Reacidification of Two Lime Amended Soils in Western Oregon

Abstract

Leaching of basic cations by winter rainfall and irrigation water and the increasing use of NH+4‐fertilizers have resulted in wide‐spread soil acidity in western Oregon. While applications of liming materials are often made in this region, the rates at which limed soils reacidify are generally not known. The objectives of this study were to: (i) quantify long‐term acidification rates of two lime‐amended soils in western Oregon, and (ii) identify soil‐plant processes which may control acidification rates. Lime applications ranging from 0 to 14 650 kg ha−1 were made on a Nekia sicl (Xeric Haplohumults, initial pH 5.0) and from 0 to 11 200 kg ha−1 on a Woodburn sil (Aquultic Argixerolls, pH 5.3) in the Willamette Valley of western Oregon in 1971 to 72. Monitoring of soil pH and levels of extractable basic cations applied in the liming materials for 11 to 12 yr permitted estimation of the rate of acidification of soils receiving different amounts of lime. Whether estimated by declines in pH or extractable basic cations, soil acidification rates increased with increasing quantities of lime initially applied. Acidification rates of unlimed Nekia soil were 0.025 pH units yr−1 and 0.17 cmol(+) Ca2+ + Mg2+ kg−1yr−1 while the unlimed Woodburn soil showed no net acidification. Maximum rates of acidification of 0.09 pH units yr−1 and 0.62 cmol(+) extractable Ca2+ + Mg2+ kg−1yr−1 on the Nekia soil and 0.08 pH units yr−1 and 0.36 cmol(+) extractable Ca2+ kg−1yr−1 on the Woodburn soil were measured on plots receiving the highest amounts of lime. Faster reacidification of soils amended with higher lime rates is explained by the pH dependence of acidifying processes such as nitrification, CO2 release via plant and microbial respiration, mineralization of organic matter and dissociation of organic acids in soil solution. Ca2+ release from mineral weathering appeared to have an important effect on soil pH and extractable Ca2+, particularly in the absence of large inputs of acidifying materials such as NH+4‐fertilizers. Accurate prediction of soil acidfication rates will require additional information concerning the pH dependence of soil acidifying processes, the quantity and composition of seasonal through drainage, and the rates of mineral weathering in soils.

Effect of trickle fertigation with three forms of nitrogen on soil pH, levels of extractable nutrients below the emitter and plant growth

“…Acidifying effects of the prolonged use of ammonium-containing or-forming fertilizers are well known (Doerge and Gardner, 1985;Mahler et al, 1985), and these effects can be magnified under fertigation because the fertilizer application is concentrated in relatively small volumes of soil rather than being spread evenly over the soil surface. Thus, in the ammonium sulphate and urea treatments, soil pH values were generally at or below pH 5.5 in the surface 30-cm of soil immediately below the emitter.…”

Assessing the potential soil acidification risk under dryland agriculture in the Mlondozi district in the Mpumalanga Province of South Africa

“…Table 3 and Figure 7 show that acidification rate ( pH unit year -1 ) was high if the initial soil pH(H 2 O or KCl) was high or extractable (Al + H), (Al) or acid saturation were low. Doerge and Gardner (1985) stated that increased pH values which are the result of lime application, stimulate soil acidification processes and net soil acidification occurs at an accelerated rate. The reasons for the increase in acidification risk with increasing pH values are due to increased decomposition rates of organic matter, resulting in a release of reduced forms of N and S. Furthermore, at high pH values, extractable Al is essentially eliminated and does not contribute to buffering.…”

Using pH-dependent CEC to determine lime requirement

“…Buffer pH methods have commonly been used because they are less time consuming than titrations and incubations and have been more accurate than existing multivariate methods (Keeney and Corey 1963;Pionke et al 1968;Viscarra Rossel and McBratney 2002). The most commonly used buffer pH method was developed by Shoemaker et al (1961), and has been named the SMP pH buffer method (Doerge and Garner 1988). Before being applied to the soils of a region, the technique needs to be calibrated by developing the relationship between the values obtained using the SMP pH buffer and a direct measurement of the amounts of lime needed to raise the pH of the soils to the desired level.…”

“…The "Centre d'expertise en analyse environnementale du Québec", The government agency responsible for accrediting Quebec laboratories, accepts an error of ± 0.2 pH units in the measurement of the SMP buffer solution, which translates into an error of ± 2.5 t ha -1 of agricultural lime. Finally, not all regions of Quebec were used for the initial calibration; this may lead to further errors when the method is applied to a soil that has different chemical characteristics (Doerge and Garner 1988).…”

“…Viscarra McBratney (2000, 2001) have tried to accommodate for some of the weaknesses of the pH buffer method with respect to precision agriculture through the development of an empirical deterministic response surface model for pH buffer methods. Although multivariate methods have so far been found to be less accurate and more costly than pH buffer methods, researchers continue to examine the relationships between exchangeable acidity and other commonly analysed soil properties such as texture, soil organic matter (SOM), extractable Fe and Al oxides and cation exchange capacity (CEC) to address the demands of precision agriculture (Keeney and Corey 1963;Pionke et al 1968;Doerge and Garner 1988;Viscarra Rossel and McBratney 2002).…”