• Authors:
    • Bridges, M.
    • Henry, W. B.
    • Shaner, D. L.
    • Khosla, R.
    • Westra, P.
    • Reich, R.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 6
  • Year: 2008
  • Summary: An area of interest in precision farming is variable-rate application of herbicides to optimize herbicide use efficiency and minimize negative off-site and non-target effects. Site-specific weed management based on field scale management zones derived from soil characteristics known to affect soil-applied herbicide efficacy could alleviate challenges posed by post-emergence precision weed management. Two commonly used soil-applied herbicides in dryland corn ( Zea mays L.) production are atrazine and metolachlor. Accelerated dissipation of atrazine has been discovered recently in irrigated corn fields in eastern Colorado. The objectives of this study were (i) to compare the rates of dissipation of atrazine and metolachlor across different soil zones from three dryland no-tillage fields under laboratory incubation conditions and (ii) to determine if rapid dissipation of atrazine and/or metolachlor occurred in dryland soils. Herbicide dissipation was evaluated at time points between 0 and 35 d after soil treatment using a toluene extraction procedure with GC/MS analysis. Differential rates of atrazine and metolachlor dissipation occurred between two soil zones on two of three fields evaluated. Accelerated atrazine dissipation occurred in soil from all fields of this study, with half-lives ranging from 1.8 to 3.2 d in the laboratory. The rapid atrazine dissipation rates were likely attributed to the history of atrazine use on all fields investigated in this study. Metolachlor dissipation was not considered accelerated and exhibited half-lives ranging from 9.0 to 10.7 d in the laboratory.
  • Authors:
    • Diaz Franco, A.
    • Salinas Garcia, J. R.
    • Garza Cano, I.
    • Mayek Perez, N.
  • Source: Revista Fitotecnia Mexicana
  • Volume: 31
  • Issue: 3
  • Year: 2008
  • Summary: Conservation tillage promotes agricultural soil sustainability and the inoculation of arbuscular mycorrhiza fungi (AMF) enhances crop growth and yields. In this study, single and combined effects of tillage systems and inoculation of AMF on charcoal rot ( Macrophomina phaseolina) incidence and severity, and grain yield in maize ( Zea mays L.) were determined. The study was conducted in semi-arid dryland conditions. Three factors with different levels were tested in maize hybrid 'Pioneer 3025W': four tillage systems (moldboard or conventional tillage, subsoil-bedding, shred-bedding and no-tillage); two fertilization levels (inoculated seeds with AMF Glomus intraradices, and fertilization rate of 60N-40P-00K); and three years of evaluation (2003 to 2005). Chlorophyll leaf index (CI), incidence (IM) and severity (SM) of M. phaseolina, arbuscular mycorrhizal colonization (AMC), and grain yield (GY) were determined. No tillage showed the lowest charcoal rot (IM and SM), but also the lowest GY. Tillage systems did not affect AMC of maize. Inoculation was similar to chemical fertilization in CI, IM, SM and GY, although with increase of AMC on mycorrhization treatment. The highest values CI, lesser IM and SM, and highest GY were found in 2004 due to the highest rain fall (460 mm) compared to 2003 (230 mm) and 2005 (125 mm). Results indicate that conservation tillage is a strategy to reduce charcoal in maize crop, although associated with grain yield losses, respect to conventional tillage.
  • Authors:
    • Endale, D. M.
    • Schomberg, H. H.
    • Fisher, D. S.
    • Jenkins, M. B.
    • Sharpe, R. R.
    • Cabrera, M. L.
  • Source: Agronomy Journal
  • Volume: 100
  • Issue: 5
  • Year: 2008
  • Summary: Corn (Zea mays L.) producers in the southeastern United States must overcome soil and water limitations to take advantage of the expanding corn market. In this 2001 to 2005 study on a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) near Watkinsville, GA, we compared dry land corn biomass and yield under conventional tillage (CT) vs. no-tillage (NT) with ammonium nitrate or sulfate (based on availability) as conventional fertilizer (CF) vs. poultry litter (PL). In a randomized complete block split plot design with three replications, main plots were under tillage and subplots under fertilizer treatments. The cover crop was rye (Secale cereale L.). Over 5 yr, NT and PL increased grain yield by 11 and 18%, respectively, compared with CT and CF. Combined, NT and PL increased grain yield by 31% compared with conventionally tilled and fertilized corn. Similarly, soil water was 18% greater in NT than CT in the 0- to 10-cm depth. In 2 yr of measurements, dry matter of stalks and leaves and leaf area index under PL were an average of 39 and 22% greater, respectively, than under CF during reproduction. Values were 21 and 6% greater, respectively, under NT than CT but during tasseling. Analysis of 70 yr of daily rainfall records showed that supplemental irrigation is needed to meet optimal water requirement. Our results indicate that corn growers can use rainfall more efficiently, reduce yield losses to drought, and expect increased corn yields with a combination of no-tillage management and long-term use of poultry litter.
  • Authors:
    • Fan, T.
    • Xu, M
    • Song, S.
    • Zhou, G.
    • Ding, L.
  • Source: Journal of Plant Nutrition and Soil Science
  • Volume: 171
  • Issue: 3
  • Year: 2008
  • Summary: Changes in grain yields and soil organic carbon (SOC) from a 26 y dryland fertilization trial in Pingliang, Gansu, China, were recorded. Cumulative C inputs from straw and root and manure for fertilizer treatments were estimated. Mean wheat ( Triticum aestivum L.) yields for the 18 y ranged from 1.72 t ha -1 for the unfertilized plots (CK) to 4.65 t ha -1 for the plots that received manure (M) annually with inorganic N and P fertilizers (MNP). Corn ( Zea mays L.) yields for the 6 y averaged 2.43 and 5.35 t ha -1 in the same treatments. Yields declined with year except in the CK for wheat. Wheat yields for N only declined with time by 117.8 kg ha -1 y -1 that was the highest decrease among all treatments, and that for NP declined by 84.7 kg ha -1 y -1, similar to the declines of 77.4 kg ha -1 y -1 for the treatment receiving straw and N annually and P every second year (SNP). Likewise, the corn yields declined highly for all treatments, and the declined amounts ranged from 108 to 258 kg ha -1 y -1 which was much higher than in wheat. These declined yields were mostly linked to both gradual dry weather and nutrients depletion of the soil. The N only resulted in both P and K deficiency in the soil, and soil N and K negative balances in the NP and MNP were obvious. Soil organic carbon (SOC) in the 0-20 cm soil layer increased with time except in the CK and N treatments, in which SOC remained almost stable. In the MNP and M treatments, 24.7% and 24.0% of the amount of cumulative C input from organic sources remained in the soil as SOC, but 13.7% of the C input from straw and root in the SNP, suggesting manure is more effective in building soil C than straw. Across the 26 y cropping and fertilization, annual soil-C sequestration rates ranged from 0.014 t C ha -1 y -1 for the CK to 0.372 t C ha -1 y -1 for the MNP. We found a strong linear relationship ( R2=0.74, p=0.025) between SOC sequestration and cumulative C input, with C conversion-to-SOC rate of 16.9%, suggesting these dryland soils have not reached an upper limit of C sequestration.
  • Authors:
    • Kang, J.
    • Osmond, D. L.
  • Year: 2008
  • Authors:
    • Parkin, T. B.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 4
  • Year: 2008
  • Summary: It is generally recognized that soil N2O emissions can exhibit pronounced day-to-day variations; however, measurements of soil N2O flux with soil chambers typically are done only at discrete points in time. This study evaluated the impact of sampling frequency on the precision of cumulative N2O flux estimates calculated from field measurements. Automated chambers were deployed in a corn/soybean field and used to measure soil N2O fluxes every 6 h from 25 Feb. 2006 through 11 Oct. 2006. The chambers were located in two positions relative to the fertilizer bands--directly over a band or between fertilizer bands. Sampling frequency effects on cumulative N2O-N flux estimation were assessed using a jackknife technique where populations of N2O fluxes were constructed from the average daily fluxes measured in each chamber. These test populations were generated by selecting measured flux values at regular time intervals ranging from 1 to 21 d. It was observed that as sampling interval increased from 7 to 21 d, variances associated with cumulative flux estimates increased. At relatively frequent sampling intensities (i.e., once every 3 d) N2O-N flux estimates were within {+/-}10% of the expected value at both sampling positions. As the time interval between sampling was increased, the deviation in estimated cumulative N2O flux increased, such that sampling once every 21 d yielded estimates within +60% and -40% of the actual cumulative N2O flux. The variance of potential fluxes associated with the between-band positions was less than the over-band position, indicating that the underlying temporal variability impacts the efficacy of a given sampling protocol.
  • Authors:
    • Tyedmers, P.
    • Arsenault, N.
    • Pelletier, N.
  • Source: Environmental Management
  • Volume: 42
  • Issue: 6
  • Year: 2008
  • Summary: We used Life Cycle Assessment to scenario model the potential reductions in cumulative energy demand (both fossil and renewable) and global warming, acidifying, and ozone-depleting emissions associated with a hypothetical national transition from conventional to organic production of four major field crops [canola (Brassica rapa), corn (Zea mays), soy (Glycine max), and wheat (Triticum aestivum)] in Canada.
  • Authors:
    • Roberts, T. L.
  • Source: Turkish Journal of Agriculture and Forestry
  • Volume: 32
  • Year: 2008
  • Summary: Public interest and awareness of the need for improving nutrient use efficiency is great, but nutrient use efficiency is easily misunderstood. Four indices of nutrient use efficiency are reviewed and an example of different applications of the terminology show that the same data set might be used to calculate a fertilizer N efficiency of 21% or 100%. Fertilizer N recovery efficiencies from researcher managed experiments for major grain crops range from 46% to 65%, compared to on-farm N recovery efficiencies of 20% to 40%. Fertilizer use efficiency can be optimized by fertilizer best management practices that apply nutrients at the right rate, time, and place. The highest nutrient use efficiency always occurs at the lower parts of the yield response curve, where fertilizer inputs are lowest, but effectiveness of fertilizers in increasing crop yields and optimizing farmer profitability should not be sacrificed for the sake of efficiency alone. There must be a balance between optimal nutrient use efficiency and optimal crop productivity.
  • Authors:
    • Gagnon, B.
    • Bertrand, N.
    • Chantigny, M. H.
    • Angers, D. A.
    • Rochette, P.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: Manure is known to increase soil N2O emissions by stimulating nitrification and denitrification processes. Our objective was to compare soil-surface N2O emissions following the application of liquid and solid dairy cattle manures to a loamy and a clay soil cropped to silage maize. Manures were applied in 2 consecutive years at rates equivalent to 150 kg total N ha(-1) and compared with a control treatment receiving an equivalent rate of synthetic N. Soil-surface N2O fluxes, soil temperature, and soil water, nitrate and ammonium contents were monitored weekly in manured and control plots. From 60 to 90% of seasonal N2O emissions occurred during the first 40 d following manure and synthetic fertilizer applications, indicating that outside that period one or several factors limited N2O emissions. The period of higher emissions following manure and fertilizer application corresponded with the period when soil mineral N contents were highest (up to 17 g NO3- -N m(-2)) and water-filled pore space (WFPS) was greater than 0.5 m(3) m(-3). The absence of significant N2O fluxes later in the growing season despite high WFPS levels indicated that the stimulating effect of organic and synthetic N additions on soil N2O production was relatively short-lived. Fertilization of silage maize with dairy cattle manure resulted in greater or equal N2O emissions than with synthetic N. This was observed despite lower overall soil mineral N contents in the manured plots, indicating that other factors affected by manure, possibly additional C substrates and enhanced soil respiration, resulted in greater denitrification and N2O production. Silage maize yields in the manured soils were lower than those receiving synthetic N, indicating that the N2O emissions per kilogram of harvested biomass were greater for manures than for synthetic N. Our results also suggest that the main source of N2O was nitrification in the loam and denitrification in the clay soil. There was no clear difference in N2O emissions between liquid and solid manures. The variable effects of liquid and solid manure addition on soil N2Oemissions reported in the literature likely result from the variable composition of the manures themselves as well as from interactions with other factors such as soil environment and farming practices. A better characterization of the availability of manure C and N is required to assess the impact of manure application on soil N2O emissions under field conditions.
  • Authors:
    • Desjardins, R. L.
    • Wagner-Riddle, C.
    • Pennock, D. J.
    • McConkey, B. G.
    • Lemke, R. L.
    • Worth, D. E.
    • Rochette, P.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 5
  • Year: 2008
  • Summary: International initiatives such as the United Nations Framework Convention on Climate Change and the Kyoto Protocol require that countries calculate national inventories of their greenhouse gas emissions. The objective of the present study was to develop a country-specific (Tier II) methodology to calculate the inventory of N2O emissions from agricultural soils in Canada. Regional fertilizer-induced emission factors (EFreg) were first determined using available field experimental data. Values for EFreg were 0.0016 kg N2O-N kg-1 N in the semi-arid Brown and 0.008 kg N2O-N kg N-1 in the sub-humid Black soil zones of the Prairie region, and 0.017 kg N2O-N kg-1 N in the humid provinces of Quebec and Ontario. A function relating EFreg to the "precipitation to potential evapotranspiration" ratio was determined to estimate annual emission factors (EFeco) at the ecodistrict scale in all agricultural regions of Canada. Country-specific coefficients were also developed to account for the effect of several additional factors on soil N2O emissions. Emissions from fine-textured soils were estimated as being 50% greater than from coarse- and medium-textured soils in eastern Canada; emissions during winter and spring thaw corresponded to 40% of emissions during the snow-free season in eastern Canada; increased emissions from lower (wetter) sections of the landscape and irrigated areas were accounted for; emissions from no-till soils were 10% greater in eastern, but 20% lower in western Canada than from those under conventional tillage practices; emissions under summerfallow were estimated as being equal to those from soils under annual cropping. This country-specific methodology therefore accounts for regional climatic and land use impacts on N2O emission factors, and includes several sources/offsets that are not included in the Intergovernmental Panel on Climate Change (IPCC) default approach.