Boles, J.C. and G.P. Robertson
Presented at the Campus Symposium (2001-04-19 )
The magnitude and importance of dissolved organic nitrogen (DON) as a vector for hydrologic N loss has been largely ignored in agricultural systems. It has only been measured in the surface horizons even in the forested systems where DON has been studied. The Long Term Ecological Research (LTER) site at the Kellogg Biological Station (KBS) provided the opportunity to measure and compare DON loss between several agronomic and forested systems. Teflon suction lysimeters were installed in the C horizon under replicated plots of four agronomic treatments, two perennial crops, early and mid-successional sites, and in both a coniferous and deciduous forest. The lack of significant differences in DON concentration between treatments, even given the wide range of inputs, disturbance, and plant communities, suggests that DON leaching is controlled primarily by hydrologic and abiotic factors. DON loss in agronomic systems was low compared to NO3-, but was 20 to 100% of total loss in perennial crops and successional systems due to low total N loss. Nitrate and total N loss tended to be greatest in the fall. DON concentrations were generally around 1 mg/l, whereas NO3- ranged up to ~ 60 mg/l, with most treatments under 30 mg/L. Nitrate loss was greatest under the four annual cropping systems. The low and zero input treatments had significantly higher nitrate loss than the perennial and successional treatments suggesting that increased N cycling, not inputs, were the cause.
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