It seems like you can’t open a magazine or webpage without reading something about soil health. What exactly is soil health, and what work is being done to understand soil health in cropping systems? According to the Food and Agriculture Organization (FAO) of the United Nations, soil health is defined as the continued capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain biological productivity, promote the quality of air and water environments, and maintain plant, animal and human health. For cropland, this definition can be interpreted as the continued capacity of soil to function as a vital living system to sustain healthy crop production.
One proven way to improve soil health is to increase soil carbon and soil organic matter. The reason no-tillage practices and cover crops increase soil health is by reducing carbon loss or increasing carbon capture through photosynthesis, respectively. The five tenets of soil health are:
- Less soil disturbance;
- Diversify soil biology with plant diversity;
- Keep a living root growing throughout the year;
- Keep soil covered as much as possible; and
- Incorporate grazing.
Soil has inherent and dynamic properties. Inherent properties, such as soil texture, surrounding landscape and depth to bedrock do not change easily; these characteristics took millennia to form. Dynamic properties, on the other hand, are affected by management and can change within months or a few years. Dynamic properties include characteristics like organic matter, soil structure and water- and nutrient-holding capacity. The ultimate goal of soil health is to manage the soil so that it is not degraded for future use by maintaining and even increasing the soil’s ability to perform its basic functions. These functions include regulating water, sustaining plant and animal life, filtering and buffering potential pollutants, cycling and storing nutrients, and providing physical support for things like human structures and plant roots.
Soil biology is recognized as an important contributor to overall soil health and makes up part of the “living ecosystem” part of the definition. Fauna inhabiting soil affect and are related to many physical and chemical characteristics critical to crop production. Soil bacteria and fungi form the base of the soil ecosystem. These organisms both create soil organic matter and are part of soil organic matter. Thus, they are a critical component of healthy soil. Soil bacteria and fungi consume organic matter, as well as animal and plant residues (i.e., manure, compost and crop stubble), which helps to cycle nutrients in soil.
The bottom line is that if soil is not healthy, crop production becomes increasingly more difficult and expensive. For example, if soil microbial populations are severely decreased (through tillage, fumigation, etc.), fewer nutrients are cycled. This means that more inorganic fertilizer should be applied and there is a higher risk for nutrient loss to the environment. Without organic matter and soil carbon, soil structure becomes a limitation due to surface crusting and compaction. Fortunately, these issues can be addressed by incorporating some (or all) of the five tenets of soil health. Healthy soil is built over time and changes to management practices can (and should) be incremental. After all, Rome wasn’t built in a day!
Potato and Soil Health Projects in Idaho
Magic Valley Soil Health Project
The general belief in southern Idaho is that the “soil health movement” has been slow to take hold. Consequently, agricultural producers have been left wondering how their management practices impact soil health and productivity. Thus, a project was initiated in southern Idaho to assess how local management practices impact soil health metrics while engaging growers in the process in order to increase adoption rates. In collaboration among 10 conservation districts, growers, NRCS and University of Idaho Extension personnel, a total of 31 production fields were assessed in the summer of 2019 across southern Idaho. These fields will be assessed each year for a total of five years. Fields represented a wide range of crops, management practices and soil textures. Samples were collected for analysis of soil’s chemical, physical and biological properties.
Results from the first year of analysis showed that total microbial biomass, which is the measure of microbial populations, were highest in perennial, no-till fields. However, there were several standout results from fields planted to annual cash crops. For example, two of the sites planted to corn had high microbial populations, which is likely due to no-tillage and cover cropping practices. Future assessments will reveal whether these are indeed actual trends. Although no potato fields were assessed in the first year, we anticipate that they will be included in future years as part of the rotation.
In order to increase project engagement in 2020, growers were encouraged to take part in the “Soil Your Undies” initiative in order to evaluate their soil’s health by burying and assessing decomposition of 100 percent cotton underwear in paired fields. This study will not only help elucidate soil health parameters that are both most indicative of soil functioning and sensitive to management changes in the Magic Valley, but also empower growers to monitor their progress toward healthier soil.
Idaho Potato Soil Health Project
Up until now, we really have not had a good way to define healthy potato soils or understand how management practices affect soil health in potato cropping systems. That situation is changing due to a new national project called “Enhancing Soil Health in U.S. Potato Production Systems” that was initiated in 2019. The project seeks to establish physical, chemical and biological indicators of soil health, especially as they relate to disease management. The project will take place through 2022 and involves over 24 researchers and collaborators in 10 states. A team at the University of Idaho is leading the part of the project that focuses on evaluating the economics of management practices that impact soil health. UI and Miller Research are also partnering to conduct long-term studies on the impact of rotation length, compost, green manures and fumigation on soil health.
Another portion of the project focuses on evaluating the spatial variability of soil characteristics that are associated with disease incidence, as well as potato yield and quality. To do that, researchers have been working with cooperating growers to grid sample commercial fields in south eastern Idaho. The fields surveyed in 2019 were near Fort Hall and have a long history of potato production. Wide ranges in levels of Verticillium wilt, marketable yield, tuber size distribution and specific gravity have been documented. The project is in the process of working to relate those production variables to the measures of physical, chemical and biological characteristics at each of the sample locations. When combined with the data from other states and across multiple years, researchers hope to gain insight into what factors contribute to healthy potato soils.
Interested readers can get more information and follow progress on the potato soil health project at https://potatosoilhealth.cfans.umn.edu.
Linda Schott is a soils and nutrient management specialist based at the University of Idaho’s Twin Falls Research & Extension Center. Mike Thornton is a plant scientist and chair of UI’s Parma Research & Extension Center