Metal Interrelationships in Plant Nutrition: 2. THE RELATION OF METAL TOXICITY, MOLYBDENUM AND NITROGEN SOURCE TO CHLOROPHYLL AND MAGNESIUM CONTENT OF BEET IN SAND CULTURE

Sugar beet and spinach beet were grown in sand culture withdifferent sources of nitrogen or iron and different levels ofmolybdenum and heavy metals. Chlorophyll and some magnesiumfractions were determined. Extra molybdenum accentuated chlorosis caused by excess of Mn⁺⁺,Cr⁺⁺⁺, Zn⁺⁺, and Cu⁺⁺ and decreased it in the presence of CrO₄^––with nitrate. In the presence of these ions urea reduced chlorophyll in youngand increased it in old leaves of sugar beet. Effects of ureaand molybdenum were additive and independent. Ammonium sulphatecaused increased chlorosis of spinach beet with Mn⁺⁺ and Zn⁺⁺. The existence of an acetone-soluble magnesium fraction otherthan chlorophyll was shown. Excess Cu⁺⁺ and Zn⁺⁺ decreased totalmagnesium; Mn⁺⁺ did not. Mn⁺⁺ and Zn⁺⁺ reduced chlorophyll,increased the non-chlorophyll acetone-soluble magnesium, butreduced other fractions. Ferrous iron ipcreased total magnesiumcontent and also increased the acetone-soluble fractions inthe presence of Mn⁺⁺ and Zn⁺⁺. Extra molybdenum decreased theacetone-soluble magnesium fractions but did not affect the totalmagnesium content. Significant interactions between Mo, N, Fe, and heavy metalswere also disclosed.