Re-uploaded.

ABSTRACT

Some areas with historically mesic climates are predicted to experience more climate extremes, including longer droughts combined with hotter days and more intense precipitation. Drought and rewetting are known to alter carbon (C) and nitrogen (N) cycling. However, little information is available on how the effects of drought on C and N cycling differ with temperature and land use in soils from humid regions. We evaluated several metrics of C and N cycling under drought with or without heat stress in a forest site and conventionally and organically managed arable sites. We sampled undisturbed soil cores from 0 to 10 cm and incubated them under either reference conditions (REF), drought (DRT), or drought combined with heat stress (D + H). Metrics of C and N cycling, including actual and potential mineralization, enzyme activities, microbial biomass, and dissolved organic C and N, and microbial community structure were assessed at the end of the stress period and 14 and 28 d after rewetting. We found that the effects of D + H differed in magnitude and direction from those of DRT: cumulative C and N mineralization followed the order DRT < REF ≤ D + H. Land management affected stress response: mineralization was always greater in the forest and organic sites than in the conventional site. Post-wet pulses of C and potential net N mineralization were 1.7 and 3.6 times higher, respectively, in the D + H soils than DRT soils, and were greatest at the forest site. Only the organic site was sensitive to DRT alone. Across sites, microbial biomass N was reduced more by stress than C, and only N-cycle parameters failed to reach reference levels after the recovery period. In agreement with previous studies, the N cycle was more affected than the C cycle. Our results suggest that climate change-induced heatwaves during drought have implications for ecosystem C and N balance in mesic climates.

In soils with very high 2:1 clay contents, the soils expand and contract as they are wetted and dried. This creates shear faces called slickenslides, like the one shown above. Essentially they clay expands so much it's forced to shear somehow, and this is the resulting shear plane.

Look how thick the Ae (first) horizon is!

Profile description:

Ah: 0-2 cm; 10YR 2/1; SCL; Weak Fine Granular; Friable

R 2-100 cm

Solonetzic soils are formed when sodium rich ground water causes 2:1 clays to disperse, forcing columns to form

The structure is caused by sodium in groundwater dispersing the clay in the soil. These soils are hard to manage since the structure creates a hardpan, which causes water to pool in the subsurface and drown agronomic plants

Note the layer of carbonates (white) in the lower profile

Soil testing a few km away in a slightly similar area indicates a grey chromosol. This area has some of the oldest soils in Australia, possibly 370 to 320 million years ago. 20km away is 160 million years and supports a rich rainforest.

https://www.qld.gov.au/environment/land/management/soil/soil-testing/types

This is a typical forest subsoil for the boreal, but the structure is a lot stronger than normal.

Not sure if this is something the community here has interest in.

A section of the creek bank has fallen away, revealing that all of the soil has been recently deposited (~ last few decades). The garbage inclusion likely spreads for dozens or maybe hundreds of cubic meters of earth. We don't want to disturb the soil to clean this out so we're limited to surface level cleaning.

On the flipside: it's lots of deep fertile topsoil. The fast growing weeds, like lantana, absolutely love it.