الملخص الإنجليزي
The study was conducted in three parts: the first part aimed to investigate the
impact of long-term farming practices on the chemical and biological properties of
soil, the second part aimed to investigate the effect of conventional and organic
greenhouse farming systems on soil chemical properties, microbial enumeration,
activity, and diversity, and the third part aimed to test the efficacy of rhizosphere
bacterial antagonists against cucumber damping-off caused by Pythium
aphanideramtum on compost amended soils under greenhouse conditions. In the first
study, the results of soil tests on samples collected from eight farms indicated
significant changes in average soil chemical and biological properties over time, such
as an increase in soil electrical conductivity from 'low salinity' to 'highly saline', a
decrease in soil pH from 8.4 to 7.5, an increase in organic matter from 'very low' to
'medium' and an increase in Olsen phosphorus from deficient to excessive. Also, an
increase in sodium, magnesium, chloride, and sulfate ions was observed while no
significant differences were observed in soil potassium and calcium concentration. In
second study, soil samples were collected from four conventional and six organic
greenhouses on farms in Oman. The results showed that on average the soil from
conventionally farmed greenhouse had significantly higher NO3-, soil respiration, and
microbial metabolic quotient than organically farmed greenhouses. On the other hand,
organic greenhouses exhibited higher soil pH and organic matter, bacterial
enumeration, and substrate-induced respiration. The results of third study revealed that
the Chryseobacterium gleum (B2) isolate was the most effective treatment among the
nine isolates tested, reducing the seedling damping-off incidence by 50% compared to
the Pythium-infected control. The C. gleum (B2) treatment also reduced the mycelium
radius and diameter growth of P. aphanidermatum by 32.8% and 34% respectively,
compared to the control. The soil amended with compost had several volatile organic
compounds compared to non-organic soil, and the Chryseobacterium gleum (B2)
bacterial isolate also released certain volatile organic compounds that showed potential
in controlling the damping-off disease. The major volatile organic compounds released
by non-organic soil were Undecane, 2,4-dimethyl- (25%), Cyclopentasiloxane,
decamethyl- (15%), Cyclotetrasiloxane, octamethyl- (13%), and Heptane, 2,4-
dimethyl-(7.85%). While those in soil amended with compost were
Cyclopentasiloxane, decamethyl- (20.58%), Cyclotetrasiloxane, octamethyl-
(18.78%), Pentane, 2-methyl- (10.21%), Acetone (8.54%), Cyclotrisiloxane,
hexamethyl- (8.2%), Cyclohexasiloxane, and dodecamethyl- (7.27%).
Chryseobacterium gleum (B2) bacterial isolate also released l-Alanine ethylamide,
(S)- (28.65%), 1-Dodecene (13.3%), Disulfide, dimethyl (9.18%), 9-Octadecenoic
acid (Z)-, methyl ester (6.04%), and Butanoic acid, and 3-methyl-, ethyl ester (5.81%).
The results of the study indicate that the C. gleum (B2) isolate shows high potential to
control damping-off disease biologically and can be used in sustainable agricultural
practices.
