A Soil Organic Nitrogen Fraction that Reduces the Need for Nitrogen Fertilization
2001
Mulvaney, R. L. | Khan, S. A. | Hoeft, R. G. | Brown, H. M.
The need to estimate mineralization has long been recognized in making N fertilizer recommendations, but little progress has thus far been made in identifying a specific fraction of soil organic N that affects crop responsiveness to N fertilization. After eliminating major defects in the methodology employed to fractionate the N in soil hydrolysates, a study was conducted to compare N-distribution analyses for soils differing in N-fertilizer responsiveness by corn (Zea mays L.). Hydrolyses with 6 M HCl were performed on composite soil samples (0–30 cm) that had been collected in late March or early April of 1990, 1991, or 1992, from 18 sites in a N-response study involving 75 site–years throughout Illinois with different soil types, crop rotations, and N management practices. Concentrations of amino sugar N were 33 to 1000% greater (P < 0.001) for 11 nonresponsive than for seven responsive soils, whereas no consistent difference was observed in their content of total hydrolyzable N, hydrolyzable NH₄–N, or amino acid N. Upon aerobic incubation for 3 mo with biweekly leaching, production of (NH₄ + NO₃ + NO₂)-N averaged 260% greater for three nonresponsive soils than for two responsive soils, and was accompanied by a net decrease in amino sugar N but not in amino acid N. Soil concentrations of amino sugar N were very highly correlated with check-plot yield (r = 0.79***) and fertilizer-N response (r = −0.82***). On the basis of amino sugar N, all 18 soils were classified correctly as responsive (<200 mg kg⁻¹) or nonresponsive (>250 mg kg⁻¹) to N fertilization.
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