Scielo RSS <![CDATA[Journal of soil science and plant nutrition]]> vol. 16 num. 1 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Microbial communities of bulk and <i>Eschscholzia californica</i> rhizosphere soils at two altitudes in Central Chile</b>]]> Despite several reports point out a rhizosphere effect shaping soil microbial communities and others an effect of altitude on plant phenotypic features, currently little is known about the impact of elevational patterns on the diversity of soil microbial communities. In this study, diversity of soil microbial communities was assessed in samples derived of bulk and rhizosphere soils associated to Californian poppy (Eschscholzia californica Cham.) populations at 1000 and 2000 m.a.s.l in Central Chile. E. californica, a native plant of North America, is considered a successful invader in Mediterranean ecosystems worldwide but its effect on diversity of soil microbial communities is yet unknown. Microbial diversity was evaluated at genetic level through T-RFLP (terminal restriction fragment length polymorphisms) using bacterial, archaeal and fungal molecular markers, and at metabolic level using CLPP (community-level physiological profiles). At genetic level, microbial diversities of bulk and rhizosphere soils at lower altitude were similar, although at higher altitude microbial diversity of both types of soils was different, suggesting a plant filtering effect more notorious at higher altitude. At metabolic level, microbial diversity of rhizosphere soils were similar independently of the altitude, suggesting a plant filtering .effect that exceeds the altitude effect observed in the case of the bulk soil. <![CDATA[<b>Soil enzymes and biological activity at different levels of organic matter stability</b>]]> Soil biological activity has important implications for soil carbon (C) sequestration. However, very little is known about the environmental factors, particularly the effect of soil mineralogy on availability of C for soil microorganisms. In this study, we have investigated the influences of soil type (clay mineralogy)on C mineralization and its effects on biological activity at different levels of soil organic matter stability. Two soils an allophanic, derived from recent volcanic ash and a kaolinitic, resulting from metamorphic parent materials were physically fractioned in to light(LF, coarse sand 250-2000 µm), intermediate (IF, fine sand53-250 µm) and mineral (MF,silt and clay < 53 µm) fractions. Several biological and biochemical analyses at Ah horizons of mineral soil and physical fractions were conducted: soil respiration, enzymatic activities, carbohydratesand microbial biomass, amongst others soil variables. The results indicated that the bulk soiland physical fractions had a significant impact on cumulative C mineralizedafter 30 days of incubation and soil enzyme activities. More than 76% of total C-CO2 variation was explained by stepwise multiple regression analysis including factors such as soil enzymes (ß-glucosidase, dehydrogenase and phosphatase) and inorganic P. Soil ATP extractionwas agood indicator of microbial activity, because of a positive and significant correlation among ATP and i) C-CO2 and ii) metabolic quotient (soil respiration rate divided by microbial biomass). We also found an inverse and significant relationship between Al pyrophosphate (Al bound to SOM) and the C-CO2 in volcanic soil, whereas the same correlation did not occur in kaolinitic soil. Our results confirmed a greater stabilization capacityof MF in allophanicthan in kaolinitic soils due to the amorphous minerals clay materials. <![CDATA[<b>Targeted yield precision model assessment for rice-rice crop sequences in Farmers' Fields in Humid, Sub-tropical Northeastern India</b>]]> On-farm trials were conducted based on an autumn rice-winter rice crop sequence in 21 farmers, fields from 2012-2014 in humid, sub-tropical northeastern India i) to verify the suitability of the formulated appropriate site-specific target yield-based fertilizer prescription models over available technology and ii) to analyze the economics of the adoption of these models to enhance the productivity and profitability of rice-rice crop sequences. The results revealed that treatments based on the targeted yield precision model with and without integrated plant nutrient supply (IPNS) components ensured higher grain yield, additional yield gains and additional net profits over the farmers, practice and conventional fertilizer recommendations. The achievements of the prefixed targets were >100% in autumn rice and 96 to 106% in winter rice. The IPNS treatments guaranteed better a benefit: cost ratio (1.7 to 2.3) vis-a-vis without IPNS. The targeted yield precision model for fertilizer recommendations was more precise to achieve the targeted yields, which additionally led to higher profits. The targeted yield approach was effective up to 4.0 and 5.0 tons ha−1 yield targets without IPNS in autumn rice and with IPNS in winter rice, respectively, in humid sub-tropical northeastern India. <![CDATA[<b>Potential repellent activity of the essential oil of <i>ruta chalepensis</i> (linnaeus) from chile against <i>aegorhinus superciliosus</i> (guérin) (Coleoptera: Curculionidae)</b>]]> The objective of this study was to evaluate the repellent effect of the essential oil of the rue (Ruta chalepensis) against the weevil Aegorhinus superciliosus, an important pest of fruit crops in Chile. Rue essential oil was obtained by steam distillation, and its components were identified by GC-MS. Their effect on adult A. superciliosus insects was evaluated using four-arm olfactometric bioassays. The extraction process had a yield of 0.3% on a dry weight basis, and a chromatographic analysis showed the presence of nine compounds, which represented 89.3% of the total components. The major compounds were 2-nonanone (41.7%) and 2-undecanone (40.1%). Behavioral bioassays showed that the rue essential oil elicited a repellent effect against male and female A. superciliosus (p ≤ 0.05) at a concentration of 1.92 x 10(7) ng/cm². However, at a lower concentration of the oil (285.7 ng/cm²), only females were repelled (p ≤ 0.05). The repellency observed against A. superciliosus could be attributed to high concentrations of both ketones, suggesting that rue essential oil can be considered as a potential repellent that could reduce the infestation of this weevil. The role of the compounds identified and the repellent activity of this evergreen shrub are discussed. <![CDATA[Ammonia emissions from livestock production in Chile: an inventory and uncertainty analysis]]> The objective of this work was to quantify the country's NH3 emissions from livestock production. This calculation was based on the mass flow of total ammoniacal nitrogen (TAN). The analysis was performed for all 15 geographical regions in Chile. The definition of livestock subcategories was based on data from the Chilean Agriculture and Forestry Census as well as technical reports published by the Chilean National Statistics Institute. Significant differences were observed among the sources of livestock emissions in Chile's regions, and there was high variability depending on the degree of livestock confinement. In 2013, the total calculated emissions were 69.1 kt NH3/year (± 31.1). The O’Higgins Region had the highest NH3 emissions in Chile, representing 45% of the total. In terms of livestock production, 45% of the emissions were generated by pigs, 22% by poultry, 16% by cattle, 11% by equines and 4% by sheep. Emissions from the TAN that was available during manure and slurry management and the degree of animal confinement were the primary sources of uncertainty. This uncertainty could be greatly reduced by developing regional emission factors and by including the degree of animal confinement in Chile's national statistics such as the Agriculture, Livestock and Forestry Census. <![CDATA[<b>Changes in P pools over three months in two soils amended with legume residues</b>]]> To assess the longer term effects of soil properties and residue addition on soil P pool concentrations, we added residues from three different legumes to two soils and measured the concentration of soil P pools over three months. The size of various P pools was assessed by sequential P fractionation on days 0, 14, 28, 56, 70 and 98. Compared to the unamended control, addition of faba bean and chickpea residues increased the concentrations of resin P, microbial P, NaHCO3-Pi temporarily whereas amendment with white lupin residues had little effect on P pool concentrations. The decrease in NaHCO3-Po and NaOH-Po towards the end of the experiment coincided with an increase in NaOH-Pi in Mt. Bold soil and of HCl-Pi in Monarto soil. These temporal changes were more pronounced in soils amended with faba bean and chickpea residues than in the unamended soil or after addition of white lupin residues. The principal component analysis (PCA) plot showed that the P pool concentrations on days 0 and 98 were quite similar and differed from those on days 28, 56 and 70 suggesting clear temporal patterns. The results of this study show that the concentration of various P pools is strongly affected by soil properties such as pH and organic matter content and further modulated by the properties of the residues. <![CDATA[<b>LInkage between herbaceous vegetation and soil characteristics along rawal dam islamabad</b>]]> This study provides an analysis of the soil, vegetation types and species distribution along Rawal Dam, Rawal Lake and its three tributaries (Bani Gala, Chattar and Bari Imam Streams and its tributaries), with a focus on the environmental factors that control species distribution. After identifying the study area’s herbaceous vegetation and analyzing the soil’s physical and chemical parameters, the variable data were connected into a relationship. TWINSPAN (Two Way Indicator Species Analysis) classified the herbaceous vegetation into seven different communities with which; the formulated groups in DCA (Deterended Correspondance Analysis) were coherent. CCA (Canonical Correspondance Analysis) produced the relationship of soil parameters such as pH, organic matter, Potassium, Manganese, Zinc, and Iron with the herbaceous vegetation. The most effectual and varied parameter was the Potassium and Manganese that was available among the heavy metals. Thus, this study analyzed the overall relationship among soil, vegetation and the species present at the selected site. <![CDATA[<b>Qualitative parameters</b> <b>of <i>pleurotus ostreatus</i> (jacq.) p. kumm. mushrooms grown on supplemented spent substrate</b>]]> In this paper, the agronomic viability of Pleurotus ostreatus (Jacq.) P. Kumm. is studied by reusing the spent substrates previously used in crops of the same mushrooms. To this substrates are applied commercial nutritional supplements (Calprozime®, Champfood® and Promycel®), to research their potential use as additives together with wheat straw (WS), calcium sulphate and calcium carbonate at different doses. After the physical and chemical characterization of the substrates, we evaluated the qualitative production parameters in one flush. The mixture of wheat straw (WS) (3,000 g) and spent Pleurotus substrate (SPS) (3,000 g) supplemented with 120 g of each of the commercial supplements (Promycel®, and Calprozime® Champfood®) are substrates that promote red-green (a*) and yellow-blue (b*) chromaticity in harvested mushrooms. This manuscript presents the results obtained in an experiment where different supplements were used to enrich substrates composed of wheat straw and spent substrate. Qualitative features of Pleurotus ostreatus mushrooms were evaluated. <![CDATA[<b>Nitrogen availability and mineralization in <i>Pinus radiata</i> stands fertilized mid-rotation at three contrasting sites</b>]]> Fertilization of Pinus radiata plantations mid-rotation after thinning can alter soil nitrogen availability. However, the magnitudes and durations of tree and stand growth responses are not well understood across different soils with specific site conditions. Two mid-rotation fertilization trials in Pinus radiata plantations with unexpected sustained growth responses for more than 6 years and volume gains of 25 m³ha-1 and 50 m³ ha-1 in sandy and granitic soil, respectively, and one trial with no response to fertilization were selected to study the monthly dynamics of nitrogen availability and net mineralization using in situ core incubations. After 2 years, the results showed that fertilization increased nitrogen mineralization and availability until 6 years in sandy soils and until 7 years in granitic soil following fertilization. This result explained the sustained stand growth response observed at these sites. When considering the magnitude of the response, large increases in mineralization rates and soil N availability were observed in the granitic soil relative to the sandy soil. Our results suggest that stands with available N-(NH4+ + NO3-) levels less than 2 kg ha-1 during spring and fall months or with N-(NO3-) levels lower than 0.2 kg ha-1 during any month may respond to N fertilization. <![CDATA[<b>Addition impact of biochar from different feedstocks on microbial community and</b> <b>available</b> <b>concentrations</b> <b>of</b> <b>elements</b> <b>in</b> <b>a</b> <b>Psammaquent and</b> <b>a</b> <b>Plinthudult</b>]]> Biochars generated from swine manure, fruit peels, Phragmites australis and Brassica rapa were applied to a Psammaquent and a Plinthudult. The Phospholipid (PLFA) markers indicating different microbial communities and available concentrations of elements (K, Ca, Na, Mg, Al, Cr, Cu, Zn, Cd, Pb, Ni, As, Mn, Fe, B, Mo) were measured. Relationships between microbial communities and available concentrations of elements were also calculated. Microbial communities such as bacteria, fungi, protozoa, actinobacteria, G+ve and G-ve were significantly changed within biochar type and application rate compared to the control soils. The ratio of PLFAs indicating nutritional and environmental stress in microbial communities were increased in all biochar treatments to the Plinthudult but reduced in the Psammaquent compared to the control soils. The biochar addition to soils also changed the soil available element concentrations. Such as, swine manure biochar 3% significantly increased the Ca, Mg, Cu, Zn, As and Mo available concentrations in both soils. Study concludes that different biochar types and addition rates to soils changed the microbial community structure and available element concentrations in soils. Furthermore, biochars containing lower concentration of elements such as fruit peel and B. rapa biochar application to soils can reduce the availability of elements in soils. <![CDATA[<b>Thresholds of copper toxicity to lettuce in field-collected agricultural soils exposed to copper mining activities in Chile</b>]]> Several previous studies highlighted the importance of using field-collected soils instead of artificially spiked contaminated soils for phytotoxicity tests. However, the use of field-collected soils presents several difficulties for interpretation of results, due to presence of various contaminants in the soil and unavoidable differences in the physicochemical properties of the tested soils. The objective of this study was to estimate thresholds of copper phytotoxicity in topsoils of 27 agricultural areas historically contaminated by mining activities in Chile. We performed standard emergence and early growth (21 days) tests (OECD 208 and ISO 11269-2) with lettuce. The response of lettuce was best explained by Cu toxicity and P deficiency. Growth of lettuce was related to soil total Cu concentration and Olsen-P and was not affected by soluble Cu (extractable by 0.1 M KNO3) or Cu2+ free ion activity of the soil solution. Thus, lettuce has a limited applicability for metal toxicity assessment in metal-contaminated soils, due to sensitivity of its response to P deficiency. However, it was possible to determine toxic thresholds for shoot concentrations of Cu in lettuce for responses of shoot and root length, suggesting that shoot concentrations of Cu in lettuce can be useful as indicators of Cu toxicity even in soils with a wide range of nutrient concentrations. <![CDATA[<b>Soil-nutrient availability affected by different biomass-ash applications</b>]]> This study, through an incubation experiment, evaluates the effect that different biomass ashes exert on the extractability of nutrients and some chemical parameters and dehydrogenase activity of a slightly acid soil. Three types of as were selected: two new ashes generated by the dry combustion of olive cake or by gasification of greenhouse vegetable wastes, and a third produced by wood combustion. The ash significantly increased the pH, electrical conductivity, and dehydrogenase activity of the soil. Dry olive-cake ash was the most effective in raising the levels of soil AB-DTPA extractable P, K, and Cu. By contrast, wood ash caused the greatest increases in soil AB-DTPA-extractable Zn. The three as he showed little effectiveness for increasing soil ABDTPA extractable Fe and Mn. Ash from dry olive cake could be used as a low-cost potassium fertilizer. <![CDATA[<b>Arbuscular Mycorrhizal symbiosis in four Al-tolerant wheat genotypes grown in an acidic Andisol</b>]]> Arbuscular mycorrhizal (AM) fungi play an important role in protecting host plant against phytotoxic aluminum (Al) in soil. The aim of this work was to analyze the effect of AM fungi native from acid soil on the growth of four Al-tolerant wheat (Triticum aestivum L.) genotypes. A greenhouse experiment was conducted using three near isogenic Chilean wheat genotypes (‘Crac’, ‘Invento’ and ‘Otto’) and one of recognized Al-tolerance (‘Atlas 66’) which were grown in an acid Andisol with 34% Al-saturation. The plant dry biomass and root colonization were determined at six early growth stages and AM spore density, glomalin (as GRSP) and acid phosphatase (P-ase) activity were analyzed at two stages; i) 11 days after sowing -DAS-, and at 60 DAS. Results showed that in all genotypes AM root colonization was not inhibited in spite of high soil Al saturation in the soil and a significant root colonization degree was observed at the first phenological stage mainly in the native wheat genotypes. Also, ‘Crac’ and ‘Invento’ genotypes showed the highest densities of AM spores and GRSP production. All wheat cultivars increased the P-ase activity overtime. Root biomass correlated positive and significantly with root colonization (r=0.71; P<0.001) and inversely with AM spores (r=-0.61; P<0.001). ‘Atlas 66’ showed a high adaptability to grow in acid conditions but produced the lesser amounts of AM propagules, which suggest that this genotype would show Al-tolerance mechanisms not fully associated to AM symbiosis as the Chilean wheat cultivars do. In conclusion, the higher early root colonization, AM spores and GRSP production associated to native wheat genotypes could indicate that AM symbiosis play a principal role in the Al tolerance capacity of T. aestivum developed in those soils with high Al levels and fungal native populations adapted to this conditions. <![CDATA[<b>Non-destructive Assessment of Highbush Blueberry Fruit Maturity Parameters and Anthocyanins by Using a Visible/Near Infrared (vis/NIR) Spectroscopy Device</b>: <b>A Preliminary Approach</b>]]> We evaluate the use of a portable and non-invasive technology based on visible and near infrared (vis/NIR) spectroscopy (Cherry-Meter) for monitoring fruit maturity parameters and anthocyanins in two highbush blueberry (Vaccinium corymbosum L.) cultivars (Misty and Sharpblue). This device measures an Index of Absorbance Difference (I AD), which showed high correlations with fruit quality parameters in other fruit crops. We found positive but differential correlations between I AD values and fruit anthocyanins, which was higher for Misty (r = 0.970, p≤0.01) than for Sharpblue (r = 0.714, p>0.05). Interestingly, Cherry-Meter measurements were also correlated with solid soluble concentrations (r = 0.685, p≤0.01) and fruit firmness (r = -0.714, p≤0.01), but only in Sharpblue. For both cultivars, I AD values were also significantly (p≤0.01) related with fruit FW (0.447 for Sharpblue and 0.559 for Misty). The High Performance Liquid Chromatography (HPLC) data indicated that I AD variations were associated with significant changes in single berry anthocyanidins levels. These findings are the first approach, highlighting the potentialities of Cherry-Meter for the non-destructive assessment of fruit maturity and anthocyanidin profile in blueberries. <![CDATA[Soil-plant characteristics in an age sequence of <em><b>coronilla varia</b></em><strong> l. plantations along embankments</strong>]]> Objectives: Coronilla varia L., a leguminous herb, is widely used in vegetation restoration programs on road embankments to enhance soil nutrients. Our hypothesis is that, under identical climatic conditions,plant and soil properties are determined by the slope aspect and stand age of legume plantations. Methods: We collected soil samples and investigated plant diversity in an age sequence of 0-, 4-, 10- and 20-year-old C. varia L. plantations and natural grasslands. Results: Stand age, rather than slope aspect, was found to be the main factor influencing the soil and plant feedback on the embankments. Planting C.varia L. on the embankments could enhance soil nutrients and improve the soil quality to the level ofa natural grass l and after 20 years of plantation.The plant diversity and species number were steady after C.varia L. had been established for 10 years. Conclusions: Planting C. varia L. on embankments is an effective method foren hancing soil nutrients and maintaining ecosystem stability in the Guanzhong Basin, China. <![CDATA[Phytase-producing <em><b>Bacillus</b></em><strong> sp. inoculation increases phosphorus availability in cattle manure</strong>]]> Organic wastes rich in phosphorus (P) are considered an alternative to decrease the dependence on chemical P fertilization in crops and pastures. Microbial inoculants are being studied as a tool to increase plant P availability in organic wastes. In this study, we explore the effect of inoculation with Bacillus sp. MQH-19 (a native phytase-producing bacterium) on the release of inorganic phosphorus (Pi) in cattle manure with low available P but a high total P content. Bacteria inoculation resulted in a higher release of Pi (8% in NaHCÜ3 and 13% in NaOH-EDTA extracts) compared with that of uninoculated manure (0.7% in NaHCÜ3 and 0.1% in NaOH-EDTA extracts). However, a greater amount of Pi was released in inoculated manure supplemented with phytate (47% in NaHCÜ3 and 117% in NaOH-EDTA extracts) compared with that of uninoculated manure supplemented with phytate (30% in NaHCÜ3 and 15% in NaOH-EDTA extracts). In addition, the use of denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR) revealed that the bacterial community structure in manure was affected by inoculation and that the prevalence of Bacillus sp. MQH-19 decreased during incubation (6 days). This study demonstrates that Pi availability in cattle manure can be increased by phytase-producing bacteria inoculation. Phytase-producing bacteria inoculation might represent an attractive strategy to increase P availability in agricultural wastes, which are used as organic fertilizers in crops and pastures. <![CDATA[Inoculation with selenobacteria and arbuscular mycorrhizal fungi to enhance selenium content in lettuce plants and improve tolerance against drought stress]]> This study evaluated the co-inoculation effect of the endophytic selenobacteria Bacillus sp., Klebsiella sp. or Acinetobacter sp. and the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices on lettuce plants grown under drought conditions. Plants inoculated with bothnmicroorganisms were able to enhance the Se content in their shoots (1 to 6 pg plant-1) and promote macro-and micronutrient uptake. Moreover, the inoculated plants showed significantntolerance to drought stress, as determined by their adaptation to physiological parameters(relative water content and stomatal conductance), increase in photosynthetic pigments (chlorophyll and carotenoids) and improvement inantioxidant enzyme levels (catalase, ascorbate peroxidase and glutathione reductase). The selenobacteria increased the Se content in lettuce plants and enhanced the effect of AM fungus in controlling the antioxidant systems that play a role as elicitors of plant drought responses and improving the nutritional quality and physiological and biochemical processes involved in plant drought tolerance. <![CDATA[Microbial consortium and pig slurry to improve chemical properties of degraded soil and nutrient plant uptake(Schoebitz and Vidal, 2016)]]> A greenhouse experiment was carried out to assess the effectiveness of commercial microbial consortium (MC) and the addition of pig slurry (PS) on the growth of L. perenne and the enhancement of soil properties. The combined treatment of microbial consortium and pig slurry (MC+PS) was the most effective in terms of root dry weight compared to the control plants, reaching a 14-fold and 4-fold increase in Quillón and Florida soils, respectively, while the pig slurry and the combined MC+PS treatments resulted in a 4-fold increase in shoot dry weight. Values of available nitrogen, phosphorus and potassium content in both soils were higher than the non-amended soils. Foliar levels of N, P and K increased with the use of pigslurry and MC+PS, but not with the use of microbial consortium alone. The combined treatment of microbial consortium and pig slurry also enhanced the chemical quality of the soil and nutrient uptake by L. perenne. The application of beneficial microorganisms to themsoil can enhance nutrient uptake and increase the efficiency of organic amendments. In this regard, the combined use of microbial consortium and pig slurry has a potential role in the development of sustainable systems for grassland production. <![CDATA[The impact of foliar nickel fertilization on urease activity in pecan trees]]> The aim of the present work is to analyze the effect of different foliar products of nickel (Ni) onthe nutrient concentration, chlorophyll content, and enzymatic activity of urease as the possible bioindicator of the levels of Ni in the leaves of pecan [Carya illinoinensis (Wangenh.) K. Koch]. The experiment consisted of the foliar application of Ni to pecan cv. Western Schley, using two commercial products: Nickel Plus®T1 and SpeedfolTM Pecano T2 , and a control T0 received no Ni treatment. The following variables were evaluated: the total chlorophyll concentration, the concentration of macro- and micronutrients including Ni, and the activity of urease. The results demonstrated that the pecan trees treated with Ni increased in the concentration of this element and that the product Nickel Plus® T1 increased by 41.24% with respect to control. The foliar application of Ni led to significant differences in the foliar concentrations of N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, and Ni. Chlorophyll showed a significant reaction to the foliar application of Ni. The enzymatic activity of urease proved to be positively related to the foliar level of Ni, and thus could be considered a good physiological bioindicator of the nutritional state of foliar Ni in the leaflets of the pecan tree. <![CDATA[Recycling pulp mill sludge to volcanic soil: a column leaching study]]> A leaching experiment was conducted to determine the influence of four successive applications of pulp mill sludge on some parameters of an Andisol. Undisturbed soil columns were treated with pulp mill sludge (0 to 30 Mg ha-1) every three months during one year with a hydraulic regime of 1200 mm per year. Leachates of each treatment were analyzed periodically and, at the end of the period, columns were fractionated at three depths (0-20, 20-40 and 40-60 cm) and soil chemical parameters were analyzed. Sludge added successively to Andisol increased the nitrate concentration in leachates. After the fourth application of 30 Mg ha-1 sludge, nitrate leaching was about 1.7 times higher than in the control column, however, this level is still lower than the limit under Chilean regulations. Low ammonium concentrations were observed in leachates as a result of nitrification processes and retention by clay and organic matter in the Andisol. In fractionated soil columns, pH, organic matter, total nitrogen and phosphorus increased as the sludge rate increased,with the highest values found in the upper part of the columns. The concentration of nitrate and ammonium in soil columns followed an inverse pattern: while ammonium concentration was the highest at 0 to 20 cm, nitrate concentration was the lowest in that fraction; sludge addition caused a linear increase in ammonium and nitrate content at the three depths analyzed.