| dc.description.abstract | Incubation experiment studies were done to determine the effect of lime
(CaC03) at a rate of 10 tons/ha, Diamonium Phosphate (DAP) and Ammonium
Sulphate (AS) at 200 Kg N/ha and Tripple Super Phosphate (TSP) at 100 Kg P/ha
on N mineralization. The three soils used were from Gituamba (Andosols), Kitale
(Ferralsols) and Katumani ( Luvisols). A secondary objective was to determine the
values for the mineralization potential (No), rate constant (k) and the rate of
mineralization using Stanford formula for untreated soils only; No=9.77Nt, where
Ntis the nitrogen mineralized in two weeks.
The soils were incubated aerobically in polythene bags for a period of 120
days in the laboratory at room temperature and available nitrogen (NH4++N03-)
was determined at specified periods during the experiment. The mineralized N was
higher where treatments were applied than in the control. Where lime was applied
in Gituamba soils, mineralized N was significantly higher (P ::; 0.05) than the
control. However, for Kitale soils, although liming increased N mineralization, it
was not significant (P ~ 0.05) as compared with the control. Where DAP and TSP
were applied, a slight effect on nitrogen mineralization was observed. This was
attributed to P which affects microbial biomass steadily. The rates of mineralization
were higher in the 0-15 em than 15-30 em sampling depths with Gituamba
indicating the highest. The mineralization potential for the 0-15 em and 15-30 ern
layers were 392.3 and 162.5 IlgN/g for Gituamba; 195.6 and 178.7 IlgN/g for
Kitale; and 198.0 and 75.8 IlgN/g soil for Katumani soils. The time required for
50% of No to be mineralised indicated that less than half the potential value would
become available in a normal growing season with the possible exception of
Gituamba (15-30 ern) and Katumani soils. The trends of the calculated values
compared well with the observed ones except for Katumani soils. The Stanford
formula appears therefore not to work well with soils low in organic matter.
Incubation experiment studies were done to determine the effect of lime
(CaC03) at a rate of 10 tons/ha, Diamonium Phosphate (DAP) and Ammonium
Sulphate (AS) at 200 Kg N/ha and Tripple Super Phosphate (TSP) at 100 Kg P/ha
on N mineralization. The three soils used were from Gituamba (Andosols), Kitale
(Ferralsols) and Katumani (Luvisols). A secondary objective was to determine the
values for the mineralization potential (No), rate constant (k) and the rate of
mineralization using Stanford formula for untreated soils only; No=9.77Nt, where
Nt is the nitrogen mineralized in two weeks.
The soils were incubated aerobically in polythene bags for a period of 120
days in the laboratory at room temperature and available nitrogen (NH4++N03-)
was determined at specified periods during the experiment. The mineralized N was
higher where treatments were appliedthan in the control. Where lime was applied
in Gituamba soils, mineralized N was significantly higher (P ::;;0.05) than the
control. However, for Kitale soils, although liming increased N mineralization, it
was not significant (P ~ 0.05) as compared with the control. Where DAP and TSP
were applied, a slight effect on nitrogen mineralization was observed. This was
attributed to P which affects microbial biomass steadily. The rates of mineralization
were higher in the 0-15 em than 15-30 em sampling depths with Gituamba
indicating the highest. The mineralization potential for the 0-15 em and 15-30 em
layers were 392.3 and 162.5 ~gN/g for Gituamba; 195.6 and 178.7 ~gN/g for
Kitale; and 198.0 and 75.8 ~gN/g soil for Katumani soils. The time required for
50% of No to be mineralised indicated that less than half the potential value would
become available in a normal growing season with the possible exception of
Gituamba (15-30 em) and Katumani soils. The trends of the calculated values
compared well with the observed ones except for Katumani soils. The Stanford
formula appears therefore not to work well with soils low in organic matter.
Organic N forms were also determined in the three soils. The hydrolysable
organic N for the 0-15 and 15-30 em layers was 57.2 and 59.3% for Gituamba;
56.9 and 61.9% for Kitale; 39.0 and 42.1 % for Katumani soils, respectively.
Amide N ranged from 11.6 to 21.4% of total N; Hexosamines from 5.2 to 10.1%
and Amino acid N from 26.2 to 37.1 %. Amino acid therefore formed the highest
portion followed by Amide N of the hydrolysable organic N. | en |
