Tillage and Crop Rotation Effects on Soil Health
The USDA-NRCS defines soil health, also referred to as soil quality, as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans”. They further state that “this definition speaks to the importance of managing soils so they remain sustainable for future generations”.
Understanding soil health involves assessing and managing a soil’s inherent properties of fertility, structure, microbial activity, etc. so that it functions to support optimal plant growth, both now and in the future. Management practices that may affect soil health must be assessed to determine if they do, and if so, what do they affect and what is the magnitude of the effect. These management practices must be sustainable both agronomically and economically so that they can be used over the long term.
An article titled “Reduced tillage and rotational diversity improve soil health in Missouri” by Veum et al. at the Univ. of Missouri provides the following information about the effects of reduced tillage and crop rotation choice on soil health.
• The objective of the work reported in the above article was to evaluate the effect of tillage and crop rotation diversity on soil health indicators across six regions in Missouri.
• Final datasets that included data from 4,755 fields for the tillage analysis and 4,765 fields for the crop rotation analysis were used to provide data for an evaluation of soil health benefits resulting from tillage and crop rotation conservation management practices.
• Soil health indicators that were measured are soil organic carbon (SOC–energy source for soil microbes), active carbon (permanganate-oxidizable organic carbon that reflects the quality of SOC), potentially mineralizable nitrogen (PMN–reflects size and activity of soil microbial community), and aggregate stability (physical soil health indicator that indicates ability of soil to withstand wind and water erosion forces and to sequester carbon in the soil). (Click here to access definitions of these soil health indicators.)
• Tillage categories were IT (intense tillage–fields tilled every year with high amounts of soil disturbance), RT (reduced tillage–soil disturbance occurred less frequently or with less intensity than with IT), and NT (negligible soil disturbance by tillage other than planting and fertilizer application).
• Crop rotation diversity categories were based on the number of different crop species within a rotation. They included monocrop (mainly corn or soybean), two-crop rotations (primarily a corn-soybean rotation), and rotations with three or more crop species (primarily a corn-soybean-wheat rotation, with the alternative third crop being grain sorghum, cotton, or rice).
• At the state level, tillage intensity had a significant effect on soil health parameters, with NT > RT > IT for SOC (NT 14.4% greater than IT ), active carbon (NT 14% greater than IT), and PMN (NT 11.9% greater than IT). Aggregate stability under NT (33.8%) was greater than under IT (28%). Thus, NT improved all four of these soil health indicators.
• At the state level, diverse rotations with three or more crops improved SOC and active carbon by up to 7.9% and PMN by up to 11.6%. Aggregate stability under rotations with three or more crops was 35.5% vs. < 31% under rotations with only two crops and a monocrop system. There were no significant differences in any of the soil health indicators between the monocrop system and the two-crop rotations.
• Across the state, the effect of tillage on the measured soil health indicators was nearly double the effect of rotational diversity.
• Overall, the authors stated that the results from this statewide study show 1) the potential for improved soil health that can be realized from the increased adoption of NT and RT vs. IT, and 2) the soil health benefits that may accrue from using rotation systems that include more than two crops.
Results from this work lend additional credence to the philosophy that a reduction in tillage that is conducted to produce crops will benefit soil health, and that an increase in diversity of crops that are grown in a rotation has the potential to improve soil health. Also, the use of large-scale datasets such as those used for this study offer the opportunity to assess the differing effects of management practices on soil health indicators at sites that differ in soil properties such as texture and climate factors such as rainfall.
Composed by Larry G. Heatherly, Jan. 2023, larryh91746@gmail.com