2017 Japanese Indigo Soil Trial
A four-month soil biology trial was conducted on Japanese indigo (polygonum tinctorium) at Vibrant Valley Farm outside of Portland, OR between April and August of 2017. Indigo is grown for fermentation and subsequent processing into a powdered dye material, which is reconstituted for fabric and textile dyeing.
The intention of this trial was to simply augment and balance the vital microorganism groups of a healthy soil food web in two Treatment groups to improve crop quality, pest/disease resistance, weed suppression and soil structure over the Control group, which did not receive any applications of soil biology.
The soil on which this trial was conducted was chosen due to it being the most challenging on the farm, a mucky clay/loam soil with approximately 6% organic matter and very poor structure from years of tillage and a lack of beneficial fungi and micrograzers.
Thistle, wild burdock, plantain and horsetail species were present in early spring followed by Canadian thistle, lamb’s quarter, pigweed and bindweed through the growing season, all of which are indicative of an early succession ecosystem and compacted, anaerobic soil conditions commonly observed in modern agriculture.
Additionally, with almost 20 times the necessary bacterial biomass in the soil at the beginning of the trial, the biotic factors of the soil were telling the same story as the abiotic factors.
The Treatment groups received applications of compost extract once per month, as well as additional compost teas and/or protozoan infusions. Treatment group 2 also received one light top-dressing of Rocky Mountain Worm Compost with the first application of compost extract, which is the only difference between the two Treatment groups. Additional compost utilized for the last two compost extract applications was made by Nick Tomasini.
The farmer also applied 500 lbs. per acre of Nutri-Rich 4-3-2, consisting of processed chicken manure only, and 500 lbs. per acre of agricultural lime to the entire plot, including Treatment Group 1, Treatment Group 2 and the Control. These applications rates were lower than the farmer initially wanted to apply, and were actually higher than the rates prescribed by Nick Tomasini due to concerns with harming soil biology.
Lower rates of lime were prescribed for Treatment Group 1 and Treatment Group 2, but a miscommunication occurred and the entire field was amended with 500 lbs. per acre. Typically when working with biology, 100 lbs. per acre of any individual mineral nutrient is the maximum, and since lime is about 30% calcium, 150 lbs. per acre of calcium from a mineral source ended up being applied, which has the ability to slow efforts to improve biology.
Control Group: One 90’ x 4’ bed with four rows (~0.01 acres). Fertility inputs only.
Treatment Group 1 (Trt1): One 90’ x 4’ bed with four rows (~0.01 acres).
Fertility inputs + compost tea + compost extract + protozoan infusion.
Treatment Group 2 (Trt2): One 90’ x 4’ bed with four rows (~0.01 acres).
Fertility inputs + compost tea + compost extract + protozoan infusion + one light top-dressing of worm castings (~20 lbs total or ~2,420 lbs/acre).
Quantification of biomass and counts for each microorganism group was carried out for Treatment and Control groups as per Soil Foodweb, Inc. protocols approximately two to three weeks after each application of compost extract.
Substantial improvements were made to the soil food web in Treatment Group 1 and Treatment Group 2 by the end of the trial, while the Control group remained largely the same.
Though crop improvements were realized in Treatment Group 1 and Treatment Group 2, bacterial biomass was still almost 10 times higher than we wanted in Treatment Group 1 and Treatment Group 2. Given the degree of challenge posed by this plot, four months was a relatively short period of time to reduce such excessive bacterial biomass and improve the fungi:bacteria (F:B) to our minimum target of 0.3.
Nonetheless, significant improvements to beneficial fungal biomass, reduction in disease-causing organisms and a slight recovery of micrograzer populations did improve nutrient cycling, overall crop vigor and indigo dye quality in Treatment Group 1 and Treatment Group 2 by harvest.
Yields for this crop were not recorded by the farmer due to drying and fermentation processes involved with producing the final powdered dye product, however initial dye quality assessment of Treatment Group 1 and Treatment Group 2 indicated improved pigmentation in the blue/indigo spectrum over the Control group, which contained more unfavorable green pigmentation.
Dye quality is the most relevant factor in determining crop quality and dye value in indigo, and is initially assessed by blending a ½ lb. of fresh leaves into 2 gallons of water followed by soaking fabric swatches twice for 30 minutes.
Furthermore, Treatment Group 1 and Treatment Group 2 crop exhibited more biomass density and height with darker green leaf pigmentation and reduced weed vigor at harvest.
The crop photo above was taken one month before harvest. No significant differences were observed between Treatment Group 1 and Treatment Group 2 in this trial.