Runoff and soil loss from midwestern and southeastern US silt loam soils as affected by tillage practice and soil organic matter content

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Abstract

No-till practices generally reduce runoff (RO) and soil loss (SL) by contributing to accumulations of soil organic matter (SOM) in the near-surface zone. This research was conducted to determine the effects of SOM contents on RO and SL from two highly erodible soils using crops that produce a wide range of residue, in the context of long-term tillage studies in widely separated climatic regions. Rainfall simulator plots, measuring 6.1m×0.9m, were imposed on a 9-year-old corn (Zea mays L.) and cotton (Gossypium hirsutum L.) conservation tillage study at Senatobia, Mississippi, and on a similar 34-year-old corn study at Coshocton, Ohio. All RO was collected from two replications of conventional (CT) and no-till (NT) treatments following application of simulated rainfall at an intensity of 50 mm h−1 for 1 h. Soil samples collected in depth increments of 0–1, 1–3, 3–7.6 and 7.6–15.2 cm were characterized for SOM content, aggregate stability (AS), water dispersible clay (WDC) and particle size distribution. Bulk density (BD) samples were collected in increments of 0–3.8, 3.8–7.6, 7.6–15.2 and 15.2–30.5 cm. Overall, RO from the CT and NT treatments averaged 27.8 and 16.5 mm, respectively. SL loss from the CT treatments averaged 3.9 Mg ha−1 and 0 for the NT. BDs in the surface 3.8 cm averaged 1.34 Mg m−3 for CT and 1.26 Mg m−3 for NT. Correlation coefficients (r) for SOM content versus AS, WDC and BD were 0.92, −0.90 and −0.64, respectively. Regression models indicated that BD, as a single-variable, explained 87% of the variability in RO from the NT treatments. BD alone was less effective in accounting for the variability in RO from CT treatments, but contributed to a three-variable model with AS and WDC to produce an R2 of 0.97. These results indicate that as SOM contents gradually increase in NT treatments, RO decreases due to the development of greater porosity in the near-surface zone attributable to enhanced AS at the soil surface. Thus, surface sealing tendencies are diminished which promotes an increase in infiltration rates.

Introduction

Runoff (RO) and soil loss (SL) are problems common to most soil resources in the world, especially those with unstable aggregates in the surface horizon both from the standpoint of sustainability and offsite environmental damage. The environmental damage factor is becoming increasingly more important as standards for sediment and chemical pollutants in water bodies become more stringent. In many instances, the adoption of no-till (NT) practices has resulted in improvements relative to the reduction of erosion-related problems. This can be attributed, in large part, to the stabilization of the surface by increased soil organic matter (SOM) contents and the accumulation of crop residues. Some studies (Reicosky et al., 1995) have reported SOM increases of 2270 kg ha−1 per year in the top 15 mm of the soil surface following the introduction of NT practices. The organic matter accumulation increases water-stable aggregation in the macroaggregate (>0.25 mm) fraction (Tisdall and Oades, 1982, Franzluebbers and Arshad, 1996, Francis et al., 1999) which normally increases infiltration rates (Triplett et al., 1968, Bradford and Huang, 1994, Reicosky et al., 1995). In some soils, the organic matter-induced improvements in surface soil properties, that affect erodibility, have been shown to occur within a minimum of the first 3–4 years of the introduction of NT practices (Francis et al., 1999, Rhoton, 2000). Further, RO and SL from NT practices were reduced by a maximum of 35 and 77%, respectively, after 13 years compared to conventional-tilled (CT) systems (McGregor et al., 1999); however, substantial reductions were recorded for both parameters after only 3 years.

Although the previous studies have documented very well the effectiveness of NT practices at reducing RO and SL, essentially little effort has been made to relate these reductions to changes in soil properties that result from increased SOM contents. Thus, this study was conducted to: (1) determine the effects of SOM on RO and SL from CT and NT practices imposed on two highly erodible soils from different climatic regions, (2) characterize the influence of a wide range of SOM contents on soil properties that control infiltration rates, and (3) evaluate the effects of a CT operation on RO and SL from a long-term sod crop.

Section snippets

Field

The long-term tillage experiments used in this study were established in 1988 at Senatobia, MS, on a Grenada silt loam (Soil Taxonomy—Glossic Fragiudalfs; FAO-Dystric Podzoluvisols), and in 1964 at Coshocton, OH, on a Rayne silt loam (Soil Taxonomy—Typic Hapludalfs; FAO-Haplic Luvisols). Conservation tillage yield plots (12.2m×5.5m) from a larger separate study were used to evaluate the effects of tillage on RO and SL at Senatobia. The experimental design and plot management aspects of that

Soil properties

The most obvious difference in the soil characterization data for the various plots (Table 1) is the greater SOM concentrations in the NT. In most cases, the NT treatments contained statistically significant (p≤0.05) greater amounts of SOM in the surface 3 cm relative to CT regardless of crop or study location. The NT plots at Senatobia had more than twice the SOM concentrations of the CT at the 0–1 cm depth, with treatment differences being greatest for corn. The NT corn also had substantially

Conclusions

The implementation of NT practices on the soils evaluated in this study created conditions at the soil surface which led to substantial reductions in RO and SL. At Senatobia, MS, RO measurements conducted after 9 years indicated an average reduction of 17% on NT cotton and 26% on NT corn relative to their CT treatments. RO from the 34-year-old NT corn treatments at Coshocton, OH, were 77% lower compared to the CT component.

The reductions in RO and the lack of any measurable SL from the NT

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