Q: Please define the primary factors that affect soil health.
A: Wayne Fredericks, farmer in Osage, Iowa: In row crop farming in my area of northern Iowa, the intensity of tillage, presence of soil cover and year-round living roots, use of multiple plant species, and, if available, the integration of livestock all affect soil health.
A: Doug Wolf, environmental safety technical expert, Syngenta: Soil health integrates physical, chemical and biological factors that impact productivity, environmental quality and profit potential. It’s assessed through multiple, interconnected indicators. I consider soil organic matter (SOM) to be the most significant soil health indicator because it plays a primary role in numerous soil functions such as soil structure, water use, nutrient cycling and availability, agrichemical fate and transport, and biological activity and biodiversity. SOM is sensitive to land use and agronomic management practices such as tillage, cover crops and crop rotation.
Q: How does tillage affect soil health and what are the benefits of reducing tillage?
A: Fredericks: Tillage reduces soil carbon, which was verified in the recently released results of a 12-year study conducted at Iowa State University. On my farm, after discontinuing full-width tillage over 20 years ago, I have seen an increase in SOM at a rate of 0.1% per year.
A: Wolf: Conventional tillage generally has a detrimental impact on soil health, especially compared to reduced tillage because it causes SOM to decompose more rapidly and disrupts the soil structure of the soil root zone. Continual conventional tillage tends to accelerate soil erosion, which has an adverse impact on soil health. Reduced tillage has been associated with increased aggregate stability, SOM, water-holding capacity, soil microbial and fungal abundance and biodiversity, reduced runoff and soil erosion, as well as economic benefits such as reduced fuel and labor costs.
Q: How can a farmer measure the impact soil health has on yield and profit potential?
A: Fredericks: I shared 18 years of digital yield and weather data with the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS), Ames, Iowa. This team of researchers did a deep-dive analysis of my farm’s information, and they were able to document reduced yield variability and improved water-use efficiency within the fields, which translates to overall improvements in yields and profitability.
A: Wolf: Syngenta is assessing the impact of soil health on yield and profit potential through projects like Bin Buster led by the Digital Agriculture Solutions Team. The Bin Buster project assesses on-farm agronomic productivity and profitability on two commercial farms in Illinois growing corn under selected treatments. I am part of a team collaborating within the Bin Buster project to evaluate soil health and sustainability parameters on both farms using Cornell’s Comprehensive Assessment of Soil Health analysis, which examines physical, chemical and biological soil health indicators. We will relate these indices to SOM, farm productivity and profitability. Tools such as the Predictive/Retrospective Soil Health Economic Calculator use soil health indices to conduct a partial budget analysis and an economic cost/benefit analysis associated with adopting soil health practices.
Q: What are some strategies to increase organic matter in soil, and why is that important?
A: Fredericks: First, farmers should look to eliminate tillage. I went to no-till soybeans and strip-till corn. You can also add cover crops to the rotation and look to plant into green cover crops, thus extending the time for them to accumulate biomass. This is important because SOM is the key to healthy, resilient soil.
A: Wolf: Strategies to increase SOM typically center on residue management systems coupled with stover and compost/manure management to yield a net accumulation of SOM. SOM, which is typically less than 5% by mass of agricultural soil, increases soil fertility as it acts as a reservoir for macronutrients and trace elements that release during microbial degradation, improving soil structure and aggregation, increasing available water-holding capacity, and enhancing soil biological diversity and abundance.
Q: How does soil health affect available water for cropping systems?
A: Fredericks: Looking back at the 18-year study by USDA ARS of my farm’s data, the biggest revolution was an improvement in water-use efficiency. Because my soil health was improving, I was raising more bushels per inch of water as the years progressed. This improvement far exceeded the change in normal trend-line yields, and the key was focusing on organic matter.
A: Wolf: Soil aggregate stability is a critical indicator of soil health. Soil aggregate stability is largely dependent on SOM and biological activity and typically increases as they increase. Stable soil aggregates increase plant-available water by increasing the amount of pore space, water infiltration and the soil’s water-holding capacity, contributing to decreased runoff and erosion. Stable soil aggregates and the associated pore space also promote crop root growth and penetration within the soil root zone.