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Drivers of nitrogen dynamics in ecologically based agriculture revealed by long‐term, high‐frequency field measurements
Author(s) -
Finney Denise M.,
Eckert Sara E.,
Kaye Jason P.
Publication year - 2015
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/14-1357.1
Subject(s) - environmental science , tillage , leaching (pedology) , plough , crop rotation , cover crop , agronomy , cropping system , ecosystem , long term experiment , agriculture , nitrogen cycle , nitrogen , soil water , ecology , soil science , agroforestry , biology , chemistry , organic chemistry
Nitrogen (N) loss from agriculture impacts ecosystems worldwide. One strategy to mitigate these losses, ecologically based nutrient management (ENM), seeks to recouple carbon (C) and N cycles to reduce environmental losses and supply N to cash crops. However, our capacity to apply ENM is limited by a lack of field‐based high‐resolution data on N dynamics in actual production contexts. We used data from a five‐year study of organic cropping systems to investigate soil inorganic N (SIN) variability and nitrate (NO 3 − ) leaching in ENM. Four production systems initiated in 2007 and 2008 in central Pennsylvania varied in crop rotation, timing and intensity of tillage, inclusion of fallow periods, and N inputs. Extractable SIN was measured fortnightly from March through November throughout the experiment, and NO 3 ‐N concentration below the rooting zone was sampled with lysimeters during the first year of the 2008 start. We used recursive partitioning models to assess the importance of management and environmental factors to SIN variability and NO 3 − leaching and identify interactions between influential variables. Air temperature and tillage were the most important drivers of SIN across systems. The highest SIN concentrations occurred when the average air temperature three weeks prior to measurement was above 21°C. Above this temperature and within 109 days of moldboard plowing, average SIN concentrations were 22.1 mg N/kg soil; 109 days or more past plowing average SIN dropped to 7.7 mg N/kg soil. Other drivers of SIN dynamics were N available from manure and cover crops. Highest average leachate NO 3 ‐N concentrations (15.2 ppm) occurred in fall and winter when SIN was above 4.9 mg/kg six weeks prior to leachate collection. Late season tillage operations leading to elevated SIN and leachate NO 3 ‐N concentrations were a strategy to reduce weeds while meeting consumer demand for organic products. Thus, while tillage that incorporates organic N inputs preceding cash crops can promote synchrony of N mineralization and crop demand, late or post‐season tillage promotes NO 3 − leaching by stimulating SIN pulses that are asynchronous with plant uptake.