• Authors:
    • Knies, A. E.
    • Streck, N. A.
    • Radons, S. Z.
    • Martins, J. D.
    • Carlesso, R.
  • Source: Ciência Rural
  • Volume: 41
  • Issue: 6
  • Year: 2011
  • Summary: The plastochron, which is the time interval between the appearance of two successive nodes and the final node number (FNN) are important variables of the vegetative development in soybean. The objective of this study was to determine the plastochron and the FNN of soybean ( Glycine max (L.) Merrill) cultivars sown in different dates under irrigated conditions in a subtropical location. A field experiment was carried out in Santa Maria, RS, Brazil during 2005/2006 growing season, with three sowing dates (09/11/2005, 09/12/2005 and 28/01/2006). It was used 15 soybean cultivars recommended for the Central and North Argentina, and South and Southeast Brazil. The variables measured were the number of nodes (NN) and the (FNN) on the main stem. The plastochron was estimated by the inverse of the slope of the linear regression between NN and the thermal time (base temperature=10degreesC) accumulated since plant emergence. The late sowing resulted in lower plastochron and FNN, probably because of the lower photoperiod under which the plants were submitted in the node phase, a typical response of short day plants.
  • Authors:
    • Ralish, R.
    • de Lima, G. P.
    • Rosa, D. M.
    • Pereira Nóbrega, L. H.
    • Mauli, M. M.
  • Source: Brazilian Archives of Biology and Technology
  • Volume: 54
  • Issue: 4
  • Year: 2011
  • Summary: This study analyzed possible interferences associated to the amount of crop residues produced by the black oats and the consortium of black oats, common vetch and forage turnip on weeds incidence and soil seed bank. It was a field trial with seven treatments and five replications. The cover crop was sown at throwing, cut at 100 days and residues were put on each respective plot, using a proportion of normal amount of produced straw, either its half and double. The heaviest weights were obtained from cover crop consortium and their application decreased weeds incidence in such area. The seeds bank and other analyzed parameters did not show statistical differences. According to these results, it was concluded that winter cover crop could be used in crops rotation with soybean.
  • Authors:
    • McSorley, R.
  • Source: Nematropica
  • Volume: 41
  • Issue: 2
  • Year: 2011
  • Summary: Studies that utilized rotation crops for management of root-knot nematodes in the southeastern United States were examined to evaluate the overall performance of rotation crops. In general, nematode-susceptible crops that followed effective rotation crops produced yields and supported nematode numbers similar to those obtained on crops treated with most standard nematicides. Fumigation with methyl bromide was an exception, and resulted in low nematode numbers up to the end of the susceptible target crop, whereas nematode numbers recovered following rotation crops. Performance of rotation crops was similar to clean fallow in most studies, and there was little evidence that rotation crops could suppress nematode numbers below levels obtained after clean fallow. Large reductions in nematode numbers often were achieved following rotation crops. In sites with relatively low initial population levels before rotation crops were used, effective rotation crops sometimes maintained relatively low nematode numbers through the following susceptible target crop, and nematode recovery was not observed until the second year of the rotation sequences. Where practical, very long rotations such as bahiagrass pastures were often effective in preventing increase in nematode numbers on subsequent susceptible crops. Rehabilitation of heavily infested sites is difficult, could require several years of rotation crops, and the benefit gained may last only through one susceptible crop.
  • Authors:
    • Lopez, C.
    • Suarez, P.
    • Gonzalez Anta, G.
    • Luca, M. J. de
    • Melchiorre, M.
    • Lascano, R.
    • Racca, R. W.
  • Source: Biology and Fertility of Soils
  • Volume: 47
  • Issue: 1
  • Year: 2011
  • Summary: Bradyrhizobium strains were isolated from nodules obtained from field-grown soybean plants sampled in 12 soybean production locations in Argentina. These fields had been annually cropped with soybean and did not show decreases in yields even though they had been neither N-fertilized nor inoculated for at least the last 5 years. We hypothesized that the isolated strains maintained high competitiveness and efficiency in fixing adequate N 2 levels. A set of strains that showed the highest nodular occupancy in each sampling location were assayed for symbiotic performance under greenhouse and field conditions and comparatively evaluated with Bradyrhizobium japonicum E109, the strain officially recommended for inoculant formulation in Argentina. An inoculant pool, formed by four strains obtained from nodules collected from Canada Rica, developed higher nodular biomass than B. japonicum E 109 in assays carried out in greenhouses under well irrigated conditions. Additionally, neither nodule production nor specific nitrogenase activity decreased with respect to B. japonicum E 109 when plants were drought stressed during 7 days from sowing. The mean yields obtained under field conditions and plotted against the principal component one (CP1) obtained with an additive main effect and multiplicative interaction (AMMI) model showed that the inoculant pool from Canada Rica had higher contribution to yield than strain E 109, although with lower environmental stability. The inoculant pool from Canada Rica could be considered an improved inoculant and be used for preliminary assays, to formulate inoculants in Argentina.
  • Authors:
    • Canaday, C. H.
    • Little, C. R.
    • Chen, P.
    • Rupe, . B.
    • Wrather, A. J.
    • Shannon, G. J.
    • Bond, J. P.
    • Arelli, P. A.
    • Mengistu, A.
    • Newman, M. A.
    • Pantalone, V. R.
  • Source: Plant Health Progress
  • Issue: September
  • Year: 2011
  • Summary: Charcoal rot, caused by Macrophomina phaseolina, significantly reduces yield in soybean more than most other diseases in the midsouthern United States. There are no commercial genotypes marketed as resistant to charcoal rot. Reactions of 27 maturity group (MG) III, 29 Early MG IV, 34 Late MG IV, and 59 MG V genotypes were evaluated for M. phaseolina between 2006 and 2008 in a non-irrigated, no-till field that had been artificially infested for three years. There was significant variation in root colonization among genotypes and years, indicating the value of screening genotypes over multiple years. Based on CFUI there was no genotype that was consistently immune to charcoal rot each year. However, there were a total of six genotypes (one genotype in MG III, one in Late MG IV, and four in MG V) that were identified as moderately resistant. Some of the commercial and public genotypes were resistant to M. phaseolina at levels equal to or greater than the standard DT97-4290, a moderately resistant cultivar. The genotypes identified as having moderate resistance across the three years could be useful as sources for developing resistant soybean genotypes.
  • Authors:
    • Mengistu, A.
    • Bellaloui, N.
    • Ray, J. D.
    • Smith, J. R.
  • Source: Plant Disease
  • Volume: 95
  • Issue: 9
  • Year: 2011
  • Summary: The seasonal progress of charcoal rot (caused by Macrophomina phaseolina) was measured over two growing seasons in four separate experiments: irrigated infested, irrigated non-infested, non-irrigated infested, and non-irrigated noninfested. Disease was assessed at V5, R1, R3, R5, R6, and R7 growth stages based on colony forming units (CFU) of M. phaseolina recovered from the lower stem and root tissues and the area under the disease progress curve (AUDPC). The population density of M. phaseolina increased slowly from the V5 to R6 growth stages and then rapidly from the R6 to R7 growth stages for all genotypes in all four experiments. Yield loss due to charcoal rot ranged from 6 to 33% in irrigated environments. The extent of yield loss was affected by severity of charcoal rot, which in turn was affected by year. Yield loss due to charcoal rot was consistently measured in all paired comparisons in irrigated environments, suggesting that charcoal rot can be an important disease in irrigated environments. Disease severity based on CFU accounted for more yield loss variation (42%) than did the AUDPC (36%) when used to assess disease. Growth stage R7 was found to be the optimum stage for assessing disease using CFU. In addition, screening soybean genotypes under irrigation environment may have utility in breeding programs where there is a need for evaluating soybean genotypes for both disease resistance and yield.
  • Authors:
    • Mutiibwa, D.
    • Irmak, S.
  • Source: Transactions of the American Society of Agricultural and Biological Engineers
  • Volume: 54
  • Issue: 1
  • Year: 2011
  • Summary: Canopy resistance (r c), which represents the composite diffusive resistance to water vapor transfer from vegetation surfaces to the atmosphere, plays an important role in describing the water vapor and energy fluxes and CO 2 exchange mechanisms and is an essential component of the complex ecophysiological and turbulent transport and evapotranspiration models. While one-step (direct) application of combination-based energy balance models (i.e., Penman-Monteith, PM) requires r c to solve for actual evapotranspiration (ET a), a remaining challenge in practical application of PM-type models is the scaling up of leaf-level stomatal resistance (r s) to r c to represent an integrated resistance from the plant community to quantify field-scale evaporative losses. We validated an integrated approach to scale up r s to the canopy. Through an extensive field campaign, we measured diurnal r s for a subsurface drip-irrigated soybean [ Glycine max (L.) Merr.] canopy and integrated several microclimatic and in-canopy radiation transfer parameters to scale up r s to r c. Using microclimatic and plant factors such as leaf area index for sunlit and shaded leaves, plant height, solar zenith angle, direct and diffuse radiation, and light extinction coefficient, we scaled up soybean r s as a primary function of measured photosynthetic photon flux density (PPFD). We assumed that PPFD is the primary and independent driver of r c; hence, the scaling approach relied heavily on measured PPFD-r s response curves. We present experimental verifications of scaled up r c by evaluating the performance of the scaled up r c values in estimating ET a. In addition, we solved the PM model on an hourly time step using the scaled up r c values and compared the PM-estimated ET a with the Bowen ratio energy balance system (BREBS)-measured ET a. The relationship between r s and PPFD was asymptotic, and r s showed strong dependence to PPFD, as PPFD alone explained 67% to 88% of the variability in r s. Beyond a certain amount of PPFD (400 to 500 mol m -2 s -1), r s became less responsive to PPFD. At smaller PPFD (0 to about 150 mol m -2 s -1) and greater r s (>70 to 80 s m -1) range, r s was very sensitive to PPFD. The r c_min, r c_avg, and r c_max ranged from 42 to 104 s m -1, 69 to 183 s m -1, and 95 to 261 s m -1, respectively, throughout the season. The seasonal average r c_min, r c_avg, and r c_max were 54, 92, and 129 s m -1, respectively. Canopy resistances were higher in early growing season during partial canopy closure, lower during mid-season, and high again in late season due to leaf aging and senescence. The ET a estimates from the PM model using scaled up r c values correlated very well with the BREBS-measured ET a. The average root mean square difference (RMSD) between the BREBS-measured and PM-estimated ET a was 0.08 mm h -1 (r 2=0.91; n=827), and estimates were within 3% of the measured ET a on an hourly basis. On a daily time step, RMSD was 0.64 mm d -1 (r 2=0.86; n=83), and the estimates were within 4% of the measured data. The approach successfully synthesized the whole-canopy resistance for use in PM-type combination-energy balance equations by scaling up from r s using a straightforward model of in-canopy radiation transfer.
  • Authors:
    • Gill, M. S.
    • Bhale, V. M.
    • Deshmukh, M. S.
    • Narkhede, W. N.
    • Gadade, G. D.
    • More, S. S.
  • Source: Indian Journal of Agronomy
  • Volume: 56
  • Issue: 2
  • Year: 2011
  • Summary: A field experiment was conducted for three consecutive years (2005-2007) at Parbhani to find out most productive and profitable cropping system. Among the different cropping systems, highest wheat [( Triticum aestivum L.) emend. Fiori & Paol] equivalent yield (19.9 t/ha) and net monetary returns (Rs 107.8*10 3/ha) were obtained from soybean [ Glycine max (L. Merr.)]-onion ( Allium capa L.) cropping system, followed by turmeric ( Curcuma domestica L.)+castor ( Ricinus communis L.) (WEY-14.0 t/ha, and NMR Rs 89.8*10 3/ha). The soybean-onion system also recorded maximum net monetary advantage per unit time (Rs 573/ha/day), employment (374 mandays) and water use efficiency (221 kg/ha-cm), followed by turmeric+castor intercropping system. The highest nutrient uptake was recorded in sorghum [ Sorghum bicolor (L.) Moench]-wheat followed by maize ( Zea mays L.)+cow-pea ( Vigna sinensis L.)-wheat and maize-wheat cropping systems. The highest soil nutrient status was observed in cotton ( Gossypium sp.)-summer groundnut ( Arachis hypogaea L.) followed by soybean-onion cropping systems.
  • Authors:
    • Nelson, S. O.
    • Trabelsi, S.
  • Source: Transactions of the American Society of Agricultural and Biological Engineers
  • Volume: 54
  • Issue: 2
  • Year: 2011
  • Summary: Based on microwave dielectric properties of wheat, corn, barley, oats, grain sorghum, soybeans, canola, shelled peanuts and pod peanuts measured over ranges of frequency and moisture content, models for predicting the dielectric constant and loss factor of these commodities are described. Nearly linear relationships between dielectric properties and log of frequency or frequency and moisture content permitted multiple linear regression models to be developed for predicting dielectric constants and loss factors for each type of grain and seed at 23degreesC. Models predicted dielectric constants with s.e. of 1 to 2% with some up to approx. 4% for grain and seed at frequencies in the range 5 to 15 GHz over given moisture ranges. Loss factors are predicted with s.e. of a few percent, but much larger errors can naturally result when loss factors are very small.
  • Authors:
    • Odhiambo, L. O.
    • Irmak, S.
  • Source: Transactions of the American Society of Agricultural and Biological Engineers
  • Volume: 54
  • Issue: 3
  • Year: 2011
  • Summary: Estimation of actual evapotranspiration (ET), especially its partitioning into plant transpiration (T) and soil evaporation (E), in agricultural fields is important for effective soil water management and conservation and for understanding the interactions between ET, T and E with the management practices. Direct field measurements of ET, T, and E rates are difficult and costly; hence, mathematical models are used for estimating them. The objective of this study was to evaluate the practical applicability of the Shuttleworth-Wallace (S-W) model to estimate and partition ET in a subsurface drip-irrigated soybean ( Glycine max L. Merr.) field with partial residue cover. While its performance has been studied for various surfaces, the performance evaluation of the S-W model for such surface has not been carried out. An integrated approach of calculating bulk stomatal resistance (r sc) as a function of soil water content (theta i) was incorporated into the model to allow simulation of T over a range of theta i, and a residue decomposition function was introduced to account for surface residue decay over time to more accurately account for the actual residue cover in field conditions. The model performance was evaluated for different plant growth stages during the 2007 and 2008 growing seasons at the University of Nebraska-Lincoln, South Central Agricultural Laboratory near Clay Center, Nebraska. The sum of estimated T and E was compared to the bowen Ratio Energy Balance System (BREBS)-measured actual ET on a daily time-step. The model was able to capture the trends and magnitudes of measured ET, but its performance differed for various plant physiological growth stages. The root mean square difference (RMSD) values between the model-estimated and measured ET values for the growing season (day after emergence until physiological maturity) were 1.26 and 1.03 mm d -1 for 2007 and 2008, respectively. Best performance was observed during the mid-season during full canopy cover with a two-year average r 2 of 0.87, average RMSD of 0.94 mm d -1, and average mean biased error (MBE) of 0.30 mm d -1. Estimates for both initial and late season growth stages where E was dominant had the least agreement with BREBS measurements. The proportion of T and E in the estimated ET varied with growth stage. The S-W estimated seasonal total ET and BREBS measurements were equal in 2007 (S-W model ET=496 mm and BREBS ET=498 mm), and in 2008 the model underestimated by only 8.2% (S-W model ET=452 mm and BREBS ET=489 mm). While, in general, the model was successful in tracking the trends and magnitude of the BREBS-measured ET, further re-parameterization of the T module of the model can improve its accuracy to estimate ET, especially T, during the initial and late season (before full canopy cover and after physiological maturity) for a subsurface drip-irrigated soybean canopy. Other enhancements needed in the model for improved estimation of the E component include accurate determination of soil surface resistance coefficients and accounting for direct evaporation of intercepted rainfall on the canopy.