The effects of water potential on some active forms of phosphorus in a calcareous soil amended with sewage sludge

Immobilization and mobilization reactions of soil phosphorus depend on biological properties of  soil and these soil properties strongly depend on the soil water potential. The objective of this study was to test theeffects of water potential on some active forms of soil P. A semiarid soil classified as Calcic Haploxerept was treated with raw sewage sludge at a rate of 20 g kg-1. Water potentials established for soil incubation were: saturation (SA, 0 bar), field capacity (FC, -0.3 bar), and permanent wilting point (PWP, -15 bar). An irrigation treatment was dryingrewetting cycle (DWC) between -0.3 to -15 bars. After 0, 20, 60 and 90 days of incubation soils were sampled for analysis. The addition of sewage sludge increased soil total P, organic P, available P, microbial P, soluble and easily soluble P contents. The increase of soluble P was relatively higher. The effects of soil moisture, incubation time andtheir interaction on all active forms of soil P were significant. During 20 days of incubation, available P and soluble P decreased, whereas microbial P, easily soluble P and dicalcium phosphate increased significantly. After that, available P and easily soluble P increased continuously, but microbial P, soluble P and dicalcium phosphatefluctuated during incubation. Microbial P had negative and significant correlations with available P and easily soluble P. Soils incubated in DWC and FC compared to soils incubated in SA and PWP had significantly higher available P,soluble P and easily soluble P contents. However microbial P and dicalcium phosphate were significantly higher in soils incubated in higher water potential

Temporal variability of available P, microbial P and some phosphomonoesterase activities in a sewage sludge treated soil: The effect of soil water potential

Available P and enzyme activities strongly depend on the soil water potential. The objective of this study was to test the effects of water potential on soil available P, microbial biomass P(MBP) and somephosphomonoesterase activities. A semiarid soil classified as Calcic Haploxerept was treated with raw sewage sludge at a rate of 20 g kg-1. Four levels of irrigation (deionized water) were established for 90days of incubation. Constant water potentials used for soil incubation were: saturation (SA, 0 bar), field capacity (FC, -0.3 bar), and permanent wilting point (PWP, -15 bar) in three treatments. An irrigation treatment was also drying-rewetting cycle (DWC) between -0.3 to -15 bars. After 0, 20, 60 and 90 days of incubation, soils were sampled for analysis. The addition of sewage sludge decreased soil pH and increased soil EC, organic C, total N, organic P, available P, MBP contents and phytase, alkaline and acid phosphatases activities significantly. The effects of soil moisture, incubation time and their interaction on soil available P, MBP and phosphomonoesterase activities were significant at different levels. During 20 days of incubation, available P and phosphatase activities decreased, whereas microbial P and phytase activity increased significantly. Thereafter, only available P increased and phytase activities decreased continuously, but microbial P, alkaline and acid phosphatase activities fluctuated during incubation. Soils incubated in DWC and FC compared to soils incubated in SA and PWP had higher available P contents. Microbial P and phosphomonoesterase activities increased with increasing soil water potentials significantly. The highest (38.7 mg kg-1) and lowest (28.9 mg kg-1) microbial P was measured in soil incubated in SA and PWP respectively. Correlation coefficient between available and microbial P was negative and significant. The activities of alkaline phosphatase,acid phosphatase and phytase were higher and lower in soils incubated in SA and PWP, respectively

Changes of Available Phosphorus and phosphatase activity in the rhizosphere of some field and vegetation crops in the fast growth stage

A large proportion of P is found in organic forms. Phosphatase, plays an essential role in the mineralization of organic phosphorus. Agronomy species can affect phosphatase activity in rhizosphere. The aim ofour study was to determine the effects of some agronomy species (Gramineae, Leguminose, Solanaceae, Labiatae, Cruciferae, Umbellifera, Alliaceae) on phosphatase activity in their rhizosphere. The agronomy species were planted in a semiarid soil in the pots under greenhouse condition. Phosphatase activity in the rhizosphere of any species was studied at middle of their growth. Phosphatase activity was greatly enhanced in the rhizosphere of all species. Alkaline phosphatase activity increased 102-325% and acid phosphatase activity increased 205-455% in the rhizosphere soil compared to the non-rhizosphere soil. This suggests that agronomy species actively promote rhizosphere phosphatase activity either directly by secretion or indirectly by stimulation of microbial activity and/or by depletion of Pi. There were significant differences between phosphatase activities in rhizosphere of plant species. The highest and lowest means of alkaline phosphatase activity were found in rhizosphere of Trifolium repens andOcimum basilicum respectively. The highest and lowest means of acid phosphatase activity were found in rhizosphere of Triticum aestium and Cicer arietinum respectively

Biodegradation of some agricultural residues by fungi in agitated submerged cultures

Digestibility of agricultural residues in animal feeding is deeply dependent on the amounts and types of their fibers. Biological treatment of agricultural residues is a new method for improvement of digestibility. Therefore, the capacity of a few fungi in biodegradation of some agricultural residues wasstudied. Losses of crude fiber (CF), neutral detergent fiber (NDF) and acid detergent fiber (ADF) of wheat, barley, rice, wood, and pea straw were investigated in agitated submerged culture during biodegradation by fungi. Biodegradation of the plant residues is dependent on the plant and fungusspecies. The biodegradation order of plant residues was  pea>barley>wheat>rice>wood. A. terreus and T. reesei were more able to degrade the easy degradable plant residues. Rice and wood were degradedmore by Armillaria sp., Polyporus sp. and P. chrysosporium. Crude fiber, NDF and ADF of agricultural residues were reduced more by P. chrysosporium. Generally, the reduction of agricultural residues NDF by fungi was more than their ADF. However, Polyporus sp. decreased ADF of wheat straw more. Thus, for improvement of digestibility of agricultural residues, the treatment by white-rot fungi may be recommended

Changes of Available Phosphorus and phosphatase activity in the rhizosphere of some field and vegetation crops in the fast growth stage

A large proportion of P is found in organic forms. Phosphatase, plays an essential role in the mineralization of organic phosphorus. Agronomy species can affect phosphatase activity in rhizosphere. The aim ofour study was to determine the effects of some agronomy species (Gramineae, Leguminose, Solanaceae, Labiatae, Cruciferae, Umbellifera, Alliaceae) on phosphatase activity in their rhizosphere. The agronomy species were planted in a semiarid soil in the pots under greenhouse condition. Phosphatase activity in the rhizosphere of any species was studied at middle of their growth. Phosphatase activity was greatly enhanced in the rhizosphere of all species. Alkaline phosphatase activity increased 102-325% and acid phosphatase activity increased 205-455% in the rhizosphere soil compared to the non-rhizosphere soil. This suggests that agronomy species actively promote rhizosphere phosphatase activity either directly by secretion or indirectly by stimulation of microbial activity and/or by depletion of Pi. There were significant differences between phosphatase activities in rhizosphere of plant species. The highest and lowest means of alkaline phosphatase activity were found in rhizosphere of Trifolium repens andOcimum basilicum respectively. The highest and lowest means of acid phosphatase activity were found in rhizosphere of Triticum aestium and Cicer arietinum respectively

The effects of water potential on some active forms of phosphorus in a calcareous soil amended with sewage sludge

Immobilization and mobilization reactions of soil phosphorus depend on biological properties of  soil and these soil properties strongly depend on the soil water potential. The objective of this study was to test theeffects of water potential on some active forms of soil P. A semiarid soil classified as Calcic Haploxerept was treated with raw sewage sludge at a rate of 20 g kg-1. Water potentials established for soil incubation were: saturation (SA, 0 bar), field capacity (FC, -0.3 bar), and permanent wilting point (PWP, -15 bar). An irrigation treatment was dryingrewetting cycle (DWC) between -0.3 to -15 bars. After 0, 20, 60 and 90 days of incubation soils were sampled for analysis. The addition of sewage sludge increased soil total P, organic P, available P, microbial P, soluble and easily soluble P contents. The increase of soluble P was relatively higher. The effects of soil moisture, incubation time andtheir interaction on all active forms of soil P were significant. During 20 days of incubation, available P and soluble P decreased, whereas microbial P, easily soluble P and dicalcium phosphate increased significantly. After that, available P and easily soluble P increased continuously, but microbial P, soluble P and dicalcium phosphatefluctuated during incubation. Microbial P had negative and significant correlations with available P and easily soluble P. Soils incubated in DWC and FC compared to soils incubated in SA and PWP had significantly higher available P,soluble P and easily soluble P contents. However microbial P and dicalcium phosphate were significantly higher in soils incubated in higher water potential