Soil nitrogen availability in the cereal zone of South Australia. II. Buffer-extractable nitrogen, mineralisable nitrogen, and mineral nitrogen in soil profile under different land usesView Altmetrics View AltmetricsTools Xu, Z., Amato, M., Ladd, J.N. and Elliott, D.E. (1996) Soil nitrogen availability in the cereal zone of South Australia. II. Buffer-extractable nitrogen, mineralisable nitrogen, and mineral nitrogen in soil profile under different land uses. Australian Journal of Soil Research, 34 (6). pp. 949-965. ISSN 0004-9573
Article Link: https://doi.org/10.1071/SR9960949 AbstractMineral nitrogen (nitrate-N+ammonium-N) and its distribution in soil profiles to 60 cm depth at sowing in 3 growing seasons, 1990-1992, were assessed for 123 field experimental sites in South Australia. The sites were used to test N fertiliser responses with cereal crops following different land uses. More than 90% of the variation in mineral N at cereal sowing was attributable to nitrate-N in the 60-cm soil profiles. Coefficients of variation (CV) for nitrate-N ranged from 37 to 45%, less than half of the CV values (88-113%) for ammonium-N. More than 70% of mineral N in soil to 60 cm depth was accounted for by mineral N in the top 20 cm of soil, and 49% by mineral N in the top 10 cm of soil. The amounts of mineral N in the 60-cm soil profiles at sowing ranged from 24 to 180 kg N/ha (median 75) at sites following pastures, and from 22 to 113 kg N/ha (median 69) following grain legumes, significantly higher than 17 to 116 kg N/ha (median 47) following cereals. Only 26% of the variation in mineral N of soils (0-60 cm depth) could be predicted by soil total N, mineralisable N assessed by the aerobic incubation method, and previous land use. Ammonium-N extracted by phosphate-borate buffer from soils sampled at 0-10 and 10-20 cm depths was directly related to soil total N and N mineralised after soil incubation, but not to mineral N accumulating at sowing in the soil profiles to 60 cm depth. Utilisation of a soil containing 15N-labelled organic residues, and sampled to 100 cm depth at sowing in 5 successive growing seasons, revealed a positive relationship between the 15N atom% enrichments of soil profile mineral N, mineralisable N from soil incubations, and plant N. Enrichments of soil profile mineral N and plant N were almost identical. However, the enrichment of buffer-extractable ammonium-N was comparatively low and unresponsive to the time of soil sampling, and unrelated to the other soil and plant N pools. Thus, buffer-extractable N was unrepresentative of plant-available N.
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