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Spatial Variability of Soil pH and its Relationship to N Reactions in Soil

Spatial Variability of Soil pH and its Relationship to N Reactions in Soil. David Kissel and Leticia Sonon University of Georgia. Why is subsoil pH important?. Low subsoil pH can result in toxic levels of Al +3 that can restrict root growth and the amount of water available to the crop. 0.

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Spatial Variability of Soil pH and its Relationship to N Reactions in Soil

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  1. Spatial Variability of Soil pH and its Relationship to N Reactions in Soil David Kissel and Leticia Sonon University of Georgia

  2. Why is subsoil pH important?

  3. Low subsoil pH can result in toxic levels of Al+3 that can restrict root growth and the amount of water available to the crop.

  4. 0 Relationship between pHCaCl2 and KCl Extractable Aluminum, 90 NAPT Soils 120 100 Critical pH 4.85 80 For Saturated Paste pH the value is 5.40 60 KCl Extr. Al (mg/kg) 40 20 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 Soil pH (1:1) CaCl2 Miller et al. 2003

  5. Soil pH in Cabin Field (Cotton) Sampling Depth Short (55 cm) Medium (85 cm) Tall (130 cm)

  6. Soil pHw vs depth, NWCrisp Co

  7. What role might nitrogen nutrition have in the formation of subsoil acidity?

  8. September 1998, ammonium (kg N/ha) distribution with depth.

  9. What is the possible role of high levels of ammonium on soil pH, especially for subsoil layers?

  10. “Plant uptake of a cation must be accompanied by uptake of an anion of equal charge or by the extrusion of H+ or other cations. The reverse is true for uptake of anions.” (C. Tang and Z. Rengel, 2003. Handbook of Soil Acidity; Marcel Dekker, Inc.

  11. Cations (positive) potassium K+ calcium Ca++ Magnesium Mg++ zinc Zn++ Manganese Mn++ Iron Fe++ Copper Cu++ Ammonium NH4+ Anions (negative) nitrate NO3- sulfate SO4-- Phosphate HPO4 - Borate H2BO3- Molybdate MoO4-- Chloride Cl- Some ions in soils used by crops

  12. If nitrification is slow and a crop takes up a substantial proportion of its N as ammonium, the crop will likely take up an excess of cations and the crop roots will respond by emitting H+. If uptake of ammonium occurs from subsoil layers, the crop will therefore tend to acidify those soil layers.

  13. Recent data of soil pH and available N with depth.

  14. March 2006 samples

  15. March 2006 samples

  16. We propose that relatively high levels of NH4+ at depth are not uncommon in S. Georgia soils and that an acid surface layer makes the problem worse because it slows the rate of nitrification, allowing N to remain as NH4+ for a longer time, increasing the probability that leaching rains will move NH4+ deeper into the soil.

  17. Nitrate formed from ammonium at 25 to 30 C in different soils (Frederick and Broadbent. 1966. Agr. Anh. NH3)

  18. wheat Al & Mn Toxicity Mn & Fe Deficiency

  19. Soil test manganese ratings

  20. H+ ion 1.6 to 1.7 x10-5 Ångstrom From Wikipedia 1.20 Ångstrom

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