Phosphorus extracted by ion exchange resins and mehlich-1 from oxisols (latosols) treated with different phosphorus rates and sources for varied soil-source contact periods

Despite the large number of studies addressing the quantification of phosphorus (P) availability by different extraction methods, many questions remain unanswered. The aim of this paper was to compare the effectiveness of the extractors Mehlich-1, Anionic Resin (AR) and Mixed Resin (MR), to determine the availability of P under different experimental conditions. The laboratory study was arranged in randomized blocks in a [(3 x 3 x 2) + 3] x 4 factorial design, with four replications, testing the response of three soils with different texture: a very clayey Red Latosol (LV), a sandy clay loam Red Yellow Latosol (LVA), and a sandy loam Yellow Latosol (LA), to three sources (triple superphosphate, reactive phosphate rock from Gafsa-Tunisia; and natural phosphate from Araxá-Minas Gerais) at two P rates (75 and 150 mg dm-3), plus three control treatments (each soil without P application) after four contact periods (15, 30, 60, and 120 days) of the P sources with soil. The soil acidity of LV and LVA was adjusted by raising base saturation to 60 % with the application of CaCO3 and MgCO3 at a 4:1 molar ratio (LA required no correction). These samples were maintained at field moisture capacity for 30 days. After the contact periods, the samples were collected to quantify the available P concentrations by the three extractants. In general, all three indicated that the available P-content in soils was reduced after longer contact periods with the P sources. Of the three sources, this reduction was most pronounced for triple superphosphate, intermediate for reactive phosphate, while Araxá phosphate was least sensitive to the effect of time. It was observed that AR extracted lower P levels from all three soils when the sources were phosphate rocks, while MR extracted values close to Mehlich-1 in LV (clay) and LVA (medium texture) for reactive phosphate. For Araxá phosphate, much higher P values were determined by Mehlich-1 than by the resins, because of the acidity of the extractor. For triple superphosphate, both resins extracted higher P levels than Mehlich-1, due to the consumption of this extractor, particularly when used for LV and LVA.

Symbiotic capability of calopo rhizobia from an agrisoil with different crops in Pernambuco

Biological nitrogen fixation by rhizobium-legume symbiosis represents one of the most important nitrogen sources for plants and depends strongly on the symbiotic efficiency of the rhizobium strain. This study evaluated the symbiotic capacity of rhizobial isolates from calopo (CALOPOGONIUM MUCUNOIDES) taken from an agrisoil under BRACHIARIA DECUMBENS pasture, sabiá (MIMOSA CAESALPINIIFOLIA) plantations and Atlantic Forest areas of the Dry Forest Zone of Pernambuco. A total of 1,575 isolates were obtained from 398 groups. A single random isolate of each group was authenticated, in randomized blocks with two replications. Each plant was inoculated with 1 mL of a bacterial broth, containing an estimated population of 10(8) rhizobial cells mL-1. Forty-five days after inoculation, the plants were harvested, separated into shoots, roots and nodules, oven-dried to constant mass, and weighed. Next, the symbiotic capability was tested with 1.5 kg of an autoclaved sand:vermiculite (1:1) mixture in polyethylene bags. The treatments consisted of 122 authenticated isolates, selected based on the shoot dry matter, five uninoculated controls (treated with 0, 50, 100, 150, or 200 kg ha-1 N) and a control inoculated with SEMIA 6152 (=BR1602), a strain of BRADYRHIZOBIUM JAPONICUM The test was performed as described above. The shoot dry matter of the plants inoculated with the most effective isolates did not differ from that of plants treated with 150 kg ha-1 N. Shoot dry matter was positively correlated with all other variables. The proportion of effective isolates was highest among isolates from SABIÁ forests. There was great variation in nodule dry weight, as well as in N contents and total N.

Soil physical properties and grape yield influenced by cover crops and management systems

The use of cover crops in vineyards is a conservation practice with the purpose of reducing soil erosion and improving the soil physical quality. The objective of this study was to evaluate cover crop species and management systems on soil physical properties and grape yield. The experiment was carried out in Bento Gonçalves, RS, Southern Brazil, on a Haplic Cambisol, in a vineyard established in 1989, using White and Rose Niagara grape (Vitis labrusca L.) in a horizontal, overhead trellis system. The treatments were established in 2002, consisting of three cover crops: spontaneous species (SS), black oat (Avena strigosa Schreb) (BO), and a mixture of white clover (Trifolium repens L.), red clover (Trifolium pratense L.) and annual rye-grass (Lolium multiflorum L.) (MC). Two management systems were applied: desiccation with herbicide (D) and mechanical mowing (M). Soil under a native forest (NF) area was collected as a reference. The experimental design consisted of completely randomized blocks, with three replications. The soil physical properties in the vine rows were not influenced by cover crops and were similar to the native forest, with good quality of the soil structure. In the inter-rows, however, there was a reduction in biopores, macroporosity, total porosity and an increase in soil density, related to the compaction of the surface soil layer. The M system increased soil aggregate stability compared to the D system. The treatments affected grapevine yield only in years with excess or irregular rainfall.

Arsenic toxicity in Acacia mangium willd. and mimosa Caesalpiniaefolia benth. seedlings

Acacia mangium and Mimosa caesalpiniaefolia are fast-growing woody fabaceous species that might be suitable for phytoremediation of arsenic (As)-contaminated sites. To date, few studies on their tolerance to As toxicity have been published. Therefore, this study assessed As toxicity symptoms in A. mangium and M. caesalpiniaefolia seedlings under As stress in a greenhouse. Seedlings of Acacia mangium and M. caesalpiniaefolia were grown for 120 d in an Oxisol-sand mixture with 0, 50, 100, 200, and 400 mg kg-1 As, in four replications in four randomized blocks. The plants were assessed for visible toxicity symptoms, dry matter production, shoot/root ratio, root anatomy and As uptake. Analyses of variance and regression showed that the growth of A. mangium and M. caesalpiniaefolia was severely hindered by As, with a reduction in dry matter production of more than 80 % at the highest As rate. The root/shoot ratio increased with increasing As rates. At a rate of 400 mg kg-1 As, whitish chlorosis appeared on Mimosa caesalpiniaefolia seedlings. The root anatomy of both species was altered, resulting in cell collapse, death of root buds and accumulation of phenolic compounds. Arsenic concentration was several times greater in roots than in shoots, with more than 150 and 350 mg kg-1 in M. caesalpiniaefolia and A. mangium roots, respectively. These species could be suitable for phytostabilization of As-contaminated sites, but growth-stimulating measures should be used.

Arbuscular mycorrhizal fungal communities and soil aggregation as affected by cultivation of various crops during the sugarcane fallow period

Management systems involving crop rotation, ground cover species and reduced soil tillage can improve the soil physical and biological properties and reduce degradation. The primary purpose of this study was to assess the effect of various crops grown during the sugarcane fallow period on the production of glomalin and arbuscular mycorrhizal fungi in two Latosols, as well as their influence on soil aggregation. The experiment was conducted on an eutroferric Red Latosol with high-clay texture (680 g clay kg-1) and an acric Red Latosol with clayey texture (440 g kg-1 clay) in Jaboticabal (São Paulo State, Brazil). A randomized block design involving five blocks and four crops [soybean (S), soybean/fallow/soybean (SFS), soybean/millet/soybean (SMS) and soybean/sunn hemp/soybean (SHS)] was used to this end. Soil samples for analysis were collected in June 2011. No significant differences in total glomalin production were detected between the soils after the different crops. However, total external mycelium length was greater in the soils under SMS and SHS. Also, there were differences in easily extractable glomalin, total glomalin and aggregate stability, which were all greater in the eutroferric Red Latosol than in the acric Red Latosol. None of the cover crops planted in the fallow period of sugarcane improved aggregate stability in either Latosol.

Ammonia volatilization and yield components after application of polymer-coated urea to maize

A form of increasing the efficiency of N fertilizer is by coating urea with polymers to reduce ammonia volatilization. The aim of this study was to evaluate the effect of polymer-coated urea on the control of ammonia volatilization, yield and nutritional characteristics of maize. The experiment was carried out during one maize growing cycle in 2009/10 on a Geric Ferralsol, inUberlândia, MG, Brazil. Nitrogen fertilizers were applied as topdressing on the soil surface in the following urea treatments: polymer-coated urea at rates of 45, 67.5 and 90 kg ha-1 N and one control treatment (no N), in randomized blocks with four replications. Nitrogen application had a favorable effect on N concentrations in leaves and grains, Soil Plant Analysis Development (SPAD) chlorophyll meter readings and on grain yield, where as coated urea had no effect on the volatilization rates, SPAD readings and N leaf and grain concentration, nor on grain yield in comparison to conventional fertilization.

Phosphorus availability in oxidic soils treated with lime and silicate applications

Based on the assumption that silicate application can raise soil P availability for crops, the aim of this research was to compare the effect of silicate application on soil P desorption with that of liming, in evaluations based on two extractors and plant growth. The experiment was carried out in randomized blocks with four replications, in a 3 × 3 × 5 factorial design, in which three soil types, three P rates, and four soil acidity correctives were evaluated in 180 experimental plots. Trials were performed in a greenhouse using corn plants in 20-dm³ pots. Three P rates (0, 50 and 150 mg dm-3) were applied in the form of powder triple superphosphate and the soil was incubated for 90 days. After this period, soil samples were collected for routine chemical analysis and P content determination by the extraction methods resin, Mehlich-1 and remaining P. Based on the results, acidity correctives were applied at rates calculated for base saturation increased to 70 %, with subsequent incubation for 60 more days, when P content was determined again. The acidity correctives consisted of: dolomitic lime, steelmaking slag, ladle furnace slag, and wollastonite. Therefore, our results showed that slags raised the soil P content more than lime, suggesting a positive correlation between P and Si in soil. Silicon did not affect the extractor choice since both Mehlich-1 and resin had the same behavior regarding extracted P when silicon was applied to the soil. For all evaluated plant parameters, there was significant interaction between P rates and correctives; highest values were obtained with silicate.

Effect of potassium sources on the antioxidant activity of eggplant¹

Potassium participates in the essential processes in plant physiology, however, the effects of K sources on plant metabolism have been little studied. Also, in certain cases, K sources and concentrations may cause undesirable effects, e.g., soil salinization. The objective was to evaluate the effect of K sources and levels on the enzyme activity of the antioxidant system and protein content in eggplant (Solanum melongena L.) leaves and to determine the most suitable K sources for these physiological characteristics. The experiment was conducted in randomized blocks, in a 2 × 4 factorial design, consisting of two K sources (KCl and K2SO4) and rates (250, 500, 750, and 1000 kg ha-1 K2O), with four replications. The following variables were evaluated: plant height, number of leaves per plant, superoxide dismutase (SOD), catalase (CAT), and leaf protein content. There was an increase in CAT activity with increasing K levels until 30 days after transplanting (DAT), when K2SO4 was applied and until 60 DAT, when KCl was used; after this period, the enzyme activity decreased under both sources. The activity of SOD increased in the presence of KCl, but was reduced with the application of K2SO4. For both K sources, increasing rates reduced the protein content and number of leaves per plant, and this reduction was greater under KCl application. Thus it was concluded that KCl tends more strongly to salinize the soil than K2SO4. Both for KCl and for K2SO4, the increasing rates adversely affected the activities of CAT and SOD and the levels of leaf protein in eggplant. The potential of KCl to reduce the enzyme activity of SOD and CAT, leaf protein content and plant growth of eggplant was stronger than that of K2SO4.

MORPHOLOGICAL AND MICROMORPHOLOGICAL CHANGES IN THE STRUCTURE OF A RHODIC HAPLUDOX AS A RESULT OF AGRICULTURAL MANAGEMENT

In evaluation of soil quality for agricultural use, soil structure is one of the most important properties, which is influenced not only by climate, biological activity, and management practices but also by mechanical and physico-chemical forces acting in the soil. The purpose of this study was to evaluate the influence of conventional agricultural management on the structure and microstructure of a Latossolo Vermelho distroférrico típico (Rhodic Hapludox) in an experimental area planted to maize. Soil morphology was described using the crop profile method by identifying the distinct structural volumes called Morphologically Homogeneous Units (MHUs). For comparison, we also described a profile in an adjacent area without agricultural use and under natural regrowth referred to as Memory. We took undisturbed samples from the main MHUs so as to form thin sections and blocks of soil for micromorphological and micromorphometrical analyses. Results from the application of the crop profile method showed the occurrence of the following structural types: loose (L), fragmented (F) and continuous (C) in both profiles analyzed. In the Memory soil profile, the fragmented structures were classified as Fptμ∆+tf and Fmt∆μ, whose micromorphology shows an enaulic-porphyric (porous) relative distribution with a great deal of biological activity as indicated by the presence of vughs and channels. Lower down, from 0.20 to 0.35 m, there was a continuous soil volume (sub-type C∆μ), with a subangular block microstructure and an enaulic-porphyric relative distribution, though in this case more compact and with aggregate coalescence and less biological activity. The micromorphometrical study of the soil of the Memory Plot showed the predominance of complex pores in NAM (15.03 %), Fmt∆μ (11.72 %), and Fptμ∆+tf (7.73 %), and rounded pores in C∆μ (8.21 %). In the soil under conventional agricultural management, we observed fragmented structures similar to the Memory Plot from 0.02 to 0.20 m, followed by a volume with a compact continuous structure (C∆μ), without visible porosity and with few roots. In the MHUs under conventional management, reduction in the packing pores (40 %) was observed, mainly in the continuous units (C). The microstructure had well-defined blocks, with the occurrence of planar pores and less evidence of biological activity. In conclusion, the morphological and micromorphological analyses of the soil profiles studied offered complementary information regarding soil structural quality, especially concerning the changes in pore types as result of mechanical stress undergone by the soil.

NUTRIENT DEMAND BY THE CARROT CROP IS INFLUENCED BY THE CULTIVAR

Farmers must carefully choose the cultivar to be grown for a successful carrot crop. The yield potential of the cultivar may influence nutrient demand and should be known to plan for fertilization application. The aim of this study was to evaluate the cultivar effect on carrot yield and on the nutrient content and quantities allocated to leaves and roots. Three experiments were set up in two crop seasons in Rio Paranaíba, MG, Brazil. In the first season, typical summer, 10 summer cultivars were sown. In the second season, summer-winter (transition), two experiments were set up, one with summer cultivars and the other with winter cultivars. The treatments consisted of the carrot cultivars distributed in randomized blocks with four replications. Fresh and dry matter of the roots and leaves was quantified. Yield was calculated based on fresh matter of the roots. The nutrient content in leaves and roots was determined at the time of harvest. These contents and the dry matter production of roots and leaves were used to calculate nutrient uptake and export. The greatest average for total and commercial yield occurred in the crop under summer conditions. Extraction of N and K for most of the cultivars in the three experiments went beyond the amounts applied through fertilizers. Thus, there was contribution of nutrients from the soil to obtain the yields observed. However, the amount of P taken up was considerably less than that applied. This implies that soil P fertility will increase after cropping. The crop season and the cultivars influenced yield, nutrient content in the leaves and roots, and extraction and export of nutrients by the carrot crop.

Hydro-Physical Properties of a Typic Hapludult under the Effect of Rice Husk Ash

ABSTRACT The combustion of rice husk generates a partially burnt mixture called rice husk ash (RHA) that can be used as a source of nutrients to crops and as a conditioner of soil physical properties. The objective of this study was to evaluate the effect of RHA levels on the hydro-physical properties of a Typic Hapludult. The experimental design was composed of random blocks with four replications, which comprised plots of 24 m2 and treatments with increasing RHA rates: 0, 40, 80 and 120 Mg ha-1. Undisturbed soil samples were collected in the soil layers of 0.00-0.10 and 0.10-0.20 m after nine months of RHA application, using steel cylinders (0.03 m of height and 0.047 m of diameter). These samples were used to determine soil bulk density (Bd), total soil porosity (TP), soil macroporosity (Ma), soil microporosity (Mi) and the available water capacity (AWC). Disturbed soil samples were collected to determine the stability of soil aggregates in water, mean weight diameter of water stable aggregates (MWD), and soil particle size distribution. The results show that, as the RHA rate increased in the soil, Bd values decreased and TP, Ma and MWD values increased. No effect of RHA was found on Mi and AWC values. The effects of RHA on the S parameter (Dexter, 2004), precompression stress and compression index (Dias Junior and Pierce, 1995) values are consistent those shown for density and total porosity. Rice husk ash was shown to be an efficient residue to improve soil physical properties, mainly at rates between 40 and 80 Mg ha-1. Rice husk ash reduces bulk density and increases total porosity, macroporosity and soil aggregation, but does not affect microporosity, field capacity, permanent wilting point, and available water capacity of the soil. The effect of rice husk ash on the S parameter, precompression stress and index compressibility coefficient values are consistent with those observed for the bulk density and total porosity.

Effect of soil interacting herbicides on soybean nodulation in Balcarce, Argentina

Two trials were performed in Balcarce, Argentina (37° 45' LS; 58° 18' LW) during 1993-94, to assess the effect of eight herbicides applied individually or in tank mixtures, on nodule number, nodule dry weight, seed yield and N percent in seed in soybean Asgrow 3205, inoculated with Bradyrhizobium japonicum CB 1809. Individual herbicides and doses in kg ha-1 of a.i. were metribuzin (0.48), acetochlor (0.90), metolachlor (1), flumioxazin (0.075), trifluralin (0.96), imazaquin (0.20), imazethapyr (0.10) and chlorimuron ethyl (0.0125). The mixtures were metribuzin+acetochlor (0.48+0.9), flumioxazin+acetochlor (0.075+0.9), imazaquin+acetochlor (0.2+0.9), metribuzin+metolachlor (0.48+1.92), and flumioxazin+ metolachlor (0.075+1.92). A control treatment without herbicides was included. Both trials were laid out as randomized complete blocks with four replicates, on a loam illitic thermic petrocalcic Paleudoll, 5.7% organic matter (OM), 25% clay, 30.4 cmol kg-1 CEC. Nodules were sampled at V2 (second node), V6 (sixth node) and R5 (beginning seed) growth stages. Herbicides did not significantly affect the beginning of nodulation or nodule number and mass at R5, not either grain yield or N accumulation. This indicates lack of interference between soil interacting herbicides and N fixation in the high organic matter, loam soils of SE Buenos Aires province, even though a tendency in less number and dry weight of nodules was evident at the two latter growth stages.

Analysis of experiments in square lattice with emphasis on variance components. i. Individual analysis

This paper focused on four alternatives of analysis of experiments in square lattice as far as the estimation of variance components and some genetic parameters are concerned: 1) intra-block analysis with adjusted treatment and blocks within unadjusted repetitions; 2) lattice analysis as complete randomized blocks; 3) intrablock analysis with unadjusted treatment and blocks within adjusted repetitions; 4) lattice analysis as complete randomized blocks, by utilizing the adjusted means of treatments, obtained from the analysis with recovery of interblock information, having as mean square of the error the mean effective variance of this same analysis with recovery of inter-block information. For the four alternatives of analysis, the estimators and estimates were obtained for the variance components and heritability coefficients. The classification of material was also studied. The present study suggests that for each experiment and depending of the objectives of the analysis, one should observe which alternative of analysis is preferable, mainly in cases where a negative estimate is obtained for the variance component due to effects of blocks within adjusted repetitions.

Agronomic performance of quinoa selected in the Brazilian Savannah

Twenty six breeding lines, selected from individual plant progenies of hybrids among varieties Amarilla de Marangani, Blanca de Junín, Chewecca, Faro 4, Improved Baer, Kancolla, Real, and Salares-Roja, had their agronomic characters evaluated, in Planaltina, DF, Brazil (15º36'S and 47º12'W), 1,000 masl, in randomized complete blocks, on a Ferralsol, previously limed and fertilized. Grain yield was positively associated with plant height, inflorescence length and diameter, and plant cycle. Genetic gain can be attained by selection based in these characters for commercial production of quinoa in tropical regions.

Designs and model effects definitions in the initial stage of a plant breeding program

The objective of this work was to compare the relative efficiency of initial selection and genetic parameter estimation, using augmented blocks design (ABD), augmented blocks twice replicated design (DABD) and group of randomised block design experiments with common treatments (ERBCT), by simulations, considering fixed effect model and mixed model with regular treatment effects as random. For the simulations, eight different conditions (scenarios) were considered. From the 600 simulations in each scenario, the mean percentage selection coincidence, the Pearsons´s correlation estimates between adjusted means for the fixed effects model, and the heritability estimates for the mixed model were evaluated. DABD and ERBCT were very similar in their comparisons and slightly superior to ABD. Considering the initial stages of selection in a plant breeding program, ABD is a good alternative for selecting superior genotypes, although none of the designs had been effective to estimate heritability in all the different scenarios evaluated.