Acidification of Soil in a Dry Land Winter Wheat-sorghum/corn-fallow Rotation in the Semiarid U.S. Great Plains

• Published in: Plant and soil 2006-05, Vol.283 (1-2), p.367-379
• Main Authors: Tarkalson, D.D, Hergert, G.W, Cassman, K.G
• Format: Article
• Language: English
• Subjects: Acid soils; Acidification; Acidity; agricultural soils; Agrology; Agronomy. Soil science and plant productions; Alkaline soils; Ammonium; Ammonium nitrate; Animal, plant and microbial ecology; Biological and medical sciences; Corn; Crop residues; crop rotation; Cropping systems; fallow; Fundamental and applied biological sciences. Psychology; Grain; grain sorghum; Leaching; Nitrates; Nitrogen; Orchard soils; Plant growth; semiarid zones; Soil acidification; Soil depth; Soil pH; Soil surfaces; Soil water; Soils; Sorghum; Sorghum bicolor; Tillage; Triticum aestivum; Urea; Wheat soils; Winter wheat; Zea mays
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-006-0027-y

Soil pH is decreasing in many soils in the semiarid Great Plains of the United States under dry land no-till (NT) cropping systems. This study was conducted to determine the rate of acidification and the causes of the acidification of a soil cropped to a winter wheat (Triticum aestivum L.)-grain sorghum [Sorghum bicolor (L.) Moench]/corn (Zea mays L.)-fallow rotation (W-S/C-F) under NT. The study was conducted from 1989 to 2003 on soil with a long-term history of either continuous NT management [NT(LT)] (1962–2003) or conventional tillage (CT) (1962–1988) then converted to NT [NT(C)] (1989–2003). Nitrogen was applied as ammonium nitrate (AN) at a rate of 23 kg N ha-1 in 1989 and as urea ammonium nitrate (UAN) at an average annual rate of 50 kg N ha-1 from 1990 to 2003 for both NT treatments. Soil samples were collected at depth increments of 0–5, 5–10, 10–15, and 15–30 cm in the spring of 1989 and 2003. Acidification ratesfor the NT(LT) and NT(C) treatments were 1.13 and 1.48 kmol H+ ha-1 yr-1 in the 0–30 cm depth, respectively. The amount of CaC03 needed to neutralize the acidification is 57 and 74 kg ha-1 yr-1 for the NT(LT) and NT(C) treatments, respectively. A proton budget estimated by the Helyar and Porter [1989, Soil Acidity and Plant Growth, Academic Press] method indicated that NO3- leaching from the 30 cm depth was a primary cause of long-term acidification in this soil. Nitrate leaching accounted for 59 and 66% of the H+ from the acid causing factors for NT(LT) and NT(C) treatments, respectively. The addition of crop residues to the soil neutralized 62 and 47% of the acidity produced from the leaching of NO3-, and 37 and 31% of the acid resulting from NO3- leaching and the other acid-causing constituents for the NT(LT) and NT(C) treatments, respectively. These results document that surface soils in dry land W-S/C-F rotations under NT are acidifying under current management practices. Improved management to increase nitrogen uptake efficiency from applied fertilizer would help reduce the rate of acidification. The addition of lime materials to prevent negative impacts on grain yields may be necessary in the future under current management practices.