Amid the COVID-19 pandemic, Casey McGrath departs the Crow Lab to (remotely) begin a Post Masters Research Associate – Environmental Data Analyst position at the Department of Energy’s Pacific Northwest National Laboratory in Richland, WA. For her M.S. Thesis, Casey established an innovative deep soil warming field experiment at the Lyon Arboretum in Hawaii and measured ecosystem carbon flux for one year of heating. Unlike any deep soil warming experiment to date, there was no significant respiration response to augmented soil temperatures past the surface layer. Multimodal analysis confirmed the hypothesis that high concentrations of amorphous minerals were the primary driver of the lack of respiration response, followed by high relative soil moisture and low bacterial richness. Casey graduated in Fall 2019 with her M.S. from University of Hawaii Manoa and a manuscript is nearly complete describing the findings. She hands off the field trial to the next student ready to pick up the project and focus the next phase on warming-related changes to microbial community structure and function. We miss Casey’s inquisitive, driven, and always positive attitude (and her baking) already in the Crow Lab, and wish her all the best in the next phase of her scientific career!
Elaine Vizka (center) shows off the range of soils and effects of bare surface, soil cover, and living roots on erosion and runoff to local high school students with the help of Casey McGrath (right).
Elaine recently received exciting news that her Graduate Student proposal to Western SARE (Sustainable Agriculture Research & Education) is funded. Her project is titled “A Hawaiʻi Soil Health Index to Guide Farmer Adoption of Sustainable Management Practices”. Her research will establish criterion for a farmer incentive program for sustainable management, use soil health to improve air and water quality, mitigate climate change, and maintain our soil resources, and empower producer decision-making through the workshops and web tool.
The State of Hawaiʻi enacted the Greenhouse Gas Sequestration Task Force act to begin establishing soil health criterion for a certification program where farmers and landowners may be rewarded for healthy management practices. For soil health to be accurately used as a tool, the indicators must be calibrated for local conditions to establish sensitive farmer accessible indicators, threshold values of measured indicators, and to understand soil health’s relationship to yield and carbon sequestration. Previous research identified 14 sensitive soil health indicators for Hawaiʻi, but these need to be further refined to calculate soil health scores and indices and to be relevant to farmer needs, including yield. Elaine’s research will address these shortcomings by establishing replicated on-field demonstration trials of varying management practices. She also will work with farmers and facilitate farmer-to-farmer training sessions and farm tours through annual soil health workshops.
Secrets of the belowground ecology of tropical perennial grasses help explain carbon drawdown in soils managed without tillage.
In three words – Roots. Microbes. Minerals.
Visible, aboveground greenery is grand and very easy to measure, but the belowground environment (and the organisms that occupy it) is more critical for climate smart and healthy soils. Belowground organisms include roots and microbes that interact with each other and soil minerals via multiple processes to collectively store carbon in high-functioning, climate smart and healthy soils.
Perennial grass species with massive root systems having characteristically low lignin concentration accumulated the most soil carbon during cultivation. Microbial decomposition of dead roots did not result in carbon losses as might be expected, but carbon gains as plant and microbe-derived organic matter quickly transformed from plant debris to mineral-bound organic molecules. Once protected on mineral surfaces, carbon resists further decomposition and accumulates.
Importantly, we tested whether warmer conditions expected with climate change may alter the balance. While the rate of accumulation slowed a bit, carbon accumulated nonetheless – a welcome bit of good news on the climate change mitigation front.
Perspectives for Hawaii – Reports on scientific papers appear in news feeds and social media, but what do the results mean for Hawaii? How, or does, it apply?
I tweeted about this Yale paper headlining “link between soil and crop yield is valid – to a point”. An assessment of available crop yield and soil carbon data globally showed more carbon associated with higher yield but only up to concentrations of 2% carbon.
In Hawaii, we’ve measured carbon in some of the most degraded agricultural settings and, at least in the surface soils, the concentration is nearly 2%. Volcanic ash soils such as those abundant on the Big Island and elsewhere, even when degraded, can range from 6 to 38% carbon.
Does this mean we can’t expect improved yields with climate smart practices meant to increase soil health and promote GHG sequestration in Hawaii? No.
The authors clarify “Because all locations will have different thresholds of how much a soil property can be changed and what level of a soil property is ‘good’ for that place”. The value of this synthesis is that it is a quantitative starting point to guide policy and practice to establish targets, but place-based relationships between soil carbon, organic matter, and crop yields must be established.
Carbon comprises about 50% of soil organic matter, which is a central component of soil health. Organic matter in soil provides substrate for the microbiome that releases nutrients through their metabolic activity, improves water relations, and increases aeration, all of which improve soil health and more.
Hawaii’s soils may have a high starting point for carbon, but they also have high potential to store even more due to deep soil profiles, volcanic ash deposits, and high productivity. The more organic matter accumulates, and is stored within multiple carbon pools in healthy, productive agroecosystems, the more climate, soil health, and yield benefits may be achieved.
Please see some of our research results on our project page for more details.
A hard deadline, such as your advisor leaving the country on sabbatical leave, is a reliable incentive for productive bursts. Two Crow lab students, Hannah Hubanks and Daniel Richardson, defended their theses late last year.
Hannah deduced parameters to comprise a future soil heath assessment for Hawaii’s range of cropland, grassland, and forested landscapes. Daniel measured the biological indicators of soil health four years after a heavily degraded agricultural soil converted to zero tillage management of tropical perennial grasses cultivated for biofuel production. The legacy of past intensive cultivation is evident in soil health even after long periods of abandonment and/or conservation management practices. Recognition and understanding of the unique challenges posed by the reclamation, reforestation, or improved management of previously intensively cultivated lands is critical for realistic expectations of carbon drawdown and productivity and provision of adequate support for those willing to invest in improving degraded lands.
M.S. student, Casey McGrath, turned on the heaters for her deep soil warming experiment at Lyon Arboretum in Manoa this week. She says “Here is a snippet from one of the five heater’s temperature sensors (at 60 cm) from the live feed of data: http://grogdata.soest.hawaii.edu under “Lyon” tab.” The protective effect of the non-crystalline minerals abundant in volcanic ash-derived soil predominant in the back of Manoa under the Tantalus formation is about to be tested. Here is a link to her blog post, check it out!
In the “Best Halloween Costume Ever” category – our fabulous departmental fiscal
support staffer, Megan, actually dressed up as a Crow Lab graduate student!!! I seem to have a bit of a reputation around here (well earned, I suspect, soil biogeochemistry cannot be done without thousands of sample analyses, I mean, come on!). Happy Halloween!
…continued from the previous post.
On the Whispering Winds farm hosting us to determine the soil carbon profile under bamboo, laying the grid and prepping the sample bags was the easy part. Two fearless graduate students (above), some hired muscle from a neighboring farm, and my dearly devoted husband spent the following two days slugging 24 1-m soil cores from the volcanic soil. As always, nothing goes as planned and a broken corer meant most of a day spent searching for a machinist in Hana to repair it while simultaneously seeking acceptable food for an 8 year old boycotting the local vegan fare. Yes, science is a family affair for us, which adds extra dimensionality to the career activities of dual-academic couples (but, that is for a different post).
We may have sampled fewer profiles and sometimes to a more shallow depth than desired. And, it sure would have been nice to have been on that outbound flight (I apologize again, Mokulele Airlines, you all are the best for dealing with us) rather than drive the Hana Highway at top speed (ha!) to make the connecting flight in Kahului. But, we made it back to Oahu where I could start separating each sample into roots, rocks, and soil. The soil is destined for carbon measurements needed to create the desired 3-D soil carbon profile. After several days: my nostalgia for lab work has worn off, I’m only 2/3’s done as the semester begins, and now a threatening hurricane is upon us.
To be continued…
The diversity of climates, biomes, and soils in Hawaii is as great as the communities, producers, and management practices that utilize the landscape there. The possible combinations of all these factors are numerous, which presents a challenge when providing recommendations for best land use and management practices to optimize economic and environmental returns. Nonetheless, an opportunity exists now to reconceive Hawaii’s agricultural systems as a critical part of achieving simultaneous state goals for carbon neutrality, 100% renewable energy, and increased local food production.
Building soil health and resilience into the landscape through diversified agricultural and managed systems is a critical climate action – one that will drawdown carbon from the atmosphere and reduce greenhouse gas emissions from the land surface. How much climate change mitigation a system may bring varies, and recently a colleague asked our research group to study the soil carbon associated with bamboo. The non-invasive, clumping bamboo varieties are beautiful and selected for building materials and landscape purposes. But, do they also sequester carbon belowground? Last weekend, we crossed some of our diverse managed landscapes on Molokai in a tiny plane bound for Hana, Maui to make some measurements.
To be continued…