Biochar Amendment to Enhance Tomato and Melon Productivity and Protect Against Phytophthora Root Rot Disease
Fresh vegetables are important commodities in Utah; 6,560 harvested acres were produced on approximately 700 farms and valued at $16 million in 2007 according to the National Agriculture Statistics Service). Most of these operations are small farms (less than 15 acres) growing high value crops, including sweet corn, melons, and squash, and many are new farms. In a 2010 survey of commercial vegetable producers in Utah (252 responses), managing irrigation and nutrition for crops grown in arid and alkaline soils was among the most pressing need. Growers also identified concern regarding losses due to diseases, in particular soil-borne pathogens such as Phytophthora root rot. This project has involved working with Utah producers and USU Extension faculty to test whether a novel soil amendment called biochar can contribute to sustainable production by improving soil water-holding capacity, crop yield, and disease resistance in tomato and melon, two important crops in the state.
Biochar is a carbon-rich material similar to charcoal, produced by heating plant biomass through the process of pyrolysis in a closed system, under a limited supply of oxygen. Valuable bio-oils and heat energy are also byproducts of pyrolysis, which has led to the expansion of pyrolysis industries in Utah and the west. Biochar is mixed in soil as an amendment to improve soil structure, increase nutrient retention, provide habitat for biological activity, and sequester carbon which can require from 4 to over 100 years to degrade. This property of Biochar makes it a desirable amendment because it does not need to be applied every year. Biochar has little nutrient value on its own and is not a replacement for fertilizer. The positive attributes of biochar are seen primarily when biochar is moistened and mixed with an organic amendment or fertilizer. Effects of biochar on plant growth have varied among soil types, biochar production practices and application rates, making this study important to evaluating its value for agriculture in Utah and the arid west.
Our cooperating producers include three vegetable farmers, two fruit growers, and the Utah State University Botanical Center in Kaysville. Pettingill Farms in Box Elder County is a 130-acre, diverse, conventionally managed farm that grows fruits and vegetables. Zoe’s Garden in Davis County is a 20-acre, diverse, organically managed farm. Day Farms in Layton is a 90-acre, diverse, conventionally managed vegetable farm. Two Utah County fruit producers agreed to provide fruit tree wood to produce biochar for the project: William McMullin, McMullin Orchard, and Phil Rowley, Southridge Farms. So far we have only collected wood from McMullin Orchard. The USU Botanical Center is partly an Agricultural Experiment Station and partly an Extension education center including buildings, landscapes, and gardens that demonstrate environmental sustainability.
1) Evaluate soil application rates of fruit wood-prepared biochar for field-grown tomatoes and melons and establish parameters for subsequent trials. This experiment was completed in 2014.
2) In collaboration with producers, evaluate how biochar amendment at the identified optimal rate influences water holding capacity, crop yield, and overall plant health of tomato and melon. The first year of collaboration was completed in 2015 and crop yield data collected.
3) Determine whether the addition of the biochar product applied at the determined rate prevents or reduces susceptibility to the root rot disease caused by the organism Phytophthora. The experiment was performed in 2015, however inoculation difficulties delayed this part of the grant project. This will be repeated in 2016.
4) Determine whether the use of soil-applied biochar could provide economic benefits to Utah’s vegetable growers.
5) In collaboration with project producers, prepare and deliver educational programming for other growers and the general public on all aspects of biochar as a soil amendment for vegetable production.
First Year of Field Trial:
Because of a delay in the biochar availability, plant establishment took place later than normal on June 18 and plants were exposed to heat stress. Plants had to be watered by hand using watering cans for the first week after planting at most sites since the growers irrigation schedule was not frequent enough to establish small plants in the summer heat.
A research assistant was employed to help collect biomass and yield data from the plots throughout the growing season. Tomato plants were pruned 5 weeks after establishment by removing 3 suckers closest to ground level on each plant. The biomass was collected and dried for each plot, and the fresh and dry weight was recorded. Tomatoes were harvested once per week from each site starting August 27, and melons were harvested once from each plot during September. One fresh fruit weight was recorded for each plot.
The data from the farm sites was compromised in several ways. Some plants died and others were stunted due to water stress. Additionally, a disease was present on one of the grower sites which stunted both the tomatoes and melons. Another site had a fence breach where goats ate some of the plants. After discussion with the growers and with the grant committee, we have prepared several strategies to avoid the same issues in 2016.
Pruning data showed slightly higher biomass in the fertilizer only treatments, followed by biochar + fertilizer, and the lowest biomass in the control treatment. Initial yield data show an irregular response to biochar at the grower sites and a uniform positive response at the USU Botanical Center plots. The data variability at the farm sites was caused by the previously mentioned issues and is unreliable due to missing plant count information. At the USU Botanical Center, both tomato and melon plots had the highest yield in the biochar + fertilizer treatment, followed by fertilizer only, and the lowest yield in the control treatment.
Phytopthora Container Trial:
On Monday, June 8, melon and tomato plants were planted into 3-gallon pots and placed in a space in the USU Research Greenhouses. The soil used was a peat, vermiculite, perlite mix with no additional amendments. Ten of each crop were potted into soil mix alone, and 10 of each were planted into soil mix amended with 2% biochar (by volume). Each 3-gal pot held 7.5 qt of soil, and a 2% volume was 29.4 cups soil and 0.6 cups char. To make the mix, soil was prepared in batches to make enough for 5 pots of soil. Plants were automatically irrigated for the next month, and then inoculated with Phytopthora in mid-July. Inoculation was unsuccessful and no disease was present in the plants or soil in 2015. A repeat experiment was scheduled for 2016.
Impacts and Contributions/Outcomes
Results of the 2014 container trial were shared with cooperating growers, presented to Extension colleagues at one local and two national conferences in 2015, and published on the Utah Biomass Resources website. Initial field study results were presented to local producers at the Urban Small Farms Conference in February 2016. The presentations helped educators and local producers understand how biochar can affect vegetable growth when added to soil.
This research is similar to projects underway in other states and has led to collaborative discussion between researchers, as well as collaboration with the pyrolysis industries in Utah and Colorado. In 2015, Britney Hunter (PI) was interviewed on the BYU Radio show Thinking Aloud during a 30 minute segment on biochar and sustainable agriculture. This project was also mentioned in an article in the December 2015 edition of Catalyst Magazine, a popular local publication.
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