ESTCP Project #1011, Rhizosphere
3.5 Testing and Evaluation Plan
3.5.1 Demonstration Installation and Start-Up. Figures 5 through 12 show maps of
each of our three locations in Alaska. At each site, we are comparing the treatment effects of
nutrient additions on a mix of three plant species and of the interactions of plants with nutrients,
with controls for each. This resulted in four treatments: 1) a control, 2) added nutrients, 3) plants
without nutrients, and 4) plants plus nutrients.
We used a mixture of annual ryegrass (Lolium multiflorum, Lam.), Arctared red fescue (Festuca
rubra, L.), and white clover (Trifolium repens, L.) at each of the three sites in this demonstration.
Low-maintenance grasses and a legume were chosen to avoid the need for intensive agricultural
practices. The initial nutrient addition to the soil and watering are all that is usually required to
create a viable stand of these grasses in these climates. We followed the RTDF-developed
guidelines for seeding mixtures, which by weight were approximately 8 lb/1000 ft2 tall fescue, 2
lb/1000 ft2 annual ryegrass, 1 lb/1000 ft2 legume (such as white clover, yellow sweet clover, or
birdsfoot trefoil). These mixes, in general, provided a seed mix that had 10 to 15% ryegrass
(annual or perennial), 20 to 25% legume (alfalfa, clover, birds-foot trefoil), and 60 to 70% fescue
(varieties chosen for local conditions) on a seed quantity basis.
Minimal soil preparation was done prior to seeding. Seeds were surface applied by hand or by
hand-held seeders and pressed into the soil surface to promote reasonable seed-soil contact and
water imbibition. Nutrients were applied by hand or by hand-held seeders. Neither seeds nor
nutrients were mixed into the soil, eliminating the need for heavy equipment mobilization to
remote sites. Plot size varied at each site due to the constraints imposed by the local conditions.
Figures 8 and 13 show how plots were arranged in blocks on Annette Island; Figures 1 and 2
show grass growth in the plots at Campion; and Figure 14 shows plots at Barrow.
Fertilizer requirements for bioremediation are controversial. For bioremediation without plants,
different ranges of C:N ratios have been proposed. A potential issue with using C:N approaches
is that for highly contaminated soils--which necessarily have high C levels--the amount of
fertilizer N that is needed to maintain many C:N ratios become quite high. This can lead to
osmotic stress on both microorganisms and plants. In theory, as microbial metabolism occurs,
much of the contaminant C is lost from the system via CO2 evolution. Nitrogen, however, cycles
within the soil-plant-microbial system. We have found that, in a number of Alaska soils,
approximately 2000 mg N/kg soil water is the maximum N addition that can be applied without
limiting soil microbial activity (Walworth et al., 1997). Note that this value is based on soil
, rather than soil. Because soil water varies with rainfall, evaporation,
value that relates to the soil must be used. We have used the gravimetric soil-water content that
corresponds to -33 kPa soil-water potential as a basis for calculating nutrient amendments. To do
this, at least a minimal soil-water response curve must be generated for each soil texture. This
calculation can have a dramatic impact on nutrient additions. The gravimetric soil-water content
that corresponded to -33 kPa soil-water potential for the Campion site soil was ~26%, but only
~1.6% for the Barrow soil. Additional fertilizer can be added to account for plant-uptake
requirements and this can be based on agronomic requirements for the plants used. If excessive