Xi Zhang and Changyoon Jeong

The southern United States, which includes Louisiana, is one of the nation’s leading commodity crop planting regions due to its intensive crop production systems. Soil is a complex and dynamic living system that is critical to agricultural ecosystem functions and crop productivity. Just as human health is essential for a prosperous life, soil health is indispensable for robust crop growth and sustainable agricultural practices. More and more producers have realized that healthy soils are more productive and lead to healthier crops. With reference to agricultural land use, soil health refers to its capacity to sustain and support the growth of crops while maintaining and improving the environment. Soil health research tends to be biased toward a biology and chemistry emphasis; however, soil health is not all biology and chemistry. Soil physical health, which is a key component of overall soil health and is often overlooked, encompasses various physical properties that are fundamental to the success of agriculture and environmental sustainability.

The soil physical environment provides information related to mass and energy transport through the soil as well as conditions affecting microbial community activity and crop growth. Soil physical health refers to the physical properties of the soil, encompassing factors such as structure, water storage and porosity, which is the proportion of pore spaces to total soil volume. These elements, by regulating water, air and heat flows, collectively influence the soil’s ability to support crop production. Understanding and managing soil physical health is essential for sustainable land use, effective water management and successful agricultural practices.

At its core, soil is a heterogeneous mixture of minerals, organic matter and pore space. The arrangement and interaction of these components give rise to soil structure, a fundamental aspect of soil physical health. Soil structure refers to the spatial arrangement of soil particles into aggregates, affecting pore spaces and overall porosity. Well-structured soils promote optimal water retention, drainage, aeration and root development, which are essential for the survival of soil-dwelling organisms, facilitating microbial activity and nutrient cycling, and enhancing crop growth (Figure 1).

Porosity, or the proportion of pore spaces to total soil volume, is critical for water infiltration, water storage, air exchange, root penetration and microbial activity. Healthy soil allows water to percolate through, preventing surface runoff and soil erosion. Healthy soil has the ability to capture a high percentage of rainfall and maximize the storage of water for crop use, which can enhance soil resilience to drought. Adequate porosity is essential for root development, as it allows plant roots to explore the soil for nutrients and water. Additionally, optimal pore volume supports beneficial soil organisms, fostering a healthy microbial community that contributes to nutrient cycling. Compacted soils, however, pose a significant threat to soil physical health. Heavy machinery and certain agricultural practices can lead to soil compaction, reducing pore space and restricting root growth. Compacted soils suffer from poor drainage and aeration, limiting the availability of oxygen to plant roots.

An optimal soil physical environment strikes a balance between water retention and drainage. Too much water retention can lead to waterlogged conditions, depriving crop roots of oxygen and promoting anaerobic microbial activity. On the other hand, poor water retention can result in drought stress for plants. A healthy soil structure with well-defined pore spaces ensures that water is retained in a manner that is accessible to plant roots while excess water drains away, preventing waterlogged conditions.

The presence of organic matter in soil is a key indicator of soil physical health. Organic matter improves soil structure by promoting the formation of stable aggregates. It acts as a reservoir for nutrients, enhances water retention and supports a diverse microbial community. However, the loss of soil organic matter in the cultivation zone has been observed in most croplands in the southern United States due to climate change, soil erosion and intensive agricultural management practices, which include residue removal and excessive tillage, for example. The depletion of organic matter is likely to pose a risk to soil functions and crop productivity.

Producers can adopt a variety of practices to maintain and enhance soil physical health and improve overall soil health. Conservation agriculture has been recommended as a solution to improve the soil physical environment and associated biogeochemical processes and promote a more sustainable form of crop production. Conservation agriculture has three principal components:

• No or minimum soil disturbance through no or minimum tillage.
• Maximum cover of living plants or residues on the soil surface.
• Diversification of plant species.

Implementing conservation practices, such as cover cropping, reduced tillage and amendments, such as manure and biochar, can increase organic matter and help preserve and enhance soil physical health, contributing to long-term agricultural sustainability.

In agriculture, soil physical health directly impacts crop productivity and the sustainability of farming practices. Recognizing the importance of soil physical health is paramount for sustainable agriculture, conservation and environmental stewardship. As we move forward, it is imperative that we adopt practices that promote and enhance soil physical health, ensuring the resilience and longevity of this precious resource, which is essential for national food security.

Xi Zhang is an assistant professor at the LSU AgCenter Red River Research Station and the School of Plant, Environmental and Soil Sciences. Changyoon Jeong is an associate professor at the Red River Research Station.

This article appeared in the winter 2024 edition of Louisiana Agriculture.

Soil structure is important for water and nutrient storage. Figure adapted from SARE "Building Soils for Better Crops."

Conservation agriculture can promote soil health. Figure courtesy of Food and Agriculture Organization of the United Nations