Tillage Practices for Improving Nitrogen Cycling and Soil Quality

View the project final report

• 1996 annual report

Commodities

• Agronomic: rye

Practices

• Crop Production: conservation tillage
• Education and Training: demonstration, extension, on-farm/ranch research
• Farm Business Management: budgets/cost and returns
• Production Systems: agroecosystems
• Soil Management: green manures, organic matter, soil analysis, nutrient mineralization, soil quality/health

This project conducted on-farm trials to examine management options for cover crops, compost, and alternative tillage practices for lettuce production in coastal California. In the intensive, large-scale vegetable production systems of the Salinas Valley, growers typically rely on frequent tillage and add little organic matter (OM) to the soil, so that levels of soil OM have decreased markedly in the last 100 years. We established two monitoring studies on growers’ fields. One study examined the changes in yield, plant disease, soil microbial biomass with three different minimum tillage methods for retaining semi-permanent beds. The other study investigated the combined effects of reducing tillage and increasing OM addition with cover crops and compost. In addition, daily responses of soil microbial activity were monitored after tillage in order to study the disruptive nature of tillage events.

In the three-year on-farm study on minimum tillage practices, shallow implements resulted in higher severity of lettuce drop disease and lettuce yield than did deeper implements. Soil microbial biomass C did not show consistent responses to tillage. The most advantageous minimum tillage method was a grower-designed, five-step set of operations to chisel, disk, and rip the soil, but keep beds intact for several years. There was less soil compaction with this method than with conventional tillage that re-makes beds between crops with disks and bed shapers.

In the two-year on-farm study on the effects of compost, cover crops and tillage practices, clear advantages to increased OM additions were observed after one year. Simultaneous use of cover crops and compost significantly increased soil microbial biomass for almost a year thereafter. Nitrate decreased after cover cropping, reducing the potential for leaching loss. Lettuce yield generally increased in the next spring and summer after these OM additions. Weed density also decreased. Shallow minimum tillage (‘Sundance’) produced lower lettuce yield than conventional tillage. Weed density was not affected by tillage treatment. Insect pests and diseases were not affected by either OM or tillage treatment. Economic analysis is now underway, as the experiment will end in April, 2000.

Overall, excellent cooperation with growers of large vegetable operations resulted in clear recommendations for increasing OM inputs with simultaneous addition of compost and cover crops, and for avoiding prolonged use of shallow minimum tillage equipment without intermittent deeper tillage. Our outreach programs have delivered the findings of this project to approximately 400 people and we have developed several written publications, and more are in progress.

1. Describe soil C and N dynamics immediately after tillage.
2. Examine the effect of OM additions on C and N dynamics after tillage.
3. Identify management options that minimize short-term C and N loss by altering the type, timing or frequency of tillage, both during crop production and during the winter fallow.
4. Analyze the costs and benefits of the new management practices in terms of economic feasibility and agroecosystem health.
5. Demonstrate these tillage options in the context of commercial agricultural practices to show their practical applicability to growers.