Development of an isotopic method for evaluation of nitrogen availability of green manure

The study was conducted on the effect of three factors, types of labelled inorganic nitrogen fertilizer, their 15N abundance and ratio of nitrogen applied of inorganic nitrogen fertilizers and green manure (mug bean vine), and on evaluation of nitrogen availability of green manure by isotopic tracer method (A-value method). It was shown that the first two factors were the primary ones. There was no significant difference in nitrogen uptake efficiencies obtained from directly-labelling method and A-value method under the condition of application of labelled ammonium-fertilizers with 3% or higher 15N abundance and application of green manure at a rate equivalent to half or the same as inorganic fertilizer-N applied