EFFECTS OF PHOSPHORUS AND IRON FERTILIZERS ON THE GROWTH OF 2 SOYBEAN VARIETIES AT 2 SOIL TEMPERATURES

The influence of FeEDDGA (0, 0.2 and 2 .mu.g Fe g-1 soil) and NaH2PO4 .cntdot. H2O (0 and 120 .mu.gPg-1 soil) on the growth of two Fe-ineffective soybean (Glycine max L. Merr.) varieties (Anoka and T203) on a calcareous soil at two soil temperatures (16 and 24.degree.C) was compared under greenhouse conditions. The two soybean varieties differed in the following respects: (a) T203 accumulated smaller concentrations of Fe in washed tops than Anoka under comparable conditions; (b) T203 was more susceptible to Fe deficiency and its accentuation by high levels of fertilizer P than Anoka; (c) T203 accumulated lower quantities of Mn in tops than Anoka under comparable conditions; (d) T203, but not Anoka, developed Mn deficiency symptoms when treated with P and 2 .mu.g Fe g-1 at 16.degree.C, Fe deficiency was more severe in both varieties at the higher soil temperature due apparently to: (a) greater plant concentration of P in tops at 24.degree.C; and/or (b) an increased rate of plant growth and greater dilution of Fe in young tissue at 24.degree.C. Foliar P concentration was increased much more than foliar Fe concentration by an increase in soil temperature. Severely Fe deficient T203 plants grown without FeEDDHA at 24.degree.C accumulated less foliar Mn than their FeEDDHA counterparts. Comparisons of Fe effectiveness of various soybean cultivars based on relative responses to FeEDDHA can be influenced by differential effects on Mn nutrition.