|Foy, Charles - CSL, COLLABORATOR|
|Davis, John - NRCS|
|Kemper, William - NPL, RETIRED|
Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 10, 1999
Publication Date: October 1, 1999
Citation: FOY, C.D., SADEGHI, A.M., RITCHIE, J.C., KRIZEK, D.T., DAVIS, J.R., KEMPER, W.D. ALUMINUM TOXICITY AND HIGH BULK DENSITY: ROLE IN LIMITING SHOOT AND ROOT GROWTH OF SELECTED ALUMINUM INDICATOR PLANTS AND EASTERN GAMAGRASS IN AN ACID SOIL. JOURNAL OF PLANT NUTRITION. 1999. VOL. 22(10). P. 1551-1566. Interpretive Summary: Shallow rooting and susceptibility to drought are believed to be caused partly by strongly acidic aluminum (Al)-toxic subsoils. The Al toxicity idea was tested on unlimed and limed plots of acid, compact, derelict soil at Beltsville, MD. Al-tolerant and sensitive cultivar pairs of barley, wheat, snap bean and soybean were used as indicator plants. Eastern gamagrass, which is reportedly tolerant to such problem soils, was used for comparison. Al-tolerant cultivars showed less lime response than Al-sensitive cultivars, indicating that Al toxicity was a growth limiting factor in this acidic soil. Differential tolerance to the acid soil was particularly marked in snap bean. Contrary to expectations, Al-indicator plants did not differ in ability to root in the 15-30 cm soil layer. Only 9 to 25% of total roots were in this zone, with the majority being in the 0-15 cm plow layer. No roots were found in the 30-45 cm zone. High soil bulk densities were found in the 15-30 and 30-45 cm layers, indicating that compaction was a primary root limiting factor. Restricted shoot growth and shallow rooting were due to a combination of Al toxicity and high soil bulk density. Eastern gamagrass showed no lime response in acidic soils and was exceptionally tolerant to severe droughts of 1997 and 1998 and produced high forage yields. Outstanding drought tolerance of the species is undoubtedly due to deep rooting. Gamagrass roots were found at a depth of 150 cm, compared with <30 cm for crop plants tested. Eastern gamagrass seems ideally suited for reclaiming many derelict soils that are underlain by strongly acidic, wet, dry or compact subsoils. These results show the potential for use of eastern gamagrass on marginal soils and demonstrate the value of well-adapted crop cultivars.
Technical Abstract: Shallow rooting and susceptibility to drought are believed to be caused, at least in part, by strongly acidic (pH <5.5) Al-toxic subsoils. The Al toxicity hypothesis was tested on a Matawan-Hammonton loam complex on unlimed and limed field plots (pH range of 5.1 to 5.8) at Beltsville, MD. Al-tolerant and sensitive pairs of barley, wheat, snap bean and soybean cultivars (cvs.) were used as indicator plants. Eastern gamagrass, cultivar "Pete," reported to tolerate both chemical and physical stress factors in soils, was grown for comparison. Al-tolerant cvs. showed less lime response than Al-sensitive cvs., indicating that Al toxicity was a growth limiting factor in this acid soil at pH 5.1. Differential tolerance to the acid soil was particularly striking in snap bean cvs. Unexpectedly, Al-tolerant and sensitive cvs. did not differ in abilities to root in the 15-30 cm soil depth. Only 9 to 25% of total roots were in this layer, and 75 to 91% were in the 0-15 cm zone. No roots were found in the 30-45 cm zone. High soil bulk density values of 1.44 and 1.50 g/cm3, respectively, in the 15-30 and 30-45 cm zones indicated that mechanical impedance was a primary root barrier. Results indicated that restricted shoot growth and shallow rooting of the Al-indicator plants were due to a combination of Al toxicity and high soil bulk density. Unlike the Al-indicator cvs., eastern gamagrass showed high tolerance to acid, compact soils and gave no lime response. It also showed exceptional tolerance to drought, yielding up to 7 Mg/ha of forage. Roots were found at a depth of up to 150 cm.