Soil erosion and agricultural sustainability

Abstract

Data drawn from a global compilation of studies quantitatively confirm the long-articulated contention that erosion rates from conventionally plowed agricultural fields average 1-2 orders of magnitude greater than rates of soil production, erosion under native vegetation, and long-term geological erosion. The general equivalence of the latter indicates that, considered globally, hillslope soil production and erosion evolve to balance geologic and climate forcing, whereas conventional plow-based agriculture increases erosion rates enough to prove unsustainable. In contrast to how net soil erosion rates in conventionally plowed fields ( approximately 1 mm/yr) can erode through a typical hillslope soil profile over time scales comparable to the longevity of major civilizations, no-till agriculture produces erosion rates much closer to soil production rates and therefore could provide a foundation for sustainable agriculture.

Fig. 1.

Comparison of rates of soil erosion from agricultural fields under conventional agriculture (n = 448) and geologic erosion rates from low-gradient continental cratons (n = 218), soil-mantled landscapes (n = 663), and alpine terrain (n = 44) (sources are listed in SI). Soil erosion rates reported in various units were converted to equivalent lowering rates assuming a soil bulk density of 1,200 kg/m³. Shaded area represents range of the USDA. T values (0.4–1.0 mm/yr) were used to define tolerable soil loss.

Fig. 2.

Probability plots of rates of soil erosion from agricultural fields under conventional (e.g., tillage) and conservation agriculture (e.g., terracing and no-till methods), with erosion rates from areas and plots under native vegetation, rates of soil production, and geologic rates of erosion (a composite distribution of the data for cratons, soil-mantled landscapes, and alpine areas in Fig. 1). Data sources for agricultural and geologic rates are the same as for Fig. 1. Shaded area represents range of USDA. T values (0.4–1.0 mm/yr) were used to define tolerable soil loss.

Fig. 3.

Box-and-whiskers plot showing the range of reported increases in erosion rate for studies reporting direct comparisons of erosion under conventional agriculture vs. native vegetation for comparable settings (n = 46, median = 18, mean = 124, minimum = 1.3, maximum = 1,878). Data include studies that reported both rates individually and those that simply reported a ratio between erosion rates under native vegetation and conventional cultivation.

Fig. 4.

Box-and-whiskers plot showing the range of reported decreases in erosion rate for studies reporting direct comparisons of conventional tillage and no-till practices for comparable settings (n = 39, median = 20, mean = 488, minimum = 2.5, maximum = 7,620). Data include studies that reported both rates individually and those that simply reported a ratio between erosion rates under conventional or no-till cultivation.

Fig. 5.

Critical time (T_c) required to erode a soil profile of differing initial thickness (S) for different net soil erosion rates set by the difference between rates of soil erosion (E) and production (P), defined by T_c = S/(E−P).