• Authors:
    • Larbi, P. A.
    • Salyani, M.
  • Source: Computers and Electronics in Agriculture
  • Volume: 87
  • Year: 2012
  • Summary: An expert system (ES) has been developed to assist citrus spray applicators in planning and evaluating their sprayer operations. The ES is partitioned into two parts: (1) spray planning (procedures and calculations for sprayer calibration as well as suitability of spraying under given weather parameters) and (2) spray evaluation (estimation of overall spray deposition, ground fallout, and drift as percentages of the total spray discharged at orchard scale). The first part is based on established procedures and the second part is built on the previously developed spray deposition model. The latter includes a "What-If" analysis function that gives feedback on changes in input variables and the corresponding outputs. Testing of the ES revealed that the trends in the outputs, reflecting the effects of application rate, travel speed, foliage density, and percent missing trees were in general agreement with literature. The ES was evaluated by five individuals with diverse experience in spray applications. Overall, the ES was found useful for calibration and evaluation of spray applications in citrus.
  • Authors:
    • Payton, P.
    • Young, A. W.
    • Mahan, J. R.
  • Source: Irrigation Science
  • Volume: 30
  • Issue: 2
  • Year: 2012
  • Summary: Water available for agricultural use is declining worldwide as a result of both declining water resources and increasing application costs. Managing crop irrigation under conditions where the water need cannot be fully met represents the future of irrigation in many areas. On the southern high plains of Texas there is interest among producers to reduce the amount of water applied to cotton. In this study, a producer's efforts to reduce water application to a cotton crop were assessed in terms of a comparison between evapotranspiration, rainfall, and irrigation that is widely used in the region. The producer was able to reduce water application to meet intended reductions relative to the evapotranspiration estimates but, depending on the method used for calculating the crop water need, he tended to over water the crop in two out of three intended deficit irrigation regimes. Analysis of continuously monitored canopy temperatures provided verification of over-irrigation. Continuously monitored canopy temperature is proposed as a useful adjunct to evapotranspiration approaches to deficit irrigation management.
  • Authors:
    • Thomashow, L. S.
    • Paulitz, T. C.
    • Kwak, Y. S.
    • Bonsall, R. F.
    • Parejko, J. A.
    • Mavrodi, O. V.
    • Mavrodi, D. V.
    • Weller, D. M.
  • Source: Applied and Environmental Microbiology
  • Volume: 78
  • Issue: 3
  • Year: 2012
  • Summary: Natural antibiotics are thought to function in the defense, fitness, competitiveness, biocontrol activity, communication, and gene regulation of microorganisms. However, the scale and quantitative aspects of antibiotic production in natural settings are poorly understood. We addressed these fundamental questions by assessing the geographic distribution of indigenous phenazine-producing (Phz +) Pseudomonas spp. and the accumulation of the broad-spectrum antibiotic phenazine-1-carboxylic acid (PCA) in the rhizosphere of wheat grown in the low-precipitation zone (
  • Authors:
    • Sanderlin, R. S.
    • Melanson, R. A.
    • McTaggart, A. R.
    • Ham, J. H.
  • Source: Plant Disease
  • Volume: 96
  • Issue: 8
  • Year: 2012
  • Summary: Xylella fastidiosa causes disease in a number of economically important crops, ornamental plants, and shade trees, including grapevine, citrus, oleander, and sycamore. In pecan, X. fastidiosa causes pecan bacterial leaf scorch (PBLS), which leads to defoliation and reduces nut yield. No economically effective treatments are available for PBLS. In order to improve PBLS management practices, it is necessary to determine the subspecies of X. fastidiosa strains that infect pecan so that potential sources of inoculum may be identified. Multiprimer polymerase chain reaction (PCR) and phylogenetic analyses using nucleotide sequence data from the 16S-23S rRNA intergenic transcribed spacer (ITS) region and pglA consistently identified strains of X. fastidiosa isolated from pecan as X. fastidiosa subsp. multiplex. Enterobacterial repetitive intergenic consensus PCR and repetitive extragenic palindromic (REP)-PCR analyses were congruent with phylogenetic analyses. REP-PCR analyses indicated genetic variation within strains of X. fastidiosa from pecan. From these same analyses, X. fastidiosa strains from sycamore, grapevine, and oleander from Louisiana were identified as subsp. multiplex, subsp. fastidiosa, and subsp. sandyi, respectively. This study provides additional information about the host ranges of X. fastidiosa subspecies.
  • Authors:
    • Jennings, K. M.
    • Meyers, S. L.
    • Monks, D. W.
  • Source: Weed Technology
  • Volume: 26
  • Issue: 3
  • Year: 2012
  • Summary: Studies were conducted in 2008 and 2009 to determine the effect of S-metolachlor rate and application time on sweetpotato cultivar injury and storage root shape under conditions of excessive moisture at the time of application. S-metolachlor at 1.1, 2.2, or 3.4 kg ai ha -1 was applied immediately after transplanting or 2 wk after transplanting (WATP) to 'Beauregard', 'Covington', 'DM02-180', 'Hatteras', and 'Murasaki-29' sweetpotato. One and three d after S-metolachlor application plots received 1.9 cm rainfall or irrigation. S-metolachlor applied immediately after transplanting resulted in increased sweetpotato stunting 4 and 12 WATP, decreased no. 1 and marketable sweetpotato yields, and decreased storage root length to width ratio compared with the nontreated check. Sweetpotato stunting, no. 1 and marketable yields, and storage root length to width ratio in treatments receiving S-metolachlor 2 WATP were similar to the nontreated check. In 2008, Covington and Hattaras stunting 12 WATP was greater at 2.2 and 3.4 kg ha -1 (11 to 16%) than 1.1 kg ha -1 (1 to 2%). In 2009, S-metolachlor at 3.4 kg ha -1 was more injurious 4 WATP than 2.2 kg ha -1 and 1.1 kg ha -1. While cultivar by treatment interactions did exist, injury, yield, and storage root length to width ratio trends were similar among all cultivars used in this study.
  • Authors:
    • Wells, R.
    • Edmisten, K. L.
    • Lanier, J. E.
    • Corbett, T.
    • Jordan, D. L.
    • Collins, G. D.
    • Nuti, R. C.
    • Grabow, G. L.
  • Source: Crop Management
  • Issue: March
  • Year: 2012
  • Summary: Irrigated cotton acreage is limited in North Carolina. Research was conducted in North Carolina from 2004 to 2007 to define interactions of planting date with either mepiquat chloride application or cultivar under sub-surface drip irrigation or no irrigation. In most instances planting date, cultivar or mepiquat chloride, and irrigation did not interact for seed cotton yield. While main effects of planting date and irrigation were often significant, mepiquat chloride did not affect cotton yield. Cotton response to irrigation and planting date was variable and was generally influenced by annual variability in rainfall. Results from these experiments suggest that sub-surface drip irrigation improves cotton yield stability over the planting dates, mepiquat chloride applications, and cultivars tested. Additionally, cotton response to planting date was independent of irrigation treatment.
  • Authors:
    • Walsh, D. B.
    • Ringer, K. L.
    • Peters, T. R.
    • Okwany, R. O.
    • Rubio, M.
  • Source: Irrigation Science
  • Volume: 30
  • Issue: 3
  • Year: 2012
  • Summary: Crop response to deficit irrigation is an important consideration for establishing irrigation management strategies when water supplies are limited. This study evaluated the response of native spearmint to water deficits applied using overhead sprinklers in eastern Washington, US. Five levels of irrigation were applied ranging from full irrigation (100%) to 5% of weekly averaged full crop water needs. Soil water monitoring with soil water balance was used to estimate soil water deficits for irrigation scheduling and soil water use. Mint oil yields, oil components, dry matter production, and the water-use efficiency of the spearmint were assessed. There was significant reduction in fresh mint hay (harvested biomass) yield with increasing water deficit. However, spearmint oil yields remained generally uniform across irrigation treatments at the first cutting but decreased at the driest plots during the second harvest due to a loss of plant stand. The wet harvest index and water-use efficiency improved significantly for both harvests with increasing water deficit. Hay yield, oil yield, wet harvest index, and water-use efficiency are pooled across sides and replicate blocks to provide trends with changes in maximum evapotranspiration. The three major monoterpenes show changes suggesting less mature oil yields. The study demonstrates the feasibility of sustaining native spearmint yields under managed deficit irrigations for deficits not lower than 0.5 ETc.
  • Authors:
    • Assefa, Y.
    • Roozeboom, K. L.
    • Staggenborg, S. A.
    • Du, J.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 2
  • Year: 2012
  • Summary: Corn ( Zea mays L.) yield has increased from about 1.5 Mg ha -1 in the early 1900s to 8.5 Mg ha -1 in the beginning of the 2000s in the United States. Information about yield and management changes in irrigated and dryland corn yields for the hybrid era is scarce. The objective of the present study was to determine the magnitude of yield and management changes in irrigated and dryland corn from 1939 through 2009. Data from selected irrigated and dryland corn performance trials conducted in Kansas from 1939 through 2009 were analyzed. On average, corn yields have increased at rate of 90 kg ha -1 yr -1 in dryland and 120 kg ha -1 yr -1 in irrigated trials. Corn yield changes from one decade to another were not similar for the seven decades considered. Both irrigated and dryland yields increased significantly at least every two decades until the last three, during which dryland yields stagnated. Changes in hybrid technology and changes in crop management factors, such as a decrease in planting and harvesting date by about a quarter of a day yr -1, increased planting density at the rate of 597 plants ha -1 yr -1, and increased N and P fertilizer rates by 2.6 and 0.40 kg ha -1 yr -1, respectively, were found for the same time period in dryland corn. In addition, climate changes contributed to yield increases in the past through increased total rainfall, average monthly minimum and maximum temperature in March, and decreased maximum temperature from July through September.
  • Authors:
    • Allen, B. L.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 1
  • Year: 2012
  • Summary: Dryland corn (Zea mays L.) production in the northern Great Plains is limited by risk of crop failure due to drought conditions. Altering the row configuration and seeding rate have reduced the risk of yield loss elsewhere, but those areas typically receive greater precipitation than the annual average 300 to 350 mm (11.8 to 13.8 in) of the northern Great Plains. A study in 2007 and 2008 determined the impact of seeding rate and row configuration on dryland corn yield, yield quality and components, and precipitation use efficiency (PUE). Four sites in northeastern Montana were planted to corn (same variety) at four target rates (25,000, 37,500, 50,000 and 62,500 seeds ha−1 [10,000, 15,000, 20,000, and 25,000 seeds ac−1]) in conventional 0.61 m (24 in) spaced rows or in a skip-row configuration, with every third row skipped. Altering the row configuration had no impact on grain yield, harvest index, or grain PUE, but biomass yield and PUE were 12% and 15% greater for the skip-row configuration, compared to conventionally spaced corn. Interactions between row configuration and seeding rate were not significant (p < 0.05). Compared to row configuration, seeding rate had a greater impact on yield and showed an inverse and linear relationship, where biomass, grain yield, harvest index, and PUE for grain and biomass were 19%, 229%, 200%, 222%, and 22% greater for the lowest seeding rate, when compared to the highest. Overall results suggest that for areas with low rainfall, skip-row spacing provides a modest increase in biomass yield and that adjusting seeding rates to 27,000 seeds ha−1 (10,900 seeds ac−1) or lower will likely increase dryland corn biomass and especially grain yield, though caution is warranted in extending broadly the results of this limited dataset considering the variable nature of rainfall in semiarid environments.
  • Authors:
    • Antle, J. M.
    • Ogle, S. M.
  • Source: Climatic Change
  • Volume: 111
  • Issue: 3/4
  • Year: 2012
  • Summary: Previous research has demonstrated that soil carbon sequestration through adoption of conservation tillage can be economically profitable depending on the value of a carbon offset in a greenhouse gas (GHG) emissions market. However adoption of conservation tillage also influences two other potentially important factors, changes in soil N2O emissions and CO2 emissions attributed to changes in fuel use. In this article we evaluate the supply of GHG offsets associated with conservation tillage adoption for corn-soy-hay and wheat-pasture systems of the central United States, taking into account not only the amount of carbon sequestration but also the changes in soil N2O emission and CO2 emissions from fuel use in tillage operations. The changes in N2O emissions are derived from a meta-analysis of published studies, and changes in fuel use are based on USDA data. These are used to estimate changes in global warming potential (GWP) associated with adoption of no-till practices, and the changes in GWP are then used in an economic analysis of the potential supply of GHG offsets from the region. Simulation results demonstrate that taking N2O emissions into account could result in substantial underestimation of the potential for GHG mitigation in the central U.S. wheat pasture systems, and large over-estimation in the corn-soy-hay systems. Fuel use also has quantitatively important effects, although generally smaller than N2O. These findings suggest that it is important to incorporate these two effects in estimates of GHG offset potential from agricultural lands, as well as in the design of GHG offset contracts for more complete accounting of the effect that no-till adoption will have on greenhouse gas emissions.