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  • Author or Editor: Dyremple B. Marsh x
  • Journal of the American Society for Horticultural Science x
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Abstract

Studies were undertaken to determine the critical Zn levels for cowpea [Vigna unguiculata (L.) Walp] grown in low N medium and inoculated with Rhizobium. Cowpea ‘California Blackeye No. 5’ was grown for 40 days in a sand culture using Zn application rates of 0, 0.06, 0.5, 1.0, 1.5, 2.0, 2.5, 2.8, 3.0, 3.1, 3.4, 3.7, 4.0, and 4.5 ppm Zn as ZnSO4. N2 fixation was estimated by acetylene reduction. Critical Zn deficiency levels were determined as 12.5, 20, 30, and 50 ppm for upper leaf petioles, upper leaf blades, lower leaf petioles and lower leaf blades, respectively, Critical Zn toxicity levels for these tissues was determined as 145, 273, 300, and 440 ppm, respectively. It was concluded that upper, recently matured, leaf petiole tissue should be used to assess plant Zn status. The percentage of reduction of N2 fixation was greater than the percentage of reduction in dry-matter accumulation under Zn-deficient conditions. N2 fixation increased linearly with increased Zn content of nodules and roots. At Zn levels above 150 ppm for both tissues, however, N2 fixation declined significantly. Applied Zn did not affect the growth and development of the root system and had little effect on reproductive development.

Open Access

Abstract

Zinc concentration, nitrogen fixation (C2H2 reduction), nodulation and dry-matter distribution in the early maturing cowpea [Vigna unguiculata (L.) Walp] line Mn 13 were examined at 5 levels of Zn (0.0, 0.6, 1.5, 2.5 and 5 ppm) under field and greenhouse conditions. Significant increases in nodule number, nodule dry weight, and acetylene reduction occurred when plants received the higher Zn levels. In all plant parts sampled, there was increased Zn accumulation with increased Zn application, with roots having the maximum accumulation. Seeds per pod and seed yield (kg/ha) were highest at the higher applied Zn levels. The yield response to added Zn was reflected primarily by an increase in the number of seeds per pod. Zinc nutrition is important to the nodulation and fixation processes, and it may affect both Rhizobium nutrition and dry-matter accumulation.

Open Access