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ARS Home » Research » Publications at this Location » Publication #144599
Title: SOYBEAN GROWTH ON A CALCAREOUS SOIL AS AFFECTED BY THREE IRON SOURCES

Author
item HEITHOLT, JAMES - TEXAS AGR.EXP.STN. DALLA
item SLOAN, JOHN - TEXAS AGR.EXP.STN.
item MACKOWN, CHARLES
item CABRERA, R. - TEXAS AGR.EXP.STN.

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2003
Publication Date: 8/1/2003
Citation: Heitholt, J.J., Sloan, J.J., Mackown, C.T., Cabrera, R.I. 2003. Soybean growth on a calcareous soil as affected by three iron sources. Journal of Plant Nutrition. 26(4):935-948.

Interpretive Summary: Iron (Fe) chlorosis can reduce yields of crops and is a common symptom in many soybean producing areas throughout the United States. On the alkaline Blackland soils found in Texas, Fe chlorosis occasionally appears during vegetative growth of soybeans but often disappears by the time plants flower. It is not clear whether preplant additions of Fe can enhance soybean growth or yield on this soil or whether different sources of Fe fertilizer is important. A preliminary greenhouse study with soybean plants grown in pots was conducted using a mineral and two chelated forms of Fe. Nutrient analysis leaf greeness measurements, and biomass accumulation was measured during vegetative and reproductive growth. Leaf Fe levels were generally greater with the chelated Fe than the mineral source of Fe. Visible symptoms of leaf Fe chlorosis were not evident at any time and were consistent with leaf Fe levels exceeding the accepted critical level for Fe stress. The overall average seed yield of plants fertilized with Fe was 12% greater than the average of plants not treated with Fe. However, statistical tests of this difference revealed that this trend was not significant. While our results do not suggest that soil-applied Fe will consistently stimulate soybean growth or yield on this soil, at least when chelate extractable soil Fe is at 12 mg/kg or greater, we believe that the trend for increased seed yield in some of the Fe treatments warrants field studies using soil- and/or foliar-applied Fe. These results will be useful to agronomists and consultants seeking to improve or eliminate potential micro nutrient stresses of soybean grown on soils similar to the high pH Blackland soils of Texas.

Technical Abstract: On Blackland soils found in Texas, Fe chlorosis may appear during vegetative growth of soybean (Glycine max L. Merr.), but often abates by flowering. It is uncertain if preplant additions of Fe can enhance soybean growth on these soils or if the source of Fe is important. In a greenhouse study, soil (10 kg/19 L pot)from a pH 8.4 Houston Black clay (fine, smectitic, thermic Udic Haplusterts), with 11.7 mg Fe/kg (DTPA-extractable), was treated with FeSO4 (0, 3, 10, 30, and 100 ppm Fe) or with 0, 0.3, 1, 3, and 10 ppm Fe as FeDTPA or FeEDDHA. 'Hutcheson' soybean seedlings were thinned to three per pot. Between 20 and 100 d after planting, six leaf chlorophyll readings (SPAD 502) were obtained from the third uppermost fully expanded leaf, which was harvested for nutrient analysis at R3 growth stage. Entire plants were harvested at R6 (mid podfill) for nutrient analysis and biomass yield. Leaf blade Fe exceeded a critical level of 60 mg/kg and ranged from 79 to 87 mg/kg in untreated plants to a high of 109 mg/kg for the 10 ppm FeDTPA-Fe treatment. Visible Fe-stress symptoms never appeared. Chlorophyll values during the R3 to R5 growth stages were greater for all of the FeSO4 treatments than for the 0 ppm treatment, while values for 10 ppm FeDTPA-Fe and 3 ppm FeEDDHA-Fe treatments exceeded those of untreated plants. The average seed yield of Fe fertilized plants was numerically 12% greater (not significant) than untreated plats. Root plus shoot biomass was not affected by the FE treatments. It is unlikely that soil-applied Fe will stimulate soybean growth or yield on this soil when DTPA-extractable soil Fe exceeds 12 mg/kg. However, a trend for increased seed yield in some of the Fe treatments, warrants field studies using soil- and/or foliar-applied Fe.