الاكسدة الاحيائية للكبريت المضاف للتربة عند مستويات رص مختلفة

Abstract

The present study was conducted to evaluate the interactive effect of agricultural sulfur, organic source and compaction on the biological oxidation of sulfur in a loamy sand soil using a complete randomization design with three replications. The study comprised of two experiments carried out under laboratory conditions using plastic cups of about 300 ml capacity. Experiment I The experiment contained 27 treatments prepared from the interactions of three levels of each of agricultural sulfur : 0 , 1 and 2 g S ْ.kg-1 soil ( (S1, S2 and S3) , organic source : 0 , dried alfalfa, and farm yard manure ( C1, C2 and C3) and soil compaction : 1.25, 1.35 and 1.45 Mg.m-3 (M1, M2 and M3), respectively. The two organic sources were applied at a similar rate equal to 6 g carbon . kg-1 soil of each. During the experiment at period (45 days) of incubation at 28 C ْ , soil moisture content of all treatments maintained at about 50 % of the available water . After 15, 30 and 45 days of incubation, soil samples were taken and used for counting the population densities of autotrophic and heterotrophic sulfur oxidizing microorganisms as well as measuring EC, pH, SO4 = and available P. Experiment II The objective of this experiment was to investigate the presence and activity of the aerobic – autotrophic S – oxidizing Thiobacillus thioparus under the same treatments of the previous experiment. The results obtained from the study could be summarized as follows: 1 – Application of sulfur significantly increased EC, SO4 = and available P and decreased pH values of the soil . 2 – Addition of 6 g carbon . kg-1 soil as dried alfalfa or farm yard manure caused in an increments in all examined parameters, except the pH which decreased significantly . Alfalfa had more effects than the manure. 112 3 – The soil with compaction level of 1.35 Mg.m-3 showed significantly higher effects compared with 1.25 and 1.45 Mg.m-3 soil ones. 4 – Population density of both autotrophic and hetrotrophic sulfur oxidizers differently affected by sulfur, organic source and compaction treatments. The highest average counts of the autotrophes were 16.6, 30.3 and 11.1 x 102 cells . g-1 dry soil were recorded under treatments S2, C2 and M2, respectively, while those of the heterotrophes ( 6.3, 7.6 and 5.6 ) x 107 cells . g -1 soil were found in S0, C3 and M2 treatments, respectively. 5 – Generally, the S*M interaction treatment showed the highest effects on the tested parameters after 30 days of incubation. The values of EC, pH, SO4 = and available P and population densities of the autotrophic and heterotrophic S – oxidizers recorded under this treatment were 4.7 dS.m-1 , 6.4 , 1575 mg.kg-1 , 9.3 mg.kg-1 , 7.98 x 102 and 7.98 x 107 cells . g-1 dry soil, respectively. 6 – The present study proved that the soil used contained the thiosulfate oxidizing autotrophes, while sulfur oxidizers were not detected. On the other hand, the heterotrophic microorganisms which are able to oxidize sulfur to thiosulfate were found and application of organic source significantly increased their population. 7 – The soil used harbored Thiobacellus thioparus species and its activity enhanced with the increase in the level of S applied and decrease in soil compaction level used. Addition of dried alfalfa plants or farm yard manure depressed the activity. The highest activity was noticed during the first interval ( after 15 days of incubation) under S3*M1*C1 and S3*M2*C1 interaction treatments. The average amount of thiosulfate oxidized and pH value in the liquid culture of these two treatments, were 550 mg. 100-1 ml and 6, respectively.