Saturday, February 24, 2007

Rejuvenating Soil Life Requires Patience

Soil data is "noisy" data. Being a difficult medium to observe and measure, soil has an almost weird capacity to mask change.

In several instances that I can recall, it seemed improvement in soil carbon status was not evident until several years after a change in management was made. The increases in soil organic matter called intervening data into question.

You can see similar data fluctuations due to individual samplers, but this delayed stepping pattern of carbon increase happens a little too often to ignore. It is as if the momentum for an increase in carbon must first collect in the biological dynamic of the soil, invisible to our simple agricultural analysis tools where we measure TKN, TOC and C:N ratios. Those were my thoughts as I read the following:

The Four Phases of No-Till

Phase one, initialization, occurs in the first five years. It is where soil structure starts to improve and microbial activity increases. Additional nitrogen is required to do that.

"As organic matter increases, you need the added nitrogen to make more of it," Towery said.

The second phase is transition from the fifth to tenth years. This is when organic matter accumulates, soil aggregation and soil microbial activity elevates, phosphorous accumulates, and nitrogen immobilization and greater mineralization occurs.

Phase three is consolidation, from 11 to 20 years. In this period, carbon accumulates and additional water is available in the soil. Further nitrogen mineralization and immobilization occurs and there is an increase in cation exchange capacity (CEC) and nutrient cycling.

"These years aren't perhaps exact, because this phase depends on your latitude and your soils," Towery said.

The fourth and final phase is maintenance, which comes after 20 years. It brings a continuous flow of nitrogen and carbon, greater availability of water and high nutrient cycling with increases in nitrogen and phosphorus.

"Twenty years is a long time. It's not like you've arrived at the Promised Land but things do change with the soil," Towery said. "It's because it is a dynamic system. The technology and management strategies you use changes over time as you go from phase to phase.

"One change we underestimate is the changes in soil biology. We can't see them but they're there."

Photo: No-Till Milo in Wheat Stubble

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