For the treatments G1 to G10, ANPP is assessed by harvesting all the above ground portion of plants that are rooted within the bounds of a harvest quadrat. The quadrat size totals 1 m 2 but the dimensions vary depending on the crop row spacing in the annual systems (G1-4) and are described in Table 1. Quadrats are oriented with the long side in an east – west direction (Table 2).This direction is perpendicular to the crop rows (in planted systems) and allows for assessment of both the row and inter-row plant communities. All plants rooted within the quadrat are clipped at ground level, bagged, and dried at 600C for a minimum of 48 hours and dry weights are recorded along with the date of harvest, field replicate, treatment, sampling station and species code. Before drying, harvested plants are separated by species and labeled following the standardized codes given under LTER datasets in above ground productivity protocol (http://lter.kbs.msu.edu/datatables/36). Six letter codes are used for woody species, using the first three letters of both genus and species to create the code. In some cases plants are composited into crop and non dominant plant component. Crops are further separated into seed and stover. In Treatment G8 (poplar plantation) biomass estimates are derived from measurements of basal diameter using an allometric relationship between diameter and biomass determined from a subset of trees harvested prior to leaf drop. Leaf production in sites with trees is estimated with two 1.0×2.0 m litter traps placed on the field floor of each site.

Table 1. Quadrats sizes and time period of biomass sampling

*Time of sampling may vary with location.

Table 2. Location of quadrats within plot with reference to stations.

*Location of quadrat is decided on the basis of quadrat size and easiness while taking samples in field.

The ANPP estimates for all treatments are categorized on the basis of crop type; annuals (Corn, Soybean and Canola), monoculture grasses (Switchgrass and Miscanthus), trees (Poplars) and multispecies (Grass mix, Native prairie and Old field). The details are provided below.

Materials

1. PVC/Wooden Quadrats
2. Paper bags
3. Weighing Balance
4. Drying oven
5. Plant grinder
6. Seed counter
7. Labels and pens
8. Meter stick
9. Calipers for poplar diameters
10. Thresher for separating grain
11. Corn, Soybean and Canola (G1-G4)

Measure biomass at or near crop physiological maturity. In corn, physiological maturity is signified by a “black layer” located within the base of a kernel, which normally forms about 60 days after silking or 20 days after denting. In soybean, peak biomass sampling should be done prior to leaf drop or when only few leaves and petioles have dropped. At this stage the pods on all positions on the stem are losing green color and at least one normal pod on the main stem has turned yellow. In canola, biomass samples should be taken before swathing. At this stage, seeds in lower pods look green-brown or green-yellow mottled. The canola crop should be monitored carefully as these stages change very rapidly during the ripening period if conditions are warm and dry.

For years with cover crops, cover crop biomass must also be measured at peak biomass, usually just prior to killing (and possibly harvesting) the cover crop at the time the main crop is planted.

Clip all the plants rooted within the quadrats to ground level and place in labeled bags. For corn, plants from each quadrat are cut into small pieces before putting them into bags. Place bags in an oven at 600C for 48 h for drying. Weigh the dried mass of plant material and record the total biomass of the plot. Bag contents are then threshed (Almaco corn or small grain thresher) to separate the seeds from stover (corn) and shells (soybean and canola). Seed biomass is recorded and moisture sub samples are taken using a Burrows Digital Moisture Computer 700. Seed, stover, and vegetative biomass is combined by tissue type within plots (over stations), and saved for later grinding and nutrient analysis.

Calculate the mean total, seed and stover biomass per plot on a dry weight basis.

ANPP: mean total biomass (g/m2/y) and standard error (SE) with n=5 reps (blocks).

Switchgrass (G5) and Miscanthus (G6)

At harvest (or at peak biomass for establishment year with no harvest) above-ground material within quadrats is clipped at ground level and partitioned into dead leaf, green leaf, pseudostem and flower/seed heads. Leaves are detached from the pseudostem at the ligule. Green leaves, green stems and senesced material are oven dried and weighed to obtain aboveground live and dead biomass. Detached senesced biomass (litter) is also gathered from the clipped area and dried and weighed. Seed heads on the ground should be added to the stem samples. After weighing the samples, plant material is ground for carbon and nitrogen analysis.

During establishment years mowing may be used to control weeds. Mown biomass must be quantified to include in the measure of ANPP. After mowing, place 1m2 (2.0 m x 0.5 m) quadrats randomly at 3 spots (in 2008-2mS, 2mW). Dry and weigh.

In the establishment year, the biomass is determined using 1 m2 quadrat but in subsequent years the quadrat size can be reduced to 0.25 m2 because by that time the stems will occupy the empty spaces between the original plants.

In addition to biomass, prior to harvest record the maximum height of each plant as measured from ground level to the tip of the extended upper leaf or inflorescence. Also record the number of stems (> 2 cm high) per 5 plants per quadrat at each station.

Calculate the mean total biomass per plot on a dry weight basis.

ANPP: mean total biomass (g/m2 /y) and standard error (SE) with n=5 reps (blocks).

Grass mix (G7), Old field (G9), and Native prairie (G10)

Above ground productivity is estimated at peak biomass, usually in August, by clipping all plants at ground level. Peak biomass is a good estimate of net primary productivity in this system because frost kills aboveground biomass during the winter and there is no carryover of biomass from year to year. The procedure for collecting biomass is same as in other treatments. Before drying the samples, plants are sorted to species. Each plant species sample is put into different bags, dried and weighed for biomass. After taking dried weight, sampled are ground for carbon and nitrogen analysis.

Calculate the mean total biomass per plot on a dry weight basis (summation of each species biomass).

ANPP: mean total biomass (g/m2/y) and standard error (SE) with n=5 reps (blocks).

Poplars (G8)

Woody increment growth

A regression equation is used to estimate woody biomass. The equation is variety-specific, so must be created over a rotation interval if it is not otherwise available. Creating the equation requires sampling and weighing several trees after diameter measurements are taken. Harvesting of poplars is done each year in December. Ten trees (2 trees/replicate plot) are chosen to cover a representation of trees in each diameter size class for that year; trees should be taken from a plot edge. Trees are measured for basal diameter at 15 cm above the soil surface, then cut at ground level and measured for dry weight of branches and stem (separately); basal diameter where cut (mm), and total tree height (m). Separate regressions are developed to relate tree height, tree diameter, and basal area to woody tree mass (branches plus stem mass) to determine the best equation to use to predict mass from diameter measurements.

Also in December, measurements of basal tree diameter (mm) at 15 cm above the soil surface are taken on 9 labeled trees per plot (3 per station, selected randomly). The same 9 trees are sampled each year to follow diameter change. The regression equation developed in the destructive harvest is used in conjunction with the diameter measures to estimate the woody biomass of each of the flagged trees.

Calculate the mean woody tree biomass (kg/tree) and convert it to mean woody areal extent on the basis of 0.27 trees per m 2. (trees are planted on a 2.43 × 1.52 m spacing)

Calculate woody growth increment: The difference of the mean woody tree biomass between successive growing seasons (g/m2/y) for each plot

Litterfall biomass

Poplar leaves drop throughout the growing season. Leaf litter is collected in 1.0×2.0 m wooden litter trap frames (size was designed to fit within or between poplar rows). Two traps are placed 2 meters towards west side of stations 1 and 3 within the rows in each plot following leaf emergence in late May. Leaves within the traps are collected throughout the season, dried, weighed, and archived for tissue analysis.

Calculate the mean litter biomass (g/m2) per plot per collection date.

Report for ANPP: Mean seasonal (sum over dates) litter drop (g/m2 /y), n=5 reps (blocks).

Total Crop (Poplars) ANPP:

Calculate on a per plot basis the sum of woody growth increment and leaf fall by plot, SE, and n=5 reps (blocks).

Report for ANPP the mean sum, SE, and n=5 reps (blocks).

Cover crop

Cover crop biomass should be measured at time of peak biomass for the crop (at or just prior to senescence or winter dormancy). If crops are mowed prior to peak biomass the mowed biomass should be added to peak biomass for an annual total, as described for the grass treatments.

References

Biomass and Carbon Partitioning in Switchgrass. Crop Science 44:1391–1396
Heaton, E., G.F. Dohlemanw, and S.P. Long. 2008. Meeting US biofuel goals with less land: the potential of Miscanthus. Global Change Biology 14:1–15.

Beale, C.V. and S.P Long. 1995. Can perennial C4 grasses attain high efficiencies of radiant energy conversion in cool climates? Plant, Cell and Environment 18:641–650.

Frank , A. B., J. D. Berdahl, J. D. Hanson, M. A. Liebig, and H. A. Johnson.2004.

KBS LTER site ANPP protocol. KBS019-prot01, V1