Soil plant nitrogen relations of tobacco at Mareeba, north Queensland

Nitrogen changes were studied in a red earth on which tobacco grew with very small additions of nitrogen fertilizer. Soil nitrate accumulation in the dry season before transplanting, and mineralization during the tobacco season, provided most of the plant's nitrogen requirements. Plant nitrogen uptake continued longer than in other countries, and the total amount was greater, particularly in stems and suckers. Though the plants gained nitrogen during the harvest period, leaf nitrogen concentration decreased. This resulted from translocation from lower leaves and growth of upper leaves. Decrease in leaf nitrogen concentration was essential to quality. The necessary sequence, of sufficient nitrogen for yield, followed by decreasing nitrogen availability for quality, occurs on this soil with small fertilizer additions. There is need for survey work on nitrogen availability and the time sequence of nitrogen uptake by plants on related Mareeba soils.