The mycorrhizal contribution to plant productivity, plant nutrition and soil structure in experimental grassland.

Previous studies have shown that arbuscular mycorrhizal fungi (AMF) can influence plant diversity and ecosystem productivity. However, little is known about the effects of AMF and different AMF taxa on other important community properties such as nutrient acquisition, plant survival and soil structure. We established experimental grassland microcosms and tested the impact of AMF and of different AMF taxa on a number of grassland characteristics. We also tested whether plant species benefited from the same or different AMF taxa in subsequent growing seasons. AMF enhanced phosphorus acquisition, soil aggregation and survival of several plant species, but AMF did not increase total plant productivity. Moreover, AMF increased nitrogen acquisition by some plant species, but AMF had no effect on total N uptake by the plant community. Plant growth responses to AMF were temporally variable and some plant species obtained the highest biomass with different AMF in different years. Hence the results indicate that it may be beneficial for a plant to be colonized by different AMF taxa in different seasons. This study shows that AMF play a key role in grassland by improving plant nutrition and soil structure, and by regulating the make-up of the plant community.

Ophiolite-related ultramafic rocks (Serpentinites) in the Caribbean region: a review of their occurrence, composition, origin, emplacements and Ni-Laterite soil formation

Ultramafic rocks, mainly serpentinized peridotites of mantle origin, are mostly associated with the ophiolites of Mesozoic age that occur in belts along three of the margins of the Caribbean plate. The most extensive exposures are in Cuba. The ultramafic-mafic association (ophiolites) were formed and emplaced in several different tectonic environments. Mineralogical studies of the ultramafic rocks and the chemistry of the associated mafic rocks indicate that most of the ultramafic-mafic associations in both the northern and southern margins of the plate were formed in arc-related environments. There is little mantle peridotite exposed in the ophiolitic associations of the west coast of Central America, in the south Caribbean in Curacao and in the Andean belts in Colombia. In these occurrences the chemistry and age of the mafic rocks indicates that this association is mainly part of the 89 Ma Caribbean plateau province. The age of the mantle peridotites and associated ophiolites is probably mainly late Jurassic or Early Cretaceous. Emplacement of the ophiolites possibly began in the Early Cretaceous in Hispaniola and Puerto Rico, but most emplacement took place in the Late Cretaceous to Eocene (e.g. Cuba). Along the northern South America plate margin, in the Caribbean mountain belt, emplacement was by major thrusting and probably was not completed until the Oligocene or even the early Miocene. Caribbean mantle peridotites, before serpentinization, were mainly harzburgites, but dunites and lherzolites are also present. In detail, the mineralogical and chemical composition varies even within one ultramafic body, reflecting melting processes and peridotite/melt interaction in the upper mantle. At least for the northern Caribbean, uplift (postemplacement tectonics) exposed the ultramafic massifs as a land surface to effective laterization in the beginning of the Miocene. Tectonic factors, determining the uplift, exposing the peridotites to weathering varied. In the northern Caribbean, in Guatemala, Jamaica, and Hispaniola, uplift occurred as a result of transpresional movement along pre-existing major faults. In Cuba, uplift occurred on a regional scale, determined by isostatic adjustment. In the south Caribbean, uplift of the Cordillera de la Costa and Serrania del Interior exposing the peridotites, also appears to be related to strike-slip movement along the El Pilar fault system. In the Caribbean, Ni-laterite deposits are currently being mined in the central Dominican Republic, eastern Cuba, northern Venezuela and northwest Colombia. Although apparently formed over ultramafic rocks of similar composition and under similar climatic conditions, the composition of the lateritic soils varies. Factors that probably determined these differences in laterite composition are geomorphology, topography, drainage and tectonics. According to the mineralogy of principal ore-bearing phases, Dominican Ni-laterite deposits are classified as the hydrous silicate-type. The main Ni-bearing minerals are hydrated Mg-Ni silicates (serpentine and ¿garnierite¿) occurring deeper in the profile (saprolite horizon). In contrast, in the deposits of eastern Cuba, the Ni and Cooccurs mainly in the limonite zone composed of Fe hydroxides and oxides as the dominant mineralogy in the upper part of the profile, and are classified as the oxide-type.

Assessment of the soil compaction of two ultisols caused by logging operations

The impact of wood loads on bulk density and preconsolidation pressure and of harvester and forwarder traffic on rut depth, bulk density and preconsolidation pressure of two Ultisols were examined in this study. Our objective was to quantify the threshold beyond which significant soil compaction and rutting would occur. This study was carried out in the county of Eunápolis, state of Bahia, Brazil, (16 º 23 ' 17 '' S and 39 º 10 ' 06 '' W; altitude 80 m asl) in two Ultisols (PAd2 and PAd3) with different texture classes, in experimental areas with eucalypt plantation. The study involved measurements at the wood load site and machine driving at specific locations in the forest during logging operations. The treatments consisted of one harvester pass and, 8, 16 and 40 passes of a fully loaded forwarder. Thresholds were established based on the rut depth and percentage of preconsolidation pressure values in the region of additional soil compaction defined in the bearing capacity model. The percentage of soil samples with values of preconsolidation pressure in the region of additional soil compaction indicated a greater susceptibility of PAd3 than of PAd2 to soil compaction. The threshold levels established here based on preconsolidation pressure and rut depth indicated that no more than eight forwarder passes should be allowed in loading operations in order to minimize soil compaction.

The effects of a non-woven cover in combination with different soil mulches in strawberry cultivation

Selostus: Katteiden käyttö mansikanviljelyssä

Aplicabilidade do lisem (limburg soil erosion) para simulação hidrológica em uma bacia hidrográfica tropical

As variáveis de entrada do modelo LISEM, mais importantes do ponto de vista da gênese do escoamento superficial direto (umidade do solo antecedente aos eventos de precipitação pluvial (θap) e espessura da camada de solo considerada no balanço hídrico) foram calibrados para eventos individuais de precipitação pluvial ocorridos na bacia hidrográfica do ribeirão Marcela, da região Alto Rio Grande, MG. Avaliou-se, também, a influência de diferentes cenários nas variáveis do escoamento superficial direto. O modelo apresentou elevada sensibilidade à umidade do solo, sendo este sua principal variável de calibração. A influência da camada de balanço hídrico esteve associada à umidade de calibração, observando-se que, quanto maior a profundidade, maior a umidade requerida para calibrar o modelo. Os cenários mata natural, eucalipto e café, aos 35 meses após o plantio, atenuaram as vazões máximas de 37,6; 42,2; e 28,0 %, cuja intensidade de precipitação pluvial foi de 48,0 mm h-1. O modelo hidrológico LISEM apresentou resultados satisfatórios na simulação hidrológica do escoamento superficial direto, mostrando que pode ser aplicado para previsão do comportamento hidrológico de bacias hidrográficas tropicais, desde que devidamente calibrado.

Organic sulfur oxidation to sulfate in soil samples for total sulfur determination by turbidimetry

Sulfur in the soil occurs in two basic forms, organic and inorganic S. The organic form accounts for 95 % of S in most soils. The effectiveness of organic S to oxidate to sulfate was evaluated for total S determination in soil samples by wet (acid) and dry-ash (alkaline) oxidation methods. To evaluate the wet method and the possible use as a reference when evaluating the dry method proposed here, a reference standard from the US National Institute of Standards and Technology (NIST) was used (Montana Soil - NIST 2710). The dry-ash oxidation process with alkaline oxidizing agents is one of the simplest oxidation methods of organic S to the sulfate form and was compared with the wet process. The objective of the study was to develop a dry method that would be easy to apply and allow the complete conversion of organic S to sulfate in soil samples and later detection by turbidimetry. The effectiveness of organic S oxidation to sulfate was evaluated by means of three alkaline oxidation mixtures: NaHCO3 + Ag2O, Eschka mixture (17 % Na2CO3, 66 % MgO, and 17 % K2CO3), and NaHCO3 + CuO. The procedure to quantify the sulfate concentration was based on the reaction with barium chloride and turbidimetric detection. Sulfur quantification in the standard sample by the wet method proved adequate, precise and accurate. It should also be pointed out that no significant differences were found (95 % reliability) between the wet and dry processes (NaHCO3 and Ag2O oxidation mixture) in six different Brazilian soils. The proposed dry method can therefore be used in the preparation of soil samples for total S determination.

Effects of variety, soil type and nitrogen fertilizer supply on the nutritive value of barley for growing pigs

Selostus: Lajikkeen, typpilannoitustason ja maalajin vaikutus ohran ruokinnalliseen arvoon lihasioilla

Tannery and coal mining waste disposal on soil

Tannery residues and coal mine waste are heavily polluting sources in Brazil, mainly in the Southern States of Rio Grande do Sul and Santa Catarina. In order to study the effects of residues of chrome leather tanning (sludge and leather shavings) and coal waste on soybean and maize crops, a field experiment is in progress since 1996, at the Federal University of Rio Grande do Sul Experimental Station, county of Eldorado do Sul, Brazil. The residues were applied twice (growing seasons 1996/97 and 1999/00). The amounts of tannery residues were applied according to their neutralizing value, at rates of up to 86.8 t ha-1, supplying from 671 to 1.342 kg ha-1 Cr(III); coal waste was applied at a total rate of 164 t ha-1. Crop yield and dry matter production were evaluated, as well as the nutrients (N, P, K, Ca, Mg, Cu and Zn) and Cr contents. Crop yields with tannery sludge application were similar to those obtained with N and lime supplied with mineral amendments. Plant Cr absorption did not increase significantly with the residue application. Tannery sludge can be used also to neutralize the high acidity developed in the soil by coal mine waste.

Soil organic matter and fertility of anthropogenic dark earths (Terra Preta de Índio) in the Brazilian Amazon basin

Fertility properties, total C (Ctot), and chemical soil organic matter fractions (fulvic acid fraction - FA, humic acid fraction - HA, humin fraction - H) of anthropogenic dark earths (Terra Preta de Índio) of the Amazon basin were compared with those of Ferralsols with no anthropogenic A horizon. Terra Preta soils had a higher fertility (pH: 5.1-5.4; Sum of bases, SB: 8.93-10.33 cmol c kg-1 , CEC: 17.2-17.5 cmol c kg-1 , V: 51-59 %, P: 116-291 mg kg-1) and Ctot (44.6-44.7 g kg-1) than adjacent Ferralsols (pH: 4.4; SB: 2.04 cmol c kg-1, CEC: 9.5 cmol c kg-1, V: 21 %, P 5 mg kg-1, C: 37.9 g kg-1). The C distribution among humic substance fractions (FA, HA, H) in Terra Preta soils was also different, as shown by the ratios HA:FA and EA/H (EA=HA+FA) (2.1-3.0 and 1.06-1.08 for Terra Preta and 1.2 and 0.72 for Ferralsols, respectively). While the cation exchange capacity (CEC), of Ferralsols correlated with FA (r = 0.97), the CEC of Terra Preta correlated with H (r = 0.82). The correlation of the fertility of Terra Preta with the highly stable soil organic matter fraction (H) is highly significant for the development of sustainable soil fertility management models in tropical ecosystems.

Effect of soil-spraying time on root-colonization ability of antagonistic Streptomyces griseoviridis

Selostus: Kasvualustan käsittelyajan vaikutus Streptomyces griseoviridis -antagonistin juurten asutuskykyyn

Comparison of estimation methods of soil strength in five soils

In agriculture, the soil strength is used to describe the susceptibility to deformation by pressure caused by agricultural machine. The purpose of this study was to compare different methods for estimating the inherent soil strength and to identify their suitability for the evaluation of load support capacity, compaction susceptibility and root growth. The physical, chemical, mineralogical and intrinsic strength properties of seven soil samples, collected from five sampling pits at different locations in Brazil, were measured. Four clay (CS) and three sandy clay loam (SCL) soils were used. The clay soils were collected on a farm in Santo Ângelo, RS (28 º 16 ' 16 '' S; 54 º 13 ' 11 '' W 290 m); A and B horizons at the Universidade Federal de Lavras, Lavras, MG (21 º 13 ' 47 '' S; 44 º 58 ' 6'' W; 918 m) and on the farm Sygenta, in Uberlandia, MG (18 º 58 ' 37 '' S; 48 º 12 ' 05 '' W 866 m). The sandy clay loam soils were collected in Aracruz, ES (19 º 47 ' 10 '' S; 40 º 16 ' 29 '' W 81 m), and on the farm Xavier, Lavras, MG (21 º 13 ' 24 '' S; 45 º 05 ' 00 '' W; 844 m). Soil strength was estimated based on measurements of: (a) a pneumatic consolidometer, (b) manual pocket (non-rotating) penetrometer; and (c) automatic (rotating) penetrometer. The results of soil strength properties were similar by the three methods. The soil structure had a significant influence on soil strength. Results of measurements with both the manual pocket and the electric penetrometer were similar, emphasizing the influence of soil texture. The data showed that, to enhance the reliability of predictions of preconsolidation pressure by penetrometers, it is better to separate the soils into the different classes, rather than analyze them jointly. It can be concluded that the consolidometer method, although expensive, is the best when evaluations of load support capacity and compaction susceptibility of soil samples are desired.

Root system distribution of sugar cane as related to nitrogen fertilization, evaluated by two methods: monolith and probes

Few studies on sugar cane have evaluated the root system of the crop, in spite of its importance. This is mainly due to the difficulty of evaluation and high variability of results. The objective of this study was to develop an evaluation method of the cane root system by means of probes so as to evaluate the mass, distribution and metabolically active roots related to N fertilization at planting. For this purpose, an experiment was conducted in an Arenic Kandiustults with medium texture in Jaboticabal/SP, in a randomized block design with four replications and four treatments: control (without N) and 40, 80 and 120 kg ha-1 of N applied in the form of urea in the planting furrow of the cane variety SP81 3250. One week before harvest, a urea-15N solution was applied at the cane stalk base to detect active metabolism in the root system. Trenches of 1.5 m length and 0.6 m depth were opened between two sugar cane rows for root sampling by two methods: monoliths (0.3, 0.2 and 0.15 m wide, deep and long respectively) taken from the trench wall and by probe (internal diameter 0.055 m). For each method, 15 samples per plot were collected. The roots were separated from the soil in a sieve (2 mm mesh), oven-dried (at 65 ºC) and the dry matter was measured. Root sampling by probes resulted in root mass that did not differ from the evaluation in monoliths, indicating that this evaluation method may be used for sugar cane root mass, although neither the root distribution in the soil profile nor the rhizome mass were efficiently evaluated, due to the small sample volume. Nitrogen fertilization at planting did not result in a greater root accumulation in the sugar cane plant, but caused changes in the distribution of the root system in the soil. The absence of N fertilization led to a better root distribution in the soil profile, with 50, 34 and 16 % in the 0-0.2, 0.2-0.4 and 0.4-0.6 m layers, respectively; in the fertilized treatments the roots were concentrated in the surface layer, with on average 70, 17 and 13 % for the same layers. The metabolically active roots were concentrated in the center of the cane stool, amounting to 40 % of the total root mass, regardless of N fertilization (application of 120 kg ha-1 N or without N).

Fine speckle contrast in InGaAs/InP systems: Influence of layer thickness, missmatch, and growing temperature

This work is focused on the study of the fine speckle contrast present in planar view observations of matched and mismatched InGaAs layers grown by molecular beam epitaxy on InP substrates. Our results provide experimental evidence of the evolution of this fine structure with the mismatch, layer thickness, and growth temperature. The correlation of the influence of all these parameters on the appearance of the contrast modulation points to the development of the fine structure during the growth. Moreover, as growth proceeds, this structure shows a dynamic behavior which depends on the intrinsic layer substrate stress.

Aggregate stability as affected by short and long-term tillage systems and nutrient sources of a hapludox in southern Brazil

The ability of a soil to keep its structure under the erosive action of water is usually high in natural conditions and decreases under frequent and intensive cultivation. The effect of five tillage systems (NT = no-till; CP = chisel plowing and one secondary disking; CT = primary and two secondary distings; CTb = CT with crop residue burning; and CTr = CT with removal of crop residues from the field), combined with five nutrient sources (C = control, no nutrient application; MF = mineral fertilizers according to technical recommendations for each crop; PL = 5 Mg ha-1 y-1 fresh matter of poultry litter; CM = 60 m³ ha-1 y-1 slurry cattle manure; and SM = 40 m³ ha-1 y-1 slurry swine manure) on wet-aggregate stability was determined after nine years (four sampled soil layers) and on five sampling dates in the 10th year (two sampled soil layers) of the experiment. The size distribution of the air-dried aggregates was strongly affected by soil bulk density, and greater values of geometric mean diameter (GMD AD) found in some soil tillage or layer may be partly due to the higher compaction degree. After nine years, the GMD AD on the surface was greater in NT and CP compared to conventional tillage systems (CT, CTb and CTr), due to the higher organic matter content, as well as less soil mobilization. Aggregate stability in water, on the other hand, was affected by the low variation in previous gravimetric moisture of aggregates, which contributed to a high coefficient of variation of this attribute. The geometric mean diameter of water-stable aggregates (GMD WS) was highest in the 0.00-0.05 m layer in the NT system, in the layers 0.05-0.10 and 0.12-0.17 m in the CT, and values were intermediate in CP. The stability index (SI) in the surface layers was greater in treatments where crop residues were kept in the field (NT, CP and CT), which is associated with soil organic matter content. No differences were found in the layer 0.27-0.32 m. The effect of nutrient sources on GMD AD and GMD WS was small and did not affect SI.

Effect of fertilization on soil phosphorus in a long-term field experiment in southern Finland

Selostus: Maan fosforitilan muutos pitkäaikaisessa kenttäkokeessa hietamaalla