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SWEEP Report #72

Evaluation of Conservation Systems: Soils and Crops
(PWS Report #4)

Researchers: 

Ecologistics Ltd., Waterloo, Ont.

View/Download Final Report  [1116 KB pdf]

 

 

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Completed: May, 1994

Executive Summary

1.0 Introduction

The mandate of the Soil and Water Environmental Enhancement Program (SWEEP) was to reduce phosphorus loadings to the Lake Erie basin and to maintain or improve agricultural productivity by reducing or correcting soil erosion and degradation. Conservation cropping and tillage systems were identified as the best means to achieve these goals over such a wide geographic region as the Lake Erie watershed. The Pilot Watershed Study (PWS) was developed as a means of evaluating the impact of conservation systems on soil erosion and degradation, water quality and crop production when implemented on a watershed basis.

The erodibility of soil is a major factor which determines the extent of soil erosion occurring on a landscape. Soil erodibility potential depends on such properties as soil particle size distribution, organic matter content, aggregate stability, bulk density and soil structure. The removal of topsoil by erosion results in changes in these soil properties. The major cause of these changes has been attributed to shifts in land management practices or cultural practices. Prominent among the factors which change soil quality are tillage practices, cropping systems or crop sequences, manure and fertilizer applications and crop residue management. Identifying the components of these systems that improve soil quality has been the focus of numerous research undertakings.

At the watershed level in the PWS the evaluation of conservation systems focused on changes in soil cover. This was the one factor affected by crop production practices that most directly influenced soil erosion control, sediment delivery and ultimately water quality as evidenced by sediment and phosphorus loadings. Target soil cover levels were set in order to provide a tangible and achievable goal for the cooperators to strive for. It was anticipated that these targets, when met, would reduce soil loss on average by at least 50%.

In the PWS the impact of conservation systems on crop production at the farm and field level were left to the cooperators to evaluate in the context of their own operations, their previous experience and their personal production goals. Since the indicators of adoption were strong and favourable it was concluded that during the study, cooperator evaluations of the conservation systems were positive.

For comparative purposes, however, information related to two crop production parameters, use of commercial phosphorus fertilizer and crop yields, is also reported on a watershed basis.

2.0 Methodology

Soil quality monitoring was implemented on a series of soil benchmark sites located within the study watersheds. Using the results of a literature search, a sampling scheme was designed to monitor a broad range of soil properties on an annual basis over the duration of the program. During the spring of 1990, the client directed that the soil monitoring component be expanded to include measurements of seasonal variability in soil physical properties. Of the 38 original soil benchmark sites, 18 were selected (3 in each of the 6 watersheds) for this additional work.

Soil cover within the cropped areas of the watersheds was estimated using either the knotted rope method or a series of assumptions based on previous knowledge or experience. Factors affecting crop production were tracked on a field basis by monitoring cooperator management decisions, weather, soil fertility and crop pests.

3.0 Objectives

The components of the study documented in this report apply specifically to the following PWS objective:

  • To determine the nature and degree of changes in relevant soil and water quality parameters and crop yields as influenced by "basin-wide" soil and water conservation practices.

Strategy:

Establish soil, water and crop yield baseline conditions and monitor changes in relevant parameters throughout the life of the program;

Correlate changes in soil, water and crop yield parameters to soil and water conservation practices and systems.

Soil Quality Monitoring Program

The specific objective of the soil quality monitoring component of the PWS was to measure changes in selected soil parameters over the life of the project at benchmark sites in the test watershed and to compare these with changes at comparable sites in the control watershed. Sites were selected on the principle soils in the watersheds on landscape positions representative of the selected soil types.

The scope of this component was:

  1. To assess the effect of conservation farming practices and systems on soil properties which are known to affect crop productivity and/or the magnitude of soil erosion, sediment yield and runoff;

  2. To provide soils information needed for comparing crop performance between conservation farming systems and conventional systems and;

  3. To provide soils data from refining preliminary estimates of soil loss using the Universal Soil Loss Equation (USLE) and to determine the extent of any changes in the soil related values of parameters in the USLE during the life of the project.

The literature review suggested that improvements would be seen in those soil parameters monitored at the soil benchmark sites managed under conservation systems relative to those managed conventionally.

Crop Monitoring Program

The specific objectives of the crop monitoring program were as follows:

  • to determine the proportion of the soil surface covered with live crop or dead crop residue at critical times in the cropping season;

  • to monitor pests, soil fertility, weather, and other factors that influence crop performance during the crop production season; and

  • to monitor whole plant grain yields of crops.

4.0 Conclusions

  • In general there appeared to be more measurable and contrasting change occurring amongst the soil quality parameters in the three test watersheds than in the three control watersheds although the change was not consistent amongst parameters or slope position.

  • Uncontrolled differences and/or similarities in tillage and cropping practices between and amongst soil benchmark pairs made it difficult to monitor significant changes in soil quality parameters in the short term (3 years) of the PWS.

  • In general the amount of soil cover and area affected increased in the test watersheds during the study and relative to the control watersheds.

  • Approximately one half to three quarters of the monitored agricultural areas within the test watersheds that were affected by elevated soil cover levels (20%+) during spring runoff, continued to be affected by soil cover levels greater than 20% after planting (during late May and early June).

  • The adoption of conservation systems during the PWS impacted to a greater degree on the soil cover remaining after spring runoff when compared to the soil cover remaining after planting.

  • Understanding the influence of the adoption of conservation measures on soil cover within the Pittock watersheds was complicated by the presence of hay-based rotations.

  • At the beginning of the PWS the actual application of phosphorus fertilizer on a watershed basis was approximately 1.4 to 3.6 times greater than recommended amounts and at the end of the PWS the actual application of phosphorus fertilizer on a watershed basis fell to approximately .8 to 1.3 times the recommended rates.

  • Over application of phosphorus fertilizers can be significantly reduced on a watershed basis if information about soil fertility levels and phosphorus loading of water courses is provided to the producers.

  • No difference in crop production potential was detected between each pair of test and control watersheds based on yield data (or any other data) collected during the PWS.

5.0 Recommendations

  • In future projects, consideration should be given to holding soil samples, or perhaps splitting each soil sample and holding one of the resulting samples, through the life of the project (or for a suitable timespan) and having all of the samples analyzed by the same laboratory at the same time. This would avoid potential problems with changes in laboratory and analytical techniques that may impact on the study results.

  • In short term projects (less than five years) it is critical that paired sites are similar not only in soil character but in soil management as well. Current management practices can influence yearly results and where long term trends are not an objective of the study, short term soil management practices should be similar between pairs and if possible groups of pairs.

  • To obtain long term trends of change the monitoring period of soil benchmark sites should be carried out over five years or more. This would allow for the adoption and incorporation of conservation practices as part of the normal farming system.

  • The soil benchmark data collected during the PWS could serve as a baseline data set from which future changes in soil quality could be monitored. In the Essex and Kettle watersheds in particular it is likely that the adoption of conservation systems will continue in the future. It is recommended that these soil benchmark sites be monitored every three to five years where adoption of conservation measures has occurred and alternatively where conventional practices have been maintained. This approach should document the long term effects of both systems on soil quality.

  • The use of conservation practices should be promoted to sustain increased levels of residue cover on a field or watershed basis.

  • Additional clarification regarding the potential contribution of commercial fertilizer to phosphorus loadings should be published.

  • Producers should be encouraged to examine their phosphorus fertilizer programs to ensure maximum efficiency.

  • The methods and equipment for calibrating fertilizer application rates should be improved.

 

 

 

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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 07:35:01 PM