New study finds that conservation tillage increases corn yields in semi-arid rainfed cropland by almost 10%

Every year, the world loses 25 billion tons of agricultural soils to erosion. A major driver of soil loss is tillage practices, or how farmers prepare the soil for seed planting. In the US Midwest, tillage-based erosion is estimated to cost more than 2 billion dollars in economic losses each year. Researchers with the NASA Harvest consortium recently co-authored a study analyzing how modified tillage practices that decrease soil erosion can impact crop yields.

One way to preserve soil health is to change how farmers prepare their fields for planting. Tillage involves turning the soil to mix it with vegetation cover that was formerly on the ground while no-tillage (or “no-till”) refers to the slicing of soil and the placing of seeds within the slices. The latter method has little to no soil disturbance, whereas the former significantly disturbs the soil leading to increased erosion. Between these methods exist a number of other techniques with varying levels of soil disruption. No till is often grouped alongside other less disturbance-inducing methods in a category called low till practices.

Low till practices have been shown to reduce soil erosion as well as improve soil health, but concerns about negative yield impacts can limit adoption rates. Previous research shows mixed results as studies have been smaller in scale and conducted in varying environments with different water availability.

This recent study can help alleviate farmer’s concerns as it explores the impact of low tillage agriculture across 4 western US Corn Belt states (North and South Dakota, Nebraska, and Kansas) with a variety of management practices.

Map of the study area is outlined in blue. States outlined in black are central US Corn Belt states analyzed in the 2019 Deines et al study.

It expands upon previous research led by Jill Deines, a NASA Harvest researcher and co-author of the newest study. In 2019, Deines found that low tillage led to a modest yield increase of 3% for corn in the central US Corn Belt, a much more humid region than the 4 states examined for this study. By looking at a more arid region this time, the authors could explore how the effects of tillage interventions varied in respect to soil water availability, specifically between rainfed and irrigated fields.

The study authors used USDA crop maps to identify corn fields across 4 states. They then used previously published tillage maps showing how each field was tilled between 2008-2020 and selected those which had been consistently high or low till during the study period. To account for the impact of water, the authors also marked each field as being rainfed or irrigated. Finally they used a crop yield model previously developed by another co-author, NASA Harvest researcher David Lobell, and used by Deines for her analysis of the central US corn belt to estimate yields for each selected field.

The results provided significant insight into how conservation tillage impacts yields across different types of watered cropland. After analyzing the results over the past twelve years, the authors found that long term adoption of low tillage practices led to no statistically significant impact on irrigated fields, however they found that yields increased by almost 10% in rainfed fields.

The authors write that this is due to increased water infiltration and retention that is enabled by low till practices. With irrigated fields receiving more consistent water, these factors would make less of an impact on yields. Rainfed fields, however, benefit from anything that allows them to store any rain that falls. These results are particularly promising for regions that experience intense water stress, and they support the implementation of conservation tillage as both a water saving and yield increasing technique in such locations.

The study also examined counties within the study area which could see improved yields if they increased adoption of low till practices. These counties were located mainly within the northern part of the study region. The authors note that developing partnerships between researchers, farmers, and extension agents to pass along the findings of this and similar studies is crucial in changing current practices and allowing farmers to better manage their fields. By identifying these counties where interventions could have the greatest impact, outreach efforts can be most effectively targeted.

a). Percentage of fields per county that have adopted low till methods.
b). Estimated yield impacts that each county would experience if they switched their high till rainfed fields to low till methods.
c). Authors identified 41 “high priority” counties with percentages of low till rainfed fields lower than the regional average as well as an estimated yield increase from switching from high till to low till.