Strategies to control nematodes and weeds with recycled olive pomace

Olive pomace, comprised of olive meat, seed and skin, has unique natural antimicrobial properties, which distinguish it from other agricultural byproducts. Biosolarization, a process which combines solar heating and microbial activity likely intensifies these effects; creating fermentation products which act as natural fumigants. This project will characterize the pest control potential of olive pomace. Objectives are to: 1) Determine which rates of pomace best suppress nematodes and weeds, 2) Determine pomace's mode of action with and without biosolarization, 3) Validate biosolarization with pomace as a pre-plant disinfestation method, 4) Characterize the efficacy of pomace applied as a post-plant strategy, 5) Perform a techno-economic analysis of feasibility, and 6) Extend results through field days, online publications, presentations and outreach to stakeholders.

Preliminary data from greenhouse and laboratory experiments suggest:

• Biosolarization with pomace can decrease pest nematodes and prevent weed germination.

• Pomace applied alone can suppress the germination of some weed species.

Soil Health in California Olives: the Effects of Microbial Inoculation with Compost Tea – A CDFA Healthy Soils Demonstration Project

Anecdotal reports from olive growers indicate that microbial inoculation with aerated compost tea (ACT) can successfully increase yields, fruit size and oil quality, potentially by improving tree nutrient uptake through introducing beneficial microbes, while enabling fertilizer reductions by up to 50%. Another innovative practice is compost application, which is known to increase soil organic matter and reduce green house gas (GHG) emissions. In olives, growers routinely apply compost to marginal soils, at substantial cost, and subjectively feel that this practice is helpful. However, a side-by-side comparison of compost’s effects and how it acts synergistically with ACT will help growers determine if these inputs are worth the costs to achieve their goals. This project investigates the potential of ACT and compost to 1) increase carbon pools 2) reduce GHG emissions, 3) increase yields and 4) improve biological soil health indicators.

Applying ACT and compost in olives could increase yields, soil organic matter and microbial activity, with the environmental benefits of reduced nitrate leaching and GHG emissions. While the ability of compost to decrease GHG emissions has been demonstrated scientifically (Favoino and Hogg 2008), there is little information on how ACT influences GHG emissions, especially in California cropping systems. Laboratory studies have indicated that ACT reduces CO2 efflux by 50% compared to fertilized treatments, but was still higher than water only controls (Scharenbroch et al. 2011). In olives, where inputs are minimal compared to other crops, anecdotal reports have indicated that ACT applications could partially or completely replace fertilization. If this is the case, then GHG emissions/acre could similarly be reduced by half, with greater reductions possible when ACT is combined with compost.

References

Favoino, E. and Hogg, D. 2008. The potential role of compost in reducing greenhouse gases Waste Management Research, 26: 61-69

Scharenbroch, B.C., Treasurer, W., Catania, M., and Brand, V. 2011. Laboratory Assays on the Effects of Aerated Compost Tea and Fertilization on Biochemical Properties and Denitrification in A Silt Loam and Bt Clay Loam Soils. Arboriculture & Urban Forestry 2011. 37(6): 269–277

Effects of recycled organic waste amendments on soil health, carbon footprints and water stress resilience

This project will evaluate three distinctly different recycled waste materials, municipal compost, biochar, and food waste hydrolysate as soil amendments in a newly planted almond orchard. We will evaluate how these amendments affect soil health, resilience of almond trees to water stress and the systems’ carbon footprints.

Compost

Composts can be made from a variety of sources, such as manure, biosolids, food waste and green waste. The compost used in our study comes from Jepson Prairie Organics and includes municipal waste streams such as yard trimmings and food scraps. Although composts often contain nutrients, they are usually applied to increase soil organic matter. Compost applications have been shown to increase soil biodiversity and resilience to water stress (Liu et al. 2016, Mikan et al. 2017). The production of yard trimming compost diverts waste from landfills, reducing greenhouse gas emissions (Brown 2016), and compost applications are often thought to reduce greenhouse gas emissions in comparison to fertilizer.

Biochar

Woody debris from old orchards was, up until recently, sent to large co-generation biomass power plants. As these large power plants are closing, growers are looking for alternative uses for this “waste” product, including smaller, local, energy generation plants which create biochar as a byproduct.  Although biochar products vary considerably, evidence suggests that biochar can increase crop productivity and reduce greenhouse gas emissions (Zhang et al. 2012). The biochar we are using in this study comes from almond wood feedstock produced by Phoenix Energy. They have developed farm sized (.5 to 2 MW) gasification power plants that generate synthetic natural gas which can then be used to produce electricity.

Food waste hydrolysate

To reduce green-house gas emissions, recent California regulations have mandated that commercially produced urban food waste be diverted from landfills (Adhikari et al. 2006; Levis et al., 2010). Additionally, the state has set the goal of nearly eliminating organic waste streams by 2025 (Gerlat, 2015). These factors have resulted in increasing interest and commercial availability of soil amendments derived from recycled food waste. One California product, Harvest to Harvest (H2H), incorporates recycled supermarket organics into a liquid soil amendment that is hydrolyzed with enzymes, homogenized into a suspension of sugars, amino acids, fatty acids, and minerals, and then pasteurized (Pandey et al., 2016). Recent studies have shown that food waste hydrolysate has beneficial effects on strawberry yield, increasing plant growth by 25% when applied with fertilizer, compared to fertilizer alone (Pandey et al., 2016). The organically certified product, H2H 3-2-1, used in this study, also includes hydrolyzed fish solubles so that it is higher in nitrogen in addition to containing 20-25% organic matter. Other studies have found that a combination of high C:N organic matter inputs and labile N stimulated soil biological activity, resulting in greater N assimilation by plants and higher yields (Bowles et al., 2015).

Carbon sequestration

Organic materials from sources previously considered waste are now being recycled into new soil amendments. For growers, the ecological and bottom-line benefits of applying these amendments is still unclear. Many soil amendments increase soil organic carbon (SOC), which enhances crop productivity and resilience to water stress by improving soil physical, chemical and biological properties (Doran and Parkin 1996; Stevenson 1994). Microbial and nematode communities can influence rates of SOC turnover (Don et al. 2017, Jiang et al. 2018), which has important implications for greenhouse gas emissions. 

Research Questions

1. How do these recycled organic waste amendments affect soil health, as indicated by SOC, microbial biomass, nematode biodiversity and nematode indicators of ecosystem function?

2. How do the amendments influence soil water retention and plant water status?

3. Which amendments have the lowest carbon footprints determined through life cycle analyses including greenhouse gas emissions?

4. What rates of each amendment are the most appropriate for yield outcomes/costs?

Preliminary Results

Both biochar and compost increased soil carbon levels. After one year, plots treated with 44.6 tons/acre biochar had 1.72% total soil carbon, 0.88% higher than controls. Plots treated with 44.6 tons/acre compost had 45% higher biologically active soil carbon compared to controls. While no changes were seen in particulate organic matter in the first year, in the second year, both the 44.6 tons/acre rates of compost and biochar increased the proportion of large microaggregates in particulate organic matter compared to control and fertilizer treatments.

Check back on this page for future research updates (Project Funded by CDFA grant: 17-0275-041-SC).

References

Akhikari BK, et al. (2006) Predicted growth of world urban food waste and methane production. Waste Management & Research. 24(5): 421-433.

Bowles TM et al. (2015) Tightly coupled plant-soil nitrogen cycling: Comparison of organic farms across an agricultural landscape. PLoS One 10(6):e0131888.

Brown, S (2016) Greenhouse gas accounting for landfill diversion of food scraps and yard waste. Compost Science & Utilization. 24:11-19.

Don A, et al. (2017) Microbial community composition affects soil organic carbon turnover in mineral soils. Biology and Fertility of Soils. 53:445-456.

Doran JW, Parkin G (1996) Quantitative indicators of soil quality: a minimum data set. In: Doran JW, Jones AE (eds) Methods for Assessing Soil Quality. SSSA, Madison WI.

Gerlat A. (2015) California Adopts Four Laws to Develop Recycling, Composting, Waste Reduction. Waste 360. http://www.waste360.com/composting/california-adopts-four-laws-develop-recycling-composting-waste-reduction

Jiang, Y (2018) Nematodes and microbial community affect the sizes and turnover rates of organic carbon pools in soil aggregates. Soil Biology and Biochemistry. 119:22-31.

Lal, R (2004) Soil carbon sequestration to mitigate climate change. Geoderma 123:1-22

Levis, JW et al. (2010) Assessment of the state of food waste treatment in the United States and Canada. Waste Management 30(8):1486-1494.

Liu T, et al. (2016) Carbon rich organic fertilizers to increase soil biodiversity: Evidence from a meta-analysis of nematode communities. Agriculture Ecosystems and Environment. 232:199-207.

Mikan B, et al. (2018) Application of compost and clay under water-stressed conditions influences functional diversity of rhizosphere bacteria. Biology and Fertility of Soils. 54:55-70.

Pandey P, et al. (2016) A new method for converting food waste into pathogen free soil amendment for enhancing agricultural sustainability. Journal of Cleaner Production. 112(1): 205-213.

Stevenson FJ (1994) Humus Chemistry: Genesis, Composition, Reactions. Wiley, New York

Zhang, A (2012) Effect of biochar amendment on maize yield and greenhouse gas emissions from a soil organic carbon poor calcareous loamy soil from Central China Plain. Plant Soil. 351:263-275.