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SWEEP Report #49a

Land Reshaping of Lowland Clay Soils:
I. Field Study

Researchers: 
L. Leskiw, A. Laycock, Can-Ag Enterprises, Guelph, Ontario

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Report  [1992 KB pdf]

Associated SWEEP/LSP Research

 

 

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Completed: May, 1992

Key Words:

surface drainage, sediment transport, phosphorus, clay soils, land planing, monitoring, soil quality, hydrology

Executive Summary

Land planing is a procedure to alter the field topography, producing a uniform slope thus improving surface drainage. Using laser technology for elevation mapping, in conjunction with computer software programs, a design plan is created outlining topsoil cut and fill depths and locations. An earth scraper with a cutting bar controlled by a laser elevation beam is then pulled across the field to produce the desired design.

Water management techniques such as the innovative approach with land planing however, must be closely examined to determine the sediment and phosphorus losses associated with the surface runoff. In the fall of 1988 Can-Ag Enterprises was awarded a contract to design and construct monitoring stations, then record and sample runoff at these stations.

The goal of this study is to determine the efficacy, costs and farm management changes associated with land reshaping, in comparison to conventional water management practices.

The study involved four farms, located in Essex and Kent counties, each with a planed and an unplaned field. Sites 2, 3, and 4 had a monitoring station at the primary surface outflow location on each field. The fields at site 1 were divided into sections, each section having a drainage furrow leading to a rock chute and therefore enabling three monitoring stations to be established on each field. The stations consisted of a V-notch weir, a stillwell with a Richards type flow meter, and later Isco automated samplers (two placed at sites 1, 2 and 3). Throughout the study, runoff volumes were logged, samples were collected, soils were evaluated and agronomic practices and responses were recorded. Analysis for total phosphorus and dissolved molybdate reactive phosphorus were performed in the Land Resource Science Department at the University of Guelph. The sediment content was determined at the Harrow Research Station where the samples were filtered before being sent to Guelph.

Results of the soil investigations indicated a lack of impact, with regard to soil quality, from planing. At all sites, topsoils were not completely removed in any locations though in a few places there was evidence of topsoil removal or addition. The assigned soil compaction ratings were similar for both the planed and unplaned field.

The results of the flow data indicated that increased runoff (l/ha) was associated with the planed field at two of the three well documented sites. Only at one site though, was the increased runoff (l/ha) on the planed field significantly greater than the unplaned field. Contrasting results were found at another site where the unplaned field contributed more runoff (l/ha) than the planed field. The fourth site had too few recorded events to be statistically analyzed.

The contrasting results between sites may be attributed to differences in the natural drainage patterns and differences in the sizes of the drainage basins. In the first year at site 2 though, we were able to construct basins of equal area on the planed and unplaned field using tomato beds. All the event occurrences with the equal area basins produced far more runoff (l/ha) from the planed field compared to the unplaned field. However there could be situations, such as at site 1, where dividing up the natural basins into smaller sections through planing would reduce the overall runoff.

The erosion characteristics of the two water management systems with regard to phosphorus and sediment losses through surface runoff are still not clearly defined. No consistent trends were observed or statistically determined, which might indicate that the phosphorus and sediment contributions to the runoff are event specific.

Differences between planed and unplaned fields appear when the sediment and phosphorus loadings are calculated with regard to total flow volumes. Sediment and phosphorus losses increased as runoff volumes increased. The planed fields on two out of the three well documented sites produced more runoff and therefore may contribute more phosphorus and sediment to the drainage channels. Obviously the key to reducing phosphorus and sediment loadings is to reduce runoff volumes. Determining the natural basins and drainage patterns within a field is the first step to choosing an appropriate water management system. Creating smaller basins through planing may reduce overall runoff (l/ha) if the natural topography is prone to extensive surface runoff into adjacent waterways. However, the situation may be reversed if the natural depressions hold back the surface runoff. Eliminating these depressions through land planing will increase the surface runoff. Therefore in this circumstance farmers wishing to reduce field surface water should consider alternatives to land planing.

The interaction of total phosphorus, dissolved reactive phosphorus and sediment appear to be event specific, depending on rainfall intensity, soil conditions, antecedent moisture, ground cover, etc.

Differences in runoff and losses from the planed and unplaned field did not show up with respect to agronomic practices and the resultant residue cover. Combining the data from the planed and unplaned fields indicated that an established crop providing ground cover during the growing season significantly reduced the phosphorus and sediment loss to the surface runoff.

The costs of land planing are high, estimated between $260/ha and $790/ha, yet increased yields (when compared to unplaned fields) may only be achieved in wet seasons. Other benefits reported by the farmers include: earlier spring start; elimination of hard spots (ponding areas); consistent crop growth; and harvesting at the opportune time. These benefits and the periodic yield advantages, however, may only justify the initial costs of the land planing procedure when lucrative cash crops (i.e. tomatoes) are grown.

The modelling component of the study provides a prediction of whether or not a runoff event will occur but further modification to the model is necessary to produce accurate assessments of runoff volumes and phosphorus loss. As well further modification is needed to allow more agronomic input.

Several recommendations were made upon completion of the study. For fields already planed, these include:

  • a reduction of drainage basin size (area with 1 outlet) to a range of two to five hectares (depending on field size).

  • construction of proper grass waterways and outlet points to reduce field edge erosion and trap sediment runoff.

For farmers who have not planed but require water management techniques, we recommend:

  • observe natural drainage patterns in the field.

  • consider costs and environmental impact of each system.

  • areas with high runoff volumes to adjacent waterways may experience a reduction in runoff if planed.

  • fields with isolated ponding areas will experience an increase in runoff if planed and therefore alternatives should be sought.

  • standpipe surface inlets and sediment traps are a cost effective alternative to the planing procedure.

For researchers, we recommend:

  • small basin monitoring provides necessary data for field scale erosion research.

  • control structures should be more permanent in nature and if economically feasible use data loggers to record flows.

  • field scale monitoring should continue, to provide accurate model calibration data.

 

Evaluation Summary

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

Ponding on flat clay soils is a significant management problem. Land planing using laser assistance to conduct cut and fill operations facilitates surface water drainage and operability of low-relief clay soils. Land planing is popular in Kent and Essex counties. This is a high risk area for surface water contamination by phosphorus and sediment. For this reason, research regarding the effect of planing on soil quality, water quality and farm/crop management was initiated in the SWEEP area.

The goals for the study were: to develop a method for estimating phosphorus movement on fields with different management; to locate and monitor sites for three years (1989-91) in the study area; and to compare the resource quality and profitability of planing to conventional practices subject to several management systems. Fields for study and monitoring stations were established on four farms. Each farm was surveyed in detail to determine micro- watershed boundaries and pre-treatment soil and water quality conditions. Monitoring stations were established in natural run-off areas to measure sediment and nutrient run-off during storm events. Climate and farm management data collection was assisted by farmers.

The results suggest that there were no net negative impacts upon soil quality. Surface run-off volumes were greater from the planed fields but not significantly. Management practices between the two areas did not have significant influence on run-off volumes and content. There were observable differences, however, between those fields with existing depressions and those found adjacent to watercourses. If fields had several depression areas and were adjacent to the stream, the redirection of surface flow caused by planing resulted in more run-off during some storm events. High concentrations of phosphorus were found in samples taken from tile outlets, particularly after manure applications. Economic analyses suggests that planing makes the timing of operations more convenient but not necessarily more profitable. Several recommendations are made. The most notable recommendations to farmers include considering other surface drainage options such as tiled drop inlets and the need for precision in the operation and timing of land planing practices.

Comments::

This was a well designed and executed study on a rather controversial subject.

However, there are several concerns :

  1. Not much can be concluded from the study.

  2. The lack of winter data due to the water sampling technology may raise further questions about the conclusions of the project stating "no noticeable differences".

  3. The long-term effect of planing on soil quality cannot be addressed by a three-year study. Topsoil made shallow by planing operations will mix with subsoil in conventional tillage systems. This will accelerate the degradation of the soil and may increase run-off rates.

In short, from the results of this survey it is not possible to judge the environmental impact of land reshaping of clay soils.

Associated SWEEP/LSP Research:

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

Further research is required in the following areas:

  1. (C) modelling of surface run-off from agricultural lands,

  2. (A) monitoring of soil and water resource quality in agricultural lands, and

  3. (A) development of reliable water and run-off monitoring technologies for use during the range of climatic conditions experienced in Ontario.

 

 

 

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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 03:35:50 PM