Soil Health 101

This is an annotated bibliography reviewing previous research and literature conducted and created by the Sustainable Agriculture, Research, and Education program (SARE).

SARE EDS21-27. (03/31/2023). Principles of Soil Health in a Variety of Market Farming Frameworks: Best Practices from the Field with Experienced Regenerative Farmers. https://projects.sare.org/project-reports/eds21-27/

The No-Till Market Garden Podcast has 9,000 weekly listeners and 86 interviews with experts on sustainable farming. They also have over 200 YouTube videos teaching no-till farming methods. The project aims to be a top resource for small-scale growers, promoting soil health and profitable, eco-friendly farming. They cover topics like mulching, keeping soil covered, minimal soil disturbance, plant biodiversity, and smart use of cover crops. Future plans include studying compost's return on investment and the social impacts of local farming resources.

SARE GNC20-312. (11/30/2023). Exploring how farmers' perceptions of soil health affect their management decisions. https://projects.sare.org/project-reports/gnc20-312/

This project aims to understand how farmers in SW Michigan conceptualize soil health and how this impacts their farming decisions. A survey was sent to over 1000 farmers and 20 were selected for interviews. Of the farmers interviewed, 50% use cover crops, and 50% do not. The project seeks to determine the misalignment of the communication between farmers and ag advisors regarding soil health. To do this, farmers filled out a workbook to illustrate and describe their personal soil health models and what management practices they most closely associate with this concept. These workbooks were used to better understand the cultural connection with farming and the perceptions farmers have of their own management practices. It is important to incorporate words and phrases local farmers use in education materials to add a cultural context to education and connection. It was found that 90% of Michigan farmers believe healthy soils can increase yields and drought resilience, but adoption of regenerative practices is low. Recommendations include improving soil health tests and linking them to farmer experiences, focusing on economic benefits of crop resilience, and building trust through workshops and online discussions.

SARE GW06-011. (12/31/2008). Soil community structure, function, and spatial variation in an organic agroecosystem. https://projects.sare.org/project-reports/gw06-011/

This project studied soil organisms and edaphic properties across an organic vegetable farm. It found that soil organisms, which contribute to all essential soil functions, can be indicators of productive soil and good management. However, these organisms are influenced by both dynamic and inherent soil quality. The study found higher microbial activity in coarser soils and a positive correlation between the dominant presence of sand + silt with bacterial and fungal-feeding nematodes. The project used geostatistics to develop maps of soil organisms and edaphic properties, develop biological indicators, recommend sampling methods, optimize farm productivity, and share results with growers. The study concluded that physical and chemical data do not necessarily indicate soil biological populations, but within certain ranges, they can affect biological variations. Recommendations included addressing soil acidity, smoothing organic matter distribution, and resting intensively farmed areas.

SARE SW20-919. (12/31/2023). Biointensive no-till farming in California: farmer-driven research and education on soil health, water efficiency and economic resiliency. https://projects.sare.org/project-reports/sw20-919/

Small-scale farmers struggle with limited land and capital investment. No-till farming can help, but the benefits have not been well-studied. The only proof of no-till being beneficial is the increased trend of practice adoption across the state of CA. A group of researchers and farmers studied how no-till farming affects soil health, water use, farm economics, and response to climate change. The project is led by farmers and focuses on their needs, and they'll start a 'community science' program to share knowledge. The project aims to understand how farmers relate to the principles of soil health and how their perceptions influence farming practices across California. The project will also look at how soil acts as a link between farmers and their communities. To do this, researchers interviewed farmers on their land and connected their perceptions to the physical management practices, to a physical map of their property. From there, a soil sampling plan is created, and samples were collected to analyze for soil organic carbon. Preliminary results show that no-till farming increases soil carbon levels over time, improves soil structure and water retention, and boosts fungal species richness and carbon cycling. It is believed that all of these results are a product of shifting pore architecture from a tilled environment to a no-till environment. Another great discovery of this project is that while compost application can account for relative changes in soil carbon quantities by management system, it does not explain the shift in the division of soil carbon across particle size within those systems.

SARE SW96-016. (12/31/1999). Tillage practices for improving nitrogen cycling and soil quality. https://projects.sare.org/project-reports/sw96-016/

The study explores yield and soil health with different tillage methods. Microbial biomass activity decreases after discing and roto-tillage. Three treatments tested: five-step minimum tillage, minimum-till chisel, and sundance (shallow reduced tillage). Lettuce and corn yields varied by treatment and year. Sundance treatment had highest inorganic N levels and microbial biomass C in top 10cm of soils. Yields were highest when both chiseling and ripping were included. Soil microbial biomass C increased after fall cover crop + compost additions. Yield was higher in lettuce crops following cover crops and compost. No effects on weed control observed, but treatments with + OM had fewer weeds. Single application of compost alone did not affect plots.

SARE SW99-008. (12/31/2003.) The transition from conventional to low-input or organic farming systems: soil biology, soil chemistry, soil physics, energy utilization, economics, and risk. https://projects.sare.org/project-reports/sw99-008/

A 12-year comparison of farming systems shows organic farming doubled soil carbon in 10 years and conventional farming was least efficient at storing Nitrogen. Agriculture, the biggest water consumer, is the main source of polluted runoff in California. Farming must change production to cut costs or increase yields due to decreasing prices received by farmers and increasing farm input costs. Alternative agriculture practices are rising due to environmental concerns, resource consumption, health risks, and rural economic decline. The Sustainable Agriculture Farming Systems (SAFS) project focuses on long-term sustainability and short-term productivity. Results show low-input and organic yields can maintain levels close to conventional methods, with reduced pesticide use and multiple benefits from cover-cropping.

Sustainable Agriculture Research and Education. (2021) Building soils for better crops. https://www.sare.org/resources/building-soils-for-better-crops/

Chapter 1. Organic matter - the key to soil health.

Soil consists of mineral solids, water, air, and organic matter. Soil health is equivalent to soil quality and requires good tilth for root development. Acidic soils are rich in clay and aluminum. Soil degradation results from erosion and reduced organic matter. Improving degraded soil requires understanding and action, as does maintaining healthy soil. Better soil management can lead to pest reduction.

Chapter 2. Organic matter - what is it and why is it so important?

Organic matter, consisting of living organisms, fresh residue, and humus, is vital for soil health. Humus improves soil properties, holds essential nutrients, and prevents harmful chemicals from damaging plants. Black carbon or charcoal, a stable form of carbon, aids in maintaining cation exchange and biological activity. Soil organic matter is critical for global and regional cycles, and its decrease leads to issues like erosion, diseases, and fertility problems in plants. Organic matter content in agricultural topsoil is usually 1-6%. Plants require eighteen chemical elements for growth, most of which are obtained from the soil. Soil organisms conduct mineralization, or, decompose organic matter into simpler inorganic forms that plants can absorb, providing essential nutrients. A diverse community of organisms protects against pests and fertility problems. Organic matter reduces pesticide leaching and stores more carbon than all plants, animals, and the atmosphere.

Chapter 3. The amount of organic matter in soils.

Soil organic matter (SOM) levels are influenced by factors such as temperature, precipitation, soil texture, vegetation type, and soil conditions. Higher temperatures and more rainfall generally increase SOM levels, while fine-textured soils with high clay and silt percentages also have higher SOM content. Organic matter is protected in soils through chemical bonds, physical protection inside small aggregates, conversion into stable substances, restricted drainage, and char production. Decomposition rates are limited in fine-textured soils due to smaller pores and less oxygen. SOM accumulation is higher in wet soil environments and areas receiving runoff, like areas of lower elevation. Root residue contributes more to particulate organic matter than above-ground residues. Erosion, tillage, crop rotation, and nitrogen levels can affect SOM levels. Increasing SOM requires sustained effort and is difficult in well-aerated soils. Soil organic matter tests require context for interpretation.

Chapter 4. The living soil.

Charles Darwin acknowledged earthworms' significance in 1881. Soil organisms and roots respire, absorbing oxygen and releasing CO2, influencing decomposition and nutrient availability. Agricultural systems aim to boost beneficial organisms while reducing harmful ones. Soil microorganisms decompose organic matter, provide nitrogen, detoxify chemicals, suppress diseases, stimulate plant growth, and are antibiotic sources. Bacteria require aerated, pH-neutral soils, increase nutrient availability, and conduct nitrogen fixation. Fungi cause plant diseases, decompose fresh organic residues, are less sensitive to acidic soils, require oxygen, and form symbiotic relationships with plants. Soils with regular disturbance have more bacteria, while untilled soils have more fungi. Protozoa eat bacteria, fungi, other protozoa, and organic molecules. Nematodes are multicellular worms that live in water films around soil aggregates, feed on fungi, bacteria, and protozoa, and can parasitize and kill insects. Earthworms restore soil fertility, mix organic matter into the soil, allow water infiltration, and thrive in aerated soils with lots of organic matter. Plant roots indicate soil quality, and a diverse population of soil organisms maintains a balanced system that can prevent disease organisms or parasites from becoming major plant problems.

Chapter 5. Soil particles, water, and air.

Soils are 50% solid particles and 50% pore space that houses water and air. Soil texture affects physical, biological, and chemical processes. Soil organisms live in pores, which management practices can alter. Water in soil is affected by gravity and its affinity for water molecules. Pore size influences the leaching of pesticides and nitrates, plant water availability, and infiltration capacity. Strong aggregation is vital for moisture extremes. Good soil management enhances resilience to weather extremes.