María-Belén Turrión

Soil organic matter quantity and quality in mountain soils of the Alay Range, Kyrgyzia, affected by land use change

Abstract Changes in soil management practices influence the amount, quality and turnover of soil organic matter (SOM). Our objective was to study the effects of deforestation followed by pasture establishment on SOM quantity, quality and turnover in mountain soils of the Sui Checti valley in the Alay Range, Kyrgyzia. This objective was approached by analysis of total organic C (TOC), N, lignin-derived phenols, and neutral sugars in soil samples and primary particle-size soil fractions. Pasture installation led to a loss of about 30% TOC compared with the native Juniperus turkestanica forests. The pasture soils accumulated about 20% N, due to inputs via animal excrement. A change in land use from forest to pasture mainly affected the SOM bound to the silt fraction; there was more microbial decomposition in the pasture than in the forest silt fraction, as indicated by lower yields of lignin and carbohydrates, and also by a more advanced oxidative lignin side-chain oxidation and higher values of plant : microbial sugar ratios. The ratio of arabinose : xylose was indicative of the removal of carbohydrates when the original forest was replaced by pasture, and we conclude that this can be used as an indicator of deforestation. The accumulation of lignin and its low humification within the forest floor could be due to the extremely cold winter and dry summer climate.

Effects of deforestation on phosphorus pools in mountain soils of the Alay Range, Khyrgyzia

Abstract The amount, quality and turnover of soil P is heavily influenced by changes in soil management. The objective of this study was to investigate the effects of deforestation and pasture establishment on the concentrations, forms and turnover rate of soil P in mountain soils of the Alay Range, Khyrgyzia. A sequential extraction was applied to distinguish soil P pools. We used particle-size fractionation to follow the dynamics of different P pools in soils under forest and pasture and 31P-NMR spectroscopy to investigate the structure of alkali-soluble P forms. In the A horizons of the forest soils, total soil P concentration was 1093 mg kg–1, organic P (Po) representing 46% of the total P. Deforestation followed by pasture establishment not only increased significantly (P<0.01) the total P concentration (1560 mg kg–1) but also the contribution of Po to total P was increased by 17%. Pasture soils had significantly higher P pools than forest soils except highly labile inorganic P (Pi NaHCO3) and primary Pi (Pi HCldil). Both in forest and pasture soils stable P increased with decreasing particle size (coarse sand 50%, clay 80% of total P) and primary P decreased with decreasing particle size. Phosphate monoesters and diesters represented 80% of P identified by 31P NMR. Low monoester to diester ratios in the alkali extracts of forest and pasture soils indicate low microbial activity. This is consistent with high C/Po ratios and high stable Po concentrations in the fine earth of forest and pasture.

Characterization of soil phosphorus in a fire-affected forest Cambisol by chemical extractions and 31P-NMR spectroscopy analysis

This study was conducted to investigate the long-term effects of fire on soil phosphorus (P) and to determine the efficiency of different procedures in extracting soil P forms. Different P forms were determined: labile forms (Olsen-P, Bray-P, and P extracted by anion exchange membranes: AEM-P); moderately labile inorganic and organic P, obtained by NaOH-EDTA extraction after removing the AEM-P fraction; and total organic and inorganic soil P. (31)P-NMR spectroscopy was used to characterize the structure of alkali-soluble P forms (orthophosphate, monoester, pyrophosphate, and DNA). The studied area was a Pinus pinaster forest located at Arenas de San Pedro (southern Avila, Spain). The soils were Dystric Cambisols over granites. Soil samples were collected at 0-2 cm, 2-5 cm, and 10-15 cm depths, two years after a fire in the burned area and in an adjacent unburned forest area. Fire increased the total N, organic C, total P, and organic and inorganic P content in the surface soil layer. In burned soil, the P extracted by the sequential procedure (AEM and NaOH+EDTA) was about 95% of the total P. Bray extraction revealed a fire-induced increase in the sorption surfaces. Analysis by chemical methods overestimated the organic P fraction in the EDTA-NaOH extract in comparison with the determination by ignition procedure. This overestimation was more important in the burned than unburned soil samples, probably due to humification promoted by burning, which increased P sorption by soil particles. The fire-induced changes on the structure of alkali-soluble P were an increase in orthophosphate-P and a decrease in monoester-P and DNA-P.

Modified method for measuring acid phosphatase activities in forest soils with high organic matter content

Abstract The acid phosphatase activity (APA) is a key factor in phosphorus (P), mineralization, P nutrition of plants, and P cycling. However, the widely used method of Tabatabai and Bremner for APA determinations is seriously restricted in soils with high organic matter contents, owing to interference in photometric detection by dissolved organic matter. The objectives of this study were: A) to modify the procedure of Tabatabai and Bremner with a view to its application to forest soils rich in organic carbon, b) to determine APA contents in forest soils of the Sierra de Gata mountains, and c) to establish relationships between the APA with different soil parameters. The modified procedure was well adapted to forest soils with high organic matter contents and had good reproducibility, while maintaining the relative simplicity and accuracy of the original Tabatabai and Bremner procedure. APA in the forest soils studied was high but did not correlate with labile P. The APA in the soils studied depended principally on availability of readily degradable energy sources and soil nitrogen (N).

Effects on soil organic matter mineralization and microbiological properties of applying compost to burned and unburned soils

This study was undertaken in the context of a project of reclamation of a burned forest area applying municipal waste compost (MWC) and it consisted of an incubation experience carried out under laboratory conditions. The objectives of this research were to asses the effect of three doses of MWC added to burned and unburned calcareous soils on a) SOM mineralization and b) soil microbiological parameters. The laboratory incubation experience was carried out with three compost doses (1, 2 and 4% w/w) on a burned soil and another unburned one from an adjacent plot, besides the corresponding control samples. The mineralization kinetics of the organic matter was studied for 92 days. The kinetics data were adjusted to a double exponential model, showing two C pools of different degrees of resistance to mineralization and concentration, with half-life times of 1.9-4.9 and 34-76 days, respectively. In the unburned soil, the initial potential mineralization rate of the labile and stable C pools showed an opposed behavior, increased and decreased with the MWC dose, respectively. However in the burned soil no significant tendencies were observed. Although applying compost tended to increase the size of more labile pool with respect to total mineralizable C, however most of the soil or compost OM did not result mineralizable in the short and medium term. The compost amendment did not increase soil microbial activity.

Extraction of soil‐available phosphate, nitrate, and sulphate ions using ion exchange membranes and determination by ion exchange chromatography

Abstract In recent years, ion exchange membranes (IEM) have been used successfully to determine the availability of soil nutrient elements for plants. In general, the procedures proposed are applied to the determination of a single ion, and in only a few of these studies, the selectivity of these IEM was considered. Therefore, this work was conducted (a) to find the most suitable extraction conditions for phosphate (H2PO4 ‐), nitrate (NO3 ‐), and sulfate (SO4 2‐) in soils by IEM and their subsequent determination by ion chromatography, (b) to test the effectiveness and selectivity of IEM, (c) to compare the results obtained by IEM with the common procedure for determining the availability of the soil nutrient elements, and (d) to verify whether a relation exits between the concentration of phosphorus (P) extracted by IEM and the plant P requirement. The soil samples used for this study were Humic Cambisols located in four forest plots under natural conditions and four plots fertilized with 100 kg P ha‐1 a...

Relationships between organic and inorganic P fractions with soil Fe and Al forms in forest soils of sierra de gata mountains (Western Spain)

The aim of this work was to study the interactions of Al, Fe and P forms in four forest soils in a Mediterranean environment. A sequential procedure was used to distinguish soil P pools, and different extractions were used to determine Fe and Al forms. The acid nature of the bedrock, in addition to the high rainfall regime, favours high contents of free forms of Al and Fe. The soils studied (Humic Cambisols) had a high total P concentration (500–1200 mg kg −1 ), but low contents of P extractable with anionic exchange membranes, (2–34 mg kg −1 ). The labile P (P extracted with NaHCO 3 ) ranged from 74–189 mg kg −1 and accounted for 15–25% of total extractable P. Soils developed on granite showed higher concentrations of labile P than did those developed on slate. The adsorbed forms of P (P extracted with NaOH) ranged from 183–420 mg kg −1 and accounted for more than 50% of total extractable P. A high percentage of soil P was occluded in soil Al and Fe forms. In the soils over slate, the most stable fractions (P extracted with NaOH after applying ultrasound) accounted for more than 80% of the total extractable P, while in the soils over granite, the stable fractions were less than 60% of the total extractable P. The ratio between the most available forms of P and total extractable P was a negative function of the total amount of Fe and Al oxides. These compounds, either by occluding or by adsorbing phosphate on high-affinity sites, are crucial for the dynamics of P in these soils.

Effects on soil phosphorus dynamics of municipal solid waste compost addition to a burnt and unburnt forest soil

The main aim of this research was to assess the effects of municipal solid waste compost (MSWC) addition to a burnt and unburnt calcareous soil, on the distribution of soil P forms in particle-size and extractable fractions. Three MSWC doses (1, 2 and 4% w/w) were added to burnt and unburnt soil samples and were incubated for 92 days at 29 °C and 75% of field capacity moisture. A particle-size fractionation followed by a sequential P extraction procedure was carried out. The burnt soil showed significantly lower concentrations of organic P forms (Porg) and significantly higher concentrations of stable P forms than the unburnt soil. Besides, in both burnt and unburnt soils, most P-forms presented higher concentrations in the clay fractions than in the sand and silt fractions, possibly due to the different proportions of microbial synthesized and plant-derived substances in the different particle-size fractions. Finer fractions of MSWC showed higher total P and Porg concentrations than coarser fractions. Our results showed that the highest dose of MSWC` was the most effective one for the rehabilitation of the burnt soil. MSWC amendment also caused an increase in soil P availability in the unburnt soil which initially contained relatively low levels of P. During the incubation process, a high proportion of organic P contained in the MSWC was mineralized into inorganic P forms. These forms were precipitated with Ca cations which are very abundant in these calcareous soils, significantly increasing the P fraction extracted by HCl in both amended soils. Hence, adding compost to the soil involved an increase in the available P reservoir in the long term. The combination of particle-size fractionation, chemical sequential extraction and incubation experiments can be a valuable tool for splitting soil phosphorus into different fractions regarding their availability in relation to short and long-term transformations in soil.