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Soil Carbon and Nitrogen Under a Long-term Fertilizer Gradient

 

The connection between commercial N fertilizer and soil organic carbon is widely debated. In a recent article in the Soil Science Society of America Journal, researchers examined how long-term nitrogen use affected soil C and N in continuous corn production. The study was conducted at a long-term research trial near Arlington, WI, established in 1958 and managed under three N rates: low (10 kg-N ha-1), recommended (168 kg-N ha-1), and high (280 kg-N ha-1).

The low rate of N application caused significant decreases in soil C and N content down to 100 cm, while no differences were determined between the recommended and high rates of N. In addition, plots receiving the low application of N were lower in elevation and had less depth of the A horizon.

Researchers also reanalyzed archived samples from 1984, which showed no significant loss in soil C and N content in surface horizons when compared to 2011 samples as long as N fertilizer was applied at the recommended rate or higher. This research shows that N fertilizer was a benefit to this cropping system as maintenance, but not building, of SOC occurred. In addition, over-application of N, while not agronomically beneficial, was not detrimental to SOC, contrasting with previous suggestions that over-application of N would lead to degradation.

The authors also note that the total C return to the soil via corn stalks (estimated from yield) have increased linearly since the inception of the study (primarily attributed to improvement in corn genetics), suggesting a continual increase in C input may be required to maintain the same SOC content of the soil in this system.   

Read the full open access article in SSSAJ.