Through collaboration between SHP and Utah State University, a new academic article was published in the June 2021 issue of Soil Security. This scholarly journal publishes original research in soil science and the article focuses on how SHP helps build soil security by supporting the adoption of soil health-promoting practices and monitoring and assessing soil health. Soil security is a multifaceted framework that considers soil as an integral part of addressing environmental challenges. The concept of soil security seeks to understand the human, economic and ecological aspects of securing soils in the same sense that food and water can be secured to ensure availability, quality and use for humanity. Measuring and monitoring soil health is a critical component of that goal. The researchers at Utah State University have been engaged in a series of data analysis projects in collaboration with SHP to investigate the relationships among soil health indicators, crop yield and variation over time and space to promote soil security.
Soil security is composed of five dimensions: capability, condition, capital, connectivity, and codification. Capability asks the question, “What can a soil do?”, while condition addresses, “Can this soil continue to do this?” Connectivity, capital and codification are related to how humans interact with and value soil resources and implement soil stewardship policy. Soil health assessments such as Cornell University’s Comprehensive Assessment of Soil Health (CASH), the USDA’s Soil Management Assessment Framework (SMAF), and the Haney Soil Health Tool utilize soil health indicators that represent soil processes relevant to a soil fulfilling its functional capability without constraint to its condition. Interpreting soil health indicators requires databases regionally calibrated to conditions on the ground.
The article published in the journal Soil Security is the product of an in-depth analysis of temporal and spatial variation within and across the SHP member sites. These variation measures are crucial to monitoring progress toward more secure soils and validating changes in soil condition from benchmark values following the adoption of soil health-promoting practices. This contrasts with other recent studies on soil health that have quantified soil health indicator values under differing agronomic systems; however, few have published descriptions of soil health indicator variation over time and space. These types of variation need to be accounted for because soils naturally differ across a field, from farm to farm, and over time. Many factors contribute to this variation. Some of those factors are field topography, crops and other vegetation, organisms living in the soil, climate, season, and management practices, such as tillage or equipment traffic patterns. Soil sampling and laboratory analysis methods are also sources of variation in soil health indicator values. To minimize these human sources of variation, SHP exercises diligent effort to standardize soil sampling and analysis procedures.
The researchers at Utah State University found that soil health indicators have different temporal and spatial variation magnitudes. Their study reported that not all soil health indicators have the same level of variation across a field or over time at the same sampling location. That in-depth understanding will allow growers and researchers to interpret soil health assessments better. For example, some soil health indicators of biological processes, such as soil microbial activity, have much higher temporal variation (inherent change over time) than soil organic matter content, which changes slowly. Physical soil health indicators, such as the components of available water holding capacity related to soil texture, do not readily change over time. In contrast, soil wet aggregate stability, a measure of how well soil aggregates remain intact when wetted, varies to a greater degree across a field and in time because of soil management, crop type, precipitation, and temperature. These examples are illustrative of patterns similarly observed in a dozen other soil health indicators.
Spatial (a) and temporal (b) variation calculated at each SHP member site for biological, chemical, and physical soil health indicators. Abbreviations: ACE, autoclaved citrate extractable soil protein; ActC, active carbon; AggStabl, aggregate stability; AWC, available water content; OM, organic matter; Resp, microbial respiration (4 d); WEOC, water-extractable organic carbon; WEON, water-extractable organic nitrogen.
This inherent variation in soil health indicators complicates interpreting a soil health assessment when many indicators are sampled simultaneously. For growers and researchers, this means that these different levels of variation may need to be accounted for to validate whether a change is taking place following a management shift that adds cover crops, for example. This study’s preliminary conclusion was that monitoring soil health needs to be scheduled consistently to minimize seasonal variations. Additionally, some indicators known to have higher variation levels should be sampled more regularly, such as measuring aggregate stability every other year while measuring ones that slowly change, such as soil organic matter, every three to five years, following a management change. The Utah State University researchers will soon also publish a study investigating whether taking temporal variation into account supports identifying changes in soil health indicators following cover crop adoption.
For further reading, see the published article at https://doi.org/10.1016/j.soisec.2021.100005