Soil Carbon Storage is Not Always Influenced by Tillage Practices

[OKIsItJustMe]

https://www.soils.org/press/releases/2009/0223/243/

Soil Science Society of America

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Contact: Sara Uttech, Soil Science Society of America, 608-268-4948, suttechatsoils.org

Soil Carbon Storage is Not Always Influenced by Tillage Practices

Although moldboard plowing combined with mineral N fertilization can lead to decreased organic carbon stocks in the soil surface relative to no-till, this effect is cancelled when the whole profile is considered.

MADISON, WI, February 23, 2009--The practice of no-till has increased considerably during the past 20 yr. Soils under no-till usually host a more abundant and diverse biota and are less prone to erosion, water loss, and structural breakdown than tilled soils. Their organic matter content is also often increased and consequently, no-till is proposed as a measure to mitigate the increase in atmospheric carbon dioxide concentration. However, recent studies show that the effect of no-till on carbon sequestration can be variable depending on soil and climatic conditions, and nutrient management practices.

Researchers at Agriculture and Agri-Food Canada (Québec City) investigated the impacts of tillage (no-till vs. moldboard plowing) and N and P fertilization on carbon storage in a clay loam soil under cool and humid conditions in eastern Canada. Corn and soybean had been grown in a yearly rotation for 14 yr. The results of the study were reported in the 2009 January-February issue of the Soil Science Society of America Journal.

The authors concluded that their investigation indicates “…no-till enhanced soil organic carbon (SOC) content in the soil surface layer, but moldboard plowing resulted in greater SOC content near the bottom of the plow layer. When the entire soil profile (0-60 cm) was considered, both effects compensated each other which resulted in statistically equivalent SOC stocks for both tillage practices”.

The effects of tillage and N fertilization varied depending on the soil depth considered. When considering only the top 20 cm of soil, the lowest C stocks were measured in the plowed soil with the highest N fertilizer level, whereas the highest SOC stocks were observed in the NT treatment with the highest N rate. The authors hypothesized that while N fertilization favored a greater residue accumulation in the top 20 cm of no-till soils, mixing of crop residue with soil particles and N fertilizer by tillage stimulated the mineralization of residue and native soil carbon. However, when accounting for the whole soil profile, these variations in the surface 20 cm of soil were counterbalanced by significant SOC accumulation in the 20- to 30-cm soil layer of tilled soils, resulting in statistically equivalent SOC stocks for all tillage and N treatments. This study further emphasizes the importance of taking into account the whole soil profile when determining management effects on SOC storage, especially when full-inversion tillage is involved. The authors conclude that “only considering the top 20 cm of soil would have led us to an erroneous evaluation of the interactive effects of tillage and N fertilization on SOC stock”.

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[Tashca]

1. First I've heard of this...

A few years ago research was showing the no-till system being superior to others in carbon retention. I find it interesting that they were not checking the whole soil profile. That would only make sense to me.
When the former research was being presented to show the no-till advantage something bothered me about it.
I could never put my finger on it.......it was being presented by people who were either no-till purists or had a financial stake in the no-till success.
I was a huge promoter of no-till in the early nineties. I thought is made sense in so many areas like soil erosion and reduced fuel usage. Like many times when we have tried to manipulate mother nature to our advantage we opened up a pandora's box of other problems. Deep compaction. ..Increased weed, insect, and disease pressure. We no longer buried the trash so to speak. This led to a massive increase in herbicide, insecticide, and fungicide applications. In a few short years I completely changed my mind about the great promise of no-till. The carbon storage ability was the only thing left that made it look promising. I was concerned we were going to have to try and make a failed system work.
Don't get me wrong there is still a place for no-till. I felt it was only a band-aid to much bigger problems that needed addressed. Soil is not dirt....it is a whole universe unto itself and we really don't know much about it.
I will follow this story closely.