Scielo RSS <![CDATA[Journal of soil science and plant nutrition]]> https://scielo.conicyt.cl/rss.php?pid=0718-951620180004&lang=pt vol. 18 num. 4 lang. pt <![CDATA[SciELO Logo]]> https://scielo.conicyt.cl/img/en/fbpelogp.gif https://scielo.conicyt.cl <![CDATA[Seedling root-dip in phosphorus and biofertilizer added soil slurry method of nutrient management for transplanted rice in acid soil]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000400921&lng=pt&nrm=iso&tlng=pt Abstract: Management of phosphorus (P) in acid soils is becoming more challenging in the anticipated scenario of potential phosphate crisis in agriculture, because the P-use and -recovery efficiencies (PUE and PRE) of existing P management methods are notoriously low in acid soils. This investigation reported a rhizosphere-based P management method for improving P nutrition of rice (Oryza sativa L.) seedlings at the time of transplantation in order to support better root growth on post transplantation. By performing two independent incubation experiments, the critical doses of orthophosphate and incubation duration for seedling root-dip (SRD) in single super phosphate (SSP) amended soil slurry (a sandy clay loam Inceptisol, pH 4.3) were found to be 112.5 mg P kg-1 soil and 10 h, respectively using the critical curve approach. In field experiments, the rhizosphere-based P method (SRD in soil slurry + phosphate solubilizing bacteria, PSB + rock phosphate, RP (30 kg P2O5 ha-1) performed better than SSP broadcast as basal application (60 kg P2O5 ha-1) in terms of more root volume and P uptake of shoot and root at 45 days after transplantation (DAT), higher P uptake and content in rice grain and straw, enhanced PUE and PRE, comparable grain yield and 50% reduction in P fertilizer input quantity. This rhizosphere based P management (SRD in soil slurry+PSB+RP) method may be vigorously exploited for managing P nutrition in transplanted rice grown in acid soils. <![CDATA[Modeling of soil mechanical resistance using intelligent methods]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000400939&lng=pt&nrm=iso&tlng=pt Abstract: In recent years, novel techniques such as intelligent techniques are being employed for developing predictive models to estimate parameters that are difficult to measure. For instance, determining soil mechanical resistance is difficult, particularly in fine-textured soils and during warm seasons. In this research, we used statistical algorithms, adaptive neuro-fuzzy inference systems (ANFIS), artificial neural networks (ANNs) and fuzzy inference systems (FIS) in order to predict soil mechanical resistance and compared them with traditional statistical models such as multiple regression (MR). To achieve this goal, bulk density, volumetric soil water content (as predictors) and soil mechanical resistance (as target variable) were used at 0-25 cm depth with sample size equals 200. The results showed that intelligent methods are appropriate tools for minimizing the uncertainties in soil engineering projects. The ANFIS model predicted soil mechanical resistance more accurately than the other models with R2 = 0.93 and RMSE= 299.41. Also, the use of intelligent methods not only provided new approaches and methodologies to estimate soil mechanical resistance, but also minimized the potential inconsistency of correlations. <![CDATA[Mixing organic amendments with high and low C/N ratio influences nutrient availability and leaching in sandy soil]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000400952&lng=pt&nrm=iso&tlng=pt Abstract: Little is known about available N and P, microbial biomass and leachate N and P concentration in mixes of organic materials differing in C/N ratio. Sandy soil was amended with wheat straw (W, C/N 71) and cow manure (CM, C/N 7) either alone (100W and 100CM) or in different ratios (values are weight percentage of the organic materials): 75W-25CM, 50W-50CM, 25W-75CM. The control was unamended soil. Moist soil was incubated for 26 days, leaching was carried out on days 10 and 25. Soil was sampled on day 9 (before first leaching) and day 26 (after the second leaching Cumulative respiration over 26 days was similar in the unamended control and 100CM, it increased with proportion of W in the amendments. Per kg of soil, amended soils did not differ in available N, microbial biomass N (MBN) and leachate inorganic N concentration, but available P and leachate inorganic P increased with proportion of CM in the amendment. However, available N, MBN and inorganic N in leachate per g N added was highest in 100W and lowest in 100CM. In contrast, available P and leachate P concentration per g P added increased with proportion of CM. Measured available N and leachate inorganic N were lower than expected values whereas measured available P and inorganic P in the leachate were higher than expected. In mixes, CM appears to reduce N mineralisation in wheat whereas W stimulates P release from cow manure. <![CDATA[Critical value of soil Olsen-P for potato production systems in volcanic soils of Chile]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000400965&lng=pt&nrm=iso&tlng=pt Abstract: The critical value of soil Olsen-P (mg Olsen-P kg-1) is the value of soil Olsen-P above which the probability of crop response to P fertilization is small or null. The aim of the present study was to determine the critical value of soil Olsen-P for potato tuber yield in volcanic soils. The data used in this study were taken from 41 experiments of P fertilization conducted in southern Chile from 1977 to 2015 by the National Potato Center at the Instituto de Investigaciones Agropecuarias (INIA). To identify the critical values of soil Olsen-P, relationships between relative yields and initial soil P-Olsen were assessed using three models (linear-plateau, boundary and Mitscherlich function). Across experiments, the average fresh tuber yield was 41.9 Mg ha-1 and varied between 4 and 89 Mg ha-1. Fresh tuber yield decreased up to 92% by P deficiency; however, yield reduction was concentrated between 20 and 40%. The critical Olsen P values determined were 41, 33 and 11 mg Olsen-P kg-1 obtained (P &lt; 0.01) with linear-plateau, boundary function and Mitscherlich function, respectively. However, linear-plateau and Mitscherlich functions showed lower coefficient of determinations (R2 = 0.23 - 0.31) than the boundary function (R2 = 0.97). Therefore, we suggest that the critical Olsen-P value of 33 mg P kg-1 determined with the boundary function is more appropriate for potato growers than the critical value determined with the other models. This information will be valuable for optimizing strategies for P fertilizer management in potato production systems aimed at achieving optimal crop yield and minimizing potential environmental risk. <![CDATA[Update of recent rates of carbon accumulation in bogs of Northern Patagonia-Chile]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000400977&lng=pt&nrm=iso&tlng=pt Abstract: Peatlands are one of the most important carbon cycle regulatory ecosystems, and are influenced by global climate change. However, studies of this kind of wetland are scarce in southern South America. In this study we performed a detailed analysis of recent accumulation rates of carbon (RERCA) in two types of Sphagnum peatland in Isla Grande de Chiloé (Chile) (42°-43°S and 75°-73°W). Monoliths of peat in continuous depths were analyzed and assigned ages using 210Pb dating. The results showed a difference between the two types of peatland; the average rate for the anthropogenic peatland (107.34 ± 113.9 g C m-2 yr-1) was superior to that of the natural peatland (78.33±77.1 g C m-2 yr-1). The surface profiles (30 cm) clearly revealed the recent rate of carbon accumulation for the past 100 years in Sphagnum peatlands of Northern Patagonia. The rate for the natural peatland is within the range found for ombrotrophic peatlands in the Northern Hemisphere. However, the rate estimated for the anthropogenic peatland was significantly greater than those reported in other parts of the world. Our results provide evidence of the importance of these unique ecosystems in the carbon accumulation process. <![CDATA[Application of the 4R nutrient stewardship concept for growing off-season tomatoes in high tunnels]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000400989&lng=pt&nrm=iso&tlng=pt Abstract: This study aimed to adopt the concept of 4R nutrient stewardship for growing off-season tomatoes in high tunnels. The tomato crop (Hybrid ‘Sahel’), grown in high tunnels, was applied with NPK fertilizer at the rate of 80:80:90 kg ha-1 (after each 15, 30 and 45 days interval) for four months and its effect on tomato yield and quality parameters was investigated. Application of NPK at 15 day intervals resulted in the highest nutritional quality of fruit (NPK uptake 4.32 kg m-2, total soluble solids 5.6°Brix, total acidity 0.43%, protein content 15.31%, β-carotenes 0.86 mg 100 g-1, total phenolics 2.34 mg 100 g-1, total flavonoids 7.14 mg 100 g−1, antioxidant activity 83.77%) and improved shelf-life (~ 10 days). However, NPK application at 15 day intervals was not economical in terms of total fertilizer cost incurred and subsequent yield obtained. Application of NPK at 30 day intervals was the most economical (value-cost ratio &gt; 9.0 PKR) among all application intervals. This study suggested that implementation of the concept of 4Rs i.e., right source, right rate, right placement and right timing of fertilizer application is an effective tool for the production of high quality off-season tomatoes in high tunnels. <![CDATA[Productivity and technological quality of sugarcane under fertilization of nitrogen and molybdenum]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401002&lng=pt&nrm=iso&tlng=pt Abstract: The increase of N fertilization in sugarcane can negatively influence the technological quality of the crop for sugar and alcohol production. The use of Mo in fertilization combined with N can reduce this effect and increase agricultural and sugar yield. The objective of this study was to evaluate the levels of Mo in soil, roots and leaves of sugarcane fertilized with N and Mo, to measure agricultural and sugar productivity and to evaluate quality of the technological attributes for production of sugar and alcohol. Two varieties were cultivated (RB867515 and RB92579) under field conditions, submitted to two doses of N (0 and 60 kg ha-1) and two doses of Mo (0 and 200 g ha-1) both applied to the soil. The source of N used was urea and the source of Mo was sodium molybdate. RB867515 was influenced by Mo and agricultural and sugar productivity increased by 21%. N fertilization did not increase agricultural productivity but reduced the technological quality of sugarcane, and Mo did not change this reduction. It is suggested that N fertilization should be reduced in first crop cycle and Mo fertilization should be stimulated. <![CDATA[Endophytic selenobacteria and arbuscular mycorrhizal fungus for Selenium biofortification and <em>Gaeumannomyces graminis</em> biocontrol]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401021&lng=pt&nrm=iso&tlng=pt Abstract: Selenium (Se) is an important antioxidant considered among the fertilization programs in developed countries. In Chile, chemical fertilization based in Se is inefficient due the physicochemical characteristics of Andisol that sustain the 60% of crop production. Andisol also are highly conductive to take-all disease caused by Gaeumannonyces graminis var tritici (Ggt). Here, we evaluated the effect of Bacillus sp.E5 and Acinetobacter sp.E6.2 and Claroideoglomus claroideum as potential inocula for Se biofortification and Ggt bicontrol in wheat. Plants inoculated with Acinetobacter sp.E6.2 showed major root growth and major Se content in shoots and grains. The antioxidant role of Se regarding DPPH activity was shown in Se-supplemented plants with small Se nanoparticles founded inside the roots. Mycorrhizal plants showed major SOD activity in shoots but no affected the Se uptake. Respect to pathogen biocontrol, plants inoculated with both bacteria showed an efficient control against Ggt independent to mycorrhization. Thus, our inocula could make important contributions to produce enriched Se flours for human nutrition and biocontrol against Ggt. <![CDATA[Volatilization and leaching losses of nitrogen from different coated urea fertilizers]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401036&lng=pt&nrm=iso&tlng=pt Abstract: Fertilizers are one of the costly inputs in agriculture and development of nutrient efficient fertilizers is need of the hour. Keeping in view of the above, slow release coated urea fertilizers are developed and the N loss from different coated urea fertilizers in a Vertisol was studied in comparison with normal urea. The coated fertilizers used were neem, 4% pine oleoresin (POR), 35% nano-rock phosphate and 2% nano-ZnO coated urea. In later two cases nanoparticles were loaded over 4% POR coated urea during preparation. Application of coated urea fertilizers such as neem coated urea and pine oleoresin coated urea in a Vertisol reduced the ammonia volatilization by 27.5% and 41.1%, respectively. Similarly, reduction of NO3-N leaching due to application of neem, resin, nano-rock phosphate and nano-ZnO coated urea were 18.3%, 28.0%, 25.7% and 35.1%, respectively. The reduction of N volatilization and leaching losses imparted by coated urea fertilizers could be a viable N source for crops. However field level validation experiments have to be carried out to assess the efficacy of these coated fertilizers in enhancing crop yield and nutrient use efficiency. <![CDATA[Foliar 2,3-dihydroporphyrin iron (III) spray confers ameliorative antioxidation, ion redistribution and seed traits of salt-stressed soybean plants]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401048&lng=pt&nrm=iso&tlng=pt Abstract: Dihydroporphyrin iron (III) chelates (also known as DHFe) have a role in plant growth regulation under normal and stressful conditions. In the present study, using Glycine max cultivars Jackson (the salt-sensitive) and Lee68 (the salt-tolerant) as the experimental materials, the physiological and molecular events contributing to the ameliorative effects of foliar DHFe spray on seedling growth; leaf photosynthetic parameters; reactive oxygen species (ROS) content; antioxidant enzyme activity; Na+, K+, and Cl- contents; and seed traits of soybean plants under control or salt-stressed conditions were investigated. The results showed that foliar spraying DHFe solution on soybean seedlings under NaCl treatment can significantly increase the leaf osmotic potential (ψs) and relative water content (RWC); reduce the Na+ and Cl- contents and Na+/K+ ratio; and simultaneously enhance the leaf antioxidant enzymes (CAT and APX, POD and SOD) activity, together with the mitigated ROS damage (lower H2O2 and MDA contents). Thus, it can apparently restore the salt stress-inhibited growth and photosynthetic capacity of Jackson and Lee68 seedlings, of which the salt-sensitive cv. Jackson displayed more pronounced effects. This may be related to the fact that, except for DHFe as a kind of antioxidant, foliar application of DHFe could enhance the transcription levels of GmCLC1 in roots and leaves and those of GmSOS1 in roots of Jackson plants under salt stress. When continuously cultivated to maturity, foliar spraying DHFe under salt stress could improve, to a certain extent, the seed traits (including the numbers of pods and seeds and seeds dry weight per plant) of both soybean cultivars. This approach may also provide a valuable theoretical basis and technical guidance for future practical application of DHFe as a type of plant growth promoter for the chemical regulation of foliar DHFe spray in mitigating salt injury to soybean and other crops under saline cultivation conditions. <![CDATA[Bioindicators of soil quality of open shrubland and vineyards]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401065&lng=pt&nrm=iso&tlng=pt Abstract: Land-use effects on microbial communities may have profound impacts on agricultural productivity and ecosystem sustainability because they are critical to soil quality and health. Within this context, soil microbiological properties such as microorganism abundance, total microbial biomass, and enzymatic activities have been used as soil quality indicators. However, these properties are very sensitive to changes triggered by agronomic management. The aim of this work was to evaluate the effect of agricultural practices in the vineyards from the Central Monte Desert, San Juan, Argentina including the effects on soil microbial biomass using soils from the open shrubland as a reference. The microbial biomass carbon was significantly greater in soils from the open shrubland than in the vineyards during April and November. The abundance of cultivable soil microorganisms (bacteria and filamentous fungi) in soil samples from vineyards and open shrubland was statistically similar. Vineyard soils showed increased enzymatic activities (both in rows and between rows) in both seasons. We used multivariate analysis of all data measured here to propose a data set of variables (amylase, cellulase, and xylanase activities, bacterial abundance, microbial biomass and water content, pH and electric conductivity) for use in future studies of soil quality in the Central Monte Desert. <![CDATA[Plant growth promoting rhizobacteria for improved water stress tolerance in wheat genotypes.]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401080&lng=pt&nrm=iso&tlng=pt Abstract: A greenhouse experiment was carried out to assess the effect of the inoculation with rhizobacterial strains on the tolerance to water stress in wheat genotypes (Triticum aestivum L.) under two different water regimes. A drought resistant (Fontagro 8) and a susceptible (Fontagro 98) genotype were studied. Soil water content was kept at 100% and 45% field capacity. The treatments were inoculations with AG-70 (Bacillus sp.), AG-54 (Pseudomonas sp.), and a mixture of both (AG-70 + AG-54); a control treatment consisting of an autoclaved nutritive solution. When applied to Fontagro 8 genotype, the AG-70 + AG-54 treatment resulted in a higher increase in shoot (88%) and root dry weight (211%) compared to the control under drought conditions. The same treatment applied on the susceptible genotype (Fontagro 98) resulted in increases of 73% and 129% in shoot and root dry weight, respectively. In addition, the inoculated plants showed significant increases in root length, stomatal conductance and chlorophyll index. The AG-54 and AG-70 treatments increased NPK contents in the drought-resistant genotype, while the AG-54 and AG-70 + AG-54 treatments increased the P content in the susceptible genotype. The treatments that showed the most positive effects on the biological quality parameters of the soil (microbial activity, microbial respiration and urease enzyme activity) were AG-54 and AG-70 + AG-54. Therefore, the use of AG-70 and AG-54, applied separately or combined, increased tolerance to water stress in both wheat genotypes and constitute a biotechnological tool for the production of crops in water-deficit ecosystems. <![CDATA[Heavy metals uptake and translocation by lettuce and spinach grown on a metal-contaminated soil]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401097&lng=pt&nrm=iso&tlng=pt Abstract: Nowadays, using sewage wastewaters in the irrigated agriculture is commune creating hazardous environment impacts. Assessment of these negative effects is vital issue to prevent heavy metals to be introduced in the food chain. Field and laboratory studies were conducted at Arab-El-Madabegh village, Assiut Governorate, Egypt, in order to evaluate the heavy metals concentrations in the edible parts of lettuce and spinach plants which irrigated with sewage water (SW). The obtained results indicated that, the soils of the studied site were contaminated by heavy metals. Zinc, Cu, Pb, Cd and Ni concentrations in the edible portions of the studied vegetables plants ranged between 75- 110, 15 - 17, 2 - 5, 1.0 -3.5 and 1.0 -2.5 mg kg−1, respectively. The obtained results showed that the concentrations of Zn, Pb, Cd and Ni in the edible parts of the studied plants were higher than the permissible limit levels but those of Cu were within the safe limit levels. It is worthy to mention that the irrigated edible vegetable crops with SW should be avoided. This study highlights the potential hazard for human health due to the uptake of high concentrations of heavy metals especially Zn, Ni, Cd and Pb by the studied vegetable crops. <![CDATA[Monitoring cell energy, physiological functions and grain yield in field-grown mung bean exposed to exogenously applied polyamines under drought stress]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401108&lng=pt&nrm=iso&tlng=pt Abstract: Polyamines are new plant growth regulators and intracellular messengers that regulate plant growth, development, and responses to abiotic environmental stresses. However, little is known about the impact of different polyamines on physiological and biochemical processes of field-grown plants exposed to water deficit stress. A two-year field experiment was conducted as a split-plot based on a randomized complete block design with four replications. Water treatments (Irrigation after 70 and 170 mm evaporation from class A evaporation pan) were assigned to main plots, and foliar application of polyamines including Putrescine, Spermidine and Spermine (at 0 and 0.1 mM) was apportioned to subplots. Average of two years results showed that compared with control, water stress significantly (P &lt; 0.05) reduced adenosine three phosphate (ATP), chlorophyll content index (CCI) and chlorophyll stability index (CSI), rubisco activity, efficiency of photosystem II (Fv/Fm), endogenous polyamine contents, membrane stability index (MSI), nitrogen (N2), potassium (K+), calcium (Ca2+), magnesium (Mg2+), and grain yield, while polyamine oxidase activity, antioxidant enzymes activity, reactive oxygen species (ROS) and lipid peroxidation (MDA) increased significantly (P &lt; 0.05) upon exposure to water deficit stress. However, exogenous application of polyamines improved ATP content, CCI, CSI, rubisco activity, Fv/Fm, endogenous polyamine content, MSI, antioxidant enzymes activity, N2, K+, Ca2+, Mg2+, and grain yield, while decreased ROS level and MDA content. Compared with the other polyamines, Putrescine showed better effects on physiological, biochemical and agronomical performance in mung bean plants under both irrigation treatments. <![CDATA[Spatial variation and predictions of soil organic matter and total nitrogen based on VNIR reflectance in a basin of Chinese Loess Plateau]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401126&lng=pt&nrm=iso&tlng=pt Abstract: Taiyuan basin in Chinese Loess Plateau was characterized as the variety of landform, land use fragmentation, low soil organic matter (SOM) and soil total nitrogen (STN) content; therefore, the predictions of soil nutrients in the area were rather difficult. In this study, three soil sampling transects of cropland soil from northwest to southeast in Taiyuan basin were established and the visible-near infrared reflectance (VNIR) of soil samples were measured. The predicting models for SOM and STN based on VNIR were established, and the predicting accuracies were assessed by traditional evaluating index, wavelet transform, and semivariance structure. The traditional evaluating index showed that the partial least square regression (PLSR) and optimum number of latent variables were suitable for SOM prediction. The accuracies were “good” (RPD ranges from 2.30 to 2.40) for calibration and “moderate” (RPD ranges from 1.80 to 1.95) for validation, whereas the model and parameters of STN were “moderate” (RPD ranges from 1.83 to 1.87) for calibration and “acceptable” (RPD ranges from 1.41 to 1.48) for validation procedure. Based on the wavelet transform, the patterns of global wavelet power spectrum for predicted and measured SOM were closer than that of STN, and their difference in local wavelet spectra could present the predicting errors in the scale and location domain. The nugget effect indicated that the stochastic variability weakened, and the spatial structure of predicted SOM and STN enhanced. The range of predicted SOM and STN were greater than those of measured. Therefore, the predicting models based on independent dataset using PLSR could be used for the prediction of SOM or STN in the un-sampled areas. Wavelet transform and semivariance parameters could be used to guide the utilization of predicted values. <![CDATA[Soil biological properties and fungal diversity under conservation agriculture in Indo-Gangetic Plains of India]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401142&lng=pt&nrm=iso&tlng=pt Abstract: A field experiment was undertaken to evaluate the effect of conservation agriculture (CA) based management on soil biological properties, and on fungal diversity and abundance after 5 years of continuous cultivation. Treatments included four crop managements viz., conventional tillage (CT) rice-wheat (CT-RW; CT based), conventional tillage rice-zero tillage wheat and mungbean (CTR-ZTWMb; partially CA based), zero tillage rice-wheat-mungbean (ZT-RWMb; full CA based), and zero tillage maize-wheat-mungbean (ZT-MWMb; full CA based). Full rice, maize, and mungbean crop residue and anchored wheat residue were recycled in CA-based managements, while CT-based management was without any residue. Full CA-based management (ZT-MWMb) recorded 43% higher organic carbon, 56% microbial biomass carbon, 70% microbial biomass nitrogen, 73% phosphatase activity, and 40% β-glucosidase activity, than CT-RW management. Ascomycota (55-74%) was the dominant phylum followed by Basidiomycota and Glomeromycota (0 to 3%); abundance of these phylavaried amongst managements. Ascomycota abundance was in order of CT-RW&lt; CTR-ZTWMb&lt; ZT-RWMb&lt; ZT-MWMb, however, Basidiomycota and Glomeromycota did not follow any trend. Diversity indices such as species richness, evenness and Shannon-Wiener diversity index were in the order: ZT-MWMb&gt; ZT-RWMb&gt; CTR-ZTWMb&gt; CT-RW. This study clearly showed that CA with all three proven principles (no-tillage, residue retention and crop diversification) in maize-wheat-mungbean system resulted in higher microbial activities, fungal diversity and species richness compared to other cereal based management systems. <![CDATA[Addition of residues with different C/N ratio in soil over time individually or as mixes - effect on nutrient availability and microbial biomass depends on amendment rate and frequency]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401157&lng=pt&nrm=iso&tlng=pt Abstract: Residues with different properties may be added to soil simultaneously (as mixes) or after each other. In most previous studies on the effect of mixes on decomposition and nutrient release, residues were added once at the start of the experiment. Less is known about the effect of mixtures added more than once on soil respiration, microbial biomass and nutrient availability and how the addition frequency influences interactions between high C/N (H) and low C/N (L) residues in mixes. In the 48-day incubation experiment with total amendment rate in all treatments was 20 g kg-1, treatments differed in addition frequency (twice, four or eight times), rate (10, 5 or 2.5 g kg-1) as well as order of H and L. Soil was sampled every 12 days. Treatments had similar total cumulative respiration, but differed in distribution over the 12 day periods. Available N and MBN changed strongly over time in treatments with 10 or 5 g kg-1, depending on the C/N ratio of the residue added before sampling. Frequent addition of small amounts of residues (2.5 g kg-1) limited microbial N uptake initially compared to higher amendment rates, but resulted in similar available N irrespective of the C/N ratio of the residue added. It can be concluded that with less frequent residue addition, microbes decompose mainly the recently added residue. With more frequent addition, microbes decompose recently added residue together with residue added before the most recent amendment. <![CDATA[Bacterial feeder Nematodes: Facilitator or competitor for Plant Phosphorus in soil]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401173&lng=pt&nrm=iso&tlng=pt Abstract: Rock phosphate is the main constituent of soil in lower Himalayan region of Pakistan but less accessible to plants. Although a lot of work has been done on the role of phosphate solubilizing bacteria for phosphorus availability from insoluble tricalcium phosphate (TCP), no significant success has yet been achieved at larger scale. The survival and function of introduced P solubilizing bacteria is directly influenced by their grazers present in soil. We hypothesized that the interactions between P solubilizing bacteria and grazer nematodes are able to improve P liberation from both TCP and bacterial biomass turnover. The hypothesis was tested by growing Pinus roxburghii seedlings in sand medium with or without TCP as a P source. The plants were grown alone or with a TCP solubilizing bacteria and bacterial-feeder nematodes. The test bacteria and the nematodes were isolated originally from pine rhizosphere of P mining zone located in lower Himalaya region of Pakistan. The grazing of bacteria by nematodes enhanced the P availability in the medium. Although bacteria were abundant in rhizosphere without nematodes they remained less efficient in P liberation compared to that measured in the presence of nematodes. Our data also showed that acidification was not the only reason of P availability from TCP. Another mechanism was prominent in liberation of the bacterial locked organic phosphorus via phosphatase secretion as a result of nematodes predation. Our results, thus, open a new window towards the success and efficiency of bacterial-based biofertilizer, which mostly fail in the soil. <![CDATA[Application of exogenous xyloglucan oligosaccharides affects molecular responses to salt stress in <em>Arabidopsis thaliana</em> seedlings<em>.</em>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401187&lng=pt&nrm=iso&tlng=pt Abstract Soil salinity is one of the most devastating problems which reduces crop production and increases desertification. New approaches to overcome the negative effect of salinity on plants include the use of plant biostimulants, such as Xyloglucan oligosaccharides (XGOs) derived from the breakdown of xyloglucans from plant cell walls. The present study aimed at verifying the influence of exogenous XGOs derived from Tamarindus indica L. cell walls, on Arabidopsis thaliana’s tolerance to salt stress by understanding the gene expression, enzymatic and metabolic changes resulting from its application. A. thaliana plants were grown in liquid media and after 15 days they were treated by a salt shock with 100 mM of sodium chloride, with or without XGOs at 0.1 mg L-1. Gene expression of four oxidative stress markers as well as catalase and peroxidase activities and content of glutathione, total carbonyl, polyphenolics and chlorophyll were quantified. Bioinformatic models were used to obtain the co-expression network of the four oxidative stress response gene markers from microarray data of Arabidopsis under salt stress. Results showed that in saline conditions, XGOs dramatically increased catalase gene expression and enzymatic activity, peroxidase activity, and chlorophyll a/b ratio, while reducing protein oxidation and total polyphenols. Thus, XGOs may act to counteract negative effects of oxidative stress under saline conditions. <![CDATA[Early responses to manganese (Mn) excess and its relation to antioxidant performance and organic acid exudation in barley cultivars]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-95162018000401206&lng=pt&nrm=iso&tlng=pt Abstract: Manganese (Mn) is an essential micronutrient for plants, and is necessary for biochemical and physiological processes. The objective of this research was to determine the early responses to Mn excess and its relation to antioxidant performance mechanisms and organic acid exudation in commercial barley cultivars. We determined early responses to Mn excess in four barley cultivars (Barke, Tatoo, Scarlett, Sebastian), which were subjected to increasing Mn concentrations (2.4-150-350-750-1500 µM Mn), pH 4.8, under nutrient solution during seven days. Results showed that plant growth parameters: biomass, length and relative growth rate (RGR) were negatively altered with the higher Mn treatments. Antioxidant performance such as antioxidant activity (AA) and antioxidant enzymes such as superoxidase dismutase (SOD) were activated in presence of excess Mn. Oxalate was the major organic acid roots exudate, and the cultivar Sebastian had the highest oxalate exudation. In conclusion, Tatoo and Sebastian are proposed as the most Mn tolerant cutvars given that the biomass parameters were not affected by increasing Mn doses, showing major oxalate exudation. It is suggested that the mechanisms associated to Mn alleviation could be attributed to SOD, AA and organic acid production, mainly oxalate, in tolerant cultivars (Sebastian, Tatoo) together to significant decrease of total phenols (TP) in shoot of sensitive cultivars (Barke and Scarlett). Non-enzymatic barriers were not related to early responses, and an enzymatic barrier and oxalate exudation were considered as early indicators of Mn stress, projecting that the tolerance of Mn-tolerant cultivars could increase under field conditions.