Even degraded soils in Hawaii often hold a lot of carbon

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?

photo_soil pit with scale

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.

M.S. Defenses (yes, two!)

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.


Deep Soil Warming Hawaii – Initiated

heating_screenshot.pngM.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!

Will run (soil) samples for pizza


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!

The realities of carbon measurement

…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…

Diverse landscapes and agricultural systems

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…

Soil Health and Carbon Assessment Tool

@ElaineViska joined the lab this summer to expand our work on soil health and carbon sequestration in Hawaii.  A new data synthesis and networking grant from USDA NIFA for a web-based soil health and carbon assessment, monitoring and planning tool will support her Ph.D. work.  Elaine comes from Iowa State University with a strong foundation in the principles of soil health as well as field, lab, and GIS skills.  We are excited for her soils expertise and look forward to the coming years of collaboration on a project with great meaning for Hawaii, where re-conceived farming systems play a critical role in collective climate change action and building resilience into the island landscape.   IMG_5932 2.jpg

Advanced to candidacy, Jon Wells: congrats!

Congratulations to Jon Wells for advancing to his Ph.D. candidacy this spring.  Jon successfully defended his proposal “Understanding carbon in large-scale agricultural production systems for bioenergy in the tropics: selecting soils, feedstocks, and conversion pathways” and will continue his soil, plant biopolymer, energy, and carbon investigations towards the completion of his degree.

Return to pristine wetlands

Getting back to my academic origin this week, I found myself in one of the remaining pristine environments in Hawaii – Pepeopae on the island of Molokai.  Pepeopae is a mountain top wetland protected within the Kamakou Preserve by The Nature Conservancy.  Aside from a stray “naughty deer” this week, the wetland is ungulate and invasive plant species free.  This magical place resembles wetlands worldwide from the United Kingdom to Svalbard – commonalities exist in the form and function of plant communities and sensory experience of the wet ground, cool humid air, and color palette. Why is this wetland here, why doesn’t the water drain down the mountainous terrain?  A clay layer exists in the bottom of the peat, is it a buried spodic horizon or a shrink-swell clay layer that swelled and never shrank under a suddenly wetter climate 14,000 years ago?