Managing soil acidity in no-till production systems

Increasing acreage of no-till (NT) cropping systems with surface applications of N fertilizer brings forth the important issue of management of acidic soils in these systems. Field studies indicated limestone movement was limited to 7.5 cm or less at all sites 3 to 5 years after initial surface application of limestone. The type of liming material or frequency of limestone application had no effect on any of the chemical soil characteristics measured at any of the four sites. Significant yield increases were not observed from limestone applications. The lack of yield response was believed to be partially explained by the interaction of exchangeable Al and organic carbon (OC). Investigation into whether or not management decisions for acidic NT soils be influenced by the interaction of Al and OC was performed. Observations from soil samples collected from a long-term tillage rotation/tillage study indicated an increase in OC concentration in NT compared to conventional till (CT). Potassium chloride and CuCl2 extractable-Al increased exponentially with decreasing soil pH. Copper chloride extractable-Al values were on average 33% greater than KCl extractable-Al levels. When using a regression model to predict the difference between CuCl2 extractable and KCl extractable-Al, inclusion of OC explained only 4% greater variability compared with inclusion of only soil pH in the model. Accurately estimating lime requirements (LR) of acidic soils has been a concern since liming practices began. The currently used SNIP buffer either overestimated LR at low values or underestimated LR at relatively high LR values compared to 60-d incubations with CaCO3. Recalibration of the SNIP with soils from Kansas did not drastically improve estimation of LR compared to 60-d incubations. The Mehlich buffer appeared to more closely estimate the actual LR of soils compared to the SMP or Ca(OH) 2. Limestone recommendations for NT production systems need to be based on correcting pH only in the surface 7.5 cm for production systems receiving 800-1000 mm of annual precipitation. Changes in OC concentrations in the surface 7.5 cm of soil often observed after reducing tillage should not be considered in determining liming strategies of acidic NT soils.