Comparison of Different Methods for Evaluation of Available Nitrogen

The nitrogen availability in intensively rice growing soils from eight districts of Andhra Pradesh was evaluated by eight methods including three soil parameters and five chemical oxidation methods. Among the chemical methods, the available N extracted by hot K₂Cr₂O₇, cold K₂Cr₂O₇ and alkaline KMnO₄ were found suitable for predicting N availability to rice. The critical limits were,515, 450 and 323 kg ha⁻¹ for hot K₂Cr₂O₇, cold K₂Cr₂O₇ and alkaline KMnO₄ methods, respectively. These methods successfully delineated the rice soils into responsive and non-responsive to fertilizer N application. The K₂Cr₂O₇ oxidizable N methods were simple, rapid, reliable and a large number of samples can be handled in a short time.