Nutrient Availability in Soil Amended with Wheat Straw and Legume Residue

wheat vs faba.png

Study: Residue addition frequency influences respiration, microbial biomass and nutrient availability in soil amended with high and low C/N residue

In the image above I’ve basically highlighted the mature dried wheat straw in yellow with a C:N of 80:1 that was first applied to soil. After two weeks the same amount of the green young dry faba bean with a C:N of 20:1 was applied at differing amounts and frequency for two more weeks.

After application of the wheat straw you can see a decline in plant available nitrogen by 75% & phosphorus by 50% in the first two weeks.

After that two week period, adding the equivalent amount of faba bean residue then doubled the original available nitrogen and phosphorus availability, and it seems to me like it may have sustained much higher levels for longer had the study continued. Soil carbon priming in action.

The H1-L4 (High C:N wheat followed by 4 applications of Low C:N faba over two weeks) part of the study however is the most interesting for me. Instead of applying all the faba bean reside in one go, applying it in stages gradually increased (red line) the available N and P. This approach would probably be the most efficient nutrient wise as plant nutrient removal increases as the plant grows, so it makes sense to add the nutrients as it needs them. Plants typically remove nutrients in a sigmoid curve.

sigmoid growth curve.png


Residue Amendment and Soil Carbon Priming for Richer or Poorer

Feed the microbes carbon in C-poor soil and they’ll have a party.
Feed the microbes carbon in C-rich soil and they’ll put it in the C-bank.
This quote is of particular interest, emphasis mine:

The shift of bacterial community composition in response to residue amendment contributes to the sequestration of residue-C in SOC fractions.

Predator-prey carbon sequestration? Sounds similar to the Arthropod predator results. May the shift be with you.

The study:

A 150-day incubation experiment was conducted with 13C-labelled soybean residue (4%) amended into two Mollisols differing in SOC (SOC-poor and SOC-rich soils). …

The amounts of residue-C incorporated into the coarse particulate organic C (POC), fine POC and mineral-associated C (MOC) fractions were 4.5-, 4.3– and 2.4-fold higher in the SOC-rich soil than in the SOC-poor soil, respectively.

Residue amendment led to negative SOC priming before Day 50 but positive priming thereafter.

The primed CO2 per unit of native SOC was greater in the SOC-poor soil than in the SOC-rich soil. This indicates that the contributions of residue-C to the POC and MOC fractions were greater in the SOC-rich soil while residue amendment had stronger priming effect in the SOC-poor soil, stimulating the C exchange rate between fresh and native SOC.

The shift of bacterial community composition in response to residue amendment contributes to the sequestration of residue-C in SOC fractions.

The fate of soybean residue-carbon links to changes of bacterial community composition in Mollisols differing in soil organic carbon

Arthropod Predator Community & Soil Carbon Sequestration

The composition of the arthropod predator community and associated cascading effects on the plant community explained 41% of variation in soil C retention among 15 old-fields across a human land use gradient. We also evaluated the potential for several other candidate factors to explain variation in soil C retention among fields, independent of among-field variation in the predator community. These included live plant biomass, insect herbivore community composition, soil arthropod decomposer community composition, degree of land use development around the fields, field age, and soil texture. None of these candidate variables significantly explained soil C retention among the fields. The study offers a generalizable understanding of the pathways through which arthropod predator community composition can contribute to old-field ecosystem carbon storage.

Predator community composition is linked to soil carbon retention across a human land use gradient. – PubMed – NCBI

Microbes measure ecological restoration success

The researchers used next generation sequencing of the DNA in soil from samples taken across the site that had a range of plantings between six and 10 years old.

The technique – high-throughput amplicon sequencing of environmental DNA (eDNA), otherwise known as eDNA metabarcoding – identifies and quantifies the different species of bacteria in a sample.

The researchers – students Nick Gellie and Jacob Mills, Dr Martin Breed and Professor Lowe – analysed soil samples at the restoration site at Mt Bold Reservoir in the Adelaide Hills, South Australia, and compared them with neighbouring wilderness areas as ‘reference sites’.

“We showed that the bacterial community of an old field which had been grazed for over 100 years had recovered to a state similar to the natural habitat following native plant revegetation – an amazing success story,” says Dr Breed, Research Fellow in the Environment Institute.

“A dramatic change in the bacterial community were observed after just eight years of revegetation. The bacterial communities in younger restoration sites were more similar to cleared sites, and older sites were more similar to the remnant patches of woodland.”

Revegetation rewilds the soil bacterial microbiome of an old field – Gellie – 2017 – Molecular Ecology – Wiley Online Library

Plant Species Diversity Improves Soil Ecosystems. [Rant]

Plant species diversity doesn’t improve soil

The above quote was left as a reply to a comment I’d left on a big ag research and education industry video talking about cover crops ages ago. It still irks me that these people are so ignorant.

Today I read the following study on plant species diversity’s impact on soil ecosystems, albeit in a conservation and restoration context that ends up restoring degraded agricultural lands these people create:

Restoring and managing for more diverse plant communities can improve recovery of belowground biology and functioning in predictable ways. Specifically, we found greater accumulation of roots, more predictable recovery of soil microorganisms (bacteria and fungal biomass), more rapid improvement in soil structure (less compaction), and less nitrogen available for loss from the system  in prairie restored and managed for high plant diversity (>30 species) relative to the low diversity (<10 species) grassland plantings.  Thus, the hypothesis that biodiversity promotes ecosystem functioning is relevant to large-scale conservation and restoration practices on the landscape.

Restoration and management for plant diversity enhances the rate of belowground ecosystem recovery


40 Years of Organic Green Manure for the Win

A new study finds:

  • Organic Green Manure and Organic Animal Manure treatments increased cumulative water infiltration by about 10 times compared with the conventional farming treatment
  • Soil aggregates increased by 50% with the Organic Green Manure and by 30% with the Organic Animal Manure treatments in the upper 15-cm depth
  • At the same depth, bulk density was 3% lower under organic practices than in the conventional farming treatment, suggesting that organic farming reduces the soil’s susceptibility to compaction.

Organic Farming and Soil Physical Properties: An Assessment after 40 Years