Nitrogen mineralisation in soils from Whakatane, New Zealand, in relation to their suitability for growing tobacco

Abstract

Mineralisation of nitrogen was studied in some Whakatane, New Zealand, soils recently converted from permanent pasture and currently under trial for the cultivation of tobacco. Amounts of nitrate and mineral-nitrogen formed on incubation were much higher than those in high-quality tobacco soils from Motueka and were comparable to those in other soils sampled under grass-clover pasture. The Whakatane soils contained about 2.5% to 4.0% allophane, which appeared to have little influence on rates of mineralisation, probably because of its low concentration.

Laboratory determinations of mineralisable-nitrogen appeared to provide a reliable guide for the behaviour of these Whakatane soils in the field. In initial plantings of tobacco on these soils, yields were low and, due to excess available nitrogen, the quality of the crops was poor. When the total and mineralisable-nitrogen of the soils decreased on continued cultivation, the quality of the tobacco crop improved considerably.