Dry aggregate stability of soils influenced by crop rotation, soil amendment, and tillage in the Columbia Plateau

Highlights

• Dry aggregate stability (DAS) is an important factor influencing soil erodibility.

• This study assessed the effect of soil type, crop rotation, soil amendments, and tillage on DAS.

• DAS was influenced by tillage but not green manure or biosolids treatments.

• Clay content was a good predictor of DAS in the Inland Pacific Northwest.

Abstract

Dry aggregate stability (DAS) is an important factor that influences soil erodibility. The purpose of this study was to measure DAS of soil, as well as assess the effect of crop rotation, soil amendment, and tillage on DAS in the main wind erosion area across the inland Pacific Northwest United States (iPNW). The stability of dry aggregates was measured using a commercial penetrometer and was found to be lower for soils in the iPNW than previously reported in other regions. Significant differences in DAS were found between tillage treatments at all locations. Dry aggregate stability was 24 to 114% higher for no-tillage summer fallow than tillage-based summer fallow treatments. Although not significant, DAS for a winter wheat-summer fallow (WW-SF) rotation was consistently higher than winter wheat-camelina-summer fallow (WW-C-SF) or winter wheat-safflower-summer fallow (WW-S-SF) rotations at two sites in central Washington. In contrast, when green manure or biosolids were applied as an amendment, there was no difference in DAS. Dry aggregate stability was more closely related to clay content than other soil properties (i.e. sand content and surface area of primary particles). Clay content, in the range 9 to 14%, can therefore be used to estimate DAS of soils in the iPNW. No-tillage management practices was beneficial to maintain greater DAS, thereby making soil aggregates more resistant to erosion and degradation.

Introduction

Dry aggregate stability (DAS) is an important factor influencing soil physical properties and processes (Skidmore and Powers, 1982) such as aggregate abrasion and soil wind erosion and dust transport. The susceptibility of soils to wind erosion largely depends on the degree of aggregation (Zobeck and Popham, 1990). Larger aggregates tend to degrade into smaller aggregates that are more susceptible to erosion by wind, particularly during winter (Tatarko et al., 2001).

Dry aggregate or mechanical stability is defined as the resistance of soil aggregates to breakdown from physical forces. Dry aggregate stability is therefore a measure of cohesive forces or strength of cementation between or within soil particles or aggregates in the dry state (Skidmore and Powers, 1982). Aggregates with greater stability tend to be more resistant to breakdown when an applied force is exerted on the aggregates. Tillage operations, for example, can impose both compressive and shearing stresses on aggregates (Cooper, 1971). Bombardment of salting particles on aggregates during wind erosion can also impose shear stresses that result in abrasion of aggregates (Liu et al., 2011).

Dry aggregate stability is affected by external as well as internal factors. Layton et al. (1993) investigated aggregate stability as influenced by seasonal climatic changes in Kansas. Freeze-drying decreased dry aggregate stability over winter. They also found DAS varied across winters, suggesting that DAS was affected by climate. Merrill et al. (1999) investigated aggregate stability as influenced by climate; they found dry aggregate stability decreased as a result of drought in the Great Plains and was affected by crop and tillage management. Skidmore et al. (1986) indicated DAS in sorghum was lower than in wheat. Hevia et al. (2007) indicated tillage produced significant differences in DAS, with DAS being 49% lower in conventional tillage than vertical tillage or no tillage. Other factors which influence DAS include water content at time of tillage (Wagner et al., 1992, Colazo and Buschiazzo, 2010), irrigation (Pi et al., 2014), and soil properties (Zobeck, 1991). Skidmore and Layton (1992) indicated that dynamic soil properties affect aggregate stability in the short term. In contrast, factors like primary particle-size distribution change slowly with time and have relatively small influence on DAS. Kohake et al. (2010) observed significant differences in DAS among four muck soils in Michigan.

The soil erodible fraction (EF), or proportion of soil that is susceptible to erosion, is influenced by aggregate stability as well as other soil properties such as aggregate size and aggregate density (Colazo and Buschiazzo, 2010). The EF is highly dependent on soil organic carbon and clay content because these constituents bind individual particles together to form soil aggregates (Skidmore and Layton, 1992, Fryrear et al., 1994, Buschiazzo et al., 1995). The Revised Wind Erosion Equation (RWEQ) describes soil properties which influence the EF as:

$$\mathit{EF}=\frac{{\beta }_{\mathrm{E}\mathrm{F}}+0.31s\mathrm{a}+0.17s\mathrm{i}+\frac{0.33s\mathrm{a}}{\mathit{cl}}-2.59OM-0.95CaCO}{100}$$

where the coefficient ${\beta }_{\mathrm{E}\mathrm{F}}$ is empirical with an assumed value of 29.09 (Pi et al., 2017). The sa, si, cl, OM, and CaCO are respectively the percentage of sand, silt, clay, organic matter, and CaCO₃. The EF is dimensionless with smaller values indicating the soil is less erodible. The Single-event Wind Erosion Evaluation Program (SWEEP) describes the empirical relationship between aggregate stability and clay content as:

$$\text{DAS}=0.83+15.7*\text{cl}-23.8*{\text{cl}}^2$$

where unit of DAS is the ln(J kg⁻¹). Although SWEEP simulates the influence of tillage on DAS, little information is available that documents the effect of tillage on stability of aggregates. Thus, field studies that investigate DAS under various tillage operations are needed to improve SWEEP (Hagen, 1995).

We are not aware of published reports that document DAS of agricultural soils across the arid and semi-arid regions of the Columbia Plateau of the iPNW where soils are often extremely susceptible to erosion as a result of little vegetative cover and surface roughness and poor aggregation (Papendick, 1998). Dry aggregate stability, however, is integral to the development of wind erosion control technologies as well as predicting wind erosion. Wind erosion in the Columbia Plateau is of concern due to its impact of soil loss and air quality (Sharratt and Edgar, 2011). Therefore, the objective of this study was to characterize the DAS of soil types in the main wind erosion area in the Columbia Plateau, as well as to analyze the effect of crop rotation, tillage, and soil amendments on DAS. Previous methods used to measure DAS have included the drop shatter technique (Farrell et al., 1967) and sieving (Chepil, 1953, Toogood,1978, Colazo and Buschiazzo, 2010). Both methods are tedious and time consuming (Boyd et al., 1983), therefore in this study we used a commercial penetrometer to measure DAS. These measurements were then compared with values in the literature.