Lime effect on soil N availability indexes as measured by plant uptake

Abstract

Lime application to acid soils usually increases N mineralization but little is known about how it affects the N determined by methods that assess organic N availability. One incubation and three chemical methods were compared in twenty samples of unlimed or limed soils in a pot experiment with maize (Zea mays, L). The N availability methods included the NH₄ ⁺‐N released from soils by: a) anaerobic incubation for 7 days at 40°C; b) 2 mol/L KC1 at 100°C for 4 hours and distilled with MgO (hot KCl); c) this same procedure but distilled with 5 mol/L NaOH (hot KCl‐NaOH); and d) 30% v/v H₂O₂ and MnO₂. In addition, inorganic N, total N and organic C were also determined in the soil samples. Readily available inorganic N presented the highest correlation coefficient with N uptake by maize but anaerobic incubation, hot KCl, hot KCl‐NaOH, and total N were also good predictors of soil N availability. The H₂O₂/MnO₂ procedure and organic C produced inconsistent results. The amounts of N extracted by the methods tested were little affected by lime application. Multiple regression analysis showed that, among the methods that assess mineralizable organic N, the hot KCl methods accounted for most of the variation in N uptake by maize.