How many acres: 280
What crops: Corn and Soybeans
Grazing systems: 24 acres of permanent pasture and concrete feedlot with silo and automatic feeder.
How long farm or ranch has been operating: Approximately 20 years
Crop production in Iowa is dominated by short rotations of GM corn and soybean relying on glyphosate (active ingredient of Roundup). Despite claims that glyphosate rapidly dissipates and becomes immobilized in the environment, recent studies report that over 1000 ppb of residues of glyphosate and its decomposition products, were detected in soils under intensive glyphosate use. Based on reports that glyphosate residues affect soil biology coupled with poor weed management due to glyphosate-resistant weeds, many farmers are considering a change toward non-GM cropping systems. However, little information is available on time required for dissipation of glyphosate/AMPA residues or for soil health buildup to guide farmers in assessing the sustainability of management during transition from GM to non-GM crops. We will monitor glyphosate soil residues and soil health indicators during transition to establish baselines for improvement of soil using ecologically sound soil and crop management, which will decrease contamination of surface water with glyphosate in runoff and improve soil biology. Transition may improve profitability as premiums are paid for non-GM grains. Decreasing or eliminating use of glyphosate promotes socially responsible benefits by minimizing exposure of the rural community to drifts of glyphosate spray and providing healthy ecosystems through improved soil health.
- Set up a glyphosate/AMPA monitoring protocol for residues in soils using an intensive soil sampling approach at sites prone to glyphosate drift or runoff and at sites not exposed to
- Concurrently monitor soil health by measuring selected indicators in crop management transition fields without glyphosate. Crop performance (tissue nutrient contents, N response and leaf chlorophyll, and grain yield) will also be measured and related to soil health
- Develop a guide for farmers to track soil health improvement after transition from GM
Progress Report: “Mitigation of Potential Adverse Effects of Transgenic Crop Production for Long-Term Improvement of Soil Health” February 2019
The results and preliminary information provided in this report originate from sampling sites on the Osweiler Farm, Delaware County, IA. As a reference the farm map and boundaries are provided in Figure 1. The results as presented are oriented toward sample sites on the farm, which are designated in Figure 1 to accommodate quick reference to details given in the text.
Figure 1. Michael Osweiler Farm, 2336 270thAve, Earlville, Iowa 52041 (Delaware County). Soil sampling sites are shown as blue circles. Note north transect sample sites (3W, 2W, 1W,1E) and south transect sites (1SW, 2SW, 3SW, 4SW); NFR, north fence row; SFR, south fence row; Check, corn with no Roundup.
Objective 1a: Monitor glyphosate/AMPA residues in soils.
Glyphosate analyses:Soil samples collected in July 2018 along transects established in non-GM corn and soybean fields, adjacent fence rows and one GM corn field with glyphosate, and waterways were analyzed for glyphosate and amino-phosphonic acid (AMPA) residues.
Soil test properties were determined for each sample site along the transects plus for samples from fence rows, adjacent GM corn field and waterways (Table 1).
Objective 2a: Monitor crop performance (tissue nutrient contents, N response and leaf chlorophyll, and grain yield).
Plant tissue analyses:
Nutrient analyses of leaves during active growth of corn and soybean revealed some insufficient nutrient levels that may have been affected by glyphosate soil residues (Table 2).
Leaf chlorophyll analyses:
A SPAD chlorophyll meter that detects differences in far red wavelengths related to leaf chlorophyll concentration was used to non-destructively measuring the chlorophyll content of leaves of corn and soybean in July 2018. Measurements are expressed in dimensionless “SPAD units” ranging from 0 to 80. SPAD units are highly correlated with chlorophyll content per unit leaf area and also indicate leaf N status, leaf senescence, overall plant health, and responses to environmental stresses. Our intent was to detect effects of soil residual glyphosate and possibly glyphosate drift on leaf chlorophyll content. Ten readings were taken for each entry and the average values are presented in Figures 3 and 4.
Glyphosate analyses. The effective glyphosate (glyphosate + AMPA) contents were highest for soils cropped to soybean; glyphosate content also varied among samples within crop field ranging from 82 to 227 ng/g soil (ppb) for corn and 318 to 440 ng/g for soybean (Figure 2). Glyphosate was last applied to these fields in 2015 thus showing long-term persistence (3 years+) and a highly variable distribution within a small field area. Some reports suggest that GM-corn may accumulate glyphosate in roots and release into soil, however this does not explain the higher glyphosate content detected in soybean soils as the previous GM corn was planted in 2015. More background investigation will be required to understand the variable glyphosate accumulation noted for corn and soybean.
Figure 2. Effective glyphosate residues detected in soils collected along two 400-ft transects established in 2018 corn and soybean fields. Samples collected at 100-ft intervals along each transect and position locations are numbered beginning with western (1) through eastern points (4). The corn transect was 50 ft from an adjacent GM corn field that received Roundup applications in 2018; the soybean transect was adjacent to the non-GM corn field.
Soil analyses: Soil test properties were determined for each sample site along the transects plus for samples from fence rows, adjacent GM corn field and waterways (Table 1). Most nutrient levels were within sufficiency ranges for both corn and soybean crop performance standards except for insufficient levels for boron, copper, and molybdenum in nearly all samples. Potassium was rated insufficient for soybean in two of four samples. Evidence for persistence of soil glyphosate contents based on relationships with soil contents of specific nutrients was not consistent. The lower phosphorus (P) contents at soybean sites (highlighted data in Table 1) suggest that glyphosate may be concentrated since it shares same soil adsorption sites as P. Also, lower soil pH in some samples (all soybean and some corn) may contribute less reactive glyphosate as the compound carries less charge under these conditions, may be less adsorbed, occur in soil water, and more available for plant uptake. This may be the case for the corn field receiving 2018 glyphosate applications (‘With RU’) on soil with a pH of 5.06, which likely led to the highest soil glyphosate content, and likely contributed to high glyphosate content at the entrance to the grass waterway (NW-2GN) in the north field via erosion and/or runoff. Higher soil organic carbon (SOC) at some sites may hold (adsorb) glyphosate, accounting higher glyphosate content relative to samples with lower SOC. Overall, most of the nutrient content in soils were similar suggesting adsorption of glyphosate by cation nutrients as a means of glyphosate retention in soil was likely similar in both fields.
Table 1. Soil analyses for 2018 production fields at Osweiler Farm for SARE Project.
**SOC = Soil organic carbon expressed as %; SOC X 1.75 will approximate % Soil Organic Matter content; Waterways: NW-2GN, grass waterway in northwest corner of north field near county road, sample position at fence line with neighbor’s corn field on the north; NW-2G, grass waterway in northwest corner of north field near county road, sample position near “outlet” at southern end near drainage into road ditch; S-3G, drainage from southwest slope in south field near gate into adjacent pasture, sample position near outlet at edge of field.
Plant tissue analyses: Nutrient analyses of leaves during active growth of corn and soybean revealed some insufficient nutrient levels that may have been affected by glyphosate soil residues (Table 2). However, the effect on nutrient level in corn was not consistent across samples likely due to variability in nutrient distribution across the field, even in the localized area of the transect. Nevertheless, low levels of potassium (K), zinc (Zn), and boron (B) might be affected by immobilization in soil by glyphosate thereby making these nutrients less available for uptake through corn roots. Molybdenum (Mo) was insufficient or deficient, however, based on past nutrient analyses records, these soils appear to be deficient in this micronutrient regardless of glyphosate application. The less than sufficient level of nitrogen (N) in corn is likely a consequence of immobilization of micronutrients (and insufficient Mo) required for N metabolism in corn thereby affecting accumulation within the plant. Interestingly, the corn sampled at the site most distant (‘No exposure’ or ‘Check’) from glyphosate-treated GM-corn showed sufficiency levels for all nutrients tested. Although soil glyphosate was not measured, results suggest that glyphosate drift from adjacent fields (as is the case for the other corn samples along the north transect) might intensify effects on nutrient uptake and metabolism in corn. Soybean was similarly affected by apparent nutrient immobilization by soil residual glyphosate, with more consistent affects across all samples for magnesium (Mg) and Cu as well as two of four samples for K.
Table 2. Plant Tissue (Leaf) Analysis – 2018 Osweiler Farm – SARE Project
Leaf chlorophyll analyses:
Field measurements taken on corn ear leaves (stage VT) showed an indirect relationship of residual glyphosate content on SPAD measurement in non-GM corn sampled along the transect (Figure 3). Interestingly, GM corn sprayed with glyphosate revealed higher SPAD, however, this may reflect selection for photosynthetic ability of a transgenic hybrid in presence of glyphosate. The non-GM corn showing highest SPAD readings under presumably lowest glyphosate exposure suggests that glyphosate detrimentally affects photosynthesis in this hybrid.
Figure 3. SPAD units of leaf area of the earleaf of corn measured on plants along the sampling transect in the north field and those in GM corn receiving glyphosate and in non-GM corn not exposed to glyphosate. Leaves were monitored at VT corn growth developmental stage (tasseling) during the 2018 growing season. Samples collected at 100-ft intervals along each transect, and position locations are numbered beginning with western (1 or 228 ppb) through eastern points (4 or 82 ppb).
Field measurements taken on trifoliate leaves at bloom stage similarly showed an indirect relationship of residual glyphosate content on SPAD measurement in soybean sampled along the transect (Figure 4). As observed for corn, soybean showing highest SPAD readings under presumably lowest glyphosate exposure in soil suggests that glyphosate detrimentally affected photosynthesis in this particular variety.
Figure 4. SPAD units of leaf area of the newest expanded trifoliate leaves of soybean measured on plants along the sampling transect in the south field. Leaves were monitored at R1 soybean growth developmental stage (flowering) during the 2018 growing season. Samples collected at 100-ft intervals along each transect, and position locations are numbered beginning with western (1 or 380 ppb) through eastern points (4 or 435 ppb) (See Figure 1 for the south field transect sample locations).
Objective 2b. Concurrently monitor soil health in crop management transition without glyphosate. – soil health analyses are currently in progress.
Objective 3. Develop a guide for farmers to track soil health improvement after transition from GM cropping. To be completed after compilation of 2018 and 2019 results.
Major Findings to Date:
- Soil glyphosate residues are variably distributed across a given field.
- Glyphosate residues persist in soil more than three years after last application.
- Glyphosate seems to be concentrated in soils under soybean production.
- Glyphosate movement offsite from adjacent GM-corn field occurred based on detection in waterway in north field.
- Glyphosate persistence in soil is complex involving the soil properties SOC, pH, and several nutrients; however, the properties vary among soil samples making interpretation difficult.
- Glyphosate appears to affect nutrient content and sufficiency in both corn and soybean likely due to effects of soil residues on nutrient immobilization and decreased plant uptake.
- Glyphosate residues appear to affect photosynthesis in corn and soybean based on
- Glyphosate drift may be an additive factor in reducing nutrient metabolism and photosynthesis in corn.
Educational & Outreach Activities
Progress in lessons learned, September 2018:
We are in the process of obtaining soil and crop tissue analyses and expect to learn whether impacts of glyphosate in field soils and/or drift from neighbor farm Roundup application impacts crop nutrient status as well as productivity and provide an indication of persistence of glyphosate and its breakdown product (AMPA) in soil after over two years of last application to these fields. So far, advantages include conducting a project that is probably one of a kind that will provide novel and useful information to farmers concerned about effects of continuous use of Roundup on their crop productivity and on soil health. After another growing season, we hope to have valid information for making recommendations on use of various weed management in cropping systems and effects on soil health.
This project is in progress. So far we have interest from those concerned about effects of glyphosate on pollinators, which may lead to another project on the same sites to evaluate beneficial arthropods exposed to glyphosate.