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SWEEP Report #45

Management of Farm Field Variability.
III. Effect of Tillage Systems on Soil and Phosphorus Loss

Researchers: 
R.G. Kachanoski and M.H. Miller, Department of Land Resource Science, Centre for Soil and Water Conservation, University of Guelph, Guelph, Ont.; J.D. Aspinall, Resources Management Branch, Ontario Ministry of Agriculture and Food, Guelph, Ont.; A.P. von Bertoldi, Department of Land Resource Science, University of Guelph, Guelph, Ont.

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Final Report [882 KB pdf]

Associated SWEEP/LSP Research

 

 

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Completed: January, 1992

Key Words:

soil erosion, 137 Cesium, tillage erosion, moldboard plow, minimum tillage, no-till, shoulder slope, crest slope, Tillage 2000

Executive Summary

This report is the second of three reports from the SWEEP/TED project "Management of Farm Field Variability". The first report documented the rational, objectives, and general methodology of the project. In addition, it summarized the work on the quantification of soil loss in a complex three dimensional landscape in southern Ontario, and the influence of tillage translocation as a process responsible for the severe soil loss on shoulder/crest slope landscape positions.

The objective of this part of the project was to measure soil and phosphorus losses on various soil landscapes, under different tillage systems. A subset of benchmark locations (soil landscape positions) were selected from the provincial Tillage-2000 research/demonstration project. A total of approximately 400 different benchmarks were selected.

At each of the benchmarks the amount of 137Cs, a soil tracer, was measured in the fall of 1987 and again in 1990. The 137Cs in the soil came from atmospheric thermonuclear testing in the early 1950's and 1960's. The cesium was dispersed into the upper stratosphere around the world, and was subsequently deposited in the soil by precipitation. The cesium binds to the soil and will not move unless the soil it is bound to, also moves.

The measurements at each sample date and location involved taking 9 soil cores (3 m by 3 m grid) for estimation of plow layer depth and two samples for bulk density and to obtain the soil sample for subsequent cesium analysis. The 137Cs was analyzed by high efficiency Gamma Spectroscopy methods. The soil was also used for measurement of total phosphorus. The purpose of the measurements was to use the change in 137Cs between measurements, to give net soil losses. The soil losses could then be combined with the phosphorus measurements to give phosphorus losses in the various soil landscapes.

The method of estimating soil loss from 137Cs is well known and used throughout the world. However, the method assumes that a relationship exists between the loss of cesium at a particular site and the amount of net soil loss. For water and wind erosion there is usually little deposition on upper, and mid-slope positions. Thus, cesium and soil loss should be related. However, as the previous report of this project has shown (from D.A. Lobb, M.Sc. Thesis, Dept. of Land Resource Science, University of Guelph), tillage translocation of soil is a major process redistributing soil in complex topography. This process results in significant lateral mixing of soil/cesium. The net effect is that cesium loss at a particular soil landscape is not necessarily related to soil loss. Thus, in the absence of a good mechanistic model or understanding of tillage translocation, only a full mass balance of cesium in the landscape can be used to estimate soil loss.

Unfortunately, the Tillage-2000 benchmarks were not established to monitor the full three dimensional landscape. Only a cross-section of the landscape was used. This is an efficient methodology to examine landscape effects on yield, water erosion, soil properties, under different tillage systems, but not for a full mass balance of cesium.

The moldboard tillage system resulted in considerably more change in 137Cs (1987 to 1990) than either minimum or no-till systems. Average soil losses across all Tillage-2000 field sites were 60.0, 30.0, and 0.0 t/ha/yr for the moldboard, minimum, and no-till systems respectively. Estimated phosphorus losses were 40.0, 20.0, and 0.0 kg P/ha/yr for the same tillage systems respectively. The minimum-till average loss values are not a good indication because most of the loss occurred on two sites. For 9 out of the 11 minimum-till sites soil and phosphorus loss was negligible. On one minimum-till site the loss was excessive which probably is the result of poor mass balance rather than an actual loss. These estimated losses are based on the assumption that the average 137Cs loss from the benchmarks is representative of the mass balance of the entire field.

Paired tillage comparisons gave similar trends in the soil and phosphorus loss estimates. Annual losses of phosphorus were on average 48.0 and 35.0 kg P/ha for the five paired moldboard versus minimum-tillage field sites respectively, and 20.0 and 4.0 kg P/ha for the paired moldboard and no-till sites respectively. The differences in the losses in the moldboard sites paired to either minimum or no-till treatments reflects differences in soil types and probably tillage intensity. The paired minimum and no-till sites had negligible losses. These sites (i.e. where minimum-till tends to be the conventional system) are lighter textured and in general are tilled less intensively than the minimum-till sites paired with the moldboard system. Thus, the data seem consistent with what is known about the influence of tillage on soil and phosphorus losses. However, it must once again be stated that the loss estimates may not represent off-field losses related to water runoff. This, however, is a scale problem regardless of the within field processes (tillage translocation or water redistribution) which can only be answered with a true three dimensional mass balance.

Average 137Cs losses from specific landscape positions were quite variable, with large losses generally observed on shoulder/crest slope landscape positions. Soil losses from these landscape positions were very large, in many cases exceeding 100 t/ha/yr. The variable nature of the losses (or gains) is consistent with the study by Battiston et al. (1987) and the previous report from this project suggesting that tillage translocation is a dominant process responsible for soil redistribution within a field.

Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)
The objective of the study was to determine the rates of soil erosion and phosphorus delivery on various soil landscapes, under different tillage systems. The benchmark locations were selected from the Tillage 2000 locations with a total of 400 different benchmarks being selected.

At each benchmark the amount of 137Cs was measured in the fall of 1987 and again in 1990. Cesium was used because it is bound to the soil and will not move unless the soil it is bound to moves as well. Tillage translocation of soil was found to be a dominant process for soil movement on complex site positions of upland soils in Ontario. The researchers conclude that the estimated soil and phosphorous loss estimates given in the report could have significant error.

Generally, the soils under the moldboard system had the highest cesium loss over the three year period. Minimum till systems were next with no-till systems having negligible cesium loss. The level of cesium loss was assumed to be directly related to the amount of soil and phosphorous lost. Also of note was that soil movement tended to be down slope but not off farm and therefore was not a factor in phosphorus loading to surface water.

Comments:

The study verifies the position that erosion increases with degree and intensity of tillage action. It also substantiates the position that tillage translocation increases when annual tillage action runs perpendicular to major slopes. Of significant interest to policy makers and programmers is that within field soil redistribution, as caused by tillage translocation, is not linked with phosphorous delivery to surface water.

Associated SWEEP/LSP Research:

  • 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 #46 - Management of Farm Field Variability. IV. Crop Yield, Tillage System, and Soil Landform Relationships
  • SWEEP Report #49A - Land Reshaping of Lowland Clay Soils. I. Field Study
  • SWEEP Report #55 - Soil Loss by Tillage Erosion: The Effects of Tillage Implement, Slope Gradient, and Tillage Direction on Soil Translocation by Tillage
  • SWEEP Report #60 - The Effect of Conservation Tillage Practices on the Losses of Phosphorus and Herbicides in Surface and Subsurface Drainage Waters
  • SWEEP Report #66 - Volume V. Economic Assessment of the Technology Evaluation and Development (TED) Program

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

(C) More work is needed to determine if the three dimensional mass balance of cesium gives a more accurate estimate of soil and phosphorous movement within field boundaries than the two dimensional. There is a need to determine what processes cause phosphorous loading to surface water, if the majority of the soil that does move remains in the field.

(A) A long-term, comprehensive research and monitoring program is needed to examine the process, practice and the remedial action of conservation management systems on a representative range of soil and landscape conditions across Ontario.

 

 

 

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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 03:24:55 PM