Table I.

Chlorophyll content and growth characteristics of sunflower as affected by N form and external pH

Plants were grown for 2 weeks in nutrient solutions supplied with 4 or 40 mm N as NO3- or with 4 mm N as either NH4+ or NH4NO3. In all treatments, Fe was applied as FeIIIEDDHA at 1 μm. Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.

Treatments Chlorophyll Biomass Leaf Area
Roots Shoot
Spectral plant analysis diagnostic units mg cm-2
NO3-; pH 5.0 (green) 34.3 ± 0.7a 147 ± 17a 647 ± 49a 211 ± 8a
NO3-, 40 mm; pH 5.0 (green) 31.7 ± 0.7a 153 ± 25a 760 ± 58a 228 ± 16a
NO3-; unbuffered (chlorotic) 16.8 ± 4.2b 128 ± 9a 580 ± 42ab 183 ± 25b
NH4+; pH 5.0 (green) 35.0 ± 2.2a 90 ± 12b 356 ± 5b 128 ± 8c
NH4+; pH 7.5 (chlorotic) 3.9 ± 0.6c 56 ± 21b 345 ± 3b 110 ± 12c
NH4NO3; unbuffered (green) 35.6 ± 1.1a 157 ± 26a 724 ± 54a 266 ± 33a
NH4NO3; pH 7.5 (chlorotic) 4.2 ± 0.5c 42 ± 5c 335 ± 17b 123 ± 9c