NITROGEN MINERALIZATION IN SOILS OF VARYING TEXTURE, MOISTURE AND ORGANIC-MATTER .1. POTENTIAL AND EXPERIMENTAL VALUES IN FALLOW SOILS

Estimates of nitrogen availability based on the nitrogen mineralisation potential, N0, and the mineralisation rate constant, k, increased within the sequence, loamy sand, coarse sandy loam and loam, and were consistently higher in the high labile organic matter counterparts of the soils. There was a similar trend in the production of inorganic nitrogen at ambient temperatures. Under these conditions, an increase between mid-April and the end of May was followed by a trough in June and July and a second increase from early August to the end of September. Nitrogen production was generally higher where soil moisture was allowed to fluctuate widely in the available range, compared with a moisture regime near field capacity. Results of short-term incubations indicated that net mineralisation was minimal or negative in June and July. There was a significant relationship between values calculated from N0 and k and those obtained near field capacity in the second period of mineralisation when soil temperature was relatively constant, but not in the first period when soil temperature was rising. The time required for mineralisation of 50% of N0 indicated that less than half the potential value would become available in a normal temperature growing season. © 1979 Martinus Nijhoff Publishers.