RELATIONSHIPS BETWEEN SOIL THERMAL UNITS, NITROGEN MINERALIZATION ANDDRY-MATTER PRODUCTION IN PASTURES

Nitrogen (N) is of environmental concern if it leaches or is released as nitrous oxide (N2O). In order to utilize N efficiently in grazed pa sture systems, the fluxes of N from various sources need to be quantif ied. One flux is N mineralization from organic sources. Previous work has examined incubation and chemical extraction of soils as methods to determine N mineralization potential. This paper re-examines new and previously published data on net mineralization, with the aim of exami ning the relationships between soil thermal units, net N mineralizatio n (measured using acetylene incubations) and dry matter production in pastures. Net N mineralization is expressed as N turnover (net N miner alization as a % of total soil N). Relationships are developed between soil thermal units, dry matter production, and N turnover. These rela tionships have potential in advising farmers on potential N mineraliza tion from soil organic matter. A second use of such relationships is t he modelling of N transformations in pasture systems. Further work sho uld explore the effect of soil moisture on such relationships and exam ine the relationship between soil thermal units and uptake of N by pas ture.