GROWTH AND NUTRITION OF YOUNG BEAN PLANTS UNDER HIGH ALKALINITY AS AFFECTED BY MIXTURES OF AMMONIUM, POTASSIUM, AND SODIUM

Abstract

High concentrations of bicarbonate (HCO⁻ ₃) cause alkalinity of irrigation water and are associated with suppression in plant growth and micronutrient deficiencies, such as iron (Fe) and zinc (Zn). Because reports indicate that the deleterious effects of alkalinity may be counteracted partially by supplementary potassium (K⁺) or ammonium (NH₄ ⁺) an experiment was designed to evaluate the response of bean plants (Phaseolus vulgaris L.) grown in high alkalinity conditions to varying proportions of NH₄ ⁺, K⁺, or sodium (Na⁺) (as a potential substitute for K⁺). Plants established in a growth chamber were grown in hydroponics for 21 days in solutions containing 5 mM HCO⁻ ₃ and a total of 5 mM of a mixture of NH₄ ⁺, K⁺, and Na⁺. The proportions of NH₄ ⁺, K⁺, and Na⁺ were designed according to mixture experiment methodology. Total N in all the mixture treatments was maintained at 10 mM by using nitrate (NO⁻ ₃)-N, thus the NH₄ ⁺:NO⁻ ₃ ratio varied according to the proportion of NH₄ ⁺ in the mixtures. Alkalinity caused suppression in plant growth and chlorophyll concentration in the younger leaves, whereas excessive NH₄ ⁺ was associated with leaf scorching and decreased leaf expansion. High proportions of K⁺ alleviated alkalinity symptoms and produced higher shoot and root dry mass provided that NH₄ ⁺ was included in the mixture. However, a proportion of NH₄ ⁺ higher than 0.333 in the mixture (>1.66 mM NH₄ ⁺) induced toxicity. The highest shoot dry mass occurred if the NH₄ ⁺:NO⁻ ₃ ratio was 0.19:0.81 and the NH₄ ⁺:K⁺:Na⁺ proportion was 0.38:0.38:0.24 (1.9 mM NH₄ ⁺ + 1.9 mM K⁺ + 1.2 mM Na⁺). Thus, an improvement in plant growth is achieved when NH₄ ⁺, K⁺, and Na⁺ are blended together, in spite of the high alkalinity treatment imposed. Optimum NH₄ ⁺ was associated with a decrease in solution pH and an increase in shoot Fe and Zn concentration.

Keywords:

• iron chlorosis
• lime induced chlorosis
• micronutrient solubility
• solution pH
• water quality

ACKNOWLEDGMENTS

The authors thank grant support from the Texas Ornamental Enhancement Program and the Fred C. Gloeckner Foundation, Inc. Special thanks to Dr. John A. Cornell for advising in trace plots interpretation.

Notes

^xMeans followed by different letter are significantly different according to the LSD multiple comparison test at P = 0.05.

^yActual pH measurements were transformed to H⁺ concentration to run ANOVA, mean estimation and comparison with SAS, and then the mean was re-transformed to pH units maintaining the results of mean comparison with data in H⁺ concentration terms.

^zSignificance according to F-test with P values indicated.

^xTo estimate the expected response of any growth parameter in this table, enter the proportion of NH₄ ⁺, K⁺, and/or Na⁺ in the solution of interest and multiply by the coefficients indicated in the respective model. The sum of the proportions of the three components must be equal to 1.

^ySignificance according to F-test with P values indicated.

^xMeans followed by different letters are significantly different according to LSD multiple comparison test at P = 0.05.

^ySignificance according to F-test with P values indicated.

^xTo estimate the expected response of any growth parameter in this table, enter the proportion of NH₄ ⁺, K⁺, and/or Na⁺ in the solution of interest and multiply by the coefficients indicated in the respective model. The sum of the proportions of the three components must be equal to 1.

^ySignificance according to F-test with P values indicated.