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LEACHN Simulations of Nitrogen Dynamics and Water Drainage in an Ultisol
Author(s) -
Johnson Alan D.,
Cabrera Miguel L.,
McCracken Daniel V.,
Radcliffe David E.
Publication year - 1999
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1999.914597x
Subject(s) - leaching (pedology) , loam , environmental science , drainage , ultisol , soil water , mineralization (soil science) , secale , cover crop , hydrology (agriculture) , agronomy , nitrification , nitrate , growing season , nitrogen , soil science , chemistry , ecology , geology , biology , agroforestry , geotechnical engineering , organic chemistry
Nitrate leached from soils can contaminate drinking water and pose a health risk at concentrations > 10 mg N L −1 . Computer models may be useful management tools for estimating NO 3 leaching, but they need to be calibrated and validated before use. The objective of this work was to calibrate and validate LEACHN to simulate soil NO 3 , soil NH 4 , water drainage, and NO 3 leaching in a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). The calibration was done by determining rate constants and parameters under laboratory conditions. The validation data was obtained from a two‐year study with conventionally tilled corn ( Zea mays L.) during summer and either a rye ( Secale cereale L.) cover crop or fallow conditions during winter. Water drainage collected by tiles was automatically measured, subsampled, and analyzed for inorganic N concentrations. During the cold season, LEACHN underestimated soil NH 4 and NO 3 in at least half of the cases. During the warm season, the model correctly estimated soil NO 3 75% of the time, but it overestimated soil NH 4 in an equal 75% of the cases. Also, LEACHN overestimated cumulative drainage and leached NO 3 at least 50% of the time during both cold‐ and warm‐season periods. These results suggest that the soil hydraulic properties and N mineralization rate constants determined under laboratory conditions did not apply to field conditions. Also, results obtained by changing rate constants for N transformations indicate that LEACHN was not properly simulating N immobilization from fertilizer N, or nitrification under dry conditions.