Tillage exacerbates the vulnerability of cereal crops to drought

Abstract

Soils used for crop production cover 15.5 million km 2 and almost all have been tilled at some point in their history. However, how the changes in soil depth and soil properties associated with tillage affect crop yields is unclear. Here, we show that tillage on slopes thins soils and reduces wheat and maize yields. At the landscape scale, tillage erosion gradually reduces crop yields as the duration and intensity of tillage increase. Over the next fifty to 100 years, the overall yields are likely to further decline as modern mechanized agriculture accelerates the process of tillage erosion compared to centuries of non-mechanized tillage. Arresting this downward trend will require more widespread adoption of no-tillage practices and avoidance of downslope cultivation. The downward pressure on landscape-scale yields due to tillage erosion is expected to be amplified by climate change-induced increases in dry spells during crop growth.

Soil erosion on arable land: An unresolved global environmental threat

“…As soils are moved downslope, there are areas of the field that lose soil, and others that gain material. Soil depths on hill crests can be reduced to zero with farmers sowing crops into the soil parent material (Fiener et al, 2018), impacting negatively on crop yields, while on foot slopes, along thalwegs and in depressions, soils become deeper leading to a positive change in crop production (Öttl et al, 2021; Van Loo et al, 2017; Quinton et al, 2022). This results in often dramatic changes in soil colour at different landscape positions (Figure 2(i)).…”

“…Reductions in soil water availability caused by soil thinning are more difficult to remedy without supplemental irrigation, although some enterprising farmers carry soil back up the slope to rebuild their soils (Lobb, 2011). Thinner soils are also less resilient to climatic shocks: in times of drought as less water can be stored and used by plants (Quinton et al, 2022) and in times of excess rainfall the lack of soil water storage increases the risks of flooding. Thickening soils may see improved yields as they can hold more water and contain more nutrients.…”

“…The extend of this process is regulated via carbon stabilisation mechanisms. These depend on: the geochemical composition of former subsoil which is mixed into the topsoil during tillage operations (Berhe et al, 2012); and carbon inputs from plants (crops), which might be negatively affected due to lateral nutrient loss and decreasing soil water storage capacity (Quinton et al, 2022). Part of the soil organic carbon might be lost during transport (Jacinthe et al, 2002) within surface runoff and also shortly after deposition (van Hemelryck et al, 2010).…”

“…However, the impact of soil erosion is closely related to the position of soils in the landscape, with water, wind and tillage erosion all leading to soil thinning or thickening at different landscape positions (Figure 1). This contributes to the development of soil patterns across landscapes and influencing heterogeneity of crop yields (Quinton et al, 2022), the exchange of water and nutrients, soil biodiversity, carbon storage and air quality.

Figure 1.Schematic illustration of erosion processes in differently managed agricultural landscapes. Soil erosion mostly leads to a redistribution of soil within (agricultural) landscapes and losses to other ecosystems.

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“…However, the impact of soil erosion is closely related to the position of soils in the landscape, with water, wind and tillage erosion all leading to soil thinning or thickening at different landscape positions (Figure 1). This contributes to the development of soil patterns across landscapes and influencing heterogeneity of crop yields (Quinton et al, 2022), the exchange of water and nutrients, soil biodiversity, carbon storage and air quality.…”