Scielo RSS <![CDATA[Journal of soil science and plant nutrition]]> vol. 10 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<strong>FORMATION OF POST-FIRE WATER-REPELLENT LAYERS IN MONTERREY PINE (</strong><em><b>pinus radiata</b></em><strong> D. DON) PLANTATIONS IN SOUTH-CENTRAL CHILE</strong>]]> A wildfire burned about 15,000 ha of Monterrey Pine (Pinus radiata D. Don) plantations near Yungay, Chile, in January of 2007. Post-fire water repellency (hydrophobicity) was measured using the water-drop-penetration-time (WDPT) method at depths of 0, 5, and 10 mm from the soil surface. These measurements were collected on burned sites of both young (4-years old) and old (11-years old) plantations having both sand- and clay-rich soils. For purpose of comparison, water repellency was also measured one year after the wildfire on four unburned sites representing the same soil types and plantation ages as those occurring on the burned sites. The statistical analyses indicated that water repellency was present only on old stands, being located on the soil surface (clay soils) or as a layer 10 mm deeper or below (sandy soils). However, a water repellent layer was found on young stands growing on sandy soils, five millimeters below the surface, assumed to be formed when a wildfire burned the area before the new plantation was established. <![CDATA[DIVERSITY OF ARBUSCULAR MYCORRHIZAL FUNGI IN HORTICULTURAL PRODUCTION SYSTEMS OF SOUTHERN CHILE]]> The diversity of arbuscular mycorrhizal (AM) fungi in six Capsicum annuum or Lycopersicum escuĂ­entum L. horticultural production systems of small farmers, and of two wheat agrosystems was comparatively investigated in Southern Chile (La Araucania). Soils in this region are mostly originated by volcanic ashes which are characterized by high organic matter content and high P-fixing capacity. Arbuscular mycorrhizal fungal symbioses are playing a key role for P uptake by horticultural crops grown there. The objective of this study was to determine AM fungal communities in cropping systems and to identify soil factors affecting their frequency and diversity. Of the totally 32 AM fungal species identified, 5 to 21 AM fungi species were found in horticultural locations and 8 to 11 AM fungi species in conventional tillage (CT) and no-tillage (NT) agroecosystems. No relationships on AM fungal diversity with soil factors were found. In wheat based agrosystems fungal diversity was somewhat lower under CT than NT whereas no such relationships between diversity and intensity of land use could be generated from horticultural systems. It is concluded that it will be advisable for farmers to inoculate their horticultural crops with selected mycorrhizal inoculants during the nursery stage, as it cannot be predicted from the soil conditions whether the native AM fungal community is sufficient to sustain a stable horticultural production in the region. <![CDATA[DIGITAL MAPPING OF FARMLAND CLASSES IN THREE LANDSCAPE IN MEXICO]]> The cartography of farmland classes allows generating land maps, using a methodology based on local knowledge, rapidly and at low cost, and with a greater number of cartographic units than conventional soil surveys maps. However, the results found when producing these maps with automated cartography techniques are contrasting. Precision and accuracy were evaluated in 324 computer generated farmland class (FLC) maps by applying the Inverse Distance Weighted (IDW) interpolation model. These maps were obtained by varying the sample size for the training, its spatial design, and the Power value of the interpolator. Moreover, the effort needed to obtain maps with acceptable reliability was quantified. The procedure was applied to FLC maps obtained from surveys with producers from three contrasting environmental zones in Mexico. The results show that the best sampling scheme in the three areas is the systematic sampling, and Power 8, giving the maps with the highest reliability. Through the criterion of map reliability and effort needed for sampling, the recommended sample size is 10% to 25% of the total plots. <![CDATA[EFFECTS OF PHOSPHORUS FERTILIZATION ON ARSENIC UPTAKE BY WHEAT GROWN IN POLLUTED SOILS]]> In this study we have examinated the results of two experiments on the uptake and distribution of arsenic (As) in roots, shoots, and grain of wheat grown in As-polluted soils and in an unpolluted soil irrigated with As-contaminated water in absence or presence of phosphorus (P) fertilization. Arsenic concentrations in wheat samples of the two experiments are higher than those in the plants grown on uncontaminated soil. In the experiments showed in this work, it is highlighted the role of P fertilization in preventing As uptake and translocation in wheat plants. These findings could have important implications to reduce the potential risk posed to human health by As entering the food-chain. <![CDATA[<strong>EFFECT OF NITROGEN FERTILIZER AND MAIZE STRAW INCORPORATION ON NH<sub>4</sub><sup>+15</sup>N AND N0<sub>3</sub> -<sup>15</sup>N ACCUMULATION IN BLACK SOIL OF NORTHEAST CHINA AMONG THREE CONSECUTIVE CROPPING CYCLES</strong>]]> A pot experiment was conducted to evaluate the effect of nitrogen (N) fertilizer and maize straw incorporation on the accumulation of NH4+-15N and N0(3)--15N in soil inorganic N pool among three consecutive cropping cycles, aimed to search for an effective N management practice to decrease superfluous accumulation of soil inorganic N and fertilizer N losses. The results showed that the amounts of soil NH4+-15N, N0(3)-15N and inorganic 15N, and their percent to applied 15N-labeled fertilizer declined significantly with sampling time (p ≤ 0.001).Compared to low N application rate (44.64 mg N kg-1 soil), high N application rate (89.28 mg N kg-1 soil) enhanced significantly the amounts of soil NH4+-15N, N0(3)--15N and inorganic 15N by 238.6%, 132.9% and 197.3%, respectively (p ≤ 0.001). In contrast, maize straw addition declined significantly the amounts of soil NH4+-15N and inorganic 15N by 21.4% and 16.1% compared to without maize straw (p ≤ 0.001). The results suggested that a combined application of chemical fertilizer and maize straw with a wide C/N ratio is an important means for reducing the superfluous accumulation of fertilizer N as soil inorganic N to subsequently lower its loss. <![CDATA[FLAXSEED AND FLAXSEED CAKE AS A SOURCE OF COMPOUNDS FOR FOOD INDUSTRY]]> Flax (Linum usitatissimum) has been used for centuries as a source for oil extraction. In recent years it has attracted considerable interest as a result of studies which attribute potential health benefits to its components, including the prevention of chronic non-communicable diseases. Among these compounds presenting biological activity, alpha-linolenic acid, lignans and soluble fibre are of special interest. Southern Chile has comparative advantages for the cultivation of this crop. Together with its full processing, this crop could strengthen regional industry. The purpose of the present work is to learn how the best use can be made of these compounds, by studying flaxseed and flaxseed cake as sources of compounds of interest for food industry. Oil extracted from flaxseed contained 51.86% of linolenic, 16.34% of linoleic and 20.98% of oleic acid. Fractioning of defatted flaxseed cake produced a polyphenol content of 0.73 mg GAEg-1 extract and a protein isolate of considerable purity, 53.15% yield with 0.78 gof albumin equivalent g-1 protein isolate. Additionally, a polysaccharide was isolated with low protein content as impurity, 10.71% yield with 1.37 mg of glucose equivalent per gram of polysaccharide. This information will form the basis for assessing the extraction of products of interest for the food industry from flaxseed cake. <![CDATA[BIOSTIMULATION OF AGRICULTURAL BIOBEDS WITH NPK FERTILIZER ON CHLORPYRIFOS DEGRADATION TO AVOID SOIL AND WATER CONTAMINATION]]> Degradation of the insecticide chlorpynfos (160 a.i mg kg-1) using a biomix of a biobed system biostimulated with inorganic fertilizer (NPK) was investigated. Three concentrations of the fertilizer (0.1%, 0.5% and 1.0% ww-1) were evaluated on chlorpynfos degradation, TCP (3, 5, 6-trichloro-2-pyrinidol) accumulation and biological activity of the biomix. The chlorpynfos was dissipated efficiently (>75%) after 40 days of incubation and no additional dissipation was obtained with increasing concentration of NPK after 20 days of incubation. TCP accumulation occuned in all evaluated NPK concentrations and its concentration increased with the increment of NPK addition raising the probability of leaching of this compound. Biological activity (FDA and ligninolytic enzyme activity) in the biomix increased by the NPK presence in all evaluated concentrations. The DGGE analyses showed that combined treatments with lower amounts of NPK (0% and 0.1%) and chlorpynfos showed no significant modifications in the microbial community in the biomix. However, combined overdoses of NPK (0.5 and 1.0%) and chlorpynfos caused significant modifications in the bacterial communities that could be associated with TCP degradation reduction in the biomix. In conclusion, the obtained results demonstrated that the biomix prepared with Andisol and biostimulated with NPK nutrient can be recommended in biobeds as a viable alternative of chlorpyrifos dissipation avoiding soil and water contamination probability. <![CDATA[MANGANESE AS ESSENTIAL AND TOXIC ELEMENT FOR PLANTS: TRANSPORT, ACCUMULATION AND RESISTANCE MECHANISMS]]> Manganese is an essential element for plants, intervening in several metabolic processes, mainly in photosynthesis and as an enzyme antioxidant-cofactor. Nevertheless, an excess of this micronutrient is toxic for plants. Mn phytotoxicity is manifested in a reduction of biomass and photosynthesis, and biochemical disorders such as oxidative stress. Some studies on Mn toxicity and Mn translocation from soil to plant cells in Mn2+ form have demonstrated their importance under low pH and redox potential conditions in the soil. When Mn is inside the cells, mechanisms that can tolerate this toxicity are also observed, being important the compartmentalization of this metal in different organdĂ­es of shoot and leaf plant cells. A key role of antioxidative systems in plants in relation to high Mn amounts has also been reported as a defense mechanism. The purpose of this review is to show the role of Mn as an essential micronutrient and as a toxic element to higher plants as well as to their transport and tolerance mechanisms. The forms and dynamics of this element in soils and the importance of the acidity for this dynamic and availability for plants are also given. <![CDATA[THE ROLE OF SOIL STRUCTURE ON THE PORE FUNCTIONALITY OF AN ULTISOL]]> A Typic Hapludult was used to evaluate the effect of soil structure and different bulk densities (reached after the destruction of macro aggregates) on functional characteristics of the pore system. The water retention curve, pore-size distribution, shrinkage curve and index were determined in disturbed and structured samples. To evaluate the effect of soil structure on the continuity of the pore system the air permeability at different matrix potentials was measured. From the relationship between the air permeability and air-filled porosity, pore continuity indexes were calculated. The destruction of the soil structure affects the function of its pores. The amount of air-filled pores increased with the reduction of the bulk density, however, the stability and continuity of these pores are low, which affects their functionality. Therefore, the formation of a stable and continuous pore system allows the soil to conduct air, even though they have a restrictive amount of air-filled pores. On the other hand, the soil structure plays a key role in pore stability during drying and, consequently, on the equilibrium between phases. Finally, the highest bulk density (1.1 Mg m-3) does not reach critical values (compaction). However, depending on the bulk density of the soil, it is possible to reach restrictive values of air capacity which affects the air transport in the soil, especially if the porous media is not continuous. <![CDATA[ANTIOXIDANT COMPOUNDS IN SKIN AND PULP OF FRUITS CHANGE AMONG GENOTYPES AND MATURITY STAGES IN HIGHBUSH BLUEBERRY <i>(Vaccinium corymbosum </i>L.) GROWN IN SOUTHERN CHILE]]> We evaluated the genotype and maturity effects on antioxidant activity and phenolic compounds of whole, skin and pulp fruits from three highbush blueberry cultivare (cv. Brigitta, cv. Bluegold and cv. Legacy) grown in southern Chile. Total antioxidant activity (TAA) in ripe fruits varied among the cultivare in the order Legacy > Brigitta > Bluegold. We found that TAA in unripe green and fully ripe fruits was high and similar between them, whereas the lowest levels were found in intermediate ripe fruits. The same trend was observed for fruit total phenolic content. This could be attributed to the higher concentrations of phenolic acids (mainly chlorogenic acid) and flavonols (mainly rutin) at immature fruit stages; whereas the high TAA in mature fruits could be explained by the elevated amounts of anthocyanin. All antioxidant compounds were mostly located in the skin. High amounts of delphinidin aglycone were found. HPLC-DAD/MS revealed that the main contents of skin anthocyanins are petunidin-3-glucoside and petunidin-3-arabinnoside followed by malvidin-3-galactoside. It is noticeable that highbush blueberry fruits grown in southern Chile have exceptionally higher antioxidant activity and anthocyanins contents compared with those cultivated in the northern hemisphere.