quadrat 6 inches above the ground (6 inches is the height of machine harvest in the other plots – adjust this if machine harvest height changes). Place plant biomass in a labeled paper bag and place in drying oven at 60C for a minimum of 48 hours. Do not separate by species. Record the dry weight, along with the date of harvest, field replicate, microplot designation (E/W or N/S), treatment, and quadrat number. After weight is recorded, combine stations from a single plot and save for later grinding and nutrient analysis.

Table 1. Location of quadrats for MI-South, WI-South, WI-Central, and WI-North, as measured from the NE corner of the plot (E microplots) or the NW corner of the plot (W microplots). Place the quadrat across the plot, so that the short ends are on the E and W sides. For E microplots, place the NE corner of the quadrat at the location specified below, and for W microplots, place the NW corner of the quadrat at the location specified below.

Table 2. Location of quadrats for MI-Central, as measured from the SE corner of the plot (S microplots) or the NE corner of the plot (N microplots). Place the quadrat across the plot, so that the short ends are on the S and N sides. For E microplots, place the SE corner of the quadrat at the location specified below, and for W microplots, place the NE corner of the quadrat at the location specified below.

Table 3. Location of quadrats for MI-North, as measured from the NE corner of the plot (E microplots) or the NW corner of the plot (W microplots). Place the quadrat across the plot, so that the short ends are on the E and W sides. For E microplots, place the NE corner of the quadrat at the location specified below, and for W microplots, place the NW corner of the quadrat at the location specified below.