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Effects of Fertilization on Soil Solution pH and Manganese Concentration¹

ABSTRACT

The effects of fertilizers on the soil solution pH and Mn concentration were studied in a laboratory experiment. A Tulana silt loam variant (medial, nonacid, mesic, Mollic Andequepts) with 18% organic matter was placed in incubation trays. Simulated fertilizer bands were made in the soil and marked with washed white silica sand. Nitrogen (N) was applied at 0 or 22 kg/ha as (NH₄)₂SO₄, NH₄Cl, or urea. Phosphorus (P) was applied at 0 or 19 kg/ha as Ca(H₂PO₄)₂ and manganese (Mn) was applied at 0 or 5.6 kg/ha as MnSO₄. All fertilizer rates were based on 0.25-m row spacing. An unaltered portion of the soil solution was removed by centrifugation. The soil solution pH and Mn concentrations were measured in samples collected in the fertilizer band and 0.025 m from the band at 7, 14, and 28 d after fertilization. At 7 d after fertilization the soil solution pH in the fertilizer band was lowered from 8.12 to 7.30 by (NH₄)₂SO₄ and from 7.75 to 7.21 by NH₄Cl. In contrast, urea fertilization increased the soil solution pH from 7.75 to 8.01. Application of Ca(H₂PO₄)₂ with N fertilizers lowered the soil solution pH regardless of N source. The soil solution pH tended to remain depressed at 14 and 28 d after fertilization when (NH₄)₂SO₄ plus Ca(H₂PO₄)₂ or NH₄Cl plus Ca(H₂PO₄)₂ were applied but increased when urea plus Ca(H₂PO₄)₂ were applied. The pH changes at 0.025 m from the fertilizer band were approximately one half those occurring in the fertilizer band. The soil solution Mn concentration in the fertilizer band increased from 7.3 x 10^–7 mol/L in the band receiving no fertilizer to 3.28 x 10^–6, 5.82 x 10^–6, and 2.18 x 10^–6 mol/L in the (NH₄)₂SO₄, NH₄Cl, and urea bands, respectively, at 7 d after fertilization. At 28 days after fertilization the Mn levels were 4.55 x 10^–6, 4.19 x 10^–6, and 5.5 x 10^–7 mol/L in the (NH₄)₂SO₄, NH₄Cl, and urea bands, respectively. When Mn was included with N fertilizer the soil solution Mn concentration increased from 7.3 x 10^–7 to 4 x 10^–4, 3 x 10^–4, and 4.8 x 10^–4 mol/L in the (NH₄)₂SO₄, NH₄Cl, and urea bands, respectively, at 7 d after fertilization. The Mn concentration in the (NH₄)₂SO₄, NH₄Cl, and urea bands fell to 2.8 x 10^–4, 2.2 x 10^–4, and 9 x 10^–5 mol/L, respectively, at 28 d after fertilization.

¹ Oregon Agric. Exp. Stn. Technical Paper no. 6428. Contribution of the Dep. of Soil Science, Oregon State Univ. The authors wish to acknowledge financial assistance from the Div. of Agric. Development, National Fertilizer Center, TVA, Muscle Shoals, AL.

² Formerly Graduate Research Assistant, Dep. of Soil Science, Oregon State Univ., now Extension Soil Fertility Specialist, Univ. of Idaho, Twin Falls Research and Extension Center, Twin Falls, ID 83301; and Professor, Dep. of Soil Science, Oregon State Univ., Corvallis, OR 97331, respectively.

Received for publication June 28, 1982. Accepted for publication November 21, 1983.