Effects of Fertilization on Soil Solution pH and Manganese Concentration

Abstract

AbstractThe 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 × 10−7 mol/L in the band receiving no fertilizer to 3.28 × 10−6, 5.82 × 10−6, and 2.18 × 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 × 10−6, 4.19 × 10−6, and 5.5 × 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 × 10−7 to 4 × 10−4, 3 × 10−4, and 4.8 × 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 × 10−4, 2.2 × 10−4, and 9 × 10−5 mol/L, respectively, at 28 d after fertilization.