Acidity of soil

Humus The dark organic material in soils, produced by the decomposition of soils. The matter that remains after the bulk of detritus has beenconsumed (leaves, roots). Humus mixes with top layers of soil (rock particles), supplies some of the nutrients needed by plants -increases acidity of soil inorganic nutrients more soluble under acidic conditions, become more available, EX. wheat grows best at pH 5.5-7.0. Humus modifies soil texture, creates loose, crumbly texture, that allows water to soak in and nutrients retained permits air to be incorporated into soil. 

High concentrations of SO, can produce tempo-rai y breathing difficulties in asthmatic children and in adults who are active outdoors. Sulfur dioxide also can directly damage plants and has been shown to decrease crop yields. In addition, sulfur oxides can be converted to sulfuric acid and lead to acid rain. Acid rain can harm ecosystems by increasing the acidity of soils as well as surface waters such as rivers, lakes, and streams. Sulfur dioxide levels fell, on average, by 39 percent between 1989 and 1998. 

Self-Test E.5B Calculate the amount of Ca(OH)2 formula units in 1.00 kg of slaked lime (calcium hydroxide), which is used to adjust the acidity of soils. 

The acidity of soils also strongly affects the availability of metal cations such as K, Mg, and Ca. Most soils contain significant amounts of clay, whose chemical composition is dominated by aluminosilicates. Silicates are anionic, and the anions can be neutralized either by accepting protons or by associating with metal cations. When soil is too acidic, protons replace these metal cations, and the soil becomes depleted in these essential nutrients. 

Explain why titration is not a generally useful method for discovering the acidity of soil. 

Orlov, D. S. (1985). Humus Acids of Soils, tranls. Kothekar, V., A. A. Balkema, Rotterdam. 

The ions in the soil solution constitutes the active acidity and are measured directly as soil pH values. On the other hand the adsorbed H+ ions held on exchange sites are not subject to pH measurements are termed as reserve acidity , both the forms contribute to soil acidity. Thus soil pH does not reflect the total acidity. However a suitable index which takes into account the reserve acidity of soil is the lime potential, which is calculated as follows ... 

For many years, farmers have used lime to lower the acidity of soil for their crops (a process called liming). Nowadays lime is also applied to lakes affected by acid rain (see Section 17.6). 

Fabbri D, Mongardi M, Mintanari L, Galletti GC, Chiavari G, Scotti R (1998b) Comparison between CP/MAS 13C-NMR and pyrolysis-GC/MS in the structural characterization of humins and humic acids of soil and sediments. 

The situation is enhanced by the synergetic influence of acidification loading from sulfur compounds, which is also dramatic in this area. Increasing acidity of soils and surface waters is known to be accompanied by the increasing mobility of most HM. This, in turn, leads to possible accumulation of HM in the food chains of both terrestrial and aquatic ecosystems (Bashkin and Wongyai, 2002). 

In agriculture, where it is used to maintain proper acidity of soil and supply calcium needed by growing plants ... 

The acidity of soils tends to increase as a result of five factors [10.2]. 

Agricultural hydrate is a relatively coarse, unrefined form of hydrated lime, used mainly for adjusting the acidity of soils. 

Table 1 shows the functional groups in water and soil humic and fulvic fractions. The major functional groups are carboxyl, phenolic hydroxyl, hydroxyl, and carbonyl. The sum of carboxyl and phenolic hydroxyl is total acidity. Total acidity of water fulvic acids is slightly higher compared to soil fulvic acids while total acidity of soil and water hiunic acids is comparable. 

In the environment, the acidity, or pH, of rain, water, and soil can have significant effects. When rain becomes too acidic, it can dissolve marble statues and accelerate the corrosion of metals. In lakes and ponds, the acidity of water can affect the ability of plants and fish to survive. The acidity of soil around plants affects their growth. If the soil pH is too acidic or too basic, the roots of the plant cannot take up some nutrients. Most plants thrive in soil with a nearly neutral pH, although certain plants, such as orchids, camellias, and blueberries, require a more acidic soil. 

TYURIN I.V. 1940. (The nature of fulvic acids of soil humus). 

LADD J.N. and BUTLER J.H.A. 1969. Inhibition proteolytic enzyme activities by soil humic acids of Soil Research, 7, 253-261. 

Significance.—(1) A Regulator of Soil Acidity.—Calcium carbonate is one of the natural factors concerned in reducing the acidity of soil, and is used for this purpose in agriculture. 

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