Progress report for GW24-016
Project Information
Climate change has already made agriculture vulnerable to prolonged dry spells which have greatly affected agricultural yields and soil fertility. Nut trees, like almonds, are the most vulnerable to increased temperatures and water-induced stress. A projected increase of 1.5℃ by the mid-2030s would thus reduce rancher quality of life caused by shortened growing seasons and reduced harvests. Considering these risks, California has started a Healthy Soils to determine sustainable soil practices that farmers can adopt to mitigate risks from climate change. Among these practices is using biochar as a soil amendment; biochar has demonstrated the potential to improve soil health through increased water retention and carbon sequestration, among other benefits. Currently, our team is working on an on-farm demonstration site on a working almond orchard in Madera County, CA to explore the effects of two biochar types applied at two application rates on soil health and greenhouse gas dynamics. We propose to expand the scope of our field demonstration by adding research and educational activities that help inform best management practices for biochar use in orchard systems. Specifically, we propose a lab incubation study using growth chambers to measure the effects of biochar, separate and combined with cover crops, on soil properties and plant productivity under elevated temperatures and CO2 enrichment. We will also develop new educational resources, including an extension publication that will address gaps between public understanding and soil management practices, and multiple workshops, include a field-day, to demonstrate biochar application in almond orchards. Through these research and educational activities, we hope to demonstrate the role of biochar on orchard soil health and resilience to climate change and to generate new knowledge to inform safe and effective practices for biochar use in agricultural ecosystems.
Research Objectives
- Quantify the impact of the addition of two biochar types and two application rates to soil health, carbon dynamics, and greenhouse gas emissions in an almond orchard system
- Determine the separate and combined effects of biochar and cover crops on soil carbon, greenhouse gas emissions, and soil water retention under projected warming
Educational Objectives
- Develop an extension publication for American Farmland Trust’s (AFT) Farmland Information Center that will address gaps between farmer awareness and current available resources for recommendations on biochar application in orchard systems
- Develop and disseminate best management practices for biochar application in almond orchards and share these practices to orchard growers through outreach events
Cooperators
- - Producer
Research
Research Objectives:
The purpose of this lab incubation study is to measure the potential of biochar in reducing GHG emissions and increasing almond production under projected warming and CO2 enrichment. The goal is to provide farmers with reliable data to show the agronomic benefits of biochar in combination with cover crops and how to prepare for future environmental conditions. This is to be achieved by improving soil health through biochar-amended agricultural soils where we expect to:
- Quantify the impact of the addition of two biochar types and two application rates to soil health, carbon dynamics, and greenhouse gas emissions in an almond orchard system
- Determine the separate and combined effects of biochar and cover crops on soil carbon, greenhouse gas emissions, and soil water retention under projected warming
To achieve objective 1, we will continue managing our field experiment and routinely measure soil health and GHG fluxes. To achieve objective 2, we will measure changes in soil properties, WHC, SOC stocks, GHG fluxes, and above and below-ground plant biomass between our treatments and control under ambient and elevated temperatures and CO2 concentrations. By comparing field data to laboratory-derived data, we will be better able to articulate the best ways to manage orchard systems under projected climate change scenarios.
Materials and Methods:
Our current Healthy Soils project in collaboration with AFT takes place in an almond orchard in Madera County owned by farmer, Matt Angell. Our established experimental site covers 16 acres out of the 85 acres that have been cultivated for almonds for the past 15 years. This almond operation has been conventionally managed; no soil amendments had been previously applied and almond trees are irrigated using dual-line drip irrigation lines. Using this irrigation system, trees are fertilized with soluble fertilizers. In November of 2023, our team went out to the site to apply biochar at two different rates and using two different feedstocks to explore the impacts of different biochar characteristics on soil health. Our project design consists of 3 blocks with 4 plots per block: 3 treatments (T1, T2, T3) and 1 control (C). Treatment 1 refers to almond pruning biochar applied at a 2.25 US tons/acre rate. Treatment 2 is almond shell biochar applied at 2.25 US tons/acre rate. Treatment 3 is almond shell biochar applied at a 1.25 US tons/acre rate. We used a spatially balanced approach to determine which plots will be assigned the different treatments. After application of biochar, soils were tilled 1.5 inches down.
Maintaining this trial is our first goal of our project proposal. Our second goal is to complement this Healthy Soils project by conducting a lab incubation study to study the impacts of biochar on soil health, GHG emissions, and drought resiliency under a projected 1.5℃ temperature increase and CO2 enrichment of 300 parts per million (ppm), using similar parameters from our Healthy Soils project field experiment.
Experimental Design:
To do so, we will carry out our lab incubation study using two identical controlled growth chambers (100’’ x 35.5’’ x 101’’) (Conviron, Controlled Environments LTD, Canada), one set at ambient temperature and CO2 and the second supplied with elevated temperature (+1.5℃) and CO2 (+300 ppm). Biochar will be produced from almond shell waste as it is a more accessible and cheaper option than almond prunings. Like our field experiment, we will apply biochar to soils at a low and high application rate and introduce cover crops into our treatments. In total, we will have four treatments (T1, T2, T3, T4) and 1 control. Treatment 1 is almond shell biochar with a low application rate in combination with cover crops. Treatment 2 is almond shell biochar with a low application rate in the absence of cover crops. Treatment 3 is almond shell biochar with a high application rate in combination with cover crops. Treatment 4 is almond shell biochar with a high application rate in the absence of cover crops. Application rates of biochar will be calculated from the application rates applied in the field. To explore how the effects of biochar and CO2 enrichment on soil health and plant growth vary with different moisture regimes, we will have a low-water availability and a high-water availability scenario, defined at 40% and 80% field capacity, respectively. Each treatment and control will be replicated three times per water level in each growth chamber for a total of 30 samples under ambient environmental conditions and 30 samples under elevated environmental conditions (n=60). Environmental conditions will be monitored throughout the experiment to avoid a large field of error. For both growth chambers, light intensity and humidity will be fixed at a 11-hour photoperiod of 400 µmol/m2/sec and relative humidity of 50%, respectively. Temperature will be continuously monitored to guarantee that at ambient conditions, temperature is set at a seasonal average high of 15.7ºC and a seasonal average low of 3.9ºC. At elevated conditions, temperatures will be set at a seasonal average high of 17.2ºC and seasonal average low of 5.4º. Similarly, CO2 will be monitored to ensure that one growth chamber is set at ambient CO2 concentration of 410 ppm and the second growth chamber set at a CO2 concentration of 710 ppm.
To replicate field conditions, soils will be sampled in December 2025 from the three control plots from the experimental field site. Using a soil auger, soils will be randomly sampled to a depth of 30 cm where the edges of the berm and the alley meet to be able to explore the influence of biochar in combination with cover crops on soil properties and root formation of almond trees. Soil samples will be brought back to the laboratory where they will be placed in pots and carefully mixed with biochar for a tillage effect. Field-capacities of soils will be determined by weighing dry soils and fully saturating them and allowing the water to drain by gravity for 24 hours. Soils will then be weighed to determine the amount of water needed to reach 80% and 40% field-water capacities. To simulate cover crops, we will use a brassica seed mix and carefully plant ~4 seeds per jar for T1 and T3. The jars will then be randomly placed inside the growth chambers, where the lab incubation study is projected to start in Spring 2026.
Objective 1: Quantify the impacts of biochar application in an almond orchard system
Annual soil sampling campaigns will take place in December to sample soils down to 40cm using a 2.25 in diameter corer. Soils will be sampled in six random locations within each plot, three samples from the berm and three samples from the alley. Samples will then be transported back to the Agroecology Lab at UC Merced and left to air-dry. Using these air-dried samples, we will quantify soil health by measuring multiple soil properties. Soil organic matter will be measured on all soils using the Loss On Ignition method. To do so, soils will be sieved to 2 mm, oven-dried at 105℃ to correct for moisture, and then heated at 400℃. The ratio of the weights after heating at 400℃ and 105℃ is the mineral content and the amount oxidized is soil organic matter. Total soil organic carbon and nitrogen will also be measured on all samples after sieving the soils to 2mm and grounding the soils using a mortar and pestle. Pulverized samples will then be analyzed for soil organic C and N using Costech 4010 Elemental Analyzer and a Delta V Plus Continuous Flow Isotope Ratio Mass Spectrometer. Soil bulk density and pH will also be measured on all samples using a quantitative corer and glass electrode, respectively. Soil moisture, temperature, and EC will routinely be monitored throughout the experiment using Meter GS3 soil sensors connected to ZL6 Data Loggers. Similarly, soil GHG fluxes of CO2 , methane (CH4), and nitrous oxide (N2O) from both the berm and alley will be routinely measured every 2 weeks during the growing season, and once a month during the dormant period using a Picarro G2508 multi-gas analyzer and Soil Flux Processor software.
Objective 2: Determine the separate and combined effects of biochar under projected warming
Improve soil health & WHC
To study the effects of biochar on soil quality and WHC under projected warming, additional samples will be retrieved and homogenized to establish composite samples which will be used to obtain baseline data of soil properties. We will quantify pH and electrical conductivity (EC) using a standard glass electrode with a 1:2 soil slurry dilution, following a 10-minute calibration. Inorganic nitrogen will be extracted from a 20g subsample shaken in 75mL of 2 M KCl. Extracts will then be measured for ammonium (NH4+) and nitrate (NO3-) using a plate reader following Weatherburn (1967) and Downes (1978), respectively. We will calculate gravimetric water content using the drying method; fresh soil will be oven-dried at 105℃ for 3 days. Soil texture will be determined following the hydrometer method on two soil samples, one sample from 0-10cm and a second sample from 10-30cm. At the end of the experiment, we will measure the same variables via destructive sampling of our soils, excluding soil texture. During the incubation study, available water content will be measured by subtracting the weight of our samples at permanent wilting point from the weight at field capacity every 2 days. We will add water to our pots according to the amount of water that was lost. Additionally, we will measure stomatal conductance as an indicator for water-induced plant stress by recording evapotranspiration rates of our cover crops using a steady-state porometer. Lastly, we will measure soil microbial biomass carbon via a chloroform fumigation extraction method.
Increase soil carbon sequestration
To measure the effects of biochar in combination with cover crops on the potential to store carbon in the long run, we will measure the amount of total organic soil carbon from baseline soils and after destructive sampling of soil samples. To do so, 10g of each sample will be air-dried in the laboratory and sieved using a 2 mm sieve. Soils will then be ground using a mortar and pestle and submitted to the Stable Isotope Ecosystems Lab at UC Merced for determination of elemental carbon and nitrogen contents in soils via combustion using a Costech 4010 Elemental Analyzer and a Delta V Plus Continuous Flow Isotope Ratio Mass Spectrometer.
Reduce GHG emissions
During the experiment, we will measure soil GHG fluxes of CO2 , CH4, and N2O of each treatment and control using a Picarro G2508 multi-gas analyzer and Soil Flux Processor software. We will measure for fluxes soon after biochar application and once a week for the duration of the study.
Increase plant productivity
To measure plant productivity, we will quantify above and below-ground plant biomass after destructive harvesting of soil samples and plants. Above-ground plant biomass will be quantified by number of stems and plant height. Additionally, we will cut the plant at the base of the stems and record the weight using a tared balance. Similarly, below-ground plant biomass will be determined by sorting the roots from the soil by hand and recording the weight in grams.
Data Analysis:
Data Analysis will be performed in R where multiple packages will be used to conduct one-way or two-way analysis of variance (ANOVA) using LSD tests (p<0.05) and pairwise comparison of means for each treatment. R will also be used to find correlations between soil parameter using multiple linear regressions.
Objective 1 Preliminary data:
Stacked bar plots display the cumulative GHG emissions (in g CO₂-eq/m²/day) for CH₄, CO₂, and N₂O across different treatments, faceted by alley and berm. Different shades of black define gases: CH₄ (black), CO₂ (dark gray), and N₂O (light gray).
The figure shows the temporal variation in the difference in total inorganic nitrogen (μg/g dry soil) for each biochar treatment compared to the control across alley (left panel) and berm (right panel) from January 2024 to January 2025. Positive values indicate higher N availability in biochar-amended soils relative to the control. Biochar treatments include prunings (2.25 tons/acre, red), shells (1.25 tons/acre, green), and shells (2.25 tons/acre, blue).
No significant reduction or increase in CO2 emissions was observed, suggesting that the 2.6 tons of biochar carbon added to the system had persisted, emphasizing its potential to sequester carbon in the long run (Figure 1). Samples are still currently in the process of being analyzed for total carbon and nitrogen, as soil processing requires a lot of time and effort. Similarly, variability regarding nitrous oxide emissions was observed across the alleys and berms, while methane emissions were observed to be relatively small and even negative across time, suggesting that the soils in this system act as a methane sink (Figure 2). We found that soils amended with almond-prunings biochar at the higher application rate of 2.5 tons/acre had driven larger NO3-N concentrations (Figure 2). Application of biochar as a soil amendment is a long-term integration process. We expect soil transformation to be slow, as indicated by our preliminary results. However, higher nitrogen retention was observed among the berms during the growing season, indicating spatial and temporal variability, but that could also capture fertigation events upon data collection (Figure 3). Gas fluxes and nitrogen availability will continue to be monitored, and soils will be analyzed for bulk density, total carbon and nitrogen, pH, EC, and texture.
Objective 2:
We have been unable to begin our proposed lab incubation study as stated in our original timeline due to multiple factors. First, we were not able to begin spending funds until we were given approval, which did not occur until after the proposed start date of lab incubation study. Second, due to political changes, our funds were frozen for a period. Now that we have been allowed to resume spending, we are pushing our start date for the study to Spring 2026.
Research Outcomes
Biochar has emerged as a novel practice that is gaining fame for its soil health benefits. Based on this study, we recommend growers not to look at biochar as a sole fertilizer replacement. Instead, growers can optimize nutrient-use efficiency and increase carbon storage in their systems by applying biochar in combination with compost. We recommend this combination as an optimal soil amendment because biochar alone may pose safety risks and economic barriers. On the practical side, Application of biochar alone, especially at a high rate, may pose a combustion risk. Thus, requiring safety and biochar handling training and suitable equipment , especially for dry/wet broadcasting application. In this study, we found that a compost spreader was not an efficient means of biochar application as it is volatile and prone to wind erosion. If applied in combination with compost, application of biochar will be smoother and less cost-intensive. On average, biochar may range from $100 to $350 a ton, which growers may find unappealing. Nonetheless, a one-time application will suffice as we expect biochar disintegration to be a slow process and therefore, we expect biochar to persist in systems and see benefits to increase with biochar aging. If applying biochar alone, we also recommend to do so before tree establishment. This way, biochar can be applied using the trench-and-fill method and be able to incorporate the biochar deep into the soil profile. If applied in a mature orchard, the trench-and-fill method may not be the most suitable as this would disrupt the rhizosphere. In our study, we applied biochar manually using the broadcasting method. First, we applied biochar at the surface and then tilled 1.5'' down. However, tilling was only possible in the alleys, and biochar across the berms were left on the surface, which was exposed to both wind and water erosion.
Education and Outreach
Participation Summary:
This study, in collaboration with American Farmland Trust, places a large focus on communicating lessons learned, results, and best management practices to growers and ag professionals. Here, the goal is to hold a minimum of three workshops during the 3-year period as indicated on our proposed timeline. Our collaborators from AFT lead coordination and outreach, in both English and Spanish. After each outreach event, participants are encouraged to fill a post-survey.
The first workshop was held in April 2024 where we largely discussed about biochar benefits, risks and takeaways from biochar application, trial design, planned suite of measurements, and funding sources. Here, we noted different topics or results that the participants would like to see in the future, which we then applied to our second workshop. The second workshop (agenda attached) was held on April 30th, 2025. In this event, we discussed the different measurements we collect, and the analyses we are conducting. We did an on-farm demonstration of how we can measure how stable soil structure when saturated, as well as live measurements of greenhouse gases. At the same time, we shared preliminary data through two-pagers that we passed around (Biochar Preliminary Data), which we found to be the best method of communicating results.