• Authors:
    • Knezevic, S. Z.
    • Leeson, J. Y.
    • Thomas, A. G.
    • Acker, R. C. van
    • Frick, B. L.
  • Source: Canadian Journal of Plant Science
  • Volume: 80
  • Issue: 4
  • Year: 2000
  • Summary: In 1997, a weed survey was conducted during July and August in fields of wheat, barley, oat, canola [rape] and flax in Manitoba, Canada. Field selection was based on a stratified-random sampling methodology using ecodistricts as strata. Species in the Poaceae family were most commonly observed in the survey, followed by species in the Polygonaceae, Asteraceae and Brassicaceae families. The six most abundant weed species were green foxtail ( Setaria viridis), wild oats ( Avena fatua), wild buckwheat ( Polygonum convolvulus) [ Fallopia convolvulus], Canada thistle ( Cirsium arvense), red-root pigweed ( Amaranthus retroflexus) and wild mustard ( Sinapis arvensis). The survey highlighted significant differences between ecoregions and between crops in residual weed infestations. The weed community in the Boreal Transition ecoregion was dominated by seven species, whereas fields in the Aspen Parkland and Lake Manitoba Plain ecoregions were dominated by two species and the Interlake Plain ecoregion was dominated by only one species. Although significant differences were found between the weed communities in crops, they were not as great as differences between ecoregions. The Manitoba residual weed community in 1997 was very similar to that reported for 1978-81 and 1986, suggesting that the same species should remain a focus for weed management.
  • Authors:
    • Bertholdsson, N. O.
  • Source: Sveriges Utsädesförenings Tidskrift
  • Volume: 110
  • Issue: 4
  • Year: 2000
  • Summary: The use of hydroponic techniques to measure the response to stress by cereals is discussed with reference to studies on drought, low N inputs and crop weed competition with barley, wheat, oats, triticale and rape.
  • Authors:
    • Follett,R. F.
    • Reule,C. A.
    • Halvorson,A. D.
  • Source: Soil Science Society of America Journal
  • Volume: 63
  • Issue: 4
  • Year: 1999
  • Summary: No-till (NT) increases the potential to crop more frequently in the Great Plains than with the conventional-till (CT) crop-fallow farming system. More frequent cropping requires N input to maintain economical yields. We evaluated the effects of N Fertilization on crop residue production and its subsequent effects on soil organic C (SOC) and total soil N (TSN) in a dryland NT annual cropping system. Six N rates (0, 22, 45, 67, 90, and 134 kg N ha(-1)) were applied to the same plots from 1984 through 1994, except 1988 when rates sere reduced 50%, on a Weld silt loam (fine, smectitic, mesic Aridic Argiustoll). Spring hal leg (Hordeum vulgare L.), corn (Zea mays L.),winter wheat (Triticum aestivum L.), and oat (Avena sativa L.)-pea (Lathyrus tingitanus L.) hay were grown in rotation. Crop residue production varied with crop and gear. Estimated average annual aboveground residue returned to the soil (excluding hay years) was 2925, 3845, 4354, 4365, 4371, and 4615 kg ha(-1), while estimated annual contributions to belowground (root) residue C were 1060, 1397, 1729, 1992, 1952, and 2031 kg C ha(-1) for the above N rates, respectively. The increased amount of crop residue returned to the soil with increasing N rate resulted in increased SOC and TSN levels in the 0- to 7.5-cm soil depth after 11 crops. The fraction of applied N fertilizer in the crop residue decreased with increasing N rate. Soil bulk density (D-b) in the 0- to 7.5-cm soil depth decreased as SOC increased, The increase in SOC with N fertilization contributes to improved soil quality and productivity, and increased efficiency of C sequestration into the soil. Carbon sequestration can be enhanced by increasing crop residue production through adequate N fertility.
  • Authors:
    • Tanni, R.
    • Pietola, L.
  • Source: Agricultural and Food Science in Finland
  • Volume: 8
  • Issue: 4/5
  • Year: 1999
  • Summary: The role of plant growth regulators (PGR) in nitrogen (N) fertilization of spring wheat and oats (CCC [chlormequat]), fodder barley (etephon/mepiquat) an oilseed rape (etephone) in crop rotation was studied in 1993-96 on loamy clay soil. Carry over effect of the N fertilization rates (0-180 kg/ha) was evaluated in 1997. N fertilization rate for the best grain/seed yield (120-150 kg/ha) was not affected by PGRs. The seed and N yields of oilseed rape were improved frequently by the recommended use of PGR. The yield of oats increased in 1995-96. Even though PGR effectively shortened the plant height of spring wheat, the grain yield increased only in 1995. N yield of wheat grains was not increased. Response of fodder barley to PGR was insignificant or even negative in 1995. The data suggest that PGRs may decrease some N leaching at high N rates by improving N uptake by grain/seeds, if the yield is improved. The carryover study showed that in soils with no N fertilization, as well as in soils of high N rates, N uptake was higher than in soils with moderate N fertilization (60-90 kg/ha), independent of PGRs. According to soil mineral N contents, N leaching risk was significant (15-35 kg/ha) only after dry and warm late seasons. After a favourable season of high yields, the N rates did not significantly affect soil mineral N contents.
  • Authors:
    • Drury, C. F.
    • McKenney, D, J.
    • vanLuyk, C. L.
    • Gregorich, E. G.
    • Oloya, T. O.
    • Tan, C. S.
  • Source: Soil Science Society of America Journal
  • Volume: 62
  • Issue: 6
  • Year: 1998
  • Summary: Various long-term crop management strategies are known to have differing effects on soil organic C. This laboratory study explored the effect of long-term (35 yr) fertilization and crop rotation on soil organic C and denitrification capacity at different depths of a Brookston clay loam soil (fine-loamy, mixed, mesic Typic Argiaquoll). We related denitrification capacity to soil biochemical (CO2 production, organic C, microbial biomass C, soluble organic C) and soil structural properties. Denitrification capacity was determined as the increase in N2O that occurred when NO-3-amended soils were incubated anaerobically in the presence of acetylene. Treatments included fertilized and nonfertilized plots of continuous corn (Zea mays L.), continuous bluegrass (Poa pratensis L.), and rotation corn (corn-oat [Avena sativa L.]-alfalfa [Medicago sativa L.]-alfalfa). Soils from an adjacent mixed deciduous woodlot were also sampled. Soils from the woodlot had higher denitrification capacities than the continuous or rotation corn treatments. Among the agricultural treatments, the soil under bluegrass had the greatest denitrification capacity followed by the soil under corn rotation, with the continuous corn having the lowest capacity. Long-term fertilization resulted in 35% higher denitrification capacity and 65% higher CO2 production than nonfertilized soils. Denitrification capacity across all depths in the agricultural soils was correlated with CO2 production (r2 = 0.76), microbial biomass C (r2 = 0.60), and organic C (r2 = 0.54); however, the relationship between denitrification capacity and soil structure was not as strong (r2 = 0.28).
  • Authors:
    • Harriss, R. C.
    • Narayanan, V.
    • Li, C.
  • Source: Global Biogeochemical Cycles
  • Volume: 10
  • Issue: 2
  • Year: 1996
  • Summary: The Denitrification-Decomposition (DNDC) model was used to elucidate the role of climate, soil properties, and farming practices in determining spatial and temporal variations in the production and emission of nitrous oxide (N[2]O) from agriculture in the United States. Sensitivity studies documented possible causes of annual variability in N[2]O flux for a simulated Iowa corn-growing soil. The 37 scenarios tested indicated that soil tillage and nitrate pollution in rainfall may be especially significant anthropogenic factors which have increased N[2]O emissions from soils in the United States. Feedbacks to climate change and biogeochemical manipulation of agricultural soil reflect complex interactions between the nitrogen and carbon cycles. A 20% increase in annual average temperature in °C produced a 33% increase in N[2]O emissions. Manure applications to Iowa corn crops enhanced carbon storage in soils, but also increased N[2]O emissions. A DNDC simulation of annual N[2]O emissions from all crop and pasture lands in the United States indicated that the value lies in the range 0.9 - 1.2 TgN. Soil tillage and fertilizer use were the most important farming practices contributing to enhanced N[2]O emissions at the national scale. Soil organic matter and climate variables were the primary determinants of spatial variability in N[2]O emissions. Our results suggest that the United States Government, and possibly the Intergovernmental Panel on Climatic Change (IPCC), have underestimated the importance of agriculture as a national and global source of atmospheric N[2]O. The coupled nature of the nitrogen and carbon cycles in soils results in complex feedbacks which complicate the formulation of strategies to reduce the global warming potential of greenhouse gas emissions from agriculture.
  • Authors:
    • Ghaffarzadeh, M.
    • Cruse, R. M.
    • Robinson, C. A.
  • Source: Soil Science Society of America Journal
  • Volume: 60
  • Issue: 1
  • Year: 1994
  • Summary: Time, fertilizer, tillage, and cropping systems may alter soil organic carbon (SOC) levels. Our objective was to determine the effect of long-term cropping systems and fertility treatments on SOC. Five rotations and two N fertility levels at three Iowa sites (Kanawha, Nashua, and Sutherland) maintained for 12 to 36 yr were evaluated. A 75-yr continuous corn (Zea mays L.) site (Ames) with a 40-yr N-P-K rate study also was evaluated. Soils were Typic and Aquic Hapludolls and Typic Haplaquolls. Four-year rotations consisting of corn, oat (Avena sativa L.), and meadow (alfalfa [Medicago sativa L.], or alfalfa and red clover [Trifolium pratense L.]) had the highest SOC (Kanawha, 32.1 g/kg; Nashua, 21.9 g/kg; Sutherland, 27.9 g/kg). Corn silage treatments (Nashua, [≤] 18.9 g/kg; Sutherland, [≤]23.2 g/kg) and no-fertilizer treatments (Kanawha, 25.3 g/kg; Nashua, [≤]20.9 g/kg; Sutherland, [≤]23.5 g/kg) had the lowest SOC. A corn-oat-meadow-meadow rotation maintained initial SOC (27.9 g/kg) after 34 yr at Sutherland. Continuous corn resulted in loss of 30% of SOC during 35 yr of manure and lime treatments. SOC increased 22% when N-P-K treatments were imposed. Fertilizer N, initial SOC levels, and previous management affected current SOC levels. Residue additions were linearly related to SOC (Ames, r2 = 0.40; Nashua, r2 = 0.82; Sutherland, r2 = 0.89). All systems had 22 to 49% less SOC than adjacent fence rows. Changing cropping systems to those that conserve SOC could sequester as much as 30% of C released since cropping began, thereby increasing SOC.
  • Authors:
    • Fausey, N. R.
    • Mahboubi, A. A.
    • Lal, R.
  • Source: Soil Science Society of America Journal
  • Volume: 58
  • Issue: 2
  • Year: 1994
  • Summary: Sustainable use of soil resources can be assessed from management-induced changes in soil properties from long-term experiments. Such data are scanty, especially with regard to changes in soil physical properties. Therefore, soil physical and chemical analyses were performed 28 yr after initiating a crop rotation-tillage experiment on a well-drained Wooster silt loam soil (fine-loamy, mixed, mesic Typic Fragiudalf) at Wooster, OH. All combinations of three rotations (continuous corn [CC; Zea mays L.]; corn and soybean [Glycine mar (L.) Merr.] in a 2-yr rotation [CS]; and corn, oat [Avena sativa L.], and meadow in a 3-yr rotation [COM]) and of three tillage treatments (no-tillage [NT]; chisel plow [CP]; and moldboard plow [MP]) were maintained on the same plots for the entire length of study. All crops were grown every year. Soil properties studied for the 0- to 15-cm layer were: structural stability of aggregates, bulk density, total porosity, penetration resistance, organic C, pH, cation-exchange capacity (CEC), and exchangeable K, Ca and Mg. Mean bulk densities measured prior to tillage treatments and planting were 1.18, 1.24, and 1.28 Mg m-3 for CC, CS, and COM rotations, respectively. The lowest bulk density was observed for the CC-NT combination. Total aggregation in CS was 26.9% greater than CC and 111.2% greater than COM. With tillage treatments, aggregation was in the order of NT>CP>MP. Rotation treatments had no effect on aggregate size. In accord with bulk density, the relative magnitude of organic C content was 100, 85, and 63 for CC, CS, and COM rotations, respectively.
  • Authors:
    • Shennan, C.
    • Stivers, L. J.
  • Source: Journal of Production Agriculture
  • Volume: 4
  • Issue: 3
  • Year: 1991
  • Summary: Results from the first 2 years of the experiment are used to compare the productivity of several legume green manures and to determine if they can provide adequate available soil N to support yields of a subsequent crop of processing tomatoes (Lycopersicon lycopersicum L. Karsten var. lycopersicum) typical for this area. Lana woolly-pod vetch (Vicia dasycarpa Ten.), bell beans (Vicia faba L.), berseem clover (Trifolium alexandrinum L.), Austrian winter peas (Pisum arvense L.), oats (Avena sativa L.), and an oats and vetch mixture, planted in October and disked under in April, were compared with various levels of ammonium sulfate fertilizer.
  • Authors:
    • Duffy, M.
    • Chase, C.
  • Source: American Journal of Alternative Agriculture
  • Volume: 6
  • Issue: 04
  • Year: 1991
  • Summary: Labor requirements, production costs, yields, and economic returns were evaluated for conventional and reduced-chemical cropping systems in northeast Iowa from 1978 to 1989. Continuous corn (C-C) and corn-soybean (C-Sb) rotations represented the conventional system; a corn-oat-meadow (C-O-M) rotation represented the reducedchemical system. The C-C and C-Sb rotations used both commercial pesticides and fertilizers. The C-O-M rotation used manure for fertilization and applied pesticides only in emergencies. Operations for all systems were implemented by one farm manager. The C-Sb rotation had the highest corn yield over the 12-year period, and the C-O-M rotation the lowest. The corn within the C-O-M rotation, however, produced the second highest average return to land, labor, and management. With costs of production substantially lower than the conventional systems, the C-O-M corn crop had competitive returns despite lower yield. The C-Sb average return to land, labor, and management was significantly higher than for the other systems. Hourly labor charges of $4, $10, $20, and $50 had little effect on the rankings of economic returns. Because of unusually high alfalfa reseeding costs and low average oat yields, returns to the C-O-M rotation were significantly lower than C-Sb but comparable to C-C. With better alfalfa establishment and higher average oat yields, the reduced-chemical system might have been competitive with the C-Sb conventional system.