Influence of lime and farm yard manure
par Dieudonne MUGOBOKA
ISAE Busogo - Bachelor's Degree 2008
Liming reaction in soil begin with the neutralization of H+ in the soil solution by adding a base (usually OH- or CO3- ) originating from the lime material.
The CaCO3 behaves as follows: CaCO3+2H+ =Ca2+ +CO2+H2O .The first reaction neutralize the H+ in soil solution. Exchangeable H+ desorbs from the CEC to buffer the decreasing H+ in solution. Two H+ on CEC are replaced by one Ca 2+.Inthis way, both soil p H and percentage B.S increase since the majority of exchangeable acidity occurs as exchangeable Al3+.
Calcium Hydroxide Ca (OH), or slaked lime, hydrated lime or builders lime, is a white powder and difficult to handle. Neutralization of acids occurs rapidly .Slaked lime is prepared by hydrating CaO (CaO+H2O=Ca (OH) 2 and has a CCE of 136 %( Havlin et al, 2005).
The Calcium Oxide (CaO) is the only material to which the term `'Lime `'may be correctly applied. Also known as unslaked lime, burned lime or quick lime, CaO is white powder, shipped in paper bags because of its caustic properties. It is manufactured by roasting CaCO3 in a furnace, driving of CO2.
CaO is the most effective of all liming materials with the C.C.E 179%, compared with pure CaCO3.When unusually rapid results are required, either CaO or Ca (OH) should be used(Havlin et al,2005).
When added to a moist acid soil, the Ca cations in calcium oxide displaces the exchangeable hydrogen and aluminum cations from the surface of soil colloids. The displaced H+ and Al 3+ react with sol water to yield insoluble hydroxyls.
Thus, the quantity of exchangeable H+ and Al 3+ cations decreases and hence, the soil p H Values increases (Rayar, 2000).
Calcium or Magnesium carbonate
Calcium Carbonate (CaCO3) or Calcite, and Calcium -Magnesium Carbonate [CaMg (CO3)], or dolomite, are common liming materials.
Lime stone is most often mined by opening -pit methods. The Quality of crystalline lime stones depends on clay content and other impurities. The CCE varies from 65to105.The CCE of pure CaCO3 is theoretically established at 100% while CCE of pure dolomite is 109%.The CCE of most agricultural lime is 80to 95%.Although dolomite has a slightly high CCE than calcite, dolomite has lower solubility and thus will dissolve more slowly. For dolomite to be as effective as calcite at the same application rate, dolomite should be ground twice as fine or react twice as long (Havlin et al, 2005).
When applied to a moisture soil, the Calcium and Magnesium carbonate displace the exchangeable hydrogen and aluminum from exchangeable site of soil colloids. The displaced hydrogen and aluminum reacts with soil water to form insoluble aluminum hydroxyls and carbon dioxide.
Thus, the quantity of exchangeable hydrogen and aluminum decreases, and consequently, the soil p H increases. In addition, the percentage base (Ca and Mg) saturation of soil colloid increases.
Slag behaves in soil as Calcium Silicate. Thus, when added to a moist acid soil, the calcium silicate displaces the exchangeable Hydrogen and Aluminum.
The displaced hydrogen and Aluminum react with water to form insoluble
Al (OH) 3.The Calcium meta-silicate fro natural deposit in North America has CCE of86%.CaSiO3 also occurs in slag by products of Iron manufacturing.
In the blast furnace reduction of Fe ores, CaCO3 looses CO2 and forms CaO, which combines with molten Si to produce a slag that is either air or water cooled.
The CCE of slag ranges from 60 to 90%, and usually contain appreciable amount of Mg and P, depending on the source of Iron ore and manufacturing process (Havlin, 2005)
Marl are soft, unconsolidated deposits of CaCO3, frequently mixed with earthen impurities and usually quite most. Marl deposits are generally thin, recovered by drag line or power shovel after the overburden has been removed.
The fresh material is stockpiled and allowed to dry before being applied in the land. Marl is almost always low in Mg, and its CCE ranges from70 to90%, depending on clay content (Havlin, 2005).
Other liming materials
Other materials used as liming agencies in the areas close to their sources include fly ash from coal-burning power generating plants, sludge from water treatment plants, lime or flue dust from lime, acetylene lime, picking house lime, and so on .These by products contain varying amount of Ca and Mg.