INTERACTIONS BETWEEN NITROGEN AND MANGANESE NUTRITION OF BARLEY GENOTYPES DIFFERING IN MANGANESE EFFICIENCY

Ammonium-fed plants may acidify the rhizosphere and thus increase avai lability of Mn in calcareous alkaline soils. The importance of N nutri tion in the differential expression of tolerance to Mn deficiency amon g cereal genotypes is not yet clear. Two factorial experiments testing effects of the NH4-N/NO3-N ratio and Mn fertilization on growth of ba rley genotypes differing in tolerance to Mn deficiency were conducted in two calcareous alkaline soils in pots in a controlled environment. In the soil containing 80% CaCO3 at pH 8.5, better root and shoot grow th and higher shoot Mn concentrations were achieved with nitrate suppl y, especially at lower rates of Mn fertilization The Mn-efficient geno type Weeah (tolerant of Mn deficiency) achieved better root and shoot growth than Mn-inefficient Galleon barley (sensitive to Mn deficiency) regardless of experimental treatment. Fertilization with Mn did not i nfluence total N concentration in barley roots and shoots. In the soil containing 5% CaCO3 at pH 7.8, ammonium-fed plants had better root an d shoot growth and, at shoot Mn concentrations above the critical leve l, Mn-inefficient Galleon performed better than Mn-efficient Weeah bar ley. It appears that differential expression of Mn efficiency among ba rley genotypes is not associated with differences in Mn availability e xpected to be produced by differential rhizosphere acidification as a response to different forms of N supply. There is an apparent preferen ce of locally selected barley genotypes for nitrate nutrition when gro wn on the highly calcareous alkaline soils of southern Australia. (C) 1997 Annals of Botany Company