ABSTRACT
The production of common bean Phaseolus vulgaris in Kenya has been reducing due
to declining soil fertility. The use of synthetic fertilizers has been linked to soil
acidification, which constrains plant growth and interferes with beneficial
rhizosphere biota. The application of composts is being encouraged, and farmers in
Western Kenya are being trained on composting of locally available organic
materials. However, there is need to establish the performance of such farmerproduced
composts in terms of improving soil fertility and biota, for instance
Rhizobium, rhizobacteria, fungi, micro- invertebrate, as well as mitigating
infestations by foliar pests such as Aphis fabae, Frankliniella occidentalis,
Colletotrichum lindemuthianum. A field experiment was conducted on Masinde
MuliroUniversity of Science and Technology farm, to assess belowground influence
of farmer-produced composts on the soil biota, the foliar pests and yields of common
bean. The experiment comprised 2 × 7 factorial treatments, with common bean
cultivar having two levels i.e. Mwezi Moja (GLP 1004) and KALRO Kakamega 8
(KK8); with seven levels of soil fertility amendments, comprising five farmerproduced
composts(FC 1-5), with varying plant and animal waste ingredients , DAP
fertilizer and untreated controls. Each of the resulting 14 treatment combinations
comprised of twin plots (3 m × 2 m) for the two bean varieties, each having n = 40
plants per variety, spaced at 50 cm × 15 cm, replicated in 3 blocks (24 m × 14 m) in a
randomized block design, over a period of 2 seasons i.e. long rains (1st April to 30th
June 2014) and short (17th July to 5th October 2014). Data collected includes, root
endophytic (Rhizobium) and rhizosphere microbes (bacteria and fungi), soil microinvertebrates
(nematodes and arthropods), the foliar pests A. fabae, F. occidentalis
and C. lindemuthianum; and plant growth and yields. Statistical analysis was
conducted using SAS 9.1 at p≤0.05. Apart from N and P, farmer-produced composts
contained a variety of additional nutrients including, K, Ca, Mg, Fe, Cu, Mn and Zn
that DAP lacks. Germination % was lowest in bean seeds grown with DAP (72.0 %
b) and highest in those receiving FPC1 (85 % a), FPC3 (86.9 % a) and the controls
(84.8 % a). Germination percentage was higher in KK8 bean variety (96 % a) than in
Mwezi Moja bean variety (67 % b) (P0.05). At harvest, compost-treated plots had pH 5.3 and
improved nutrient concentrations than DAP and control plots. The results of this
study shows that, trained farmers produced composts contained important nutrients
that were utilized by common bean to promote growth and yields, while enhancing
endophytic colonization by beneficial Rhizobium species, and promoting rhizosphere
colonization by bacteria and fungi, but suppressing soil nematode populations.
Farmer-produced compost CF3 was relatively better in performance. However, there
was no evidence that farmer-produced composts influenced bean infestation by the
foliar pests.