• Authors:
    • Evett, S. R.
    • O'Shaughnessy, S. A.
    • Colaizzi, P. D.
    • Howell, T. A.
  • Source: Transactions of the American Society of Agricultural and Biological Engineers
  • Volume: 55
  • Issue: 2
  • Year: 2012
  • Summary: Studies using the time-temperature threshold (TTT) method for irrigation scheduling have been documented for cotton, corn, and soybean. However, there are limited studies of irrigation management of grain sorghum ( Sorghum bicolor, L.) with this plant-feedback system. In this two-year study, the TTT method was investigated as an automatic irrigation control algorithm for a late-maturing grain sorghum hybrid (Pioneer 84G62) grown in 2009 and an early maturing hybrid (Moench, NC+ 5C35) grown in 2010. The method was evaluated by comparing grain sorghum responses of biomass and dry grain yields, crop evapotranspiration (ET c), water use efficiency (WUE), and irrigation water use efficiency (IWUE) between automatic and manual control methods of irrigation scheduling at different deficit irrigation treatments (i.e., 80%, 55%, 30%, and 0% of full replenishment of soil water depletion to 1.5 m depth). Irrigation scheduling using the TTT method produced mean response variables of yield (biomass and grain), WUE, and IWUE that were similar or better than those from the manually scheduled method in both years. Water use efficiency was highest at the 80% and 55% levels in 2009 and 2010, respectively. Average IWUE was highest at the 55% level in 2009 and at the 30% level in 2010. For both of these responses, differences among irrigation treatment levels were not always significant. Crop production functions were curvilinear in both years as dry grain yields began to plateau between water application amounts delivered from irrigation treatments at the 55% and 80% levels. Results from this study indicate that both late and early maturing hybrids of grain sorghum are responsive to the TTT method of irrigation scheduling. Irrigation management with this algorithm can produce biomass and dry grain yields, ET c, WUE, and IWUE levels that are similar to those achieved with an accurate irrigation scheduling method based on direct soil water measurement.
  • Authors:
    • Paul, O. V. de
  • Source: Earth & Environmental Sciences
  • Volume: 3
  • Issue: 2
  • Year: 2012
  • Summary: A growing world population and possible liquid fuel energy shortages are likely to result in worldwide agricultural intensification, and the possible expansion of non-sustainable practices. The adoption of non-sustainable practices could result in the loss of currently productive land, with potential impacts on human welfare and economic viability. One of the easiest techniques to maintain productivity is to maintain surface soil organic matter. However, developing reliable, cost effective and accurate methods for quantifying and monitoring crop residue cover (a major source of soil organic matter) that remains on top of the soil over large spatial extents constitutes a significant challenge. This article reviews potential remote sensing approaches for estimating surface residue cover with a view to mapping tillage practice.
  • 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:
    • 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:
    • Feng, G.
    • Wendling, L.
    • Sharratt, B.
  • Source: Aeolian Research
  • Volume: 5
  • Year: 2012
  • Summary: Winter wheat - summer fallow is the crop rotation used on more than 1.5 million ha in the Pacific Northwest United States. Land maintained using conventional summer fallow is susceptible to wind erosion because multiple tillage operations during the fallow period expose the soil to high winds. Alternative management strategies are needed that protect the soil surface from erosion during summer fallow. Surface characteristics were examined after subjecting the loessial soil to seven (conventional), five (reduced), three (minimum), and zero (no) tillage operations during the fallow period. Surface residue biomass and roughness and soil crust, aggregation, strength, and water content were measured after tillage and sowing operations. No tillage resulted in a more persistent and thicker soil crust and greater residue cover, silhouette area index (SAI), and penetration resistance than conventional and reduced tillage. For those treatments subject to tillage, minimum tillage resulted in a thicker soil crust and greater residue cover, SAI, ridge roughness, mean aggregate diameter, and penetration resistance as compared to conventional or reduced tillage after primary tillage. Near the end of the fallow period, minimum tillage resulted in 15% greater residue cover than conventional tillage. Soil loss from minimum tillage is expected to be 50% of conventional tillage based upon these differences in residue cover. This study suggests that minimum tillage is an alternative strategy to conventional tillage for reducing wind erosion in the wheat-fallow region of the Pacific Northwest. Published by Elsevier B.V.
  • 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:
    • Vencill, W.
    • Schomberg, H. H.
    • Phatak, S. C.
    • Díaz-Pérez, J. C.
    • Skinner, E. M.
  • Source: HortScience
  • Volume: 47
  • Issue: 1
  • Year: 2012
  • Summary: Sunnhemp (Crotalaria juncea L.) is a tropical legume that could be an important summer cover crop in the southeastern United States, but it has the potential for suppressing both crops and weeds. Allelopathic effects of sunnhemp on weeds, vegetable crops, and cover crops were evaluated in greenhouse and growth chamber experiments. In the greenhouse, ground dried sunnhemp residues (applied mixed with the soil at 1.6% w/w) reduced percent germination of lettuce (Lactuca sativa L.) and smooth pigweed (Amaranthus hybridus L.) to a similar degree as that caused by cereal rye (Secale cereale L. subsp. cereale) residues (applied at 1.5% w/w). The allelopathic activity of sunnhemp was greater in the leaves than in the roots or stems. In growth chamber studies, the mean reduction in germination (relative to the control) caused by sunnhemp leaf aqueous extracts was: bell pepper (100%), tomato (100%), onion (95%), turnip (69%), okra (49%), cowpea (39%), collard (34%), cereal rye (22%), sweet corn (14%), Austrian winter pea (10%), crimson clover (8%), cucumber (2%), and winter wheat (2%). In lettuce, carrot, smooth pigweed, and annual ryegrass, sunnhemp aqueous leaf extract reduced seedling length to a degree similar as that produced by rye aqueous leaf extract. Sicklepod [Senna obtusifolia (L.) H.S. Irwin & Barneby CA] germination was not inhibited by any of the sunnhemp or rye aqueous extracts. In conclusion, sunnhemp reduced the germination percentage and seedling growth of various crop species. The allelochemical activity in sunnhemp was primarily in the leaves and remained active at least 16 d after harvest under dry conditions. Sunnhemp's allelochemical effect may be a useful attribute for weed management in sustainable production systems. However, plant growth in the field in crops such as bell pepper, tomato, onion, and turnip may be impacted as a result of allelopathic activity of sunnhemp residues. Thus, weed management may be more effective when sunnhemp is grown in rotation with crops that tolerate the allelochemicals from sunnhemp, resulting in optimization of the rotation effects.
  • 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.