Why care about soil health?
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 as well as drought during the growing season.
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 (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 human 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 water infiltration and storage in the soil, and they support human health and wildlife habitat.
What affects 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 (see chart). 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% to 5% or greater by dry weight depending on soil type and other formation factors).
The point is, organic matter is essential for the soil’s physical, biological and chemical functions, and the general soil ecosystem services.
The key services of healthy soil 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 is key factor
The increased use of intensive tillage and other management practices in row crop production can increase soil erosion, reduce soil health and water quality, and decrease the capacity to achieve sustainable agricultural production systems. Soil erosion is always associated with tillage intensity, especially during spring 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 amounts 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 the prairie system in the late 1800s.
This loss in soil organic matter by cultivation is in part caused by the oxidation of organic matter and the release of carbon dioxide, in addition to losses through surface runoff and soil erosion.
Soil management practices that protect soil health are not only economically and environmentally necessary, but also 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 (strip tillage), which leave postharvest crop residue to cover the soil surface. In addition, many soil conservation plans include practices such as cover crops and construction of grass waterways, terraces, buffer strips and pasture erosion control systems with manure application and soil testing.
Al-Kaisi is a professor of agronomy specializing in soil and water management and environment at Iowa State University.
This article published in the April, 2016 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2016.
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