Influences of Alternative Vegetable Systems on Arthropods/Soil Biological Dynamics and Soil Quality Trajectory

Influences of Alternative Vegetable Systems on Arthropods/Soil Biological Dynamics and Soil Quality Trajectory

Summary

Objectives

1. To identify and explore sensitive early indicators of changes in soil quality useful to agroecosystem analysis and farm management.
2. To identify and explore linkages between changes in vegetation, soil management, and associated C inputs with soil community structure and processes and above-ground arthropod dynamics.
3. To test and adopt strategies for conducting participatory research and education programs.

Abstract

This is an in-depth study in western Oregon of soil quality, soil biology and above-ground arthropods in alternative vegetable systems that include cover crops and reduced tillage. The work was conducted at two experiment station research sites (fully replicated with statistically valid experiments initiated in 1989 and 1993) and on fields of six farmers who each split their fields into two management systems.

We have identified certain soil enzyme activities and increases in large aggregate fractions (1-2 mm) that are early indicators of changes in soil quality due to improved soil management. A cotton strip decomposition method was tested as a simple measure of soil biology activity, but we concluded that it must be used under the same environmental conditions each year to give comparable results. These results are encouraging in that certain microbial and physical properties are sensitive to changes after only one year of a change in management, which holds potential for guiding farmers to manage soil for long-term sustainability. Furthermore, using cover crops improves soil quantity. To date, evidence suggests that microbial communities are improved by cover cropping practices.

Earthworms appear to be stimulated by cover cropping even under conventional tillage, but more in-depth studies are needed to confirm this. Nutrient-mobilizing species such as fungus-feeding springtails and mites are conserved by cover crops and reduced tillage. Deposition of green manure cover crops on the soil surface supports high populations of a mite (Pergamasus) that is currently being developed as a bio-control agent of symphylans. The beneficial predator, P. melanarius (ground beetle), was conserved in cover crop systems.

A major accomplishment of the project was the development of a soil quality card and an accompanying guide that was done at farmer focus sessions. Besides being able to use these tools to assess their own soil quality, the participating farmers are using the card to evaluate the two systems they are testing, providing data that can be compared to the more rigorous laboratory-based measurements.

Although we have only preliminary results from the research, we have extended the results in various workshops and popular outlets. It has been well received and encourages farmers to adopt certain sustainable practices that will improve soil quality.

Potential Benefits or Impacts on Agriculture

The results have shown that cover cropping and reduced tillage have significant impacts on microbiology, soil fauna, and certain above-ground arthropod predators. Cover crops have also affected soil aggregation and water infiltration. Our farmers are very interested in these results because they tell us they often try various soil management practices but have no idea of the effects on the soil.

Identifying sensitive soil quality indicators holds potential to assist farmers in determining which management practices will improve their soils. We suspect earthworms respond to cover cropping and that they play a part in the improvements that appear to be happening in soils under cover cropping. We are finding that cover cropping conserves certain beneficial predators, which may permit reduction in the amount of pesticides needed.

The exciting thing is that we were able to show that these changes in soils occurred within one to two years after a change in management and that some integrative soil measurements were sensitive to these measurements.

Farmer Adoption and Direct Impact

Farmers have been asking us for methods that quantify whether management has been improving or degrading soils before it impacts crop productivity. Our work in cooperation with farmers has demonstrated that cover cropping can have a positive impact on soil properties and that using cover crops is economically feasible. This provides convincing evidence to encourage farmers to adopt cover crop systems.

This project and related extension work has greatly increased the use of cover cropping in the Willamette Valley. We do not have quantitative data, but informal observations over the last two winters indicate that 40 to 60 percent of the row crop acreage is under some type of vegetative cover. This is quite a change from 15 years ago when there was virtually no deliberate planting of winter cover crops.

Reactions from Farmers and Ranchers

All of our cooperating farmers are extremely enthusiastic about the project and want to continue the on-farm plots we have established. Furthermore, at talks we have given about the project we have had a strong response and numerous follow-up questions about soil quality, sustainable management, and cover cropping specifics.

Producer Involvement

The eight growers have been closely involved with designing and implementing an improved system on half of their fields while using a conventional system on the other half. They all filled out Soil Quality Scorecards on each treatment. Approximately 35 to 40 growers participated in the development of the Willamette Valley Soil Quality Scorecard. This has been an extremely successful project that has provided numerous learning experiences for both farmers and scientists in how to manage soils to improve soil quality and how to quantify these improvements with more subjective means.

Future Recommendations

This project needs to be continued to determine the trajectory of soil quality that has started on the on-farm research sites with the improved cover crop systems. These studies need to be continued to track crop productivity and how this relates to soil quality. Detailed studies are needed on how earthworms are involved in affecting soil quality.

The role of earthworms in row crop systems needs to be investigated. We think they may be important in improving soil quality and that cover crops may provide food for earthworms. We need to do more robust sampling under farmer field conditions and set up controlled experiments at the research station to fully understand how earthworms affecting soil quality and how to manage the system to encourage earthworms.

We believe that cover cropping promotes fungi, which are important in formation of large aggregates. Furthermore, they are an important food source for higher soil fauna trophic levels. More work is needed on biodiversity and how this may affect plant growth. Can we manipulate the soil biological community to suppress certain diseases or pests?

This summary was prepared by the project coordinator for the 2000 reporting cycle.

Collaborators: