Multivariate analysis applied to the study of the relationship between soil and plant properties in a peach orchard

In the State of Rio Grande do Sul, the municipality of Pelotas is responsible for 90 % of peach production due to its suitable climate and soil conditions. However, there is the need for new studies that aim at improved fruit quality and increased yield. The aim of this study was to evaluate the relationship that exists between soil physical properties and properties in the peach plant in the years 2010 and 2011 by the technique of multivariate canonical correlation. The experiment was conducted in a peach orchard located in the municipality of Morro Redondo, RS, Brazil, where an experimental grid of 101 plants was established. In a trench dug beside each one of the 101 plants, soil samples were collected to determine silt, clay, and sand contents, soil density, total porosity, macroporosity, microporosity, and volumetric water content in the 0.00-0.10 and 0.10-0.20 m layers, as well as the depth of the A horizon. In each plant and in each year, the following properties were assessed: trunk diameter, fruit size and number of fruits per plant, average weight of the fruit per plant, fruit pulp firmness, Brix content, and yield from the orchard. Exploratory analysis of the data was undertaken by descriptive statistics, and the relationships between the physical properties of the soil and of the plant were assessed by canonical correlation analysis. The results showed that the clay and microporosity variables were those that exhibited the highest coefficients of canonical cross-loading with the plant properties in the soil layers assessed, and that the variable of mean weight of the fruit per plant was that which had the highest coefficients of canonical loading within the plant group for the two years assessed.

Variability of root traits in common bean genotypes at different levels of phosphorus supply and ontogenetic stages

Selection of common bean (Phaseolus vulgaris L.) cultivars with enhanced root growth would be a strategy for increasing P uptake and grain yield in tropical soils, but the strong plasticity of root traits may compromise their inclusion in breeding programs. The aim of this study was to evaluate the magnitude of the genotypic variability of root traits in common bean plants at two ontogenetic stages and two soil P levels. Twenty-four common bean genotypes, comprising the four growth habits that exist in the species and two wild genotypes, were grown in 4 kg pots at two levels of applied P (20 and 80 mg kg-1) and harvested at the stages of pod setting and early pod filling. Root area and root length were measured by digital image analysis. Significant genotype × P level and genotype × harvest interactions in analysis of variance indicate that the genotypic variation of root traits depended on soil nutrient availability and the stage at which evaluation was made. Genotypes differed for taproot mass, basal and lateral root mass, root area and root length at both P levels and growth stages; differences in specific root area and length were small. Genotypes with growth habits II (upright indeterminate) and III (prostrate indeterminate) showed better adaptation to limited P supply than genotypes of groups I (determinate) and IV (indeterminate climbing). Between the two harvests, genotypes of groups II and III increased the mass of basal and lateral roots by 40 and 50 %, respectively, whereas genotypes of groups I and IV by only 7 and 19 %. Values of the genotypic coefficient of determination, which estimates the proportion of phenotypic variance resulting from genetic effects, were higher at early pod filling than at pod setting. Correlations between shoot mass and root mass, which could indicate indirect selection of root systems via aboveground biomass, were higher at early pod filling than at pod setting. The results indicate that selection for root traits in common bean genotypes should preferentially be performed at the early pod-filling stage.

Occurrence and Structure of Arbuscular Mycorrhizal Fungal Communities in Cassava after Cultivation of Cover Crops as Observed by the “PCR-DGGE” Technique

ABSTRACT Cassava (Manihot esculenta Crantz) is a highly mycotrophic crop, and prior soil cover may affect the density of arbuscular mycorrhizal fungi (AMFs), as well as the composition of the AMFs community in the soil. The aim of this study was to evaluate the occurrence and the structure of AMFs communities in cassava grown after different cover crops, and the effect of the cover crop on mineral nutrition and cassava yield under an organic farming system. The occurrence and structure of the AMFs community was evaluated through polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE). A randomized block experimental design was used with four replications. Six different cover crop management systems before cassava were evaluated: black oats, vetch, oilseed radish, intercropped oats + vetch, intercropped oats + vetch + oilseed radish, plus a control (fallow) treatment mowed every 15 days. Oats as a single crop or oats intercropped with vetch or with oilseed radish increased AMFs inoculum potential in soil with a low number of propagules, thus benefiting mycorrhizal colonization of cassava root. The treatments did not affect the structure of AMFs communities in the soil since the AMFs communities were similar in cassava roots in succession to different cover crops. AMFs colonization was high despite high P availability in the soil. The cassava crop yield was above the regional average, and P levels in the leaves were adequate, regardless of which cover crop treatments were used. One cover crop cycle prior to the cassava crop was not enough to observe a significant response in variables, P in plant tissue, crop yield, and occurrence and structure of AMFs communities in the soil. In the cassava roots in succession, the plant developmental stage affected the groupings of the structure of the AMF community.

Water Balance Components in Covered and Uncovered Soil Growing Irrigated Muskmelon

ABSTRACT Knowledge of the terms (or processes) of the soil water balance equation or simply the components of the soil water balance over the cycle of an agricultural crop is essential for soil and water management. Thus, the aim of this study was to analyze these components in a Cambissolo Háplico (Haplocambids) growing muskmelon (Cucumis melo L.) under drip irrigation, with covered and uncovered soil, in the municipality of Baraúna, State of Rio Grande do Norte, Brazil (05º 04’ 48” S, 37º 37’ 00” W). Muskmelon, variety AF-646, was cultivated in a flat experimental area (20 × 50 m). The crop was spaced at 2.00 m between rows and 0.35 m between plants, in a total of ten 50-m-long plant rows. At points corresponding to ⅓ and ⅔ of each plant row, four tensiometers (at a distance of 0.1 m from each other) were set up at the depths of 0.1, 0.2, 0.3, and 0.4 m, adjacent to the irrigation line (0.1 m from the plant row), between two selected plants. Five random plant rows were mulched using dry leaves of banana (Musa sp.) along the drip line, forming a 0.5-m-wide strip, which covered an area of 25 m2 per of plant row with covered soil. In the other five rows, there was no covering. Thus, the experiment consisted of two treatments, with 10 replicates, in four phenological stages: initial (7-22 DAS - days after sowing), growing (22-40 DAS), fruiting (40-58 DAS) and maturation (58-70 DAS). Rainfall was measured with a rain gauge and water storage was estimated by the trapezoidal method, based on tensiometer readings and soil water retention curves. For soil water flux densities at 0.3 m, the tensiometers at the depths of 0.2, 0.3, and 0.4 m were considered; the tensiometer at 0.3 m was used to estimate soil water content from the soil water retention curve at this depth, and the other two to calculate the total potential gradient. Flux densities were calculated through use of the Darcy-Buckingham equation, with hydraulic conductivity determined by the instantaneous profile method. Crop actual evapotranspiration was calculated as the unknown of the soil water balance equation. The soil water balance method is effective in estimating the actual evapotranspiration of irrigated muskmelon; there was no significant effect of soil coverage on capillary rise, internal drainage, crop actual evapotranspiration, and muskmelon yield compared with the uncovered soil; the transport of water caused by evaporation in the uncovered soil was controlled by the break in capillarity at the soil-atmosphere interface, which caused similar water dynamics for both management practices applied.

Effect of soil-water tension on herbaceous cotton yield

A field experiment was conducted during two years, 1990/91, in an alluvial soil, in the State of Paraíba, Brazil, to study the effect of the levels of soil-water tension, 50, 100, 200, 300, 400 and 600 kPa, at 20 cm depth, on upland cotton (Gossypium hirsutum L.r. latifolium Hutch, cv. CNPA-6H) yield. The experimental design was a complete randomized block with six treatments and four repetitions. There was an effect of the treatments on plant height, leaf area index and cotton yield, but the precocity index was not modified. Water should be applied when the soil-water tension, measured at 20 cm depth, reaches values around 200 kPa. There was a quadratic (R² = 0.893**) response of cotton yields to soil water tension, with the maximum when water was applied at 52% of soil water depletion.

Combining ability of twelve maize populations

Genetic progress depends on germplasm quality and breeding methods. Twelve maize populations and their crosses were evaluated to estimate combining ability and potential to be included as source populations in breeding programs. Plant height, point of insertion of the first ear, number of ears per plant, number of grains per ear, root and stalk lodging and grain yield were studied in two locations in Brazil, during the 1997/98 season. Genotype sum of squares was divided into general (GCA) and specific (SCA) combining ability. Results indicated the existence of genetic divergence for all traits analyzed, where additive effects were predominant. The high heterosis levels observed, mainly in Xanxerê, suggested the environmental influence on the manifestation of this genetic phenomenon. Populations revealed potential to be used in breeding programs; however, those more intensively submitted to selection could provide larger genetic progress, showing the importance of population improvement for the increment of the heterosis in maize.

Thidiazuron effects on shoot growth, return bloom, fruit set and nutrition of apples

Apple (Malus domestica Borkh.) trees, cultivars Gala and Fuji, were sprayed at full bloom with thidiazuron (TDZ) at doses of 0, 5, 10, or 20 g ha-1 of a.i. in order to evaluate its effects on plant growth and development, return bloom, fruit set, nutrition, and fruit yield. Fruit set increased with TDZ dose in 'Gala' but not in 'Fuji'. TDZ did not affect fruit yield in any cultivar. In 'Gala', the return bloom was reduced in about 50% at TDZ doses of 10 or 20 g ha-1. TDZ increased shoot growth in both cultivars. In leaves, TDZ decreased the concentration of Ca and Mg in 'Gala' and of Mg in 'Fuji', but did not affect the chlorophyll content, leaf area, length, width, and dry mass per cm² regardless of cultivar. In fruits, the effect of TDZ varied according to the portion evaluated. Highest doses of TDZ decreased the concentration of Ca and K in 'Gala' and of K in 'Fuji' in the entire fruits (flesh + skin); in the skin, highest doses of TDZ reduced the levels of N, Ca, and Mg in both cultivars, in addition to the level of K in 'Fuji'.

Simulation of growth and development of irrigated cowpea in Piauí State by CROPGRO model

The objective of this work was to adapt the CROPGRO model, which is part of the DSSAT system, for simulating the cowpea (Vigna unguiculata) growth and development under soil and climate conditions of the Baixo Parnaíba region, Piauí State, Brazil. In the CROPGRO, only input parameters that define crop species, cultivars, and ecotype were changed in order to characterize the cowpea crop. Soil and climate files were created for the considered site. Field experiments without water deficit were used to calibrate the model. In these experiments, dry matter (DM), leaf area index (LAI), yield components and grain yield of cowpea (cv. BR 14 Mulato) were evaluated. The results showed good fit for DM and LAI estimates. The medium values of R² and medium absolute error (MAE) were, respectively, 0.95 and 264.9 kg ha-1 for DM, and 0.97 and 0.22 for LAI. The difference between observed and simulated values of plant phenology varied from 0 to 3 days. The model also presented good performance for yield components simulation, excluding 100-grain weight, for which the error ranged from 20.9% to 34.3%. Considering the medium values of crop yield in two years, the model presented an error from 5.6%.

Cultivar response to fungicide application in relation to rice blast control, productivity and sustainability

Four field trials were conducted, from 1995 to 1997, with the objective of studying the response of four upland cultivars to foliar fungicide application in relation to panicle blast control, grain yield and sustainability. Differential disease control and yield response of cultivars to fungicide treatment were obtained. Losses in grain yield of cultivars IAC 202, Caiapó, Rio Paranaíba and Araguaia due to panicle blast were 44.8%, 27.4%, 24.4% and 18.2%, respectively. Two applications of tricyclazole or benomyl controlled panicle blast, as indicated by lower values of disease progress curve and relative panicle blast severity, and increased grain yield of the cultivar IAC 202. The losses in 100 panicle grain weight and grain yield were significantly reduced by 22.3% and 25.1% in IAC 202 and 23.6% and 20.5% in Caiapó, respectively, with two sprays of tricyclazole. Sustainable value index for yield was maximum with two applications of tricyclazole (0.59), followed by one application at booting (0.46) and at heading (0.40) in cultivar IAC 202. Results showed no yield response of the cultivars Rio Paranaíba and Araguaia to fungicide applications for panicle blast control.

Sweet orange trees grafted on selected rootstocks fertilized with nitrogen, phosphorus and potassium

The majority of citrus trees in Brazil are grafted on 'Rangpur lime' (Citrus limonia Osb.) rootstock. Despite its good horticultural performance, search for disease tolerant rootstock varieties to improve yield and longevity of citrus groves has increased. The objective of this work was to evaluate yield efficiency of sweet oranges on different rootstocks fertilized with N, P, and potassium. Tree growth was affected by rootstock varieties; trees on 'Swingle' citrumelo [Poncirus trifoliata (L.) Raf. × C. paradisi Macf.] presented the smallest canopy (13.3 m³ in the fifth year after tree planting) compared to those on 'Rangpur lime' and 'Cleopatra' mandarin [C. reshni (Hayata) hort. ex Tanaka] grown on the same grove. Although it was observed an overall positive relationship between canopy volume and fruit yield (R² = 0.95**), yield efficiency (kg m-3) was affected by rootstocks, which demonstrated 'Rangpur lime' superiority in relation to Cleopatra. Growth of citrus trees younger than 5-yr-old might be improved by K fertilization rates greater than currently recommended in Brazil, in soils with low K and subjected to nutrient leaching losses.

Combining ability and heterosis in common bean cultivars

The objective of this work was to determine the combining ability and heterosis, for productivity and yield components, in diallel hybrids derived from crossings between BRSMG-Talismã, IPR Uirapuru, FT Soberano, BRS Campeiro, IAC Tybatã, and IPR Juriti parent cultivars. Fifteen hybrids were generated from diallel crosses, excluding reciprocals. The general and specific combining abilities were significant for plant height, number of pods per plant, number of seeds per plant, number of seeds per pod, 50-seed weight, and grain yield, indicating the occurrence of both additive and nonadditive genetic effects. The best strategy to be adopted is the use of BRS Campeiro, FT Soberano and BRSMG-Talismã cultivars in common bean breeding programs involving selection. The most promising combinations were 'IPR Uirapuru' x 'IAC Tybatã', 'IPR Uirapuru' x 'FT Soberano', 'BRS Campeiro' x 'IPR Juriti', and 'BRS Campeiro' x 'IAC Tybatã'. The parents of these hybrids presented high estimates of specific combining abilities. Hybridization of cultivars belonging to distinguished commercial groups propitiates higher heterosis values in the segregant population.

Combining ability of maize grain yield under different levels of environmental stress

The objectives of this work were to caracterize the tropical maize germplasm and to compare the combining abilities of maize grain yield under different levels of environmental stress. A diallel was performed among tropical maize cultivars with wide adaptability, whose hybrid combinations were evaluated in two sowing dates, in two years. The significance of the environmental effect emphasized the environmental contrasts. Based on grain yield, the environments were classified as favorable (8,331 kg ha-1), low stress (6,637 kg ha-1), high stress (5,495 kg ha-1), and intense stress (2,443 kg ha-1). None of the genetic effects were significant in favorable and intense stress environments, indicating that there was low germplasm variability under these conditions. In low and high stresses, the specific combining ability effects (SCA) were significant, showing that the nonadditive genetic effects were the most important, and that it is possible to select parent pairs with breeding potential. SCA and grain yield showed significant correlations only between the closer environment pairs like favorable/low stress and high/intense stress. The genetic control of grain yield differed under contrasting stress environments for which maize cultivars with wide adaptability are not adequate.

Heliotropic responses of soybean cultivars at three phenological stages and under two water regimes

The objectives of this work were to determine the heliotropic movements of the upper trifoliates for two soybean cultivars, BR 16 and Embrapa 48, during a daily cycle, in three phenological stages and two water regimes, and to estimate the impact of irrigation and daily leaflet movements on agronomic characteristics and grain yield. Heliotropic movements were studied in three phenological stages: V4-V6, V7-V10, and R5 in irrigated and non-irrigated plots. For each stage, the leaflet elevation and azimuth were measured hourly. Under a low (V4-V6 stage) and mid (V7-V10 stage) leaf area index (LAI) the diaheliotropism was slightly more frequent and intensive in non-irrigated than in irrigated plants, only at early morning and late afternoon hours. At R5 stage (high LAI) the paraheliotropism of superior trifoliates was predominant and more intensive in non-irrigated plants. The heliotropic movements are correlated to carbon gain, but not to environment (light intensity or temperature), for measurements at 11h. 'Embrapa 48' expresses greater paraheliotropism than 'BR 16' at high LAI, while 'BR 16' displays lower heliotropic plasticity under irrigation. In spite of significant heliotropic differences, genotype and water availability treatments did not influence the final grain yield.

Prediction of direct and indirect genetic gains and genotypic correlations in rubber tree progenies

The objective of this work was to estimate the genetic parameters, genotypic and phenotypic correlations, and direct and indirect genetic gains among and within rubber tree (Hevea brasiliensis) progenies. The experiment was set up at the Municipality of Jaú, SP, Brazil. A randomized complete block design was used, with 22 treatments (progenies), 6 replicates, and 10 plants per plot at a spacing of 3x3 m. Three‑year‑old progenies were assessed for girth, rubber yield, and bark thickness by direct and indirect gains and genotypic correlations. The number of latex vessel rings showed the best correlations, correlating positively and significantly with girth and bark thickness. Selection gains among progenies were greater than within progeny for all the variables analyzed. Total gains obtained were high, especially for girth increase and rubber yield, which were 93.38 and 105.95%, respectively. Young progeny selection can maximize the expected genetic gains, reducing the rubber tree selection cycle.

Dual-purpose wheat grain and animal production under different grazing periods

The objective of this work was to evaluate the influence of different grazing periods on beef animal production and on wheat forage and grain yield. The experiment was carried out in Pato Branco, PR, Brazil. Six grazing periods were evaluated (0, 21, 42, 63, 84, and 105 days) on dual-purpose wheat cultivar BRS Tarumã. Purunã steers, with average live weight of 162 kg and ten months of age, were kept under continuous grazing using a variable stocking rate, in order to maintain the established sward height of 25 cm. Greater increases in total animal gain (TAG) occurred with longer grazing periods. However, there was little increase after 63 days (490 kg ha-1), and TAG decreased from 552 to 448 kg ha-1 between 84 and 105 days. Grain yield decreased from 2,830 to 610 kg ha-1 when the grazing period increased from 0 to 105 days, but there was little change after 63 days (750 kg ha-1). Cultivar BRS Tarumã shows excellent animal production potential, and the decision on how long wheat pastures should be grazed must be based on relative prices of grain and livestock.