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The mechanisms by which organic materials affect soil pH are not fully understood. This study for the first time compared the short-term effect of various model organic compounds on pH change of two soils differing in initial pH (Podosol of pH 4.4 and Tenosol of pH 6.1). Eight organic compounds, representing common compounds in plant residues, were selected based on the number and type of chemical functional groups. The addition of organic acids (acetic, malic, citric, and benzoic acid) reduced soil pH immediately due to H dissociation. The magnitude of pH decrease depended on the rate of application, degree of dissociation of the acids, and initial soil pH. During a subsequent incubation, pH was slowly restored as these compounds were decomposed. The degree to which pH was restored was reduced with increasing addition rate. The production of H ions was increased with increasing rate of acid addition and decreased over time. When potassium citrate (organic anion) was added, soil pH increased due to H consumption upon decomposition. Compounds with amine groups (glucosamine hydrochloride) and less easily decomposable compounds (phenol) did not significantly alter pH during 16-day shaking. Changes in pH after glucose addition were relatively small compared with other compounds and were not expected because hydroxyl chemical groups of glucose are neutral. The present study demonstrated that the addition of model organic compounds to soil caused soil pH to increase, decrease, or remains unaffected. The extent and direction of pH change was dependent on the chemical functional group, addition rate, decomposition, and the initial soil pH. [ABSTRACT FROM AUTHOR]

We determined the effects of wood ash fertilization, given together with nitrogen (WAN), and nitrogen given together with P, B and Cu (SSF), on soil and foliage nutrients and fine root biomass in a 45-year-old Norway spruce stand in southern Finland. Fine roots were sampled 9 years, and the soil 10 years after ash (3 t/ha) and nitrogen (150 kg/ha) application. Fine root biomass tended to be lower, the necromass higher, and the fine root distribution relatively deeper on the WAN than on the control and SSF plots. The response of fine root biomass to WAN was probably related to changes in soil acidity. pH, base saturation, total and extractable concentrations of Ca, K, Mg and P, and total B, Cd, Mn, Ni and Zn concentrations in the organic layer were significantly higher on the WAN plots than on the SSF and the control plots with no ash and nutrient addition. On the WAN plots, the pH was 1.2 pH-units higher, the exchangeable Ca concentrations fourfold and those of Mg over twofold compared to the control plots. WAN increased the concentrations of K but decreased those of Mn and Ni in the needles compared to the control and SSF treatment. Even though ash and nitrogen fertilisation tended to decrease the fine root biomass, this decrease was not likely to affect tree growth during a 10-year period. [ABSTRACT FROM AUTHOR]

There is an assumption in much recent literature that secreted organic anions (OAs) protect the root meristem from Al toxicity by complexation of Al ions. In fact, several possible mechanisms exist by which common OA might afford some degree of protection. Plants can excrete OA which undergo chemical association with protons (hereafter referred to as protonation) in the soil and increase rhizosphere pH. The cost in reduced carbon relative to protons consumed, C:H+, ranges from 2–6. The efficiency of this mechanism can be enhanced in the presence of soil organisms which can oxidise the OA that remain dissociated at soil pH to CO2 and H2O, thereby consuming protons which associate with lower p K functional groups (p K 1.2 to ~ 4). For fully dissociated organic acids the C:H+ ratio decreases to the range 1–3. The C cost to plants is further minimised if MnO2 is the terminal electron acceptor rather than O2, resulting in C:H+<1. OA might also complex or chelate Al. Complexes of Al3+ with oxalate appear to be effective, with some C:H+≤1. However, citrate complexation appears to be more stable in pure solutions and might offer the additional benefit of enhanced P acquisition. Our assessment is that the most efficient strategy for a plant to employ to protect itself from Al toxicity is to increase pH near the root apex by secreting OA into soil where the microbial oxidation of reduced C could be coupled with the reduction of MnO2. This would consume 0.2–0.67 mole of C per H+, which is the order of magnitude better than the C:H+ ratio of 2–6 that would occur if only protonation of OA was to be relied upon. These mechanisms have implications for the effectiveness of programs aimed at selecting cultivars for resistance to acidic soils. [ABSTRACT FROM AUTHOR]

Critical load calculations in the Czech part of 'the Black Triangle' show exceedance of critical load in 75% of the forest area. A comparison with forest damage data shows an insignificant tendency toward more forest damage in areas with high exceedance. We conclude that high exceedance of critical load is a probable contributing factor to forest damage in the area. [ABSTRACT FROM AUTHOR]

A field experiment with five lime rates (0, 3.75, 7.50, 11.25, and 15.00 Mg ha-1) was maintained on a red soil (Ultisol) for 15 years to determine changes of soil acidity and effect on crop yields. The soil acidity decreased while exchangeable Ca in plough layer (0-20 cm) increased with lime rate and time. The decreased subsoil (20-60 cm) acidity started to occur four years after liming, and the extent of decreased soil acidity increased with lime rate and time. The increased ranges of exchangeable Mg2+ in subsoil were greater than that of exchangeable Ca2+, suggesting that downward movement of Mg2+ into the subsoil was faster than that of Ca2+. Lime application significantly increased the yields of crops studied. During the period of experiment, the maximum yield increased 4.67 times for barley, 2.24 times for mungbean, 57.3% for wheat, 53.4% for sesame, 52.8% for broad bean, 44.1% for potato, 35.1% for rapeseed, 32.1% for cotton, 28.4% for corn, 18.5% for watermelon, 11.0% for cowpea and 8.8 % for soybean. Liming at the highest rate was in favor to the decline in subsoil acidity and yield increase, especially for the later period of the experiment. Residual effects of reducing soil acidity by liming for the treatments of 0.5 L, 1.0 L, 1.5 L, and 2.0 L could last for 5, 7, 12, and 14 years, respectively, and the effects of lime application on the yields could last for more than 15 years. [ABSTRACT FROM AUTHOR]

Only very limited information exists on the plasticity in size and structure of fine root systems, and fine root morphology of mature trees as a function of environmental variation. Six northwest German old-growth beech forests (Fagus sylvatica L.) differing in precipitation (520 – 1030 mm year-1) and soil acidity/fertility (acidic infertile to basic fertile) were studied by soil coring for stand totals of fine root biomass (0–40 cm plus organic horizons), vertical and horizontal root distribution patterns, the fine root necromass/biomass ratio, and fine root morphology (root specific surface area, root tip frequency, and degree of mycorrhizal infection). Stand total of fine root biomass, and vertical and horizontal fine root distribution patterns were similar in beech stands on acidic infertile and basic fertile soils. In five of six stands, stand fine root biomass ranged between 320 and 470 g m-2; fine root density showed an exponential decrease with soil depth in all profiles irrespective of soil type. An exceptionally small stand fine root biomass (<150 g m-2) was found in the driest stand with 520 mm year-1 of rainfall. In all stands, fine root morphological parameters changed markedly from the topsoil to the lower profile; differences in fine root morphology among the six stands, however, were remarkably small. Two parameters, the necromass/biomass ratio and fine root tip density (tips per soil volume), however, were both much higher in acidic than basic soils. We conclude that variation in soil acidity and fertility only weakly influences fine root system size and morphology of F. sylvatica, but affects root system structure and, probably, fine root mortality. It is hypothesized that high root tip densities in acidic infertile soils compensate for low nutrient supply rates, and large necromasses are a consequence of adverse soil chemical conditions. Data from a literature survey support the view that rainfall is another major environmental factor that influences the stand fine root biomass of F. sylvatica. [ABSTRACT FROM AUTHOR]