Long-term land
management effects on soil properties and microbial
populations in a maize-bean rotation at Kabete, Kenya
Catherine N. Kibunja1*, F.
B. Mwaura2 and D. N. Mugendi3
1Kenya
Agricultural Research Institute, NARL-KARI, P. O. Box
14733-00800, Nairobi, Kenya.
2School
of Biological Sciences, University of Nairobi, P. O. Box
30197, Nairobi, Kenya.
3School
of Environmental Studies, Kenyatta University, P. O. Box
43844, Nairobi, Kenya.
*Corresponding author. E-mail:
catherine.kibunja@yahoo.com.
Accepted 7 December, 2009 |
|
The effect of continued application of mineral and organic
fertilizers on soil agro-properties and soil microbial
populations and activity, was studied in a long-term field
experiment at Kabete,
in the highlands of Kenya.
The area is sub-humid with an average bimodal rainfall of
980 mm and two cropping seasons per year. The main
treatments were 3 rates of inorganic N and P fertilizers,
farmyard manure (FYM) with or without stover retention.
Maize and beans were
planted during the long and short rain seasons,
respectively. Total % N declined by 25% from 0.16%
while soil organic carbon decreased from 2 to 1.2%. The soil
pH value dropped by 1.3.units from 5.5 but the decrease in
bulk density from 1.04 to 1.08 g cm-3 soil in the
no-input control treatment was not significant. Use of FYM
alone or in combination with chemical fertilizers led to
higher numbers of microbes and enhanced microbial
respiration than use of chemical fertilizers alone. The
topsoil layer had significantly (p = 0.05) higher microbial
activity than the sub-soil regardless of management
strategy. Bacteria were more numerous {1 × 105
cfu
(colonies forming units) g dry wt. soil -1}
than fungi (1 × 103 cfu g dry wt. soil -1),
which may lead to more soil organic matter (SOM)
mineralization and less SOM retention in this cropping
system. Integrated use of organic inputs such as farmyard
manure and chemical fertilizers is recommended to maintain
soil productivity under continuous cultivation.
Key words:
Land management, fertilizers, farmyard manure, crop
residues, soil properties, mineralization, microbial
population. |
