Seasonal variation of mineral nitrogen, its leaching losses and nitrogen mineralization under different management practices: A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Agricultural Science in the University of Canterbury

Most of the nitrogen in soils is organically bound. This organic nitrogen is not available to the growing plants unless mineralized to the inorganic forms, namely: ammonium, nitrite and nitrate. On most normal soils however, the amount of nitrite present is usually negligible. Nitrogen mineralization is essentially a biological process. The pattern and amount of mineral-N produced annually must to a large degree be influenced by the environmental factors and therefore both are subject to seasonal variations. Also of particular interest is the efficiency with which the nitrogen mineralized each year is utilized in crop production. In recent years, there has been a growing concern on the extent of leaching losses. Allison (1965) pointed out that recoveries in harvested crops of nitrogen released from the soil, or added as fertilizer, were generally less than 50%. The aim of this study was to establish the seasonal variations of inorganic nitrogen levels, leaching losses and nitrogen mineralization, under different management practices