The objectives of this were to investigate the response of Lupinus albus sp. to
phosphate rock (PR) as a source of phosphorus (P) nutrition, and to study the role organic
acid (Citric and Malic) in phosphorus dissolution from PR. Tow experiments we
re
conducted: 1) A greenhouse pot experiment, in order to study the response of white lupin
to the application of PR and Triple super phosphate TSP at three application rates (100-
450-800 ppm). 2)- A laboratory experiment in order to study the role of Citric and Malic
acids concentration and initial pH in P- release from PR. The results showed that Lupinus
albus sp. was able to use PR for P-nutrition, and has a relative agronomic effectiveness of
61% when compared to TSP. The possible Exuded organic acids such as Citric and Malic
were responsible for PR dissolution due to tow mechanisms: 64% of PR dissolution was
due to pH decrease in the rhizosphere area, and 34% due to chelating of calcium cations.
PR dissolution was increased by the increase organic acid concentration, but decreased
when the initial pH value increased. Dissolution was always more pronounced with citric
than malic acid.
A pot experiment was conducted to evaluate the relative agronomic
effectiveness (RAE%) of a Syrian phosphate rock when it is added alone and as
mixture with elemental sulfur with three different ratios (PR:S) (2:1) (5:1) (8:1)
and compared with tr
iple superphosphate. The main results of this study
showed that Ain Layloun phosphate rock was not effective for direct use by
Rye grass when used alone, but it became effective when mixed with elemental
sulfur. The relative agronomic effectiveness was varied following mixing ratios,
it was 50%, 76% and 87% in (8:1), (5:1) and (2:1) (PR:S) mixing ratios
respectively. This is due to the increase of available soil phosphorus content
which is related to the increase of phosphate rock solubility due to decrease of
pH derived from oxidation of sulfur by Thiobacillus spp.
A field experiment was carried out during 2003 and 2004 in Edleb
governorate to study the effect of phosphate solubilizing bacteria (Bacillus
megaterium) and cows manure on solubilization of phosphate rock, cotton
productivity, and phosphate uptak
e. The amounts of phosphate rock and
superphosphate were added by the same amount of P2O5.
An amount of nitrogen fertilizer as urea, was added to treatment 1, 2, 3, 4,
5, and 6 , whereas treatment 7, 8, 9, 10, 11, and 12 received amounts of organic
fertilizer having the same amount of N added to treatment 1-6 (MAAR
recommendation).
