• Authors:
    • Roostaee, M.
    • Liaghat, A.
    • Parsinejad, M.
    • Tabrizi, M. S.
    • Nahvinia, M.
  • Source: International Journal of Agriculture: Research and Review
  • Volume: 2
  • Issue: 3
  • Year: 2012
  • Summary: Sustainable irrigated agriculture entails monitoring water, salt balance and effective depth of root zone. A lysimeter study was based absorption of plant water requirement beyond predefined root depth. Experiment was conducted with three treatments in three replications at the research field of the University of Tehran in Karaj, Iran, in 2007 on soybean including: treatment A at MAD (Maximum Allowable Depletion) of 55%, treatment B at MAD=65% and treatment C also at MAD=65% but with 30% excess irrigation. The results showed in treatment C crop yield not only did not significantly decrease as compared with treatment A but water application efficiency increased by 11.2%. Water extraction of plants at the deeper soil layers in response to longer irrigation intervals can result in increased plant water uptake efficiency.
  • Authors:
    • Teixeira Junior, T.
    • Colombo, G. A.
    • Afferri, F. S.
    • Cancellier, L. L.
    • Pires, L. P. M.
    • Peluzio, J. M.
    • Ribeiro, G. R. dos S.
  • Source: Ciência Rural
  • Volume: 42
  • Issue: 3
  • Year: 2012
  • Summary: In order to evaluate the genetic divergence among soybean cultivars, an assay was carried out at Formoso do Araguaia, TO, Brazil, in off-season of 2007, in irrigated lowland conditions. The experimental design were randomized blocks with 12 treatments and three replications. Genetic divergence was evaluated by multivariate procedures: Mahalanobis distance, Tocher clustering method's and nearest neighbor method. It was observed the formation of two distinct groups by the dendrogram of genetic dissimilarity, which were identical to those groups formed by Tocher's method. The Tocher optimization method and the nearest neighbor agreed among themselves. The traits number of days to maturity, plant height and weight of 100 seed were the ones that most contributed for genetic dissimilarity. The presence of genetic variability allowed the identification of dissimilar cultivars with high average for the evaluated traits. The hybridations 'DOKO' * 'CONQUEST' and 'DOKO' * 'FT-2000' are promising to obtain segregating populations with high variability.
  • Authors:
    • Gitelson, A. A.
    • Peng, Y.
  • Source: Remote Sensing of Environment
  • Volume: 117
  • Issue: 440–448
  • Year: 2012
  • Summary: The synoptic quantification of crop gross primary productivity (GPP) is essential for studying carbon budgets in croplands and monitoring crop status. In this study, we applied a recently developed model, which relates crop GPP to a product of total crop chlorophyll content and incoming photosynthetically active radiation, for the remote estimation of GPP in two crop types (maize and soybean) with contrasting canopy architectures and leaf structures. The objective of this study was to evaluate performances of twelve vegetation indices used for detecting different vegetation biophysical characteristics, in estimating GPP of rainfed and irrigated crops over a period from 2001 through 2008. Indices tested in the model exhibited strong and significant relationships with widely variable GPP in each crop (GPP ranged from 0 to 19 gC/m 2/d for soybean and 0 to 35 gC/m 2/d for maize), however, they were species-specific. Only three indices, which use MERIS red edge and NIR spectral bands (i.e. red edge chlorophyll index, MERIS Terrestrial Chlorophyll Index and red edge NDVI), were found to be able to estimate GPP accurately in both crops combined, with root mean square errors (RMSE) below 3.2 gC/m 2/d. It was also shown that two indices, red edge chlorophyll index and red edge NDVI with a red edge band around 720 nm, were non-species-specific and yielded a very accurate estimation of GPP in maize and soybean combined, with RMSEs below 2.9 gC/m 2/d and coefficients of variation below 21%.
  • Authors:
    • Oliveira, E. B. de
    • Moraes, A. de
    • Pelissari, A.
    • Reis, E. F. dos
    • Ruaro, L.
  • Source: Pesquisa Agropecuária Brasileira
  • Volume: 47
  • Issue: 4
  • Year: 2012
  • Summary: The objective of this work was to assess the effect of soil management systems and winter cover crops on the number of propagules of Fusarium spp. in soil, the incidence of sudden death syndrome (SDS), and the productivity of the soybean cultivars CD 206 and FT Fenix. Two experiments were carried out in the 2006/2007 and 2007/2008 crop years. The experimental design was a randomized complete block in a split-split plot arrangement, with three replicates. Two soil tillage systems were evaluated: no-tillage and plowed soil at a depth of 25 cm. The soil covers used were: black oat, with two planting densities; black oat+vetch; ryegrass; and fallow. The incidence of the disease in the 2006/2007 crop year in the cultivar FT Fenix was lower than in CD 206. In the 2007/2008 crop, there was no significant difference. There was an increase in productivity, of 125 kg ha -1, in the plowed treatment, when compared to no-tillage. The cover with black oat+vetch showed a higher number of propagules of Fusarium spp. in soil in the 2006/2007 crop year. However, in the second year, this difference was not observed. The soil management systems and winter cover crops used do not influence the incidence of SDS in soybean cultivars or the number of Fusarium spp. propagules in soil. The plowed system provides an increase in soybean yield in the second year of management.
  • Authors:
    • Portela, S. I.
    • Andriulo, A. E.
    • Restovich, S. B.
  • Source: Field Crops Research
  • Volume: 128
  • Year: 2012
  • Summary: The agricultural system of the Humid Pampas consists of continuous cropping of soybean and maize under no tillage. This system may loose nitrogen (N) through leaching during the early and final stages of summer crops and during fallow. In this study (2005-2011) we evaluated the effect of fall-winter species (rescue grass, ryegrass, oats, barley, vetch, rape seed and forage radish) and a mixture of vetch and oats used as cover crops on water and N dynamics and main crop yield. Above-ground biomass production and N uptake by cover crops ranged from 1.1 to 11.9 Mg ha(-1) and from 17 to 223 kg N ha(-1), respectively, depending on sowing and killing dates and on the preceding crop. At killing, soil nitrate content in treatments with cover crops was 50-90% lower than in the control, reducing spring N leaching risk. When preceding maize, cover crops were killed in winter or early spring and their low C/N ratio (12-38) favored N release through residue decomposition. Vetch and rape seed as predecessors of fertilized maize increased residual N by approximate to 50 kg NO3-N compared to the control, posing the risk of fall N leaching. When preceding soybean, cover crops were killed in spring and, although their C/N ratios were higher (13-85), crucifers and legumes increased soil nitrate content. Maize yield was related to soil N availability at sowing (control and legumes > crucifers > grasses) which was inversely related to the preceding cover crop C/N ratio at killing. In normal to high rainfall years there were no differences in soybean yield among treatments. Water use by cover crops did not affect the main crop production except during an exceptionally dry year. Best synchronicity between N release from cover crop residues and harvest crop demand was achieved with the oats-vetch mixture before maize and with grasses before soybean. (C) 2011 Elsevier B.V. All rights reserved.
  • Authors:
    • King, C. A.
    • Edwards, J. T.
    • Carter, T. E.
    • Purcell, L. C.
    • Ries, L. L.
  • Source: Crop Science
  • Volume: 52
  • Issue: 1
  • Year: 2012
  • Summary: Delayed wilting is observed in a few unusual soybean [ Glycine max (L.) Merr.] genotypes, but the reasons and importance of this trait for conferring agronomic drought tolerance are poorly understood. We hypothesized that soybean genotypes with delayed wilting conserve soil moisture by restricting transpiration and that this would be reflected in decreased radiation use efficiency (RUE) and/or improved water use efficiency (WUE). Water conserved when soil moisture was plentiful would be available later in the season when drought is usually more severe. Irrigated field experiments in eight environments compared RUE of genotypes known to wilt differently during drought. In addition, we measured stomatal conductance, carbon isotope discrimination (CID), volumetric soil-moisture content, stomatal density, and canopy temperature depression. In six of the eight environments, slow-wilting genotypes generally had lower RUE than fast-wilting genotypes, which is consistent with our hypothesis. Three of four slow-wilting genotypes had higher soil moisture immediately before irrigation than fast-wilting genotypes, which is also consistent with the hypothesis. Genotypic differences in CID (a proxy for WUE) were present but were not consistently related with slow wilting. No genotypic differences were detected in stomatal conductance or canopy temperature. These results suggest that multiple mechanisms involving RUE and WUE could result in soil-water conservation in these diverse genotypes.
  • Authors:
    • Skaggs, K. E.
    • Irmak, S.
  • Source: Journal of Irrigation and Drainage Engineering
  • Volume: 138
  • Issue: 2
  • Year: 2012
  • Summary: The use of Penman-Monteith (PM)-type combination-based energy-balance equations to estimate reference evapotranspiration (ET ref) requires climatic data measured over well-watered and well-maintained reference grass or alfalfa vegetation surfaces. However, establishing and maintaining reference weather stations for a long period of time is a very formidable and expensive process. Thus, expansion of the microclimate data available for use in the PM equation for estimating ET ref is needed. In the absence of reference weather stations, one alternative is using microclimatic data measured over other well-watered vegetation surfaces as inputs to the PM equation. This study determines if weather data collected from a well-watered soybean surface in a semihumid climate can be used for this purpose. Measured and estimated microclimate variables, including net radiation ( Rn ), average air temperature ( Tave), dew-point temperature ( Td ), average relative humidity (RH ave), aerodynamic resistance ( ra ), and wind speed at 3 m ( u3) of a soybean and a grass canopy in South Central Nebraska, were analyzed and compared. The aerodynamic resistances of the soybean and grass canopies showed the largest percent difference of any of the microclimate variables for both 2007 and 2008. Wind speed was the primary microclimate variable with the largest percent difference between the two fields. The average percent differences in u3 between the soybean and grass field were 9.0 and 9.8% for 2007 and 2008. Although Tave, RH ave, and Td percent differences were not that large, there were distinct seasonalities to the differences. Grass and alfalfa reference evapotranspiration (ET o and ET r, respectively) calculations using data from the soybean (ET o-s and ET r-s ) and grass (ET o-g and ET r-g ) canopies were compared daily and seasonally. Seasonal total ET o and ET r estimates using soybean and grass microclimate data were very close, and within 1 and 2% during 2007 (ET o-g =583 mm and ET o-s =576 mm; ET r-g =751 mm and ET r-s =733 mm), and 4 and 5% during 2008 (ET o-g =554 mm and ET o-s =531 mm; ET r-g =707 mm and ET r-s =669 mm). In 2007, differences in temperature variables were most correlated to differences in ETref estimates. In 2008, the greatest correlations of differences in ET o and ET r were with differences in Tave, RHave, and u3. The results indicated that the microclimate data measured over an irrigated soybean canopy during normal or wet years (rainfall ≥300 mm during the growing season) can be used in place of measurements taken over a grass canopy to estimate ET o and ET r in climatic conditions similar to semihumid climatic conditions of South Central Nebraska when reference weather station data are not available to solve the standardized PM equation.
  • Authors:
    • Nichols ,R. L.
    • Webster, T. M.
  • Source: Weed Science
  • Volume: 60
  • Issue: 2
  • Year: 2012
  • Summary: Changes in the weed flora of cropping systems reflect the impacts of factors that create safe sites for weed establishment and facilitate the influx and losses to and from the soil seedbank. This analysis of the annual surveys of the Southern Weed Science Society documents changes in the weed flora of the 14 contiguous southern states since the advent of transgenic, herbicide-resistant crops. In 1994 and 2009, the top five weeds in corn were morningglories, Texas millet, broadleaf signalgrass, johnsongrass, and sicklepod; in this same period Palmer amaranth, smartweeds, and goosegrass had the greatest increases in importance in corn. In cotton, morningglories and nutsedges were among the top five most troublesome weeds in 1995 and 2009. Palmer amaranth, pigweeds, and Florida pusley were also among the five most troublesome species in 2009; the weeds with the largest increases in importance in cotton were common ragweed and two species with tolerance to glyphosate, Benghal dayflower and Florida pusley. In soybean, morningglories, nutsedges, and sicklepod were among the top five weed species in 1995 and 2009. Two species with glyphosate resistance, Palmer amaranth and horseweed, were the second and fourth most troublesome weeds of soybean in 2009. In wheat, the top four weeds in 2008 were the same as those in 1994 and included Italian ryegrass, wild garlic, wild radish, and henbit. Crop production in the southern region is a mosaic of various crop rotations, soil types, and types of tillage. During the interval between the surveys, the predominant change in weed management practices in the region and the nation was the onset and rapid dominance of the use of glyphosate in herbicide-resistant cultivars of corn, cotton, and soybean. Because of the correspondence between the effects of glyphosate on the respective weed species and the observed changes in the weed flora of the crops, it is likely the very broad use of glyphosate was a key component shaping the changes in weed flora. Only eight of the top 15 most troublesome weeds of cotton and soybean, the crops with the greatest use of glyphosate, were the same in 1995 and 2009. In contrast, in corn and wheat where adoption of glyphosate-resistant cultivars lags or is absent, 12 of the 15 most troublesome weeds were the same in 1994 and 2008. These findings show on a regional scale that weeds adapt to recurrent selection from herbicides, currently the predominant weed management tool. Future research should seek methods to hinder the rapid spread of herbicide-tolerant and evolution of herbicide-resistant weed species. As new tools are developed, research should focus on ways to preserve the efficacy of those tools through improved stewardship. Nomenclature: annual bluegrass, Poa annua L. POAAN; Benghal dayflower, Commelina benghalensis L. COMBE; broadleaf signalgrass, Urochloa platyphylla (Nash) R.D. Webster BRAPP; common ragweed, Ambrosia artemisiifolia L. AMBEL; Florida pusley Richardia scabra L. RCHSC; goosegrass Eleusine indica (L.) Gaertn. ELEIN; groundcherries, Physalis spp.; henbit, Lamium amplexicaule L. LAMAM; horseweed, Conyza canadensis (L.) Cronq. ERICA; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot LOLMU; johnsongrass, Sorghum halepense (L.) Pers. SORHA; morningglories, Ipomoea spp.; nutsedges, Cyperus spp.; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pigweed, Amaranthus spp.; sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby CASOB; smartweeds, Polygonum spp.; Texas millet, Urochloa texana (Buckl.) R. Webster PANTE; wild garlic, Allium vineale L. ALLVI; wild radish, Raphanus raphanistrum L. RAPRA; corn, Zea mays L.; cotton, Gossypium hirsutum L.; soybean Glycine max. (L.) Merr.; wheat, Triticum aestivum L.
  • Authors:
    • Ferguson, R.
    • Shapiro, C. A.
    • Wortmann, C. S.
    • Mainz, M.
  • Source: Crop Management
  • Issue: May
  • Year: 2012
  • Summary: High-yield soybean (Glycine max L.) has a high rate of N uptake during grain fill which may exceed N available from biological N fixation and mineralization of soil organic N. Other research findings show a low probability of response to N applied at early grain fill for yield 60 bu/acre yield are inconsistent. The effect of applying N and S to the soil at early podfill was determined in Nebraska by conducting 56 irrigated trials, including 44 with mean yield >60 bu/acre. Mean yield increases with 27 lb/acre N applied and >60 bu/acre yield were 2.5 bu/acre in south-central, 1.6 bu/acre in northeast, and not significant in southeast Nebraska. There was no added yield with applying 54 compared with 27 lb/acre N or with the addition of 4.5 lb/acre S. Variations in soil properties and in leaf N and S concentrations were not related to yield or the response to applied N. Depending on the grain to fertilizer price ratio, application of N at early pod fill may be profitable, especially if the cost of application is low such as through fertigation.
  • Authors:
    • Li, Y. Q.
    • Liu, H. B.
    • Li, M. F.
    • Fan, L.
    • Wu, W.
  • Source: Transactions of the Chinese Society of Agricultural Engineering
  • Volume: 28
  • Issue: 3
  • Year: 2012
  • Summary: The records of daily solar radiation (Rs, MJ.m -2.d -1) are the important inputs for crop simulation models. However, for some model users, Rs at longer temporal intervals are more available than that at daily scale. The objective of this study was to analyze the sensitivity of simulated crop growth and production using CERES-Maize and GROPGRO-Soybean, two widely used crop growth models, to uncertainty in Rs at different time scales (5-day, 10-day, and monthly). Daily radiation data (1961-1990) from Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) for the state of Georgia, USA were used to create 5-day, 10-day, and monthly mean daily Rs data sets. Datasets related to daily Rs were used as background baselines. The overall performance of the models was not significantly affected by Rs under the studied time scales. Within locations, the simulated days to anthesis and grain yields from 5-day, 10-day, and monthly Rs were close to that from daily Rs for maize and soybean under rainfed and irrigated conditions, respectively. Mean values of relative mean bias error (RMBE), mean bias error (MBE) and root mean square error (RMSE) of the simulated days to anthesis were 0, 0 and 3.5 d for the two crops under the studied scenarios, respectively. The simulated yields were underestimated for maize and overestimated for soybean using 5-day, 10-day, and monthly Rs for both rainfed and irrigated conditions, respectively. Under rainfed and irrigated conditions, the average RMBE and RMSE were -0.59%, 120 kg/hm 2 and -0.52%, 129 kg/hm 2 for maize yield, and 5%, 152 kg/hm 2 and 4.7%, 165 kg/hm 2 for soybean, respectively. Short-term bias in the difference between evaluated time scales and daily scale could affect the outputs of the crop models. Under the scenarios evaluated, CGOPGRO-Soybean model showed higher sensitivity to changes in multi-temporal Rs and water regimes than CERES-Maize model. Based on the results of this study, it can be concluded that 5-day, 10-day, and monthly mean daily Rs could be used as an input for crop growth simulation models when daily Rs are not available.