Phosphorus and potassium balance in soil under crop rotation and fertilization

The use of crop rotation and manure application can provide sustainability for an agricultural production system by improving soil quality and increasing nutrient use efficiency. This study aimed to evaluate the effect of mineral, organic and mineral+organic fertilization on grain yield and on soil phosphorus and potassium balance, in two crop systems under no-till, with and without rotation of cover crops. The experiment was carried out from 2006 to 2008 on a clayey Rhodic Hapludox in Marechal Candido Rondon, Parana State, Brazil. The cropping sequence in the rotation system involving cover crops was black oat + hairy vetch + forage turnip/corn/pigeon pea/wheat/mucuna + brachiaria + sunn hemp, and in the succession system was wheat/corn/wheat/soybean. Organic and mineral+organic fertilizations consisted of the application of solely manure and manure combined with mineral fertilizer, respectively. Soil P and K balances were calculated after the second year of the experiment, up to a depth of 0.40 m. First year corn yields were higher in the crop succession system accompanied by mineral fertilization. In the second year, wheat and soybean yield did not vary between crop systems and nutrient sources, demonstrating the residual effect of crop rotation and manure use. Crop rotation with cover crops resulted in an increase in soil K levels by promoting the recycling of this nutrient in the soil. In both crop systems, the application of mineral and organic fertilizers - either in isolation or in combination - resulted in a negative soil P and K balance in the short term. This represents a threat to the sustainability of the agricultural production system in the long term, due to the depletion of soil nutrient reserves.

Inter-relation between soybean yield and soil compaction under degraded pasture in Brazilian Savannah

As pastagens cultivadas do Cerrado brasileiro são responsáveis pela metade da produtividade da carne bovina destinada à alimentação da população, enquanto as culturas agrícolas o são pela terça parte de sua produtividade de grãos, desempenhando importante papel econômico-financeiro para o país. Dessa forma, no ano agrícola 2005/2006, na Fazenda de Ensino e Pesquisa da Faculdade de Engenharia de Ilha Solteira - FEIS/UNESP, foram estudadas a variabilidade e a dependência espacial entre atributos físicos do solo e a produtividade da soja, quando rotacionados após a pastagem degradada com Brachiaria, sobre um Latossolo Vermelho distroférrico. Também foram estudadas correlações lineares e espaciais entre esses atributos, apurando condições que proporcionassem aumento da produtividade agrícola. Para isso, na área com a referida pastagem instalou-se uma malha contendo 124 pontos amostrais, com espaçamentos de 10,0 x 10,0 e de 5,0 x 5,0 m entre eles, numa área total de 7.500 m². Dos pontos de vista linear e espacial, a elevada produtividade de grãos de soja pode ser explicada em razão do número de grãos por planta e da macroporosidade do solo. A alta variabilidade obtida na maioria dos atributos do solo denotou que a integração lavoura-pecuária é um sistema que proporciona heterogeneidade do ambiente físico do solo.

Mites (Acari: Mesostigmata, Sarcoptiformes and Trombidiformes) associated to soybean in Brazil, including new records from the cerrado areas

In Brazil, soybean Glycine max (L.) Merril crops are subjected to incidence of several pests, which are mainly insect species. However, the occurrences of other pest species are growing. In this context, outbreaks of phytophagous mites are becoming more frequent. Nevertheless, records of mites in such crop are available only for Maranhao, Mato Grosso, Minas Gerais and Rio Grande do Sul states. Thus, this work gathers all information published about the diversity of mites found in soybean in Brazil, and also new records of mite species made on samplings taken from the central Cerrado area. In the whole, occurrence of 44 species of plant mites in soybean has been recorded in Brazil. Data from prior studies and the results of this work present the tetranychid Mononychellus planki (McGregor) as the mite species most frequently occurring in the Brazilian soybean crops. A large portion of Phytoseiidae species has occurred in crops from Rio Grande do Sul state. In addition, spontaneous soybean has hosted almost half of the phytoseiid species sampled in Cerrado region. High diversity of Tarsonemidae has been found in the cultivated soybean. More studies about soybean mites are needed to clarify the damage potential of phytophagous mites and the biological role of predatory mites in this crop.

Gibberellin and cytokinin effects on soybean growth

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of the type of environmental stress on the emergence of sunflower (Helianthus annus L.), soybean (Glycine max (L.) Merril) and maize (Zea mays L.) seeds with different levels of vigor

Sowing is a critical time in the cycle of a crop and the seeds are frequently exposed to adverse conditions that may compromise the establishment of seedlings in the field. on this basis, the objective of the present study was to determine the effect of types of environmental stress on the emergence of sunflower, maize and soybean seeds with different levels of vigor. High vigor seeds were artificially aged in order to obtain medium and low vigor seeds and then they were sown in clay soil in plastic boxes and submitted to the following types of environmental stress during the germination process : 1) high temperature (35degreesC), 2) low temperature (15 or 18degreesC), 3) water excess (Psi > -0.0001 MPa), 4) water deficiency (Psi approximately equal to -1.1; -1.2 and -0.6 MPa for sunflower, maize and soybean, respectively), 5) sowing at a depth of 7 cm and 6) pathogenic infection of sunflower seeds with Alternaria helianthi, of maize seeds with Fusarium moniliforme and of soybean seeds with Colletotrichum dematium, var. truncata. The results were compared to those obtained with controls sown under optimal condition. It was concluded that: 1) the effect of seed vigor on emergence depends on the type of enviromental stress to which the seeds are exposed, 2) the stress to which the the seeds demonstrated highest sensitivity varied with species and 3) high temperature stress was the one that most impaired the emergence of the three species.

Effect of doses of fungicides and plant resistance activators on the control of Rhizoctonia foliar blight of soybean, and on Rhizoctonia solani AG1-IA in vitro development

Rhizoctonia foliar blight (RFB) of soybean [Glycine max (L.) Merrill] occurs in many tropical and subtropical regions, causing yield reductions of up to 70% and in Brazil, up to 60%. The disease is caused by Rhizoetonia solani AG1-IA and AG1-IB, and by AG2-3 in Japan. RFB occurs in the North, Northeast and Mid-west regions of Brazil. Chemical control remains the only effective method of controlling RFB, but its efficiency depends upon environmental conditions. In this study, 18 fungicides, salicylic acid (SA) and acibenzolar-s-methyl (ASM) were evaluated on R. solani AG1-IA in vitro, by mycelial growth rating and estimating effective concentration for 50% (EC 50) and 90% (EC 90) inhibition of mycelial growth, and in vivo by reduction of disease severity on soybean plants in greenhouse conditions. Mycelial growth was strongly inhibited by the fungicides pyraclostrobin + boscalid and fludioxonil. Preventive fungicide applications were the most effective. Strobilurins were more efficient both in preventive and curative applications. Best results with plant resistance activators were obtained with SA (2.5 mM) sprayed at 20 d before inoculation and with ASM (12.5 mg a.i. l(-1)) 10 d before inoculation. (c) 2005 Elsevier Ltd. All rights reserved.

EFFECT OF DROUGHT AND DEFOLIATION STRESS IN THE FIELD ON SOYBEAN SEED-GERMINATION AND VIGOR

Although drought and defoliation stress have been shown to reduce soybean [Glycine max (L.). Merr.] yield, little information has been published regarding their effects on soybean seed quality. Field experiments were conducted in 1986, 1987, and 1989 to evaluate the effect of drought and defoliation (1989 only) stress during soybean seed development on seed germination and vigor. Essex (MG [maturity group] V) and Union (MG III) were grown in 1986 and 1987, and Harper (MG III) and McCall (MG 00) in 1989. Moisture treatments were either well watered or drought stressed during seed development (R5 to R7). In 1989, a total defoliation treatment was also imposed at R6 as an additional stress factor. There were significant reductions in yield and yield components following drought stress in all 3 yr and following defoliation in 1989. Leaf conductance and transpiration also decreased in the drought stress treatments. There was no effect of drought stress on seed germination or seed vigor as measured by accelerated aging germination and the cold test across the four cultivars (determinate and indeterminate) and 3 yr. In 1989 slight changes in 3-d germination and conductivity occurred for some drought stress treatments. Most of this response, however, was related to increased occurrence of hard seed, which does not represent an indication of a change in vigor. Seed germination and vigor were significantly reduced for small, flat, shriveled, and underdeveloped seeds that only occurred following defoliation. These seeds represented a small portion of the seed lot that would normally be removed during conditioning. The data suggest that drought stress would have no effect on seed germination or vigor, unless the stress was severe enough to produce shriveled, flat, underdeveloped seeds.

Effect of Alternaria cassiae, Pseudocercospora nigricans, and soybean (Glycine max) planting density on the biological control of sicklepod (Senna obtusifolia)

The interactions of two fungal biocontrol agents, Alternaria cassiae and Pseudocercospora nigricans, and soybean planting density on sicklepod mortality and dry weight were studied in the field over 2 yr. The experimental field was divided into three equal areas: one without soybean and two where the soybean was sown in densities of 20 and 36 seeds per meter row with a 0.95-m row spacing. The fungi were sprayed alone or in a mixture at three growth stages of sicklepod plants grown at three levels of crop interference resulting from the three soybean planting densities. The fungal treatments were: an untreated control, A. cassiae (105 spores/m2), P. nigricans (3.3 g mycelium/m2), and the mixture of these two fungi. Sicklepod was at the cotyledonary leaf, two-leaf, and four-leaf stages when treated. Alternaria cassiae was most effective in reducing both sicklepod survival and dry weight. The mixture of P. nigricans and A. cassiae was generally comparable to but not better than A. cassiae alone in killing the weed (mortality) and reducing its growth (dry weight). Soybean density did not have significant effects on the mortality or the dry weight of sicklepod. Thus, there is no advantage to combining the highly effective biocontrol agent A. cassiae with the less effective P. nigricans or with soybean interference to control sicklepod. However, the results validate the efficacy of A. cassiae by itself as a bioherbicide.

An alternative field method for screening soybean genotypes for resistance to Heterodera glycines

The soybean cyst nematode (Heterodera glycines) has become an increasingly severe problem in soybean production areas in Brazil. The development and use of resistant cultivars is the most efficient method of minimizing losses due to this pathogen. Our objective was to test the efficiency of an alternative method for screening soybean genotypes for resistance to H. glycines in field plots. The alternative method was compared to the standard method of sowing the test genotypes in fields found to be infested during the previous crop season. In the alternative method, the test genotypes are sown in the furrow following the uprooting of 45-day-old infected plants. The alternative method resulted in twice the cyst population and fewer escapes, and more consistent results than the standard method. The major advantage of the alternative method is that it permits screening in a more homogeneous distribution of H. glycines in the soil.

Analysis of combining ability in soybean cultivars

Eight soybean cultivars (Doko, Bossier, Ocepar-4, BR-15, FT-Cometa, Savana, Paraná and Cristalina) were crossed in a diallel design. Plants of the F1 generation and their parents were evaluated under short-day conditions for the determination of the general (GCA) and specific (SCA) combining ability. The estimated GCA and SCA values were significant for the evaluated traits except for the total cycle. Highest GCA effects for the traits days to flowering, plant height, insertion height, number of branches and total cycle were estimated for the cultivars Doko, Cristalina and Savana. The variability observed in the trait days to flowering can, for the most part, be explained by additive effects.

Path analysis and expected response in indirect selection for grain yield in soybean

This study aimed to determine the best auxiliary trait for indirect selection of soybean grain yield, through path analysis and in avoidance of the adverse effects of multicollinearity and expected response. Seventy-nine F5 soybean genotypes from the cross FT-Cometa x Bossier were used. The populations were distributed on the field was the families inserted with replicated controls. Primary and secondary traits of grain yield were evaluated in four phenotypically superior plants per family. The traits number of pods, height and number of nodes were considered as the most important, showing the best combination of direct effect and genotypic correlation. The number of pods achieved the highest expected gain through the estimation method based on the selection differential. On the other hand, plant height, by the method based on selection intensity, was not a good indicator of the most productive plants.

Development of SCAR marker linked to stem canker resistance gene in soybean

Stem canker caused by the fungus Diaporthe phaseolorum f. sp. meridionalis is a disease that limits soybean cultivation. Phenotypic evaluations aiming at disease resistance require labor-intensive processes, as for instance handling and transport of phytopathogens. The use of DNA markers in the selective procedures eases certain phases, besides being practical, safe and reliable. A RAPD fragment of 588pb was identified among bulks of resistant and susceptible plants in the cross BR92-15454 (R) x IAC-11 (S). Through co-segregation, the distance between the resistance locus and the fragment was estimated at 7.4 ± 2.1 cM, with a Lodmax. of 23.072 (first year) and at 6.0 ± 3.4 cM with a Lodmax. of 7.806 (second year). The fragment was converted into a SCAR marker and digested with enzyme Hinc II, which made the classification in homozygous resistant, heterozygous resistant and susceptible plants possible. This SCAR marker is suitable for use in the improvement program conducted in Jaboticabal.

Analysis of direct and indirect selection and indices in soybean segregating populations

Estimates of gain with selection are very useful in breeding programs to predict the success of selection. Index-based simultaneous selection makes breeding more successful. The objective of this report was to estimate and compare the genetic gain obtained by direct and indirect selection and using the classical and based on desired gain indices. The experiment was set up in the design of families with intercalated checks with 293 F3 soybean genotypes, distributed in 32 families derived from five crosses. Individual gains obtained with direct selection among and within families and mass selection were similar and in most cases higher than selection by indices. On the other hand, the highest total gains were obtained with selection indices and distributed across all traits. The classical index obtained the highest genetic gains.

Phosphorus and potassium budget in the soil-plant system in crop rotations under no-till

Soil management and crop rotations can affect P and K budget in soil, decreasing losses, and increasing fertilizer use efficiency. The P and K budget in the soil-plant system at depths up to 60. cm was studied for different soil managements and crop rotations under no-till for three years in Botucatu, São Paulo, Brazil. The investigated crop rotations were: triticale (X Triticosecale) and sunflower (Helianthus annuus) cropped in autumn-winter; pearl millet (Pennisetum glaucum), forage sorghum (Sorghum bicolor), and Sunn hemp (Crotalaria juncea) were grown in the spring, as well as an additional treatment with chiseling followed by a fallow period; and soybean (Glycini max, L., Merril) was cropped in the summer. Each year triticale and sunflower were grown in plots and pearl millet, forage sorghum, Sunn hemp and of chisel/fallow in sub-plots. The triticale/millet rotation led to the largest decrease in available P within the 0-0.60. m layer of the soil profile and the largest K increase within the 0-0.05. m layer. Potassium mobility in the soil profile and the increases in the available K content in the 0.40-0.60. m layer were independent of the management system. Crop rotations with or without chiseling are not effective in preventing soil P losses. There is considerable K leaching below 0.60. m, but chiseling and the use of high K accumulating plants as triticale results in lower K losses. © 2012 Elsevier B.V.

Effects of superficial liming and silicate application on soil fertility and crop yield under rotation

Soil acidity and low natural fertility are the main problems for grain production in Brazilian 'cerrado'. Although lime has been the most applied source for soil correction, silicate may be an alternative material due to its lower solubility and Si supply, which is beneficial to several crops. This work aimed to evaluate the efficiency of superficial liming and calcium/magnesium silicate application on soil chemical attributes, plant nutrition, yield components and final yield of a soybean/white oat/maize/bean rotation under no-tillage system in a dry-winter region. The experiment was conducted under no tillage system in a deep acid clayey Rhodic Hapludox, Botucatu-SP, Brazil. The design was the completely randomized block with sixteen replications. Treatments consisted of two sources for soil acidity correction (dolomitic lime: ECC=90%, CaO=36% and MgO=12%; calcium/magnesium silicate: ECC=80%, CaO=34%, MgO=10% and SiO2=22%) applied in October 2006 to raise base saturation up to 70% and a control, with no soil correction. Soybean and white oat were sown in 2006/2007 as the main crop and off-season, respectively. Maize and bean were cropped in the next year (2007/2008). Products from silicate dissociation reach deeper soil layers after 18months from the application, compared to liming. Additionally, silicate is more efficient than lime to increasing phosphorus availability and reducing toxic aluminum. Such benefits in soil chemical attributes were only evidenced during bean cropping, when grain yield was higher after silicate application comparatively to liming. Both correction sources were improved mineral nutrition of all the other crops, mainly Ca and Mg levels and agronomical characteristics, reflecting in higher yield. © 2012 Elsevier B.V.