Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2008
Publication Date: 5/1/2008
Citation: Brown, T.T., Koenig, R.T., Huggins, D.R., Harsh, J.B., Rossi, R.E. 2008. Lime effects on soil acidity, crop yield and aluminum chemistry in inland Pacific Northwest direct-seed cropping systems. Soil Science Society of America Journal 72:634-640. Interpretive Summary: Background: The use of fertilizers for crop production is acidifying soils in the Inland Pacific Northwest. As soils acidify, Aluminum (Al) toxicity increases and adversely affects crop productivity. Currently, soil acidity is at levels where Al toxicity would be predicted to threaten crop productivity either now or in the near future. Management strategies to counter soil acidity and Al toxicity include the application of liming materials that raise soil pH. Unfortunately, the current availability of lime within the region is limited and prohibitively expensive to use at recommended agronomic rates. Description: We field tested alternative liming strategies to evaluate their effects on soil pH, Al toxicity and crop yield. Surface broadcasting lime significantly increased soil pH and reduced Al toxicity in the surface six inches. Banding small quantities of lime with the fertilizer did not result in any measurable effects on soil pH or Al toxicity. Crop yields were not affected by any of the liming treatments. Impact: Our results show that declining soil pH and Al toxicity are not yet at levels that are detrimental to crop yields. Consequently, in the short-term, crops are not likely to respond to applications of lime. However, the continuing decline of soil pH will result in greater incidence of Al toxicity in the near future and economic means of slowing or reversing this trend are needed.
Technical Abstract: The pH of agricultural soils in the Inland Pacific Northwest (IPNW) has declined below established critical levels for cereal and grain legume crops. Our objective was to assess the effects of broadcast or subsurface banded lime treatments on soil acidity, crop yield, and aluminum (Al) chemistry in a direct-seeded (DS) cropping system in the IPNW. Treatments initiated in 2002 consisted of subsurface banded nitrogen (N) fertilizer (120 to 168 kg N ha-1 yr-1) alone or with annual subsurface banded lime (224 kg ha-1), or a one-time broadcast application of lime (7000 kg ha-1) or elemental sulfur (1000 kg ha-1). Yield was measured annually from 2002 to 2005 in a spring barley (Hordeum vulgare)–spring wheat(Triticum aestivum)– winter wheat rotation. Soil was sampled in spring 2004 to assess pH and model Al speciation in 1:1 soil:water extracts. A zone of low (<5.0) pH was evident at the depth of fertilizer placement (5 to 10 cm). Broadcast lime significantly increased pH in the surface 15 cm, though reductions in Al 3+ activity [(Al 3+)] were observed only in the surface 0 to 5 cm layer. No increase in pH at the 5 to 10 cm depth was measured where subsurface banded lime was placed, while lower pH values were observed at the 0 to 5 cm depth with the broadcast sulfur treatment. Grain yields were not affected by lime or sulfur treatments. Speciation modeling suggested total soluble Al was dominated by organic matter-Al complexes (fulvic acid, FA; FA2Al+ and FA2AlOH0). Solid and solution phase organic complexes may exert considerable control over soil solution(Al 3+)at pH <5.5. Although soil acidity is a growing concern in the IPNW, the higher soil organic matter content inherent in the surface of DS soils may buffer these systems against Al phytotoxicity at this time.