Calcium Deficiency in Sorghum Grown in Controlled Environments in Relation to Nitrate/Ammonium Ratio and Nitrogen Source
- H. M. Murtadha,
- J. W. Maranville and
- R. B. Clark
Sorghum [Sorghum bicolor (L.) Moench] grown under growth chamber and greenhouse conditions often develops Ca deficiency. Since information on factors affecting Ca uptake and distribution in sorghum is limited, experiments were conducted to better understand factors associated with the enhancement of this disorder. Sorghum genotypes ‘Redlan’ and ‘Martin’ were grown in a growth chamber with 21.4 mM N (300 mg L−1) at NO−3/NH+4 ratios of 300:0, 250:50, 200:100, and 150:150, with Ca levels of 1.25 or 2.50 mM(50 or 100 mg L−1, respectively) to determine the effects of these N ratios on sorghum growth in nutrient solution and the occurrence of Ca deficiency. The same genotypes and conditions were used in a N source experiment where NO−3, NO−3/NH+4 (1:1), NH+4, and urea were compared. Symptoms of Ca deficiency were visible on young leaves of plants grown in solutions containing high proportions of NO+4 and low levels of Ca, but not with NO−3 only or urea. The pH of solutions in the NO−3/NH+4 ratio experiment were higher with NO−3 as the predominate N source. Growth and Ca concentrations decreased but total plant N concentrations increased with high proportions of NH+4 in the treatment solutions and with decreased Ca levels. Thus, N/Ca ratios increased progressively as the proportion of NH+4 in the nutrient solution increased, which also corresponded to increasing severity of Ca deficiency observed on leaves. Lower leaves had higher Ca concentrations than upper leaves indicating the relative immobility of Ca in sorghum. When comparing N sources, plants grown with NO−3 or urea as the sole source of N generally had the best growth and the highest Ca concentrations, followed by plants grown with 1:1 NO−3/NH+4, and NH+4 only, respectively. Dry matter yields increased with increasing solution Ca levels regardless of N source. The enhance uptake of Ca in sorghum when grown with only NO−3 is believed to occur partially as a mechanism to counterbalance anion absorption and maintain proper cation/anion balance. It is likely that a reduction in Ca concentration in plants grown with high NH+4 was partially a result of reduced solution pH exerting antagonistic effects on Ca absorption or releasing Ca from cell wall anionic sites. Reduced and abnormal root growth resulting from high solution NH+4 may have enhanced the appearance of Ca deficiency symptoms by reducing Ca uptake due to reduced absorbing surface or lack of root tip growth.
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