Fertilizante microbiano em solo salino-sódico condicionado por enxofre com Acidithiobacillus em interação com resíduo orgânico

Abstract

The soil salinization has been widely discussed, especially in arid and semi-arid regions. The recovery of salinized soils allows the reduction of soluble salts concentration, the exchangeable sodium and the pH in the soil profile. Many methods are used to recovery the soil salinization, and the use of sulfur is important because interfere in the soil reaction. Elemental sulfur inoculated with the oxidative bacteria Acidithiobacillus produce sulfuric acid that may be used in the correction of saline sodic soil. Fertilization with organic matters seems to promote satisfactory results on soil availability and on microbial attributes. The objective of this work was to evaluate the efficiency of microbial fertilizers in saline-sodic soil recovered by elemental sulfur inoculated with Acidithiobacillus bacteria, an interaction with organic residue. The experiment was conducted in greenhouse and divided into two stages. The first stage for soil correction and the second to observe the soil fertilization. Sulfur inoculated with Acidithiobacillus was used for sodium correction based on the recommended dose for sodium saturation. The organic residue (sewage sludge) was used in different proportions (sludge: soil): 1- (0.15: 5.85) and 2- (0.3: 5.7). The recovery treatments were: (1) C1- Sulfur inoculated with A. thiooxidans and ferrooxidans; (2) C2- Sulfur inoculated with A. thiooxidans and A. ferrooxidans + 2.5% sewage sludge (soil: sludge) (50 t ha-1); (3) C3- Sulfur inoculated with A. thiooxidans and A. ferrooxidans + 5.0% sewage sludge (soil: sludge) (100 t ha-1); (4) C4- Sulfur without inoculation with the oxidizing bacteria; (5) C5- No corrective added. The pots were incubated for 45 days, followed by application of water to remove soluble salts. The experimental design was processed in randomized blocks with four replications. The second part of the experiment was to evaluate the different fertilizer sources, using three of the previous recovery treatments (C1, C2 and C3), arranged in randomized blocks, in the factorial scheme 3x6, with 3 replicates. The fertilizers were calculated based on the supply of P for economical crops, according the soil analysis. The dose 1 was equivalent to 120 kg ha-1 (P2O5) and dose 2 equivalent to 180 kg ha-1 of P2O5. The fertilization treatments consisted of: 1) Microbial fertilizers (BP1), inoculated with Acidithiobacillus thiooxidans, Beijerinckia indica and Cunninghamella elegans; 2) Microbial fertilizer (BP2) inoculated with Acidithiobacillus thiooxidans, Beijerinckia indica and Cunninghamella elegans; 3) Microbial fertilizer (BF) at dose 1, inoculated with Acidithiobacillus thiooxidans and Beijerinckia indica; 4) Soluble fertilizer in dose 1 (SF1) 5) Soluble fertilizer in dose 2 (SF2); 6) Control treatment (without fertilization). The addition of sulfur inoculated with oxidizing bacteria in interaction with sewage sludge showed positive and evident effect on soil pH reduction. Microbial fertilizers in interaction with the sewage sludge also influenced the soil microbial attributes. The sewage sludge reduced the exchangeable cations in the soil. The microbial fertilizer contributed to the fertility and microbial activity in the saline-sodic soil and may be a viable alternative for replacement of soluble fertilizers.