Field Testing of Several Nitrogen Availability Indexes
1978
Fox, R. H. | Piekielek, W. P.
With no quick, reliable soil N availability test for humid region soils, N fertilizer recommendations in these areas are being made on the basis of crop N requirements. When the variability in N-supplying capability of soils is not taken into account, most N fertilizer recommendations will be inaccurate, leading to inefficient use of N, less economical crop production, and the potential for N pollution of the nation's air and water. Although several N availability indexes have proved to be well correlated with the N-supplying capability of a soil in greenhouse or laboratory experiments, very little testing of these indexes has been done with field experiments. Eight N availability indexes were correlated with the capability of eight Pennsylvania soils to supply N to field-grown corn (Zea mays L.) in 1976 and 1977. Boiling 0.01M CaCl₂ and 0.01M NaHCO₃-extractable N were both significantly correlated at the 1% level (r = 0.86 and 0.77, respectively) with the N-supplying capability of the soils from the combined 1976 and 1977 experiments. Autoclave-extractable NH₄-N and total soil N were significantly correlated with the soil supplying capability at the 5% confidence level (r = 0.70 and 0.68, respectively). Walkley-Black soil organic matter, soil NO₃⁻, and H₂SO₄-extractable and KCl-extractable N were not significantly correlated with N availability in the field. Though four of the indexes were well correlated with the N availability in the soil, time and expense necessary for these analyses may preclude their being used routinely by soil testing laboratories.
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