Figure 2. Corn grown in No-till system.
Figure 2. Corn grown in No-till system.

The benefits of healthy soil in sustaining crop production are most evident when growing conditions are less than ideal. Healthy soils increase the capacity of crops to withstand weather variability, including short term extreme precipitation events and intra-seasonal drought. The extreme drought in 2012 resulted in variable yield reduction to corn and soybean production in Iowa with the worst impact on fields with conventional tillage systems (i.e., chisel plow, deep ripping, etc.). Increasingly highly variable weather conditions present increased risks to crops and require more careful attention to conservation planning to mitigate impacts on soil health and crop productivity.

Soil health is defined by the level to which it is able to continually provide multiple functions to sustain plants, animals, and humans’ lives. The complex biological, physical, and chemical interlink of a healthy soil can influence plant water availability under dry conditions,  off-field nutrient losses to nearby streams during rain events, and the availability of nutrients through nutrient cycling for food and fiber production. Furthermore, healthy soils maintain or enhance water and air quality through the improvement of soil C storage and water infiltration, and support human health and wildlife habitat.  

What influences soil health?
Soil management practices, cropping systems, and weather conditions influence soil health. Therefore, a healthy soil that is well managed can increase soil water infiltration and storage, storage and supply of nutrients to plants, microbial diversity, and soil carbon storage. Soil organic matter (SOM) is a central soil property that is heavily affected by management practices, which in turn influences soil physical, biological, and chemical functions.

The relationships between soil organic matter and management inputs such as tillage and cropping systems can be documented through the evaluation of soil health indicators (Fig. 1). Those indicators reflect the level of response of the soil system to different management inputs. Field and laboratory evaluation of these different indictors can aid in fine tuning management practices to optimize soil biological, physical, and chemical functions.

The central soil property that influences soil functions is organic matter. The organic matter component of the soil system is only a small fraction of the topsoil horizon (ranging from 1-5% or greater by dry weight depending on the soil type and other formation factors), but essential for the soil physical, biological, and chemical functions and general soil ecosystem services. The key services for production agriculture are: nutrient provision and cycling, pest and pathogen protection, production of growth factors, water availability, and formation of stable aggregates to reduce the risk of soil erosion. However, these functions are sequentially influenced by each other starting with organic matter as the building block for the well linked functions.

Tillage effects on soil health 
The increased use of intensive tillage and other management practices in row crop production systems can increase soil erosion, reduce soil health and water quality, and the capacity to achieve sustainable agricultural production systems. Soil erosion is always associated with tillage intensity, especially during the spring season when soils are most vulnerable to water erosion due to lack of vegetation or residue cover to protect the soil surface from high rain intensity.

Many factors contribute to this problem, but tillage is the prime contributing factor. Soils under modern production agriculture have lost significant amount of their carbon pool because of erosion, decomposition, and leaching. The magnitude of soil organic carbon (SOC) loss from cultivated soils in the Midwest region of the United States is estimated to be in the range of 30% to 60% of the amount present under virgin soil conditions since the conversion from prairie system in late 1800s. This loss in soil organic matter by cultivation is in part caused by the oxidation of organic matter and CO2 release in addition to losses through surface runoff and soil erosion.

Conservation practices improve soil health
Soil management and conservation practices that protect soil health are not only economically and environmentally necessary, but the right approach to sustain and increase soil resiliency. This can be achieved by adopting conservation plans that are practical, site specific and an integral component of the overall agriculture production system to achieve intended objectives.

These conservation plans would include no-tillage and reduced tillage (i.e., strip-tillage), which leave post-harvest crop residue to cover the soil surface. In addition, many soil conservation plans include practices such as cover crops, the construction of grass waterways, terraces, buffer strips, and pasture erosion control systems with manure application and soil testing.

Summary

  • The benefits of healthy soils in sustaining crop production are most evident when growing conditions are less than ideal. Healthy soils increase the capacity of crops to withstand weather variability and short term extreme precipitation events and intra-seasonal drought. 
  • Soil health functionality is highly influenced by soil organic matter, a central soil property that influences soil physical, biological, and chemical functions. 
  • The interrelationships between soil organic matter and management inputs such as tillage and cropping systems can be documented through the evaluation of soil health indicators of biological, physical, and chemical properties.
  • Best management practices that build soil health and sustain productivity are many and can lead to better ecosystem and societal services. The implementation of such practices should be considered on regional and site specific basis. Site specific adoption of different tillage and conservation practices integrated within the overall production system can effectively increase crop productivity and soil ecosystem services. These conservation practices include, but are not limited to, no-tillage, strip-tillage, cover crops, perennials, grass waterways, terraces, buffer strips, and other measures for erosion control.
  • A systems approach to conservation management of row cropping systems is important to enhance soil health and improve water quality. As an effective solution to building soil health and improving water quality, conservation practices should be an integral and essential component of nutrient reduction loss, sediment and nutrient loading plans.