Micronutrients

Abstract

Four crops, corn, pearl‐millet, sorghum, and cowpea were evaluated for their relative Zn response at 0 (original Zn deficient soil), 1, 2, 3, 4, 5, 10, 20, 40 and 100 mg Zn kg^‐1 soil under greenhouse conditions. Corn and pearl‐millet were harvested at earing, and sorghum and cowpea at maturity.

Crops differed in their response to Zn deficiency in soil. Zinc deficiency symptoms were more severe in corn and cowpea than sorghum and pearl‐millet. The maximum yields in corn, pearl‐millet, sorghum‐stover, sorghum‐grain, cowpea‐straw and cowpea‐grain were recorded at 4, 4, 1, 5, 2, and 5 mg Zn kg^‐1 soil, respectively, which were 5628, 191, 86, 563, 304 and 723% more than at 0 Zn. Adverse effects of Zn deficiency were more pronounced on grain yield of sorghum and cowpea than their stover/straw components. Zinc, more than 20 mg kg^‐1 soil, caused depressed pearl‐millet and cowpea yields.

In corn and cowpea, showing severe Zn deficiency symptoms, shoot Zn at 0 Zn was more than plants receiving 10 and 2 mg Zn kg^‐1 soil, respectively, but uptake was much less than those receiving Zn. In all the crops, Zn increased with increasing Zn level from 1 to 100 mg kg^‐1 but not in the same proportion. More Zn was accumulated in grain than stover/straw at low levels of Zn, but the pattern was reversed at high Zn levels. Cowpea grain and straw accumulated proportionately more Zn than sorghum grain and straw with increasing Zn level.

Differential response among crops to Zn deficiency in soil was closely related to their capacity to exploit soil Zn. Results also showed that under severe crop Zn deficiency conditions tissue Zn concentration might not be a suitable parameter for predicting Zn requirement. Magnitude of Zn response to applied Zn was related to P/Zn ratio of crops at 0 Zn level. Cowpea cv F68 could also be used as an indicator crop for Zn deficiency in soil.

Key words:

• Genotypic variability
• Zn‐response
• forage crops