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Soil Fertility & Plant Nutrition

Estimating Soil Mineralizable Nitrogen under Different Management Practices

^a USDA-ARS, Central Great Plains Research Station, 40335 County Rd. GG, Akron, CO 80720
^b Dep. of Agronomy, 2004 Throckmorton Plant Sciences Center, Kansas State Univ., Manhattan, KS 66506

^* Corresponding author (Maysoon.Mikha{at}ars.usda.gov)

Predicting in situ nitrogen (N) mineralization has been one of the greatest challenges to improving N management in agriculture. This study investigated the effect of tillage and residual N on soil N supplying capacity and evaluated the relationship between measured and estimated mineralizable N. The experiment was established in 1990 on a moderately well-drained Kennebec silt loam (Fine-silty, mixed, superactive mesic Cumulic Hapludoll) with continuous corn (Zea mays L.). The study was a split-split plot design replicated four times. The main plot treatment was tillage (no-tillage [NT] and conventional tillage [CT]), the subplot treatment was N source (manure and NH₄NO₃ fertilizer [F]), and the sub-subplot treatment was the length of residual period. Residual N was studied 1 yr after cessation of a 10-yr N application (R₁) and 6 yr after cessation of a 5-yr N application (R₆). Measured in situ N mineralization (N_min), laboratory potentially mineralizable N (N_o), and estimated N mineralization under field conditions (N_estimated) were evaluated. Nitrogen mineralization was studied in situ in an unplanted, sheltered area. Samples were collected from 0- to 5-, 5- to 15-, and 15- to 30-cm depths. No-tillage and manure significantly increased soil total N, N_min, and N_o. The combination of NT and manure significantly increased N_o in both R₁ and R₆. High correlation was observed between N_min and N_estimated for 0 to 5 cm (r = 0.79) and for 0 to 30 cm (r = 0.77). No-tillage and manure sustained soil N 6 yr after discontinued N application. Potential mineralizable N, for site specific conditions could be used to estimate in situ N mineralization after adjustment to field conditions (soil water and temperature).

Abbreviations: CT, conventional tillage • DOY, day of year • F, NH₄NO₃ fertilizer • N_estimated, estimated potentially mineralizable N from field conditions • N_min, measured in situ N mineralization • N_o, potentially mineralizable N • NT, no-tillage • R₁, 1 yr after cessation of a 10-yr N application • R₆, 6 yr after cessation of a 5-yr N application • SOM, soil organic matter

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