Date of Award

2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Rebecca Brown

Abstract

Vegetable farming is an intensive practice that typically relies on several tillage passes to prepare fields for production. Repeatedly tilling the soil, however, is unsustainable and has been shown to decrease soil structure and organic matter while increasing erosion rates. A 3-year experiment was conducted in a mixed vegetable production system in southern New England to determine how crop yield, weed abundance, and soil health were affected by conservation tillage practices. Three conservation tillage systems were compared to conventional tillage to determine the effects on yields of six vegetable crops, weed abundance, and soil health.

Six 50 m planting beds were created within each treatment with the four middle rows planted to vegetable crops. In every treatment group, six vegetable crops were grown. These included tomato, cabbage, carrot, melon, cucumber, and lettuce. Two of the four rows were planted with the tomato and cabbage crops while melon / cucumbers, and lettuce / carrots were planted together in the remaining rows. Drip tape, with 30 cm emitter spacing, was used to irrigate to each crop in each treatment at a rate of 2.54 cm per week. All vegetables received one line of drip tape except the carrot / lettuce row, in which two lines were used. Crops were fertilized at recommended rates using organic fertilizers applied at planting and through fertigation. To determine the conservation tillage treatments effects on yield, marketable yields were harvested throughout the season. Marketable yield totals were used to establish kg·ha-1 estimates for all crops in all years. These estimates were used to gauge the conservation tillage treatments' ability to produce yields comparable to the conventional treatment. Due to large amount variability across replications, marketable yields were transformed using a log(x) +1 transformation to normalize the data.

To determine differences in weed abundance among treatments, counts were taken four times in both the 2011 and 2012 seasons.

Tallies determined total weed populations and species compositions within each treatment. In 2012, dried biomass measurements were collected for broadleaf and grass weeds, in addition to cover crops.

Soil samples were collected in April every year and sent to the Cornell Nutrient Analysis Laboratory for the comprehensive Soil Health Test to measure the effects of the treatments on soil health. Additionally, in 2011 and 2012 soil respiration and nitrate levels were measured biweekly during the growing season. Six 15 cm soil cores were collected from four locations in each replication of each treatment. The soil was dried and then analyzed for soil respiration and nitrate levels The conventional tillage (CT) system was managed as follows: In the spring, fall seeded (123 kg·ha-1) winter rye was incorporated using a moldboard plow and disked twice. Weeds within the treatment were controlled with tractor-mounted and walk-behind rototillers. In the fall, plots were disked twice before seeding winter rye. Establishment of the rolled crimped zone builder (RCZB) treatment: After the fall vegetable harvest, the plots were plowed and disked prior to seeding the winter rye with a seed drill. The winter rye was seeded at a rate of 123 kg·ha-1. In the spring, when the rye reached anthesis, it was rolled and crimped. A zone builder was then used to strip till planting beds into the treatment. The winter rye seeding rate was increased to 184 kg·ha-1 in 2012 after a low biomass of winter rye was observed in 2011. The winter rye biomass was expected to provide adequate weed control between the strip tilled rows throughout the season. Hand weeding was used to control weeds in the strip-tilled rows. Raised planting beds and a cover crop mixture of perennial ryegrass (27.20 kg·ha-1) and Dutch white clover (2.72 kg·ha-1) seeded in the aisles between the beds made up the PLM treatment. Post harvest, the raised beds were seeded with winter rye (123kg·ha-1). The following spring, the rye was mowed and the beds were rototilled with a walk-behind tiller to prepare them for planting. A walk behind mower was used to control weeds between the beds, while hand weeding was used in the planted rows. The crimson clover (CC) treatment was established as follows: The plots were plowed and disked twice before planting the vegetable crops. Following vegetable crop planting, crimson clover seed was mixed with pelletized lime at a 1:2 ratio and seeded at a rate of 25 kg·ha-1 using a drop seeder. Mowing was used to prevent the crimson clover from competing with the vegetables. Hand weeding was used to control weeds that the cover crop was unable to control. Yield, weed abundance, and soil health analysis results varied by treatment. Redroot pigweed, crabgrass, purslane, and lady's thumb were the most abundant weeds in our fields. Soil respiration rates, nitrate levels, and soil health test results found the active carbon, nitrate, and biological activity in our soils to be lacking. Individual results between treatments varied. CT - Vegetable yields were consistently higher than or equal to the other treatment yields over all three years. Weed abundance in 2011 was not significantly different from the other treatments, however, an additional tillage pass in 2012 reduced the weed populations by 42%. The reduction in abundance lead to no significant differences between the CT and PLM treatments. Organic matter levels were reduced over the three-year study. The 2012 nitrate levels were higher than the RCZB and PLM treatments, however, the soil respiration rates were lower than the conservation tillage treatments RCZB - Yields throughout all three years, for all vegetables, were severely reduced in this treatment. The rolled and crimped winter rye failed to control weeds effectively and demonstrated reduced nitrate levels. The 2012 respiration levels, however, were the highest of any treatment.

PLM - Yield results varied by crop in this treatment. The melon, cucumber, and carrot yields were similar to the CT treatment yields, while the tomato, lettuce and cabbage yields were reduced. This treatment was very effective at broadleaf weed control, however, it was not effective against crabgrass. Soil respiration rates were higher than in all other treatments in 2011 and were greater than the CT treatment in 2012. Soil nitrate levels were lower than in the CT treatment in 2012. CC - Vegetable and cover crop plant residue was left on the soil surface until the following spring. This treatment's yields were comparable to or greater than those of the CT treatment for all crops and all years, except cabbage 2011.

Conclusion

Each of the conservation tillage treatments showed one or more attributes that could potentially increase on-farm sustainability. The conservation tillage treatments have a higher average soil health score, reduced weed abundance, and produced yields similar to or greater than the conventional treatment. The CC treatment, however, was the only conservation tillage treatment comparable to the CT treatment in all three categories. Further experimentation is needed to improve upon these treatments and should include a greater emphasis on nutrient cycling in conservation tillage systems.

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