Scielo RSS <![CDATA[Journal of soil science and plant nutrition]]> http://www.scielo.cl/rss.php?pid=0718-951620160004&lang=es vol. 16 num. 4 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.cl/img/en/fbpelogp.gif http://www.scielo.cl <![CDATA[<b>Clay addition to sandy soil</b>: <b>effect of clay concentration and ped size on microbial biomass and nutrient dynamics after addition of low C/N ratio residue</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400001&lng=es&nrm=iso&tlng=es Addition of clay-rich subsoil to sandy soil has been shown to increase crop production on sandy soils. The added clay is present as peds ranging in size from a millimetre to several centimetre. In this experiment clay soil (73% clay) was added to sandy soil (3% clay) at 10 and 20% clay w/w as 1, 3 and 5 mm peds. Shoots of young Kikuyu grass (C/N 20) were ground and added at 10 g kg-1, and soils were incubated for 45 days at 80% of water holding capacity. The study confirmed that clay addition to sandy soil increased soil organic carbon retention but decreased cumulative respiration and available P compared to sandy soil alone. Ped size had little effect on respiration and nutrient availability. Over the course of 45 days peds broke down and organic C was bound to the < 53 µm fraction. The greatest proportion of peds and total organic carbon (54-67%) was in the initially added ped size. The TOC content of < 53 µm fraction of initially added peds was 0.38% and at the end of the experiment (after 45 days) the TOC had increased by 24, 19 and 10% in 1, 3 and 5 mm peds respectively. <![CDATA[<b>Adsorption and native microbiota of an agricultural soil are involved in the removal of fluoranthene</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400002&lng=es&nrm=iso&tlng=es Several factors can influence the removal of polycyclic aromatic hydrocarbons from agricultural soils, such as the native microbiota, the physicochemical properties of the soil, soil management and addition of exogenous microorganisms. Nevertheless, the involvement of these factors has not been studied during fluoranthene removal at the microcosm level. In the present study, the effects of these factors were evaluated in microcosms composed of an organic agricultural soil (OAS-microcosm) and conventional agricultural soil (CAS-microcosm) contaminated with fluoranthene. According to their physicochemical properties, both soils were classified as silt loam. They had similar cation exchange capacities, water holding capacities and P-PO4(3-), but different pHs, electrical conductivities, and percentages of N, C, silt, clay and sand. Fluoranthene did not alter the native microbiota of the OAS- and CAS-microcosm because similar banding profiles were obtained in PCR-DGGE analysis of the 16S rRNA gene, and the total heterotrophic bacteriacount as well as fluoranthene-degrading bacteria count were similar between microcosms with fluoranthene and their controls without fluoranthene. However, OAS- and CAS-microcosms showed higher respiratory activity than their controls (p<0.05). At the beginning of the degradation kinetics, OAS- and CAS-microcosms reached a higher percentage of fluoranthene removal than their abiotic counterparts (adsorption controls; p<0.05); towards the end of the degradation kinetics, no significant difference was observed between the OAS- and CAS-microcosms and their corresponding adsorption controls. The bioaugmentation assay using a fluoranthene-degrading bacterial consortium increased fluoranthene removal. This work showed that fluoranthene adsorption to soil and native microbiota of agricultural soils were involved in fluoranthene removal. <![CDATA[<b>Influence of artificial grassland restoration on soil carbon pool in an arid mining land</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400003&lng=es&nrm=iso&tlng=es Successful reclamation of degraded mine land can contribute to recuperate the vegetation and soil carbon sequestration. In this study, soil carbon pool was assessed in a mining land after short-term reclamation. We measured above- and belowground biomass and soil carbon storage of artificial grassland (Astragalus adsurgens and Medicago sativa), which was established in the reclamation of mining land. The results showed that artificial grassland establishment significantly increased above- and belowground biomass after four-year restoration. Artificial grassland establishment increased soil inorganic and organic carbon content and storage. Soil organic and inorganic carbon content showed a positive increasing along the restoration time. Higher SOC and lower soil bulk density and water content all were attributed to the growth of artificial grassland. These results suggest that establishing artificial grassland with legumes is an effective restoration approach for improving soil carbon pool in the reclaimed mine soils. <![CDATA[<b>Biological and morphological traits of sugarcane roots in relation to phosphorus uptake</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400004&lng=es&nrm=iso&tlng=es Appropriate management of phosphorus (P) in soil will lead to higher yields and sustainability for sugarcane production. Our study evaluated the importance of differences in root structure and function, and the differential composition of the bacterial community in four sugarcane cultivars, in relation to the efficiency for P uptake and also to assess changes in soil P with distance from the rhizoplane. Experiments were performed in pot trials using a sandy clay loam Ferralsol. In the first experiment, the effect of P application (78.4 mg P kg-1 soil as triple superphosphate) on sugarcane cultivars RB92-579; RB85-5156; RB86-7515 and RB96-6928 was investigated. Secondly, we evaluated P rates of 0; 9.8; 19.6; 39.2 and 78.4 mg kg-1 soil using cultivar RB96-6928 which was shown to be one of the more growth responsive cultivars. The cultivar RB96-6928 exhibited the highest root dry matter and root surface area, while the bacterial communities found in the rhizosphere of these plants were not different from other cultivars, as determined by PCR-DGGE. From the P dose-dependent experiment for this cultivar, optimal plant performance occurred at a P supply up to 38.5 mg P kg-1 soil. Collectively, our results indicate that P efficiency in sugarcane was predominantly associated with the generation of high root biomass and surface area. <![CDATA[<b>Arbuscular mycorrhizal assemblages along contrasting Andean forests of Southern Chile</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400005&lng=es&nrm=iso&tlng=es Southern Chilean pristine temperate rainforests have been floristically stable during the Holocene, thus representing a pre-industrial baseline of forest ecology. Given this and its edaphic limitations, it is imperative to better understand these forests ecological patterns of mycorrhizal symbiosis. Therefore, here we compare the arbuscular mycorrhizal (AM) communities in three tree line Nothofagus pumilio contrasting plots of Chilean Andes (a volcano crater, pristine forest, and disturbed forest). The AM community assemblages were determined by morphological identification and spore counting, in three A horizon soil samples by plot. In the same nine soil samples, standard chemical analysis was performed. Eighteen AM species were described; Acaulospora was the most abundant genus. The forest plot had the highest AM species richness compared to the disturbed and crater plots. Interestingly, soils Olsen P (plant available phosphorus), pH, and Al+++ saturation similarly affected the AM assemblages. We suggest that some AM species could be specially adapted to extremely high Al saturation and extremely low plant available P conditions, as those experienced on Andean Nothofagus forests. These species may help initiate biological succession on highly disturbed ecosystems. We suggest that mycorrhizal fungi play a key role in seedling colonization of extreme environments such as the Andean tree line. <![CDATA[<b>Effect of exotic invasive old world climbing fern (<i>lygodium microphyllum</i>) on soil properties</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400006&lng=es&nrm=iso&tlng=es Old World climbing fern (Lygodium microphyllum) has become one of the most serious ecological threats to the integrity of the greater Everglades ecosystem of south Florida. In this study, we analyzed the effects of Old World climbing fern on surface soil characteristics at invaded sites in Florida. We compared soil characteristics of six invaded and adjacent uninvaded plots at three different locations. Our results show that the fern can grow and thrive in a wide range of soil types and the impact on the soil was site specific with effects being more prominent in sites with low nutrient status. Additionally, there were significant differences in the soil nutrient status and microbial population in the invaded and uninvaded sites. Sites with Old World climbing fern had significantly higher nutrient concentrations that correlated with higher soil organic matter. Overall our results indicate that this exotic pest plant can potentially alter its below ground environment to its own benefit by enhancing the soil nutrient status by adding soil organic matter. <![CDATA[<b>Biochar amendment of grassland soil may promote woody encroachment by Eastern Red Cedar</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400007&lng=es&nrm=iso&tlng=es Although carbon (C) additions to soil have been used in restoration to combat invasive species through changes in soil nitrogen (N) availability, carbon amendments to soil derived from plant material can impact soil N availability in a species-specific manner. As such, amendment-driven feedbacks on N may impact invasive species success and woody encroachment. Soil amendments like biochar, which is often added to soil to increase C storage in grassland systems, may unintentionally encourage woody encroachment into these grasslands by changing soil N dynamics. Few studies have examined biochar impacts on non-agricultural species, particularly invasive species. Woody encroachment of Eastern Red Cedar (Juniperus virginiana) into grasslands provides an ideal context for examining the impact of biochar in grasslands. In the greenhouse, we examined the effect of biochar or leaf litter derived from native and exotic grasses on J. virginiana seedling growth. Juniperus virginiana seedlings grew 40% bigger in biochar amended soil as compared to seedlings grown in litter amended soil. Additionally, we found a more than 2 order of magnitude increase in available NH4+ in the biochar treatments compared to the litter amended soils. Furthermore we found that biochar feedstock type did not have an impact on the effect of biochar, as both native and exotic grass biochar had similar impacts on soil N levels and J. virginiana growth. Our work suggests that once grassland litter is converted to biochar, species impacts on soil N may disappear. In conclusion, our data suggests soil amendments of biochar may encourage woody encroachment into grasslands. <![CDATA[<b>Low soil water content during plant growth influences soil respiration and microbial biomass after plant removal and rewetting</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400008&lng=es&nrm=iso&tlng=es The aim of this experiment was to study the effect of previous water content in planted and unplanted soil on microbial biomass and nutrient availability after plant removal and rewetting. A silt loam was maintained 10-50% of water holding capacity (WHC) and planted with wheat or left unplanted. After four weeks, plants were removed and soils were kept at the same water content as in the pots (original) or rewetted to 50% WHC (rewet). Then, soil respiration was measured continuously for 20 days, available N and P and microbial biomass C, N and P were measured on days 5, 10 and 20.In original soil, cumulative respiration, MBC and MBN decreased with water content in planted soil and were higher in planted than unplanted soil only at 30-50% WHC. Available N was up to 3-fold higher in un-planted than planted soil at 30-50% WHC. Only in planted soil, available N increased with decreasing water content. Rewetting increased cumulative respiration and MBN only in soil that had been at 10-20% WHC. In rewet soil, the previous water content had no effect on cumulative respiration, MBC and MBN in unplanted soil. In planted soil, cumulative respiration, MBC and MBN remained lower in soil that was at 10% WHC previously compared to that at 50% WHC. It is concluded that the effect of low water content on soil microbes is exacerbated by reduced plant growth and the reduced C input, even if soils are rewet. <![CDATA[<b>Arbuscular mycorrhizal fungal diversity in wheat agro-ecosystems in Southern Chile and effects of seed treatment with natural products</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400009&lng=es&nrm=iso&tlng=es Arbuscular mycorrhizal (AM) fungi are important for P uptake in Andisols cultivated with wheat. We assessed AM fungal diversity in field experiments established with wheat cultivated after AM host plants and non-host plants at three locations of the Araucanía Region. Wheat seed was treated with two natural products: Fosfobio (FOS), mixture of P-solubilizing bacteria and N2-fixing bacteria; and Myconate (MYC), product containing formononetin. For investigations of AM fungal diversity, soil samples were taken before planting and after harvest of wheat. The morphological spore analyses resulted in 26 species, belonging to 10 families and 16 genera; 5 species belonged to Acaulospora (31.2% of total), and 3 to Claroideoglomus (18.8%). Claroideoglomus claroideum was the prevalent while Ambispora leptoticha, Dominikia aurea, and Glomus badium presented the lowest frequency.The AM fungal species distribution was strongly dependent on the location, and richness at planting of wheat was higher when a non-host for AM fungi had been grown before. There appeared to be a tendency that through wheat cultivation, the richness of AM fungal species decreased from time of planting to harvest when the pre-crop was a non-host; when the pre-crop was AM host there was no apparent decrease in AM species richness through wheat cultivation. Natural products did not significantly influence grain yields. However, there was a tendency that MYC increased average grain yields by 7%. It is discussed that increased AM root colonization, as by MYC and improved P-uptake by AM fungi is more important than inoculation of seed with P-solubilizing microbes. <![CDATA[<b>Gene expression related to molybdenum enzyme biosynthesis in response to molybdenum deficiency in winter wheat</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400010&lng=es&nrm=iso&tlng=es Molybdenum (Mo) is an essential trace element for higher plants. Mo enzyme biosynthesis is regulated by several plant genes. A hydroponic trial was conducted to investigate the effect of Mo deficiency on the expression of genes that are related to Mo enzyme biosynthesis in winter wheat. The results showed that Mo deficiency decreased the activities of nitrate reductase (NR), sulphite oxidase (SO), aldehyde oxidase (AO) and xanthine dehydrogenase (XDH) in the leaves or roots of winter wheat by regulating the expression of NR, SO, AO and XDH genes. Mo deficiency induced the expression of TaCnx2 and TaCnx5, which might result in the accumulation of cyclic pyranopterin monophosphate (cPMP) and molybdopterin (MPT) in wheat. Mo deficiency significantly decreased TaCnx1 expression, which is expected to reduce molybdenum cofactor (Moco) formation. Moco shortage induced the expression of TaAba3 in winter wheat. The blockade of Moco biosynthesis under conditions of Mo deficiency might decrease the activities of Mo enzymes. <![CDATA[<b>Influence of salinity on transport of Nitrates and Potassium by means of the xylem sap content between roots and shoots in young tomato plants</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400011&lng=es&nrm=iso&tlng=es Salinity is well known to reduce plant growth and yield by reducing water availability; it does so by interfering with both nutrient uptake and translocation. The objective was to determine the nitrate and potassium contents in xylem sap and the root-shoot transportation of both as a function of the salinity of the nutritional solution provided. We compared NO3-and K+ contents and flux in xylem sap collected from cut stems of tomato seedlings, based on electric conductivity (EC) tests among five nutrition solutions for soilless crops ranging from medium to high salinity. The EC was 2.2, 3.5, 4.5, 6, and 12 dS m-1. The concentration of nitrates and potassium in the xylem sap remained constant, while the external concentration in the rhizosphere varied greatly. Notwithstanding, the xylematic flux was strongly affected by the salinity of the nutritional solution: at maximum salinity, EC reached 3.5 dS m-1; at minimum, EC was 12 dS m-1. For similar reasons, the longest NO3- and K+ transportation distance between root and shoot was achieved when the EC read 3.5 dS m-1, but was reduced by up to 80% when EC was 12 dS m-1. <![CDATA[Nitrogen use and rice yield formation response to zeolite and nitrogen coupling effects: Enhancement in nitrogen use efficiency]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400012&lng=es&nrm=iso&tlng=es Objective of the article was to assess the coupling effects of zeolite (Z0, 0 t ha-1; Z0.9 and Z0.22, 10 t ha-1 in different diameter of 0.45-0.9 mm and 0.17-0.22 mm) and Nitrogen (N0, N52.5, N105, N157.5 kg ha-1) application on N use, leaf area index (LAI) and rice grain yield in 2014 and 2015. Results showed that both Z0.9 and Z0.22 at N105 and N157.5 application rates could greatly enhance the biomass, dry weight of root, LAI and N uptake. However, at initial tillering stage of rice, Z decreased N content in plant for its high absorption capacity and hence lowered biomass and N uptake. The highest value of N recovery efficiency (NRE) and N use efficiency (NUE) was obtained from N105Z0.22. Z input contributed to higher NRE and NUE. At N157.5 application rate, Z0.9 and Z0.22 significantly increased rice grain yield by 14.6% and 15.3%, respectively. However, Z mattered little to rice grain yield at N0 and N52.5. There was no significant difference in rice grain yield between Z0.22 and Z0.9. Z0.22 and Z0.9 clearly increased the 1000-grain weight. N application significantly lowered unfilled grain percentage and 1000-grain weight. <![CDATA[<b>Combined application of microbial consortium and humic substances to improve the growth performance of blueberry seedlings</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400013&lng=es&nrm=iso&tlng=es A field experiment was carried out to assess the effectiveness of microbial consortium (bacteria and fungi) and humic substances separately, as well as the effect of the combined application of them on the growth of blueberry (Vaccinium corymbosum L.) seedlings and the physicochemical and biological properties of a volcanic ash-derived soil. One year after seedlings were planted, the treatment consisting of the combined application of microbial consortium and humic substances was the most effective, recording a 50% increase in shoot dry weight and a 43% increase in root dry weight compared to the control plants. Similarly, the microbial inoculant treatment also showed increased shoot and root dry weights, with values 32% and 31% higher than the control plants. The combined application of microbial consortium and humic substances improved nitrogen and potassium uptake compared to the unamended soil. Regarding soil properties, the soil nitrate content was higher when applying the humic substances alone, while changes were also observed in the rhizobacterial community composition. This suggests that the use of humic substances substantially modifies the bacteriological characteristics, but not the mycological characteristics of the rhizosphere. The combined treatment had positive effects on both plant performance and nutrients uptake in a volcanic ash-derived soil. <![CDATA[<strong>Effects of water, salt and nitrogen stress on sunflower (<i>Helianthus annuus </i>L<i>.</i>) at different growth stages</strong>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400014&lng=es&nrm=iso&tlng=es Experiments in soil columns were conducted to evaluate the single and interactive effects of water, salt and nitrogen stress at different sunflower (Helianthus annuus L.) growth stages in Hetao Irrigation District, China. The study factors included soil salinity (S0: ECe=2.5-3.6 dS m-1; S1: ECe=9.6-10.7 dS m-1), soil moisture (W0: 35%-55%of field water capacity; W1: 75%-100%of field water capacity), and nitrogen application rates (N0: 0 kg N ha-1; N1: 135 kg N ha-1). The results indicated that the S1 treatments increased the duration of the seedling stages by 23.91% but decreased the duration of maturity by 33.09% on average compared with the S0 treatments. Similarly, water deficit significantly retarded anthesis and prolonged the total growth period. The comprehensive stress assessment index (CSAI) was obtained using principal component analysis (PCA) and membership function analysis (MFA). The CSAIs in different treatments showed that soil salinity was the main limiting factor for sunflower vegetative growth from seeding to bud (SS1), whereas water stress dominated the development from bud to flowering (SS2) and flowering to maturity (SS3). Although statistically non-significant, nitrogen stress was intensified after bud initiation and the CSAI in W1S0N0 treatment was 40.68% lower than W1S1N1 treatment in SS3. Moreover, the interactive effects of the three factors were complicated. Our experiments suggested that adequate water supply after bud initiation and the reasonable nitrogen application rate (135 kg N ha-1) can alleviate adverse effects on sunflower reproductive growth under different saline conditions. <![CDATA[<b>Relative influence of soil chemistry and topography on soil available micronutrients by structural equation modeling</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400015&lng=es&nrm=iso&tlng=es Soil chemical and topographic properties are two important factors influencing available micronutrient distribution of soil in the horizontal dimension. The objective of this study was to explore the relative influence of soil chemistry (including soil pH, soil organic matter, total nitrogen, available phosphorus, and available potassium) and topography (including elevation, slope, aspect, and wetness index) on the availability of micronutrients (Fe, Mn, Cu, Zn, and B) using structural equation modeling (SEM) at the watershed scale. To do this, levels of soil micronutrients, pH, soil organic matter, total nitrogen, available phosphorus, available potassium, and topographic factors were measured at 523 sampling points of Fanshi County on the Chinese Loess Plateau, and the spatial distribution of soil available micronutrients were analyzed by geostatistical method. The results showed that topography had both direct effects and indirect effect on some soil micronutrients, while the indirect effect indicated effects from topography on soil chemistry and then further on micronutrient concentration. Soil chemistry had direct effects on levels of all soil micronutrients, and topography had direct effects on levels of all micronutrients except for Cu and B, and indirect effects on Fe, Zn, and B. The direct effect of soil chemistry on Fe levels was greater than the total effects (including both direct and indirect) of topography. Topography had a stronger direct effect on Mn than soil chemistry, and topography had less direct but stronger total effects on Zn than soil chemistry. Soil chemistry directly influenced both Cu and B, but topography only influenced B in an indirect manner. The semivariance indicated that the micronutrients had moderate spatial dependency except for B which had weak spatial dependency. Within the spatial distribution of the micronutrients, there was a zone in the middle of the watershed with lower values than in the northern and southern areas for Fe, Mn, Zn, and B, which were related to the characteristics of topography and soil chemistry. These results may guide the management of soil micronutrients of the Chinese Loess Plateau and other similar regions in the world. <![CDATA[<b>Effectiveness of native arbuscular mycorrhizal consortia on the growth of A<i>gave inaequidens</i></b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400016&lng=es&nrm=iso&tlng=es The aim of this study was to evaluate the effect of eight native consortia of arbuscular mycorrhizal fungi (AMF), a commercial strain and a control without AMF on the growth of Agave inaequidens. Agave seedlings were inoculated and kept under greenhouse conditions for 300 days. At 90, 180 and 270 days after inoculation, the number of leaves and plant height were recorded; at the end of the experiment, fresh and dry weight, head (also known as heart or piña) diameter, leaf area and root length and volume were recorded. The percentage of mycorrhizal colonization, the relative mycorrhizal dependency index and the Dickson index were also calculated. Results showed a growth-promoting effect on agave plants when inoculated with native consortia, namely Barranca de las nueces, El Limón, Agua Dulce and Huizachal, compared to the control. Colonization values were high (45%) and similar to those reported in other studies with agaves. Plants inoculated with the Huichazal consortium obtained the highest Dickson index (9.6). It can be concluded that native consortia are a feasible alternative for use as growth promoters in Agave inaequidens and that they can be a good option as biofertilizers under nursery conditions. <![CDATA[<strong>Soil surface roughness under tillage practices and its consequences for water and sediment losses</strong>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400017&lng=es&nrm=iso&tlng=es The present study aims to determine the effects of soil management practices on soil surface roughness and the consequences of these phenomena on water and sediment losses. Laboratory experiment was conducted on a Chernozems clayey soil subjected to a sequence of two 30 min simulated rainfall of 50.8 mm h-1 and 114.3 mm h-1and four soil management practices: contourtillage (CT), downhill tillage (DT), no-tillage simulated (NTs) and bare soil (BS). Soil surface roughness was evaluated using a laser distance meter. Results showed that the soil tillage in downhill or contour increased soil roughness by 2.90 and 2.76, respectively, reducing the water losses under low rain intensity by 12.8% and 6.4%. Soil surface roughness quickly changed after the onset of rain, and higher values of changes in soil roughness were observed for contour (22.73%) and downhill tillage (21.05%) managements. Soil coverage factor and the direction of tillage were the most important characteristics in contrast with soil surface roughness to reduce the sediment losses. No-tillage simulated (0.59 tha-1) and contourtillage (1.30 t ha-1) were the soil management practices with lower sediment losses compared to other managements studied. The principal theoretical implication of this study is that land use planning with agriculture, livestock must be designed to prevent the soil from being exposed, or if exposed, tillage in contour should be adopted. The input of litter on soil surface had an important role in reducing the sediment and water losses. <![CDATA[<b>Effect of</b> <b>salicylic acid</b> <b>on protease and urease activity in soils under Norway spruce pure stands</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400018&lng=es&nrm=iso&tlng=es This study tested the hypothesis that soil protease and urease activity is inhibited by salicylic acid. This was tested in soils from spruce monocultures of different ages and treated by different forest management methods at the Rájec-Němčice Ecosystem Station. Surface organic H-horizons from three study plots were sampled: a mature spruce monoculture of 105 years and two young spruce monocultures of 33 years, one of which was thinned from above and the other thinned from below. Statistically significant differences between the measured values confirm that young stands are sensitive to the presence of 2-hydroxybenzoic acid as a phytotoxic substance. The results of this study do not conclusively show whether the effect of salicylic acid on protease activity inhibition increases when the protease activity itself is high. The impact of salicylic acid on soil urease activity was not clearly evident either. <![CDATA[<b>Effects of biotic and abiotic factors on soil organic carbon in semi-arid grassland</b>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400019&lng=es&nrm=iso&tlng=es Carbon sequestration in grassland soil has been paid considerable attention in recent decades. However, the changes of soil organic carbon (SOC) still need clarification under the effect of environmental factors in semi-arid area. Here, twenty sampling sites were selected to study the effects of plant community (plant cover, biomass, litter, composition and diversity) and environmental factors (i.e. mean annual precipitation, mean annual temperature) on SOC sequestration in the semi-arid grasslands. The results showed that SOC was significant positively related to mean annual precipitation, soil water content and soil pH. The higher above- and below-ground biomass, species evenness and diversity presented the higher SOC. Specially, the species richness and proportion of gramineous species functional group significantly increased SOC. Below-ground biomass affected SOC mainly in the top 30 cm soil. Our results suggest that higher plant species richness and gramineous species proportion play a positive role in increasing the potential of soil carbon sequestration in semi-arid grassland. <![CDATA[<strong>Organic acid coated-slow-release phosphorus fertilizers improve P availability and maize growth in a tropical soil</strong>]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-95162016000400020&lng=es&nrm=iso&tlng=es In this paper, we report the results of studies on the solubility (water solubility trial) and the response by plants (greenhouse pot experiment using Zea mays) for four types of monoammonium phosphate fertilizers (Conventional MAP - MAP1, MAP coated with a natural organic acid - MAP2, MAP coated with a synthetic organic acid - MAP3, and MAP coated with a peat humic organic acid - MAP4) applied at five increasing doses (0, 100, 300, 600 and 1200 mg P dm-3) and pre-incubated with the soil for five lengths of time before planting (0, 15, 30 and 60 d). The coating with organic acids reduced the water solubility of the P fertilizers - MAP4 provided a more gradual release of P over time. In the soil pot experiment, it was found that MAP1 required the highest dose to reach 90% of dry matter accumulation by the maize plant, followed by the Coated-Slow-Release Fertilizers (CSRF). The agronomic efficiency (AE) of P applied as the CSRF was 3 to 13% greater than that of MAP1. In addition, MAP4 led to higher values of AE (+11%) and apparent P recovery by maize (+41%) in comparison to MAP1. The physicochemical properties imposed by the chemical composition of the organic acid coatings generated fertilizers with distinct release rates and improved agronomic efficiencies.