Friday, 10 May 2013

Deep, permeable soils buffer impacts of crop fertilizer on Amazon streams, MBL study finds

Science Codex reports on research carried out in the Southern Amazon showing that some of the damaging impacts of agriculture on fresh water may be buffered by the very deep and highly permeable soils that characterize large areas of the expanding cropland.

The researchers looked specifically at the impacts of soybean agriculture on water quality and quantity at Tanguro Ranch, a 200,000-acre farm similar in climate and geography to large tracts of the Amazon where soybean production, largely for export as animal feed, is expanding rapidly. The ranch has watersheds that are entirely forested, as well as watersheds that are now entirely soybean cropland, allowing for a comparison.
"We were surprised to find that, despite intensive agriculture at Tanguro Ranch, the streams do not appear to be receiving a significant amount of either nitrogen or phosphorus, despite a high application of phosphorus fertilizer to adjacent cropland," says lead researcher Christopher Neill, director of the Ecosystems Center at the Marine Biological Laboratory (MBL).
This is in contrast to many Northern Hemisphere cropland areas where fertilizers are known to add nutrients to the soil that, with rainfall, run off into freshwater streams and rivers, leading to over-fertilization and low-oxygen conditions that endanger fish and other aquatic life.
At Tanguro Ranch, however, "the soils are old and highly weathered, very deep, and likely to be fairly uniform over great depths," Neill says. "Water infiltrates the soil very rapidly, and the soil has a great capacity to absorb the nutrients. It appears to act as an enormous buffer."

Read more here.