Use of a germination bioassay to test compost maturity of willow (Salixsp.) sawdust

Abstract

Willow (Salix sp.) sawdust (WS) is used as a component of growing media in horticultural crops and potted plant production in Santa Fe, Argentina. We evaluated the use of the germination bioassay as an indicator of WS maturity/phytotox‐icity by comparing bioassays results with dry matter production of plants growing in the same substrate. Lettuce (Lactuca sativa L.) seeds were sown on filter paper moistened with extracts of WS composted for different times. Germinated seeds were counted (G) and the radicle growth (L) measured. Germination index (Gi) = G/G₀ × L/L₀ × 100, where G₀ and L₀ are values obtained using distilled water (control). The global germination index (GI) was the Gi average of the 50 and 75% extract dilution. GI of lettuce increased from 5% in the non‐composted WS to 93.3% in the WS composted for 40 days. GI did not change significantly after 40 days of composting. Calendula dry matter production increased from 8 g/plant in non‐composted WS to 17.1 g/plant in WS composted for 40 or 60 days. The addition of nitrogen and pH corrector did not affect GI of the WS growth media but they both increased calendula dry matter production to 21.1–22.7 g/plant when WS composted for 40 or 60 days was used as a growth medium.