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Ultisols are widely distributed in the subtropical regions of China as well as in the world. High acidity of Ultisols limits plant growth and reduces crop yields. Amelioration of an acid Ultisol was investigated by incorporating the residues of canola ( Brassica campestris L.), wheat ( Triticum aestivum L.), rice ( Oryza sativa), corn ( Zea mays), soybean ( Glycine max), peanut ( Arachis hypogaea), faba bean ( Vicia faba L.) and pea ( Pisum sativum) and Chinese milk vetch ( Astragalus sinicus L.) shoots after incubation of the agricultural by-products for a maximum of 75 days, soil pH was increased by each of the plant materials. The degree of amelioration of the soil acidity by the plant materials was found to depend on the ash alkalinity and N content of the materials; the legumes of higher ash alkalinities and lower N contents, such as peanut straw and faba bean straw, led to the largest increases in soil pH, while the legumes of higher N contents showed less amelioration of the acidity to a certain degree, because of the release of protons during nitrification of NH [ABSTRACT FROM AUTHOR]

Incubation of soil with CaCO3 is generally considered a reliable method to determine the lime requirement (LR) of acid soils. Because of their considered reliability, these incubations are often used to calibrate buffer methods; however, one study reported that the use of room temperature incubation with CaCO3 overestimated the actual LR determined by field testing. The objective of this study was to compare the pH change following CaCO3 incubations for 60 d with those following 3-d incubations with Ca(OH)2 and to determine the possible role of soil N reactions causing any differences in pH change. Seventeen soils were incubated with either CaCO3 for 60 d at approximately 85% field capacity or for 3 d with an equivalent amount of Ca(OH)2 solution plus water to maintain a 1:1 soil/solution ratio. Both were incubated at room temperature (23 ± 2°C), followed by measurement of pH (1:1 in water). Ammonium-N and NO3--N were analyzed at Days 0 and 60 of the incubation. Soil pH was lower following the 60-d CaCO3 incubation than after the 3-d incubation with Ca(OH)2. The analysis of N transformations indicated that positive values of H+ (more H+ was produced than consumed) were generated from nitrification after 60 d of incubation in 14 out of 17 soils. Furthermore, incubations with soils that have been air dried produced a flush of nitrification that increased the ionic strength and decreased pH even further. These effects from long-term incubation would erroneously increase the LR. Incubation with Ca(OH)2 for 2 to 4 d avoids these errors. [ABSTRACT FROM AUTHOR]

Soybean [Glycine max (L.) Merrill] often shows symptoms of iron deficiency chlorosis (IDC) on high pH, calcareous soils of the U.S. Midwest. The objective of this study was to assess the variation in soybean yield that could be explained by soil pH and carbonate concentration in Iowa fields. Color aerial images of soybean canopy taken from 2000 to 2002 from 12 fields having acid to calcareous soils were used to select 10 to 28 sampling areas 10 to 25 m² in size to encompass significant variability in early soybean growth and IDC symptoms in each field. Representative areas 0.93 m² in size were identified through field observations to collect soil samples and measure grain yield. Soil pH measured to a 15-cm depth across fields ranged from 5.6 to 8.2 and calcium carbonate equivalent (CCE) ranged from 0 to 30%. Soil CCE varied from 2.5 to 30% as pH ranged from 7.7 to 8.2. Grain yield decreased with increasing pH and CCE in 9 and 11 fields, respectively. Soil pH and CCE explained 30 and 41% of the variability in relative yield across sites, respectively. An alkalinity stress index (ASI) that combined both measurements (pH + 0.14CCE) was developed based on the relative effects of each measurement on yield and explained 45% of the yield variability across sites. The index developed was a better predictor of soybean yield in fields with high-pH soils than each measurement alone. [ABSTRACT FROM AUTHOR]

Due to their high, degree of reactivity, Mn oxides in soil systems may exert a greater influence on trace metal chemistry than that suggested by their relatively low abundance. In particular, Mn is the only known oxidizer of trivalent Cr in soils. We investigated soil properties that influence the Cr oxidizing capacity of Mn oxides in eight well-aerated high Mn soils. Total and easily reducible Mn abundance were quantified by extraction with 1.5 M NH2OH-HCl and 0.02 M hydroquinone. Relative average Mn oxidation state in soil samples was determined by x-ray absorption near edge structure spectroscopy (Mn-XANES) main edge energy position. Soils ranged in percentage of NH2OH-HCl-extractable Mn between 0.14 and 1.27, pH between 4.4 and 7.2, and percentage of C between 9.0 and 27.2. Manganese- XANES spectra showed that most of the study soils had a high Mn(IV)/Mn(III) ratio with edge energy position intermediate to that of a synthetic birnessite and a synthetic pyrolusite. In these high Mn soils, Mn-XANES edge energy was positively correlated with soil pH, suggesting a linear increase, over the normal range of soil pH, in the Mn(IV)/Mn(III) ratio of soil oxides. Soils with more total reducible Mn generally demonstrated greater net Cr(VI) production, but this pattern was moderated by soil pH and relative Mn oxidation state. High Mn soils with low pH and Mn oxidation state were weaker Cr oxidizers than their Mn abundance would suggest. Our data provide evidence that greater Mn abundance and greater Mn(IV)/Mn(III) ratio in soil Mn oxides enhances Cr oxidation. [ABSTRACT FROM AUTHOR]

A simple method for titrating acidic soils could be used by soil testing laboratories as an alternative method for routinely determining the lime requirement (LR) of soils. Because soil pH as a function of added base is linear in the pH range of 4.5 to 6.5, it may be possible to determine the slope of this relationship by regression analysis using a minimum number of base additions. The LR could then be determined by calculating the corresponding amount of lime required to reach the target pH using the regression equation. Our objectives were to determine reaction times needed for saturated Ca(OH)2 solution to reach an equilibrium pH with 17 widely different soils, and then test a simple titration procedure for its ability to predict the LR, determined first by a full titration curve and then by a standard incubation method. All titrations were performed in a 1:1 soil/water ratio with calcium hydroxide as the base. Using the regression procedure to estimate LR, equilibration times of 30 rain between base additions gave greater LRs than 15-min equilibration, but the same as 45-min equilibration. When all 17 soils were considered, the LR from extrapolation of the linear regression yielded the same, as did the full titration curve (TC). The LR from titration with three base additions and 30-min equilibration time between additions estimated an average of 80% of the LR determined by the 3-d incubation. The Adams-Evans (AE) buffer procedure overestimated and underestimated the LR for soils with relatively Iow- and high-LRs, respectively. Based on these results, titration appears promising for routine use, but it needs more research to determine whether it can be simplified further. [ABSTRACT FROM AUTHOR]

Four maize cultivars, which differ in tolerance to acid soils under field conditions (Zea mays L., acid soil-tolerant C 525 M, BR 201 F and Adour 250, and acid soil-sensitive HS 7777) were used to study the influence of pH (4.3 and 6.0) and Al (0, 20 and 50 µM) on the elongation of seminal roots in nutrient solution. Root elongation was inhibited by high H+ concentrations (pH 4.3) in cultivars C 525 M, Adour 250 and HS 7777 but not in BR 201 F. After 20 h exposure to Al, root elongation rates were more inhibited in cultivars BR 201 F and HS 7777 than in C 525 M and Adour 250. The use of a computerized linear displacement transducer system with high resolution (1 µm) allowed the monitoring of short-term responses of root elongation to Al. In the three cultivars affected by H+ toxicity, but not in the acid-tolerant BR 201 F, Al supply caused an immediate, but transient increase of relative root elongation rates. This result supports the hypothesis that Al-induced growth stimulation is caused by amelioration of proton toxicity. The time required for 20 µM Al to induce a 5% decrease of root elongation rates was shorter in the Al-sensitive BR 201 F (33 min) and HS 7777 (86 min) than in the Al-tolerant C 525 M (112 min) and Adour 250 (146 min) cultivars. However, the response-time to Al may be overestimated in the proton-sensitive cultivars, due to the transient stimulation of root elongation rates induced by Al. According to our results, experiments intended to investigate primary mechanisms of Al toxicity should be started after less than 30 min exposure to toxic Al concentrations, using pH conditions which avoid Al-induced growth stimulation due to amelioration of proton toxicity. [ABSTRACT FROM AUTHOR]

The article investigates the seasonal variations in the acidity of woodland soils in chosen stations in Bagley Wood, near Oxford, England at monthly intervals from December 1932 to November 1937. Specifically, the authors investigate the acidity on the upper and lower layers of soil in seven stations which represent three types of woodland soil. Findings show that there are statistically significant annual and monthly variations in soil acidity, and these variations are related to total annual rainfall and monthly variations in rainfall, respectively.

The article offers information on soil acidity in relation to vegetational succession in Calthorpe Broad, Norfolk, England. It states that the river valleys of the Bure, Waveney, Yare, and Thurne have extensive fenlands and the large system of shallow lakes called the Norfolk Broads. Relative to this, the author said that the only study conducted on the Norfolk Broads is the one conducted by M. Pallis. Moreover, the open water of the Broads is alkaline in reaction and the vegetation is considered as typical of "Niedermoor." It is mentioned that acidiphilous species have long known to thrive in the Broads area. The author also mentioned that Pallis carrried out her study before soil acidity had been extensively studied.