Tracking improved soil health after transitioning from GM cropping can be done using simple qualitative measures of soil health indicators in the field. Many of the following are based on Magdoff & Van Es (2009) fully cited in the Resources page. As with all assessments, soils and crops from “reference” sites should be included for comparison. These could include fencerow soils, soil and crops from fields planted to GM crops.
Indicator What to look for
Earthworms: More than 10 earthworms in top foot of surface soil (shovelful); casts and wormholes in soil peds
Surface soil color: Clearly define darker topsoil layer relative to lower horizons (subsoil)
Subsurface compaction: Wire flag easily pushed by hand into topsoil to subsoil layer
Soil tilth: Soil crumbles easily with hand manipulation; soil surface “spongy” when walking over
Water-holding capacity: Soil holds water for long periods without puddling
Erosion: After long-term and/or heavy rainfall, no gullies or rills apparent; clear or no runoff
Water infiltration: After rainfall, no ponding, no runoff evident; water moves into soil steadily; soil not waterlogged, not dry
Crop condition: Normal health dark green leaf color; can be quantified with use of SPAD meter as described in Project Outcomes page
An inexpensive refractometer can be used to measure plant sap for Brix (% sugar level); optimum health for grasses=12 and above; legumes=14 and above
Root health: Dense root biomass reaching to subsoil layer; root exterior and interior white coloration; no off-color in roots that could indicate disease or nutrient deficiency
Quantitative assessment guide:
Several labs in the U.S. and Canada can run soil health assessment tests for producers and return results with interpretive guidelines. Some laboratories are listed in Resources page. State and federal agencies in many states may subsidize costs of these assessments as means of aiding the farmer in adopting management practices for improving soil conservation and environmental quality and ultimately soil health.
Key indicators for a soil health assessment:
Standard soil nutrient analysis; Active C; aggregate stability; potentially mineralizable N; soil microbial activity (soil respiration or CO2 evolution); soil microbial biomass; soil enzyme activity
Soil health assessment test results will provide ratings or scores to help identify management practices that are promoting soil health and indicate where management can be improved. This information is important in adjusting the farmer’s management strategy during transition and beyond.