FoxPatch Field Experimental Protocol
The experimental protocol is divided into a core protocol, and then suggested enhancements that individuals may choose to explore.
The 5 step basic protocol:
Step 1: Collect a bulk sample of foxtail spp. seed as it matures in the autumn (August-November).
Step 2: Send an aliquot to Jack Dekker for dormancy state assay characterization.
Step 3: Bury aliquots of the seed in weed-free soil near the soil temperature and moisture monitoring equipment.
Step 4: Record soil temperature and moisture at depth from the time of burial until completion of the experiment on an hourly, continuous basis all year.
Step 5: Record foxtail seedling emergence numbers weekly from the buried cores for the entire year when the soil is not frozen.
Enhanced protocol and step explanations:
Step 1. The first population should be your locally adapted genotype. Population genetic structure (Wang et al., 1996a, b, c) tells us that a "patch" of foxtail is more than likely to be a single genotype; with giant foxtail this is almost a surety. Any of the weedy foxtails are OK: giant, green, yellow, bristly, knotroot (correct ID of yellow and knotroot is difficult). Consider more than one locally adapted foxtail species; more than one locally adapted foxtail population within a species; exchanging locally adapted populations between regional sites (common nurseries can provide information about local adaptation); starting the experiment in more than one burial year; following the buried seed from one year over several emergence years (i.e. emergence in year of burial, year 1, year 2, year 3, etc.).
Collect a large bulk sample so that there is enough for dormancy assay, burial and storage (-20° C) for related studies later. Physically stir and homogenize the bulk sample when collection is over to ensure "uniformity".
Harvest the seed from one local patch (e.g. 1-25 m2 plot), and all at one time or over a 1-3 day period maximum to ensure similar dormancy. In general the most seed comes from primary panicles at the beginning of the season (August), and the quantity decreases thereafter as 2° and 3° panicles shed seed.
Step 2. Dry the seed on screens at room temperature for 1-3 days. This will also allow you to store the unused seed at -20° C without to much loss of viability. Separate the large, dark, mature seed from the lighter seed and chaff (blower). Immediately assay, bury and store the seed after drying. Collect thousands of seeds (30-100 grams) for each population you study.
The standard assay to determine dormancy state heterogeneity within a single foxtail population involves testing the seed in controlled environment germination cabinets after various after-ripening (4° C, moist, dark) periods (0-100 days). Considerable experimentation has resulted in the specification of "ideal" germination conditions: a sealed 30 ml vial, germination paper, 1 ml H2O, and 10 foxtail seeds (Dekker and Hargrove, 2002). These vials are used for both after-ripening and germination. The 8 day germination assay per se is conducted at 32° C, 15 h light period:12° C, 9h dark period for each diurnal period.
Step 3. Possible variations include 3-6 replications; use small (11 cm dia.) unprotected, 3-flagged, cores; cores at different locations with the same seed to get a local look at variation; vary burial depth: shallow or uniformly to 12 cm to simulate plow-cultivation distribution; vary seed number per core, more is better to detect the infrequent post-July late emergers; bury near other's temperature and moisture monitoring equipment. Find a spot with no foxtail seeds, convenient to collect weekly emergence data and near or at where the temperature and moisture monitors are. Bury 200 or more seeds per core (replication; 11cm diameter X 12 cm deep cylindrical core). Extract soil and mix with the seed in a bucket. Mark the soil-foxtail seed core. We use a 3 wire flag system, the cores and seed move very little so there is no need for bags or rings: they create their own artifacts. How you bury and mark, as long as there are no contaminating foxtail seeds, is very flexible.
Step 4. Soil temperature measurements at depth (e.g. surface, 1, 2, 4, 8 cm. etc.) is very standard at state Experiment Station farms. Soil moisture measurement is the hardest measurement to make in this protocol. In Iowa we have 2 stations on the Iowa Environmental Mesonet that records soil temperature and water content hourly and uploads it continuously via a solar-powered cell phone, and then reported immediately on the IEM web site (in easily downloadable files).
Step 5. More frequent emergence counts than weekly is not necessary. In the spring when the big flush comes it may help, but weekly really is as accurate a prediction as we can ever hope for. Emergence counting has to be consistent from soil thaw in the spring to soil freeze in November and December. After counting each week, cut the seedling off with a sharp blade at the soil surface. Grow a soybean, or corn, crop over the core areas so the soil environment is similar to that of a no-till crop. Plant and weed by hand at the normal times except the core areas. Emergence from bare soil will be different than that with a crop.