Effects of regenerative, organic, and conventional soil management and glyphosate on crops’ chemical composition

View the project final report

Commodities

• Agronomic: peas (field, cowpeas), amaranth
• Vegetables: beets, greens (leafy), okra, radishes (culinary), sweet corn, tomatoes

Practices

• Crop Production: fertilizers, food product quality/safety, no-till, organic fertilizers
• Education and Training: demonstration
• Farm Business Management: budgets/cost and returns
• Pest Management: chemical control, mulches - general
• Production Systems: organic agriculture
• Soil Management: composting, organic matter, soil analysis, soil chemistry
• Sustainable Communities: food quality: nutrient density & heavy metal exposure

My 2019 SARE Farmer Rancher grant project explored crops’ nutrient density as a function of soil management. An intense, expensive program to restore trace elements and soil organic matter unexpectedly decreased nickel content across diverse crops, and decreased several heavy metals in amaranth leaves and seeds, compared to conventional fertilization. Effects on selected nutrient compound densities were muted. Weed control using physical methods was challenging.

Dietary nickel at levels found with conventional fertilizers probably exacerbate Systemic Nickel Allergy Syndrome (SNAS) in a minority of susceptible individuals, and might contribute to other common diseases. Heavy metal exposure obviously should be minimized.

Other SARE-sponsored reports suggest that no-till management allows soil microbiomes to supply major and trace elements to annual crops. Concerns exist that glyphosate (Round Up) and chemical fertilizers injure the soil microbiome. A main hypothesis was that no till strategies could reduce input costs while achieving crop yield and quality comparable to balanced organic amendments: this ecologically sound practice could improve economic viability and social health. 

This proposal compared 9 crop species grown in 5 soil and weed management conditions:

1. No till with tailored surface fertilizer
2. Sheet mulch (no till/market garden) with general purpose surface fertiliser
3. Tilled with tailored fertilizer 
4. Wheat cover crop, tilled, with tailored fertilizer
5. Tilled with tailored fertilizer plus early season (pre-planting) glyphosate

The crops included 3 staple crop representatives, Sweet corn (Non-GMO) for maize and other grains, Cowpeas for legumes, and Better Boy Tomatoes for tomatoes and perhaps other Solanaceae. Each fertilizer was applied in two conditions, organic and conventional (NPK). The organic fertilizer was always accompanied by 1/4 to 1/2 inch of rich compost, or a row of compost through sheet mulch. As this is a rapid soil-building management plan, I refer to it as regenerative. Three objectives achieved were (1) measuring glyphosate content and (2) comparing yields on selected crops across the 4 conditions,  and (3) comparing elemental composition of all crops as a function of product, soil management, and weed control measure. 

Glyphosate and its degradation product, AMPA, were not detected in the three crops tested, suggesting that glyphosate applied for early season weed control generally does not persist to contaminate harvested crops. Most crop yields were higher in regenerative strips than in the corresponding NPK strips, with the exception of cowpeas. The NPK+glyphosate strip was usually particularly impaired, especially for sweet corn and amaranth, although cowpeas and okra tolerated the combination well. Glyphosate rarely affected elemental composition, and almost never in the three staple crops. Regenerative management significantly affected composition by lowering nickel (Ni) broadly; avoiding cadmium (Cd) accumulation in leafy greens, increasing molybdenum (Mo) and zinc (Zn) broadly, and slightly increasing the low iron (Fe) levels in tomatoes and sweet corn. 

The no-till attempts did not dominate other strategies, although surface application of rich compost was helpful. Early season glyphosate treatment did not contaminate the fall harvest, but appears to impair soil health. Compost and organic fertilizer counteracted the detrimental effects of glyphosate on soil health: based on other data collected on the farm, I expect that this is mostly or entirely due to the compost, not the organic salt fertilizers. I continue to observe sufficiently large elemental changes in crops to be clinically meaningful, always in favor of regenerative management rather than conventional NPK fertilisation. Leafy greens for human consumption probably should be grown in regenerative soil conditions. 

1. Estimate net profit for each crop in the different weed and fertilizer management strategies (no till, sheet mulch, till, till+glyphosate x organic, conventional fertilizer):

There was no dominating strategy. Yields generally varied inversely with input intensity, and crop responses differed across strategies. Market gardens (sheet mulch, in its second year) with rich compost and minimal fertilizer is attractive when practical.  
2. Describe how different weed and fertilizer strategies affect:
a. dietary nickel exposure from diverse crops. Weed control methods were irrelevant to nickel, but all conventional fertilisers (general purpose vegetable fertilizer or bulk urea, potassium, and phosphate) increased nickel relative to the regenerative organic strategy. 
b. dietary heavy metal exposures from amaranth leaves and seeds. Amaranth leaves were under attack by pigweed flea beetles and were not assayed, being unmarketable. None of the interventions changed amaranth seed accumulation of heavy metals. However, several leafy greens showed much more cadmium accumulation in conventional fertilizers. 
3. Quantify dietary glyphosate and aminomethylphosphonic acid (AMPA) exposure following use for weed control. Glyphosate and AMPA levels in harvested crops were not detectable. 
4. Share results in peer reviewed professional publications, conferences, a site tour, and social media. Site tours and one Youtube video have been produced so far. I still expect to publish in peer-reviewed literature and to produce additional videos based on these data.