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SWEEP Report #54

Rainfall Simulation to Evaluate Erosion Control
on TED Research Sites

Researchers: 
G. Schell, Ecological Services for Planning Ltd., Guelph, Ontario

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Final Report [1394 KB pdf]

Associated SWEEP/LSP Research

 

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Completed: July, 1992

Key Words:

erosion, erosion control, conservation technology, rainfall simulation, Universal Soil Loss Equation, cover crops, conservation tillage, phosphorus, run-off, no-till, conventional, reduced tillage, manure, aeration tillage, residue cover, slope.

Executive Summary

Rainfall simulations were conducted in 1989, 1990 and 1991 on twenty-two occasions at fourteen different farms. A wide range of conservation farming systems, involving different tillage, cover crop and manure management systems, were evaluated in terms of runoff and soil and phosphorus losses resulting from a simulated rainstorm.

The rainfall simulations took place on research plots set up within ongoing TED studies, following consultation with the TED research contractor and the farmer cooperator. Runoff and erosion data were collected within one set of replications set up under the main research trials.

The erosion control offered by aeration tillage, reduced tillage (using a chisel plow or offset disk) and zero-tillage systems was evaluated, and compared against a conventional (moldboard plow) tillage system. At some sites, the erosion control provided by cover crops of red clover, rye, barley, annual ryegrass, hairy vetch or oilseed radish was compared against treatments where the only surface residue cover was from the previous main crop. The susceptibility of soils to erosion and phosphorus losses following applications of raw and composted beef manure, and liquid swine manure was also examined.

The runoff and erosion data provided by the rainfall simulations were highly variable at many of the sites. However several trends emerged from the research. In most cases, the conservation tillage systems resulted in reduced runoff and erosion rates. Aerway tillage shows promise as an effective management tool for high residue cropping systems. It leaves sufficient residue on the surface to reduce the amount of soil detachment and erosion due to rainfall, and does not appear to lower the infiltration rates in comparison with moldboard plow tillage, as indicated by runoff volumes. Furthermore, it can be pulled in tandem with the planter, providing secondary tillage with relatively little soil disturbance.

Reduced tillage systems tended to lessen the amount of sediment loss due to the simulated rainstorm, in comparison with moldboard plow tillage. In most cases, the degree of control over sediment losses was proportional to the amount of residue cover remaining on the surface and the amount of disturbance to the soil surface by the tillage operation.

Many cover crop systems were tested by rainfall simulation. When they were growing, or had been killed but not disturbed by tillage, they provided nearly complete surface cover and appeared to be equally effective in controlling soil erosion. After spring cultivation and planting, some cover crops, most notably hairy vetch, appeared to provide lasting erosion control benefits, possibly due to soil structural improvements and persistent surface residue. Other cover crops, in particular oilseed radish, provided no lasting erosion control benefits. In general, the residue from cover crops with more fibrous plant growth was more persistent and effective in controlling soil erosion.

Applications of raw and composted beef manure in summer onto perennial forages and applications of liquid swine manure in summer and spring did not affect erosion rates or phosphorus losses in comparison with similar treatments where manure was not applied. However, when poultry manure was applied in the fall and incorporated by aerway tillage only, soluble orthophosphate-P losses by rainfall simulation were very high (3.6 mg/m2) in comparison with losses of 0.13 mg/m2 when the manure was incorporated by moldboard plowing.

Several factors contributed to high variability or possible non-treatment related differences in the rainfall simulation results. Soil cracks on some plots caused major reductions in runoff. Due to the experimental set-up, the slopes of some treatments were significantly different than the slopes of the treatments to which they were being compared. Nevertheless, many of the rainfall simulations provided excellent results and demonstrated that reductions in soil and phosphorus erosion can be achieved by the adoption of conservation farming measures.

 

Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)

The purpose of this study was to use rainfall simulation to evaluate the relative effectiveness of the different conservation and erosion control technologies tested in the TED program of SWEEP.

Rainfall simulation was conducted during the summers of 1989-91 on fourteen farms. On- farm research on these areas was initiated, previous to this study, to evaluate the effectiveness of one of the following: conservation tillage, residue management, nutrient management and cover crops. Sample design followed the replications and comparisons established in the TED projects. Rainfall simulation methods established by the Ontario Institute of Pedology were adopted for the study. Benchmark soil conditions were sampled for soil particle size, moisture content, organic matter content and initial concentrations of available phosphorus. One metre square run-off plots were placed, to collect run-off, and was sampled for water volumes, sediment loads, sediment P and soluble phosphorous concentrations.

Mean values of each treatment for before and after rainfall conditions were analyzed using the Duncan multiple range test. The results of the rainfall simulation were found to be highly variable and definite conclusions regarding the effectiveness of specific conservation treatments was difficult to ascertain. However, certain trends in the data were observed. For example, as expected, conservation tillage systems yielded less run-off and soil loss. The higher the residue level - the lower the run-off. The investigators found that cover crops with fibrous rooting (e.g. hairy vetch) were more effective at erosion control.

Variability in the data was attributed to variation in the slope and soil conditions between plots on each farm.

Comments:

The identification of the need to test the relative efficiency of several conservation technologies at controlling soil loss and run-off was a positive step: any on-farm conservation agronomy research should be subjected to standardized objective evaluation. There are several problems relating to the use of rainfall simulation:

  1. Topographic position and soil type were not used rigorously as criteria for the establishment of the on-going TED study sites. This does not only make the design of original studies suspect but raises serious questions about the design of this study. If observations across treatments were not made on similar site (soil and slope position) conditions, the subsequent flow of logic from observations to conclusions and recommendations is likely flawed.

  2. The Universal Soil Loss Equation (USLE) was referred to in the treatment of the literature but was not used as a model to help verify the appropriateness of specific sites chosen for the simulation work. If this had been done it would have indicated the relative potential influence of the variation of LS and K factor-values on predicting soil loss for the TED study areas.

  3. It is not readily apparent that spatial influences on run-off were considered in the design. The potential for aggregation of detachment, sheet and inter-row erosion was not accounted for with one metre square plots within treatments. Further, the influence of micro-topography over a larger area was not addressed. In addition, the effectiveness of cover crops in early spring would have been more appropriately tested in March or April.

It is difficult to place confidence in those results, where physical conditions were not similar between treatments.

Associated SWEEP/LSP Research:

  • SWEEP Report #12 - Choice and Management of Cover Crop Species and Varieties for Use in Row Crop Dominant Rotations

  • SWEEP Report #27 - Cereal Cover Crop Study

  • SWEEP Report #38 - Management of Farm Field Variability. I. Quantification of Soil Loss in Complex Topography. II. Soil Erosion Processes on Shoulder Slope Landscape Positions

  • SWEEP Report #58 - Manure Management in Conservation Farming

Future Research: ( ) indicates reviewers suggestion for priority, A - high, C - low.

(C) Better standards, with particular emphasis on design and field variability, for evaluating conservation technologies with rainfall simulation should be developed. Research toward this end should be supported.

 

 

 

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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 04:05:19 PM