Effects of forms of nitrogen fertilizers on growth and nitrogen uptake by Arawa and Hilgendorf wheat varieties, and on soil exchangeable ammonium and nitrate nitrogen levels : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science (Honours) in the University of Canterbury

Abstract

The essentiality of nitrogen for plant growth has long been established. However, the forms in which plants usually take in nitrogen from soils, have not been fully elucidated. It is commonly accepted that both exchangeable ammonium (NH₄-N) and nitrate (NO₃ -N) nitrogen are equally available to most plants, although more recent works have indicated that some plants can utilise a wide range of amino acids directly. Studies of changes in the levels of soil ammonium and nitrate nitrogen under wheat crops in Canterbury have led Ludecke (1972) to conclude that Arawa wheat plants could not use exchangeable ammonium directly as a nitrogen source. The present study was undertaken to examine this factor further. For this purpose, a second variety of wheat, Hilgendorf, which is more acid tolerant than Arawa, was also included. A pot trial was set up using four different forms of nitrogen fertilizer. A nitrification inhibitor, 'N-Serve', was used together with one of the fertilizer forms in an attempt to create different levels of soil exchangeable ammonium and nitrate, and to examine the effect of this on wheat performance.