Soil is one of the most crucial components in supporting life, food security, and ecosystem services on Earth. As a key part of critical zone that determines agricultural and environmental sustainability, soils transform and supply water, energy, nutrients, and organic materials and moderate supply of water and nutrients for plants. Soil is where biological and chemical transformations occur, and it is the domain that sustains all flora and fauna ecosystem cycles. Meanwhile, changing societal food and energy demands, land use and climatic conditions are imposing ever greater stresses on soil. Recognizing the importance of soils for food security, agriculture, and in mitigation of climate change and sustainable development, the United Nations declared the International Year of soils, 2015 (IYS 2015) to raise awareness worldwide. The protection and stewardship of this crucial resource can be only assured through a better understanding of soil processes at different space and time scales.

Soil physics plays a critical role in understanding soil resources and functions, and it has made outstanding progress in recent years and not considering soil anymore as a homogeneous porous medium composed of various primary and secondary particle sizes but better understanding the roles of soil structure and flux heterogeneity across scales for compensating extreme events and anthropogenic impacts. Storage, redistribution, transport and transformation processes of water, heat and chemicals are understood for relatively small-scale systems in the vadose zone. However, Nielsen (1997) stated with regard to the vadose zone, “it is there but nobody cares.” Since then, much has been learned and documented in the “Vadose Zone Journal” among other esteemed outlets.

Whereas traditionally soil physics has largely been developed for and continues to contribute to agricultural sciences such as in irrigation management, nutrient management,  and crop growth, its scope has evolved over the last 30 years, with relevant applications to many other disciplines in earth and environmental sciences, including ecology, hydrology, geology, biogeochemistry, engineering, climate science, and plant sciences. This trend of an evolving soil discipline is especially recognizable when reviewing this Regional Project over its past, as it has adapted from a strictly soil physics domain with fundamental physical applications towards transdisciplinary approaches and outcomes. This change has been critical as soil continues to undergo profound changes due to human activities such as land use change and agricultural intensification.           

Despite considerable scientific advances in soil physics research in general and the efforts made by this multistate team in particular (described above), knowledge gaps still remain in measurement and modeling, transfer across spatio-temporal scales, and multidisciplinary integration of results. Without addressing these knowledge gaps,  we would not be able to meet contemporary and emerging societal challenges and needs, and to respond and engage across the earth and environmental sciences in central issues such as climatic change, ecosystem services, food security, and energy production (see Wendroth et al., 2018 and contributions therein). To advance soil physics as a central solution for dealing with this multitude of socio-environmental challenges, we will develop and improve measurement tools and process-based models for quantifying soil ecosystem processes. Statistical analyses and modeling will help us to disentangle processes and their relationships at different scales to improve our ability to transfer information between scales. Finally, we will use our skills as soil physicists and environmental physicists and the knowledge we have gained through decades of studying this critical zone to advise and participate in national and international interdisciplinary projects to impart the importance and management of soil resources.         

The collaborations created and fostered through the multistate research program have spanned generations of soil physicists and hydrologists, and it is the collective opinion of the participants that multi-institutional and multi-PI collaborations have been significantly enhanced because of the multistate program. Indeed, maintaining the focus of such a large group would not be possible without this multistate program. Using these collaborations, significant benefits have been realized through understanding soil physics principles and applying them to agricultural and environmental sustainability of soil resources, protecting ground and surface waters, improving agricultural production, and promoting ecosystem biodiversity, to name only a few areas. Members of this group tend to form and re-form around new multi-investigator programs to address emerging critical questions for sustainable solutions to grand challenges. This flexible and synergistic approach has been extremely productive, and it encourages a rich pollination of ideas and solutions to complex problems. The multistate committee structure is a convenient and efficient platform for establishing national research collaborations, validating approaches and techniques, pooling data, creating rigorous peer reviews, sharing equipment and developing the next generation of highly-trained soil scientists, environmental scientists, and engineers. This proposal seeks to maintain the ties between this extremely productive and creative group that, without the W4188 committee, would not be as focused on national needs research. The proposal also highlights our efforts to improve environmental monitoring, implement basic soil physics research, reach out to a broader scientific community (e.g., plant science, ecology, chemistry, and microbiology), and educate and communicate to stakeholders and colleagues within and outside our traditional disciplines.

Soil is one of the most crucial components in supporting life, food security, and ecosystem services on Earth. As a key part of critical zone that determines agricultural and environmental sustainability, soils transform and supply water, energy, nutrients, and organic materials and moderate supply of water and nutrients for plants. Soil is where biological and chemical transformations occur, and it is the domain that sustains all flora and fauna ecosystem cycles. Meanwhile, changing societal food and energy demands, land use and climatic conditions are imposing ever greater stresses on soil. Recognizing the importance of soils for food security, agriculture, and in mitigation of climate change and sustainable development, the United Nations declared the International Year of soils, 2015 (IYS 2015) to raise awareness worldwide. The protection and stewardship of this crucial resource can be only assured through a better understanding of soil processes at different space and time scales.

Soil physics plays a critical role in understanding soil resources and functions, and it has made outstanding progress in recent years and not considering soil anymore as a homogeneous porous medium composed of various primary and secondary particle sizes but better understanding the roles of soil structure and flux heterogeneity across scales for compensating extreme events and anthropogenic impacts. Storage, redistribution, transport and transformation processes of water, heat and chemicals are understood for relatively small-scale systems in the vadose zone. However, Nielsen (1997) stated with regard to the vadose zone, “it is there but nobody cares.” Since then, much has been learned and documented in the “Vadose Zone Journal” among other esteemed outlets.

Whereas traditionally soil physics has largely been developed for and continues to contribute to agricultural sciences such as in irrigation management, nutrient management,  and crop growth, its scope has evolved over the last 30 years, with relevant applications to many other disciplines in earth and environmental sciences, including ecology, hydrology, geology, biogeochemistry, engineering, climate science, and plant sciences. This trend of an evolving soil discipline is especially recognizable when reviewing this Regional Project over its past, as it has adapted from a strictly soil physics domain with fundamental physical applications towards transdisciplinary approaches and outcomes. This change has been critical as soil continues to undergo profound changes due to human activities such as land use change and agricultural intensification.           

Despite considerable scientific advances in soil physics research in general and the efforts made by this multistate team in particular (described above), knowledge gaps still remain in measurement and modeling, transfer across spatio-temporal scales, and multidisciplinary integration of results. Without addressing these knowledge gaps,  we would not be able to meet contemporary and emerging societal challenges and needs, and to respond and engage across the earth and environmental sciences in central issues such as climatic change, ecosystem services, food security, and energy production (see Wendroth et al., 2018 and contributions therein). To advance soil physics as a central solution for dealing with this multitude of socio-environmental challenges, we will develop and improve measurement tools and process-based models for quantifying soil ecosystem processes. Statistical analyses and modeling will help us to disentangle processes and their relationships at different scales to improve our ability to transfer information between scales. Finally, we will use our skills as soil physicists and environmental physicists and the knowledge we have gained through decades of studying this critical zone to advise and participate in national and international interdisciplinary projects to impart the importance and management of soil resources.         

The collaborations created and fostered through the multistate research program have spanned generations of soil physicists and hydrologists, and it is the collective opinion of the participants that multi-institutional and multi-PI collaborations have been significantly enhanced because of the multistate program. Indeed, maintaining the focus of such a large group would not be possible without this multistate program. Using these collaborations, significant benefits have been realized through understanding soil physics principles and applying them to agricultural and environmental sustainability of soil resources, protecting ground and surface waters, improving agricultural production, and promoting ecosystem biodiversity, to name only a few areas. Members of this group tend to form and re-form around new multi-investigator programs to address emerging critical questions for sustainable solutions to grand challenges. This flexible and synergistic approach has been extremely productive, and it encourages a rich pollination of ideas and solutions to complex problems. The multistate committee structure is a convenient and efficient platform for establishing national research collaborations, validating approaches and techniques, pooling data, creating rigorous peer reviews, sharing equipment and developing the next generation of highly-trained soil scientists, environmental scientists, and engineers. This proposal seeks to maintain the ties between this extremely productive and creative group that, without the W4188 committee, would not be as focused on national needs research. The proposal also highlights our efforts to improve environmental monitoring, implement basic soil physics research, reach out to a broader scientific community (e.g., plant science, ecology, chemistry, and microbiology), and educate and communicate to stakeholders and colleagues within and outside our traditional disciplines.