Scielo RSS <![CDATA[Scientia Agricola]]> http://www.scielo.br/rss.php?pid=0103-901620130006&lang=pt vol. 70 num. 6 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<b>A decision-tree-based model for evaluating the thermal comfort of horses</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600001&lng=pt&nrm=iso&tlng=pt Thermal comfort is of great importance in preserving body temperature homeostasis during thermal stress conditions. Although the thermal comfort of horses has been widely studied, there is no report of its relationship with surface temperature (T S). This study aimed to assess the potential of data mining techniques as a tool to associate surface temperature with thermal comfort of horses. T S was obtained using infrared thermography image processing. Physiological and environmental variables were used to define the predicted class, which classified thermal comfort as "comfort" and "discomfort". The variables of armpit, croup, breast and groin T S of horses and the predicted classes were then subjected to a machine learning process. All variables in the dataset were considered relevant for the classification problem and the decision-tree model yielded an accuracy rate of 74 %. The feature selection methods used to reduce computational cost and simplify predictive learning decreased model accuracy to 70 %; however, the model became simpler with easily interpretable rules. For both these selection methods and for the classification using all attributes, armpit and breast T S had a higher power rating for predicting thermal comfort. Data mining techniques show promise in the discovery of new variables associated with the thermal comfort of horses. <![CDATA[<b>Quality of cut and basecutter blade configuration for the mechanized harvest of green sugarcane</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600002&lng=pt&nrm=iso&tlng=pt Quality control is used to evaluate processes and products, and is a powerful tool for reducing variability. The objective of this study was to evaluate the quality of green sugarcane (Saccharum spp.) cutting for mechanized harvest, using statistical quality control tools. Cutting height and damage to ratoon stalks caused by different blade and disc combinations of the basecutter mechanism were used as indicators of quality. Cutting height showed high variability with a controlled process for some treatments. However, these treatments were incapable of producing satisfactory results. The damage index was lower in treatments that used tilted blades, but above the target for all treatments, which caused significant damage to the ratoons. In general, the process of mechanized harvest as assessed by these indicators was found incapable of achieving targeted results and staying below specification limits, and thus requires corrective actions to improve quality. <![CDATA[<b>Volume application rate adapted to the canopy size in greenhouse tomato crops</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600003&lng=pt&nrm=iso&tlng=pt The application rate of plant-protection products is indicated as a concentration or amount of product per area. Greenhouse crops grow swiftly, and an application rate based on a fixed amount of product per hectare can result either in large losses and overdoses when the plants are small or to be insufficient when the plants are fully developed. To solve these problems, the application rates of plant-protection products need to be adapted to the plant mass present in the greenhouse when the spray is applied. Two models were developed to estimate the leaf area based on easily measured geometric data of the vegetation in a greenhouse tomato crop. The model based on the PRV (Plant Row Volume) had that best results. The calculation of the volume application rate from the PRV has resulted in a reduction of more than 30 % of the quantity of plant protection product sprayed, without decreasing yield. The PRV of a greenhouse tomato (Lycopersicon esculentum Mill.) is an easily measured parameter that enables the estimation of the leaf area index and the use of application strategies adapted to the changes in the plant canopy, saving major amounts of plant protection product used, compared to the conventional system. <![CDATA[<b>Symbiotic nitrogen-fixing bacterial populations trapped from soils under agroforestry systems in the Western Amazon</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600004&lng=pt&nrm=iso&tlng=pt Cowpea (Vigna unguiculata) is an important grain-producing legume that can forego nitrogen fertilization by establishing an efficient symbiosis with nitrogen-fixing bacteria. Although inoculating strains have already been selected for this species, little is known about the genotypic and symbiotic diversity of native rhizobia. Recently, Bradyrhizobium has been shown to be the genus most frequently trapped by cowpea in agricultural soils of the Amazon region. We investigated the genetic and symbiotic diversity of 148 bacterial strains with different phenotypic and cultural properties isolated from the nodules of the trap species cowpea, which was inoculated with samples from soils under agroforestry systems from the western Amazon. Sixty non-nodulating strains indicated a high frequency of endophytic strains in the nodules. The 88 authenticated strains had varying symbiotic efficiency. The SPAD (Soil Plant Analysis Development) index (indirect measurement of chlorophyll content) was more efficient at evaluating the contribution of symbiotic N2-fixation than shoot dry matter under axenic conditions. Cowpea-nodulating bacteria exhibited a high level of genetic diversity, with 68 genotypes identified by BOX-PCR. Sequencing of the 16S rRNA gene showed a predominance of the genus Bradyrhizobium, which accounted for 70 % of all strains sequenced. Other genera identified were Rhizobium, Ochrobactrum, Paenibacillus, Bosea, Bacillus, Enterobacter, and Stenotrophomonas. These results support the promiscuity of cowpea and demonstrate the high genetic and symbiotic diversity of rhizobia in soils under agroforestry systems, with some strains exhibiting potential for use as inoculants. The predominance of Bradyrhizobium in land uses with different plant communities and soil characteristics reflects the adaptation of this genus to the Amazon region. <![CDATA[<b><i>In situ</i></b><b> rumen degradation kinetics as affected by type of pasture and date of harvest</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600005&lng=pt&nrm=iso&tlng=pt Botanical composition affects the nutritive value and nutrient degradation kinetics of pastures. However, there is little information about pastures composed of various species. The present study was conducted to evaluate in situ degradation kinetics of dry matter (DM), crude protein (CP) and neutral detergent fiber (NDF) of a naturalized non fertilized pasture (NNF), naturalized fertilized pasture (NF), sown pasture with Lolium perenne L. and Trifolium repens L. (RGWC), and sown pasture with Bromus valdivianus Phil., Dactylis glomerata L., Holcus lanatus L., L. perenne and T. repens (MIXED); at three dates of harvest (early-spring, mid-spring and autumn). Duplicate bags were incubated in the rumen of three cannulated cows for 2, 4, 8, 12, 24 or 48 h. Zero-hour bags were washed with water. Ruminal degradation was evaluated according to exponential models with or without lag phase. Pasture chemical composition showed on average low DM, high CP and digestible organic matter (DOMD). Degradation parameters of DM, CP and NDF exhibited strong pasture type*date of harvest interactions. In general, high potential degradability and fractional degradation rates of DM, CP and NDF were observed. Nutrient supply was generally higher for RGWC and NF, especially compared with NNF during autumn. Naturalized fertilized pastures supply similar amounts of nutrients to grazing cattle as sown pastures. However, it is necessary to consider other variables that determine the productive performance such as DM intake and rumen fermentation products. <![CDATA[<b>Nitrogen contributions of legume roots to cabbage nutrition</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600006&lng=pt&nrm=iso&tlng=pt The effects of roots are generally not considered in studies assessing crop responses to green manure. However, measuring such effects can contribute to a better understanding of crop rotation. In two experiments, we evaluated the content of legume-N in crop tissue and the fertilizer value of the roots and shoots of two legume species. Roots, shoots, or whole plants of the legumes sunhemp (Crotalaria juncea) and jack beans (Canavalia ensiformis) were cropped as green manure to supply nitrogen to cabbage crops (Brassica oleracea var. capitata). The principle of the A-value technique was applied to estimate the fertilizer value of each plant part. In a pot experiment, both the content of legume-N in cabbage and the fertilizer value of the whole plant was higher than the shoots, which was in turn higher than that of the roots. In field condition, roots had a decreasing effect on the N content of cabbage plants. Growing cabbage on legume root residue resulted in an increased absorption of 15N-urea, resulting in negative values ​​for legume-N content: -13.59 g kg-1 and -3.51 g kg-1 for sunhemp and jack beans, respectively. Suggesting both low N supply by roots and N immobilization in soil organic matter or microbial biomass. Future research should focus on estimating the net N acquisition by plants from root residues under field conditions, where rooting patterns and biomass distribution differ from those in pot experiments, therefore giving a more realistic quantitative estimate. <![CDATA[<b>Performance of 'Okitsu' Satsuma Mandarin on nine rootstocks</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600007&lng=pt&nrm=iso&tlng=pt Mandarins have become increasingly valued as citrus fruits for the fresh market due to the easy peeling, attractive flavor, and health and nutritional properties. Plant growth and yield, and characteristics of fruits of 'Okitsu' Satsuma mandarin (Citrus unshiu Marc.) trees grafted on nine rootstocks were evaluated in Londrina, northern Paraná, Brazil. The rootstocks were: 'Rangpur' lime (Citrus limonia Osb.); 'Cleopatra' (Citrus reshni hort. ex Tanaka) and 'Sunki' mandarins (Citrus sunki hort. ex Tanaka); 'C-13' [Citrus sinensis × Poncirus trifoliata (L.) Raf.] and 'Carrizo' citranges [C. sinensis × P. trifoliata (L.) Raf.]; 'Volkamer' lemon (Citrus volkameriana V. Ten. & Pasq.); trifoliate orange [P. trifoliata (L.) Raf.; 'Caipira DAC' sweet orange [C. sinensis (L.) Osb.] and 'Swingle' citrumelo [Citrus paradisi Macfad. cv. Duncan × P. trifoliata (L.) Raf.]. The highest plant growth was for the trees on 'Cleopatra' mandarin and 'Caipira DAC' sweet orange. In contrast, the smallest size was for the trees on 'Volkamer' lemon and trifoliate orange. The largest difference between the trunk diameter below and above the grafting point was induced by 'Swingle' citrumelo. Trees of 'Okitsu' Satsuma mandarin on 'Swingle' citrumelo presented the highest yield, while 'C-13', 'Carrizo', 'Sunki', and 'Swingle' induced the largest fruit masses. With regard to fruit characteristics, 'Carrizo' and trifoliate orange induced the best ratio and juice content. Based on theoretical values, 'Rangpur' lime and 'Volkamer' lemon induced the lowest yields <![CDATA[<b>Molecular identification based on coat protein sequences of the <i>Barley yellow dwarf virus </i>from Brazil</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600008&lng=pt&nrm=iso&tlng=pt Yellow dwarf disease, one of the most important diseases of cereal crops worldwide, is caused by virus species belonging to the Luteoviridae family. Forty-two virus isolates obtained from oat (Avena sativa L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), corn (Zea mays L.), and ryegrass (Lolium multiflorum Lam.) collected between 2007 and 2008 from winter cereal crop regions in southern Brazil were screened by polymerase chain reaction (PCR) with primers designed on ORF 3 (coat protein - CP) for the presence of Barley yellow dwarf virus and Cereal yellow dwarf virus (B/CYDV). PCR products of expected size (~357 bp) for subgroup II and (~831 bp) for subgroup I were obtained for three and 39 samples, respectively. These products were cloned and sequenced. The subgroup II 3' partial CP amino acid deduced sequences were identified as BYDV-RMV (92 - 93 % of identity with "Illinois" Z14123 isolate). The complete CP amino acid deduced sequences of subgroup I isolates were confirmed as BYDV-PAV (94 - 99 % of identity) and established a very homogeneous group (identity higher than 99 %). These results support the prevalence of BYDV-PAV in southern Brazil as previously diagnosed by Enzyme-Linked Immunosorbent Assay (ELISA) and suggest that this population is very homogeneous. To our knowledge, this is the first report of BYDV-RMV in Brazil and the first genetic diversity study on B/CYDV in South America. <![CDATA[<b>Aggregate breakdown and dispersion of soil samples amended with sugarcane vinasse</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600009&lng=pt&nrm=iso&tlng=pt Soil aggregation is a very complex issue related to important soil attributes and processes. The aggregate breakdown and dispersion of soil samples amended with sugarcane vinasse were evaluated using ultrasonic energy. Vinasse is an important byproduct of sugarcane industries, intensively applied to soils in Brazil as liquid fertilizer. Samples of two Oxisols and one Ultisol were used in this study. The physical and chemical characterization of soils was performed, and the 1 to 2 mm size aggregates (200 g) were packed in PVC columns (6.0 cm high and 4.0 cm internal diameter) and incubated with sugarcane vinasse under lab conditions for 1, 30 and 60 days. After incubation, aggregates were submitted to levels of ultrasonic energy, and the particle size distribution (53 to 2,000 µm, 2 to 53 µm, and < 2 µm fractions) was quantified. Mathematical equations were used to relate the mass of aggregates in each of these fractions to the applied ultrasonic energy, and parameters related to aggregate stability were then obtained. Soils showed an aggregate-hierarchy resulting in a stepwise breakdown under ultrasonic agitation. Considering this soil-aggregation hierarchy, vinasse contributed even in a short time to the bonding between and within 2 to 53 µm aggregates, mainly in the Oxisols. This may be related to organic compounds present in the vinasse, cementing soil particles. Potassium enrichment of soil samples did not contribute to soil dispersion. <![CDATA[<b>Carbohydrate production and transport in cotton cultivars grown under boron deficiency</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600010&lng=pt&nrm=iso&tlng=pt An adequate supply of boron (B) is required for the optimal growth and development of cotton (Gossypium hirsutum L.) plants, but the low phloem mobility of B limits the possibilities of correcting B deficiency. There are indications that different cotton cultivars could have different responses to B deficiency. The differences in responses of cotton cultivars to B regarding photoassimilate production and transport were studied in a greenhouse experiment with nutrient solution. Treatments consisted of three cotton cultivars (FMT 701, DP 604BG and FMX 993) and five concentrations of B (0.0, 2.5, 5.0, 10.0 and 20.0 µmol L−1). Sampling began at the phenological stage B1 (first square) and continued for four weeks. The leaf area and the number of reproductive branches and structures decreased due to B deficiency. A higher level of abortion of reproductive structures was observed under B deficiency. Boron deficiency increased the internal CO2 concentration but decreased the transpiration rate, stomatal conductance and photosynthesis. Despite the decrease in photosynthesis, nonstructural carbohydrates accumulated in the leaves due to decreased export to bolls in B-deficient plants. The response to B deficiency is similar among cotton cultivars, which shows that the variability for this trait is low even for cultivars with different genetic backgrounds. <![CDATA[<b>Climatic effects on sugarcane ripening under the influence of cultivars and crop age</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162013000600011&lng=pt&nrm=iso&tlng=pt The lack of information about the effects of cultivars, crop age and climate on the sugarcane (Saccharum ssp.) crop yield and quality has been the primary factor impacting the sugar-ethanol sector in Brazil. One of the processes about which we do not have a satisfactory understanding is sugarcane ripening and the effects of cultivars, crop age and climate on that. Sugarcane ripening is the process of sucrose accumulation in stalks, which is heavily influenced by several factors, mainly by climatic conditions such as air temperature and water deficits. Because it is a complex process, studies of the variables involved in sugarcane ripening can provide important information, resulting in a better use of commercial cultivars, bringing advantages to growers, processing units, breeding programs and scientific community. In this review, we discuss the available knowledge of the interaction between climate conditions and sugarcane ripening, under the influence of genotypic characteristics and crop age. In several studies, the main conclusion is that sugarcane ripening depends on a complex combination of climate variables, the genetic potential of cultivars and crop management. Soil moisture and air temperature are the primary variables involved in sugarcane ripening, and their combination stimulates the intensity of the process. In addition, the need for studies integrating the effects of climate on plant physiological processes and on the use of chemical agents to stimulate sugarcane ripening is highlighted.