How important is soil depth in ecology?

How important is soil depth in ecology?

A popular topic today is ecology management, and what we can do to help restore and repair the damage that has been caused due to human activities. What if I told you that there was a deeper understanding of the way soil repairs itself so that a former farm field could be put back to use faster, that sounds pretty good doesn’t it?
A recent study in the Loess Plateau, China looked at how this was possible. More specifically they looked at soil organic carbon (SOC) and total nitrogen (TN) at depths up to 100cm to see what was happening and what could be done to reduce the time to full soil recovery.
The study found several interesting facts. The first is that carbon and nitrogen increased in frequency when both were present. The more that carbon and nitrogen were available, the better the soil was over time. A similar study by Wang et al showed the same results.
This leads to my second point, the more time that a field was left to its own devices, the better the quality of soil, especially in carbon and nitrogen. It took greater and greater time for the deeper levels to return to their previous levels.
This does not mean that all levels had a dramatic increase in SOC and TN. The deepest levels had the least amount of variation in soil levels, but the older fields had higher levels because they had a longer time to return to their previous state. Depths between 20-70cm for SOC and 30-70cm for TN showed the same trends as the deeper levels.
The depths with the greatest variation in carbon and nitrogen were the 0-5cm ranges. At first SOC and TN concentrations were much lower, they increased somewhat, and within a range of one to thirteen years the soil layer was back to its previous state.
The reason why the carbon and nitrogen levels were the lowest initially is due to farming itself; a certain amount of straw and nutrients were removed the last time the field was used. With no fertilizer and plants to replenish the soil, it is lacking many nutrients.
At time goes by, plants begin to take over the field, which supplies carbon and nutrients through degradation of dead plant matter and interactions between the soil and plants themselves. Over a period of 30 years the plants help to restore the soil back to its previous state.
Additionally, belowground biomass, plants and animals below the ground, which include dead roots, mycorrhizae, and exudates, are important to recharging carbon and nitrogen in the soil. Since farming activities is not disturbing the soil the plants and animals are better able to do the activities that come naturally to them.
It is clear that we are closer to understanding how to repair the damage that has been caused by human activities, especially farming but there is no clear answer into how we may speed up that repair. The study above is a promising lead but shows that we need to investigate further how animals and plants affect SOC and TN levels in deeper soil levels. With a better understanding of nature in soil, we can repair the damage humans have caused faster.

Smt8 (Stephen Truch)
Picture courtesy of http://www.upload.wikimedia.org
Informal
Source: Deng, Lei; Shangguan, Zhou-Ping; Sweeney, Sandra. “Changes in Soil Carbon and Nitrogen following Land Abandonment of Farmland on the Loess Plateau, China.” (August, 2013): 8p. PLOS ONE. 14 October. 2013.

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