Article
Weathering the Storm (and the Dry)
by Dr Ash Martin PhD BSc(For)Hons
Think about how your soil reacts when it goes through a dry spell and then gets wet again – that’s what this study looked at. They wanted to understand how this wetting and drying affects important things like carbon (C), phosphorus (P), and nitrogen (N) in the soil. These are all crucial for healthy plants.
What they did: Scientists took soil from different parts of southern Australia – different soil types and farms with different histories. They dried out the soil and then re-wetted it, like a mini-drought and rain event. They then measured how much the soil “breathed out” carbon dioxide (CO₂), which tells us how active the soil microbes are and how quickly they’re breaking down organic matter. They also looked at how much nitrogen and phosphorus became available for plants.
What they found:
- Wetting after drying can give the soil a “boost”: In many of the soils (13 out of 32), the dry-rewetting actually increased both the amount of carbon that could be broken down and how fast it was broken down. It’s like the soil microbes got a burst of energy when the water came back.
- Sometimes it just speeds things up: In another group of soils (17), the rate of carbon breakdown increased after wetting, but the total amount of carbon that could be broken down didn’t change.
- Clay matters: The amount of clay in the soil seemed to be a big reason why some soils had a bigger “boost” in carbon breakdown after wetting and drying. Soils with more clay tended to have a bigger increase.
- It’s complicated: While clay was important, looking at a whole bunch of things together (like different types of carbon in the soil) gave a better picture of how the soil would react to wetting and drying.
- Nitrogen and phosphorus didn’t follow the same pattern: The “boost” in carbon breakdown didn’t necessarily mean a big release of nitrogen and phosphorus for the plants right away.
What this means for you:
- Dry and wet cycles are a natural part of farming, and they can have a real impact on your soil. This study shows that these cycles can actually make some carbon more available in the short term.
- Soil type matters, especially clay content. Soils with different amounts of clay might react differently to dry and wet periods.
- Carbon is a key player: The way carbon behaves after a dry-rewetting event is important for overall soil health and how nutrients cycle.
- Don’t expect a simple relationship with nutrients: Just because carbon is being broken down faster doesn’t automatically mean more nitrogen and phosphorus will be available to your crops immediately. The release of these nutrients is a complex process.
In simple terms, this research tells us that when your soil goes through a dry spell and then gets rain, it can stir things up. It can lead to a flush of activity where carbon is broken down more quickly. Clay in your soil plays a role in how big this effect is. Understanding this helps us appreciate how dynamic our soils are and how weather patterns can influence soil health.
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Read the in-depth article:
Butterly et al. (2010). Rewetting CO2 pulses in Australian agricultural soils and the influence of soil properties. Biology & Fertility of Soils. 46: 739–753.
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