Macro and micronutrient density in staple grains and amaranth grown on conventionally versus sustainably managed silt loam soil

Project Overview

FNC19-1195
Project Type: Farmer/Rancher
Funds awarded in 2019: $9,000.00
Projected End Date: 02/28/2021
Grant Recipient: Sumner's Farm, LLC
Region: North Central
State: Missouri
Project Coordinator:
Dr. Walton Sumner, II
Sumner's Farm, LLC

Commodities

  • Agronomic: corn, peas (field, cowpeas), rye, sunflower, wheat, Amaranth
  • Vegetables: beans, cucurbits, okra, sweet corn, sweet potatoes

Practices

  • Crop Production: food product quality/safety, nutrient management
  • Education and Training: Medical education

    Summary:

    Many processes in conventional farming could cause trace element deficiencies in row crops, while crop selection and rising COlevels sustain or increase carbohydrate and calorie content. If food has a low ratio of trace elements to calories, consumers may overeat calories to acquire sufficient trace elements. The resulting nutritional imbalance would affect health, but some effects should be quickly reversible.

    We are experimenting with sustainable, “balanced” fields, amended with major chemicals as guided by soil analyses, and with organic matter and trace elements from a low cost compost of tree leaves, spent coffee grounds, and charcoal made from waste debris and chaff. Compared to control fields managed with only lime and nitrogen, our crops grow faster and yield qualitatively different produce in balanced fields. In 2018 we prepared samples of multiple high yield, nutrient-dense crops for trace element analysis, including winter wheat, amaranth, okra, sweet potatoes, and pumpkins. For most crops, we are obtaining one trace element analysis in each growing condition. To prepare for human studies of nutrient dense crops on health, we sought SARE funding to conduct additional analyses of trace elements, selected organic compounds, macronutrients, and calories from staple crops in balanced and control growing conditions.

    The low cost compost did not contain sufficient trace elements to correct soil imbalances, We therefore mixed mostly organic mineral amendments guided by recommendations from OrganicCalc, an online service, into compost, and spread nearly finished compost at 1/4 to 1/2 inch depth over balanced plots. This was substantially more expensive than coffee grounds and oak and maple leaves. One of these amendments was Azomite, which contains multiple essential trace elements as well as several potentially toxic elements, like lead. Conventional fields were fertilized using commercial products, typically starting with 12-12-12 NPK and adding urea for nitrogen, bone meal or superphosphate, and muriate of potash as needed to achieve recommended rates. Plots were tilled simultaneously in late spring to mid summer, depending on when the winter monoculture cover crop was ready to harvest. 

    Soil measurements nearly always changed in the expected direction, but OrganiCalc targets were not met consistently. OrganiCalc limits annual repletion rates for elements that would be toxic and hard to remove if overdone, such as copper and zinc. Consequently, the program may take several years to achieve the targeted level of some elements. Nevertheless, zinc levels in the balanced plots rose to 4-7 times the levels in conventional plots. Although the extension service amendment recommendation program was capable of including zinc and sulfur, it never did. Soil organic matter rose from 2-3% in the conventional plots to 3-4% in the balanced plots, which seemed remarkably modest for the amount of labor invested in the compost piles. 

    Samples were harvested, dried, ground to dust, and submitted to the Ohio State University Service Testing and Research Laboratory for elemental analysis. Several edible portions of weeds were included, as these plants’ genetics would not be directly altered by human breeding efforts, although indirect effects are possible (e.g. selection pressures from previous land management). Samples also were submitted to Midwest Laboratories for proximate analysis (e.g. caloric content, total protein) and selected vitamins, such as B2, B3, and B6. Vitamin assays are very expensive compared to elemental assays. Knowing that our soil at baseline was rich in magnesium, iron, and manganese, but relatively zinc deficient, we selected vitamins requiring at least one zinc dependent enzyme, as documented in the BRENDA enzyme database, for a step documented in the KEGG database of biosynthetic pathways. BRENDA always documents a preferred cation, but often also describes slightly slower synthesis with alternative cations, especially in microbes and fungi. This raises the possibility that “life will find a way” even in the face of seemingly stringent constraints. 

    Proximate analyses were very consistent across crops and soil management strategies: soil management did not change calories and protein per gram of dry weight to any clinically significant degree within the crops that we tested. This result may not be generalizable due to the limited number of crops and samples within crop that we tested. For now we feel comfortable comparing nutrients per unit of dry weight with the expectation that calories per dry weight are fairly constant for each crop, meaning that within crop comparisons of nutrient density depend only on nutrients per dry weight.

    Levels of zinc-dependent vitamins within crops were not significantly affected by soil management (ANOVA, p=0.7). Pyridoxine data are shown for wheat and rye, as an example with plenty of data points. See Pyridoxine data.

    Within crops, levels of major nutrient elements were generally similar across the soil management strategies. Phosphorus was the most different across soil management strategies, but probably not enough to be clinically important. See Phosphorus graph. Below the x-axis, the dagger (†) locates the soil target level in µg/ml, and the short color-coded line segments indicated measured levels in 2 soil samples. Zinc and sulfur levels were different across crops, but not particularly different across soils. 

    Within crops, levels of most trace nutritive elements were similar. Cobalt levels were essentially fixed across both crops and soil management, all values being in the remarkably narrow range between 0.83 and 0.87 µg/g, with a single outlier at 0.91, in spite of the balanced soil getting a boost from the Azomite. Molybednum levels were much higher in the balanced soil crops, presumably due to direct supplementation with Azomite and a molybdate mineral; nevertheless, this probably would have almost no impact on health in most people, due to an exquisite ability to regulate molybdenum levels across a wide range of intake values. 

    Nickel and manganese were interestingly different, however. Both are essential nutrients for plants and people, but problematic when presented in excess. Manganese is massively above target in the original soil, and should have been slightly increased by Azomite additions to the balanced soil, yet the balanced soil crops had much lower levels of manganese. See Manganese graph. 

    Nickel is especially interesting. Unlike Mn, Ni levels in our soil were well below Missouri and US farmland averages, as indicated by the marks below the x axis on the graph. Trace amounts of nickel were added in Azomite, again. Nickel levels in crops and wild edibles were consistently higher with conventional soil management than with balanced management, except in the case of winter rye, where nickel was always below the detection limit. See Nickel graph. What makes this so interesting is that for a decade or more dermatologists have been dabbling in low nickel diets as a treatment for people with systemic nickel allergy syndrome (SNAS). Low nickel diets typically start to worry about foods with a nickel content of 100 µg/kg (e.g. carrots), and may outright exclude foods exceeding 500µg/kg, such as legumes, with the general goal of limiting total daily nickel consumption. This is spectacularly constraining for the patient. If those foods are 90-95% water, then the range of worry starts at 1-2µg/g dry weight, and exclusion starts at 5-10µg/g of dry weight, as indicated by the small arrows under the attached graph. For people who believe that they suffer from SNAS that is responsive to dietary limitation of nickel, eating crops from balanced soil fields might allow a much more diverse diet if every food item has lower Ni concentration than predicted. Other specialties have started to look at dietary nickel as an exposure that might provoke some of their common diseases. One intriguing result is that Ni may alter gut flora and gut epithelial tight junctions, which prevent systemic exposure to large, potentially allergenic food molecules before those are digested well. 

    Why did these plants accumulate nickel? We have an experiment underway trying to test two hypotheses. One is that Ni is a useful substitute for some catalytic cation missing in the conventionally managed soil, but present in the balanced soil. Another possibility is that Ni is specifically sought because the plant is deploying one of the two plant enzymes known to require nickel: those are a hydrogenase and a urease. This could mean that the plants took up nickel to metabolize the urea based fertilizer applied to the conventional plots. Serendipity. 

    Levels of toxic elements were rarely elevated, but when cadmium (Cd) and lead (Pb) were elevated at all, elevations were much higher in the conventional soil crops than in the balanced soil crops. See Cadmium graph. This was particularly true for Cd in sunflower seeds and amaranth leaves. This is clinically interesting because amaranth is grown as a vegetable in west Africa and India, and is renowned for being a protein-rich crop that will grow on poor soils. This result suggests that local consumers nevertheless could pay a price in exposure to some toxic metals when vegetable amaranth grows on soils that are deficient in some respect, such as trace elements or soil organic matter. Another general way to say this is that some edible parts of these heavy metal accumulators (tobacco deserves examination, too) contain much lower concentrations of toxic metals when grown in nutrient rich soil. 

    The general theme that emerges is that many crops accumulate lower amounts of heavier nutritive and non-nutritive elements when grown in chemically balanced soil with slightly increased levels of soil organic matter. Whether this trend would be still more dramatic if SOM reached 5-10% and all trace elements were fully balanced remains to be seen. 

     

    Project objectives:

    1. Calculate ratios of trace elements and selected essential nutrients to calories in crops grown with conventional fertilizers versus balanced amendments of organic matter, major, and trace elements. The hypothesis that these ratios would be lower in conventional compared to balanced field crops was not well supported by the data collected for elements and vitamins, but could be true with further soil improvement or with other essential nutrients, such as selected amino acids. We have some evidence, not part of the original SARE proposal, that essential amino acid density increased with balanced soil management.

    2. Pilot test a year-long schedule for providing diabetic human subjects with a diet based on seas, trees, and rich row crops versus conventional diabetic diet advice and row crops. This would determine resource requirements for human studies using nutrient dense foods to prevent infections in diabetic employees, replicating a similar 2003 study of multivitamins. This particular study design is probably impractical at current scale, and will require better weed control than we achieved without herbicides. However, the nickel findings suggest that some short-term experiments are possible with SNAS patients, such as a crossover trial where gut leakage is monitored following a single meal comprised of produce from balanced versus conventional soils. 

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.