J.D. Gaynor, C.S. Tan, C.F. Drury and T.W. Welacky
Agriculture & Agri-Food Canada, Harrow Research Centre,
Harrow, Ontario, N0R 1G0

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RATIONALE AND OBJECTIVES

Soil and crop management practices have changed dramatically within the Great Lakes basin during the last decades. Livestock-forage based farming has been replaced with monoculture cash-cropping and there has been an accompanying increase in the use of fertilizers, pesticides and large machinery. However, these changes have resulted in soil compaction and structural deterioration and, therefore, increased surface runoff and erosion. Application of more chemical inputs to sustain productivity, in conjunction with increased erosion and runoff has resulted in contamination of surface water by pesticides.

It is increasingly evident that herbicide losses are greatest in runoff events following herbicide application (Gaynor et al., 1992). Herbicide losses increase with the amount applied and volume of runoff (Gaynor et al., 1992). Current research indicates that conservation tillage alone will not reduce pesticide (Gaynor et al., 1992; Issensee et al.,1990; Sauer and Daniel, 1987) pollution of surface runoff or tile drainage water which eventually discharges into the Great Lakes. Therefore, management strategies that alter the hydrology of runoff or reduce inputs hold the greatest potential to improve water quality and sustain agricultural production. In accordance with our existing knowledge, the integrated management system incorporates controlled drainage, reduced tillage and herbicide input and intercropping as sustainable soil management practices. Banded herbicide application is reintroduced as a management strategy necessitated by the introduction of intercropping for nitrogen management and weed control between the crop rows. Reduced herbicide input associated with banding technology should result in immediate improvement in water quality. Controlled drainage regulates tile discharge to provide storage of rain received after herbicide application. Water which would otherwise have been lost through drain discharge or leached out of the root zone can then be used by the crop later in the growing season. The more moist environment in the root zone with controlled drainage will also aid in dissipation of the herbicide reducing after harvest losses and residue carry over of the herbicide. Therefore, controlled drainage should reduce herbicide concentrations in drainage water. The controlled drainage structures can also be modified to provide for subirrigation during low rainfall periods.

STUDY CONCLUSIONS

The integrated crop management, controlled drainage/subirrigation project provided individual and collective assessment of each of the components of the agricultural practices on water quality. Following this approach allows producers to adopt part or all of the management practice dependent upon economic considerations and expected improvements in water quality.

Control of herbicide inputs and runoff volume are essential components of the management strategy to improve water quality. Herbicide loss is the product of runoff volume and herbicide concentration of the runoff. Large runoff volumes of small herbicide concentration or small runoff volumes of large herbicide concentrations could result in large herbicide losses. Herbicide applied in a band over the seeded row reduces herbicide use and improves water quality in direct proportion to the area treated. Applying herbicide to 50% of the area will reduce herbicide loss and improve water quality 50%. Intercrop and tillage hold potential to improve water quality greater than that achieved by banded herbicide application alone but the extent of improvement will depend upon environmental factors such as the incidence and intensity of rainfall after herbicide application and intercrop establishment. Water quality was improved 16% with the intercrop and 30% with conservation tillage. The combined tillage and intercrop practice improved water quality 46% compared to conventional tillage with banded herbicide application. A conservative estimate indicates water quality was improved greater than 70% had these losses been compared to a conventional treatment with broadcast herbicide application. Controlled drainage increased aqueous transport by surface runoff but decreased loss through tile drainage so that total loss remained unchanged.

NEW TECHNOLOGIES AND BENEFITS

New Technology

The introduction of an integrated management system which incorporates controlled drainage/subirrigation, conservation tillage and intercrop as sustainable production management practices.

Benefits

All or part of the integrated management system can be adopted depending upon farmer acceptance and cost. The extent of adoption will determine the extent of improvement on water quality. Banding of herbicide is immediately adoptable which will provide the greatest benefit with respect to herbicide loss independent of weather factors.

The integrated management system should result in improved water quality (ie. reduce herbicide loss), increased crop yields (ie. improve soil water regimes by controlled drainage/ subirrigation) and lower input costs (ie. reduce herbicide input 50%). Therefore, the integrated management system developed at Harrow addresses both environmental quality and agricultural production issues in a balanced way.

IMPLICATIONS FOR GREAT LAKES ECOSYSTEM

The integrated management system developed at Harrow provides technology to reduce non-point contributions of herbicide to the Great Lakes ultimately improving the lakes' ecosystem. Also, reduced herbicide input will decrease potential for leaching to the groundwater.

TECHNOLOGY TRANSFER POTENTIAL

Components of the integrated management system:

1. banded herbicide application

2. conservation tillage

3. intercrop

4. controlled drainage/subirrigation

The integrated management system is based on existing farming structures (ie. tile drains). The existing drainage structures with minor modification can be converted to a controlled drainage/subirrigation system for better management of water and nutrients. Furthermore, the controlled drainage/subirrigation system incorporated with intercrop dramatically reduces herbicide losses because of alterations in runoff volume and increased herbicide dissipation rate.

Part or all of the integrated management system can be easily adopted and implemented as a sustainable agricultural management practice to minimize use and transport of agricultural chemicals.

GAPS NEEDING FUTURE RESEARCH

1. Determine the effectiveness of controlled drainage/subirrigation and intercrop on herbicide losses from other soils, crops and crop rotation systems.

2. The emphasis of the GLWQ project centred on surface and subsurface runoff water quality. The ground water quality and the migration and dissipation of herbicide in soil from the integrated management system needs to be studied further.

3. Determine the relative contributions of drainage outflow over tile and between tile area in the integrated management system using a non-reactive tracer (results could impact management practices by changing fertilizer/herbicide placements, use of intercrop over tiles or direction of planting etc.; results should also provide a useful database for model calibration).

4. Utilize our field and climatic data to verify and/or develop models for estimating herbicide transport (ie. surface runoff, subsurface drainage, leaching and dissipation).

5. Identify transport mechanisms from farm gate to lake system.

6. Insect and disease incidence with the integrated management practice needs investigation.