C.F. Drury, C.S. Tan, J.D. Gaynor and T.W. Welacky
Agriculture and Agri-Food Canada, Harrow Research Center,
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, erosion and decreased productivity. Application of increased chemical inputs to counter decreased productivity, in conjunction with increased erosion and runoff has resulted in contamination of surface and ground water by nutrients and pesticides.

The development and implementation of an integrated soil, crop and water management system shows promise as a means to manage agricultural chemicals within the root zone and maintain soil structure while sustaining crop production. Current research indicates that conservation tillage alone will not reduce pesticide (Gaynor et al., 1992; Issensee et al., 1990; Sauer and Daniel, 1987) or NO^-₃ pollution of tile drainage water (Drury et al., 1993) which eventually discharges into the Great Lakes. Some studies suggest most pollutants are discharged during the first stages of runoff events after herbicide and fertilization applications, thus retention of early runoff events (Jury et al., 1985) may also significantly reduce field losses of pesticides and nutrients (Gillam et al., 1979). Improving soil structure and managing nutrient uptake and release through intercropping, cover crops and enhancement of root uptake efficiency may also significantly reduce runoff for nutrients and pesticides (Smith, 1982).

In this study, the integrated management system incorporates water table control, reduced tillage and intercropping as sustainable soil management practices. Water table management regulates tile discharge to provide storage of rainfall water received after herbicide and fertilizer N application. Water and NO^-₃ can then be used by the crop during dry periods in the growing season which would otherwise have leached out of the root zone. Therefore, this system should reduce herbicide and NO^-₃ concentrations in drainage water. The water table control management can also be used for subirrigation during low rainfall periods.

STUDY CONCLUSIONS

Nitrate leaching through the soil profile and contamination of groundwater has become a serious environmental and economic problem (loss of fertilizer) for intensive agricultural systems. Nitrates in drinking water in excess of 10 mg N L^-1 can lead to blue-baby syndrome (methaemoglobinaemia) and stomach cancer. Previous research has indicated that the volume of water that flowed through the soil was the primary factor responsible for N loss. In this study a controlled drainage/subirrigation systems was used to manage drainage water and reduce tile drainage volume by 21%. Flow weighted mean nitrate concentration was reduced by 25% from 11.2 mg N L^-1 for the drainage treatments to 8.5 mg N L^-1 for the controlled drainage/subirrigation system. The average yearly nitrate loss was reduced by 41% from 32.5 kg N ha^-1 for the drainage system to 19.1 kg N ha^-1 for the controlled drainage/subirrigation system. Moldboard plow tillage resulted in the lowest nitrate losses through tile drainage for the drainage treatments at 28.3 kg N ha^-1 whereas the soil saver tillage treatment resulted in the lowest nitrate losses in the controlled drainage/subirrigation system at 14.8 kg N ha^-1. Therefore controlled drainage subirrigation system combined with soil saver tillage reduced nitrate loss by 48% to the conventional moldboard plow tillage. Annual loss of nitrates through surface runoff with drainage treatments was 1.1 kg N ha^-1 which is only 3% of the total nitrate loss. Annual nitrate loss through surface runoff was increased to 1.9 kg N ha^-1 with the controlled drainage/subirrigation systems, but this loss was minor compared to losses incurred through tile drainage.

The controlled drainage/subirrigation system reduced nitrate concentration by 25% and in combination with soil saver tillage effectively reduced the nitrate loss in tile drainage water by 48%. This system improved nitrogen fertilizer efficiency for corn production systems. The controlled drainage/subirrigation system is a technological breakthrough as it enables farmers to increase nitrogen fertilizer efficiency, reduce nitrate contamination of drainage water, and provide their crops with water during dry periods in the summer.

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. The controlled drainage/subirrigation will reduce nitrate loss through tile drainage and increase water and nitrate use efficiency.

The integrated management system should result in improved water quality by reducing nitrate loss and increased crop yields (ie. improve soil water regimes by controlled drainage/subirrigation) and lower input costs (ie. improve N fertilizer efficiency). Therefore, the integrated management system being developed at Harrow should be able to address both environmental quality and agricultural production issues in a balanced way.

IMPLICATIONS FOR GREAT LAKES ECOSYSTEM

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

TECHNOLOGY TRANSFER POTENTIAL

Components of the integrated management system are 1) controlled drainage/subirrigation, 2) conservation tillage and 3) intercrop. 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 proves to be a dramatic means of reducing nitrate losses because of reductions in tile drainage volumes and nitrate concentrations in tile drainage water which result in improved nitrogen fertilizer efficiency.

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

GAPS NEEDING FUTURE RESEARCH

1. Determine the effect of controlled drainage (i.e. without subirrigation) on water quality and crop performance. This is important for farms which do not have a supply of water fro subirrigation and/or cannot afford to install a subirrigation system.

2. Determine the effectiveness of controlled drainage (with/without subirrigation) in a no-till system on water quality and crop performance.

3. Determine the effectiveness of the controlled drainage/subirrigation on nitrate and herbicide losses on other crops, crop rotations and soils.

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

5. Determine the effect of the integrated management system on soil organic matter, soil structure and microbial biomass activity.

6. 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).

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