• Authors:
    • Merrill, S. D.
    • Black, A. L.
    • Bauer, A.
  • Source: Soil Science Society of America Journal
  • Volume: 60
  • Issue: 2
  • Year: 1996
  • Summary: In dryland cropping, no-tillage ran increase small grain crop growth compared with conventional tillage. Because root systems develop ahead of aboveground growth and are affected by soil environment, observation of root growth will show the mechanisms by which no-till enhances crop growth. Wheat (Triticum aestivum L.) was grown in a spring wheat-winter wheat-sunflower (Helianthus annus L.) rotation begun in 1984 on Temvik-aWilton silt loam (fine-loamy, mixed TS pic and Pachic Haploborolls) under conventional till (CT: spring dishing), minimal till (hlT: spring undercutting) and no-till (NT). Root length growth OULG) was measured by microvideo camera in pressurized-wall minirhizotrons, and soil water was measured by neutron moisture meter. Relative to CT, NT generally enhanced RLG more than aboveground growth; RLG averaged 65, 130, and 145 km/cm(2) in 1988, 1989, and 1990, respectively. In 1988, RLG was 37% greater than hlT (P < 0.1), with CT intermediate. In 1989, RLG was 40% greater in NT than in CT, with ILIT intermediate, and RLG in 1990 was 112% greater in NT than CT (no MT). Final biomass averaged 380, 1730, and 3090 kg/ha in 1988 through 1990, and was 36% greater, not significantly different, and 44% greater in NT than CT, respectively. Root penetration was shallow (1.1 m or less) in dry subsoil, but in each year roots penetrated to greater soil depths under NT than under hlT or CT. Amounts of stored soil water were generally not significantly different among tillages, but more water was depleted in 1990 under NT than CT. Cooler soil under NT (measured in 1989) and superior soil water conservation in the near-surface zone appear to confer a root growth advantage to the NT treatment.
  • Authors:
    • Sinclair, T. R.
    • Amir, J.
  • Source: Field Crops Research
  • Volume: 47
  • Issue: 1
  • Year: 1996
  • Summary: Cereal Cyst Nematode (CCN, Heterodera avenae Woll.) has been shown to be a devastating pest for wheat (Triticum aestivum L.) in dryland regions. Following in the season preceding the cropping season has been hypothesized to sanitize the soil of CCN and allow wheat production. This paper explores management options that might allow the continuous production of wheat in these regions. In a 20-year study in the Negev, Israel, on a sandy loam, loessial, soil, it was found that in those seasons with high rainfall there was virtually no decrease in annual wheat yields for continuous crops as compared to biennial fallow yields obtained with the conventional wheat system. The hypothesis that high soil water content substantially alleviates the damage resulting from CCN infestation was confirmed in a pot study. A practical solution for maintaining high soil water content in the field was to leave a straw mulch on the soil surface to decrease soil evaporation. A chopper was added to a grain harvester to finely chop the straw so that it settles to the soil surface through the stubble, and a no-till drill was used for sowing through the straw. The straw-mulch system was shown to result in annual yields from continuous wheat that were equivalent to yields in alternate years with the conventional fallow wheat system, thereby doubling wheat production in this dryland region.
  • Authors:
    • Dhuyvetter, K. C.
    • Thompson, C. R.
    • Norwood, C. A.
    • Halvorson, A. D.
  • Source: Journal of Production Agriculture
  • Volume: 9
  • Issue: 2
  • Year: 1996
  • Summary: Dryland wheat (Triticum aestivum L.) in the Great Plains generally is planted in a wheat- fallow (WF) rotation. Wheat grown in rotation with a summer row crop like corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], or sunflower [Helianlhus annuus var. macrocarpus (DC,) Ck11.] increases cropping intensity, allowing a crop to be produced annually on 67 to 100% of tillable acres. A review of economic analyses of dryland cropping systems in the Great Plains was conducted to compare net returns, production costs, financial risk, and compatibility with the 1990 Farm Bill. Seven of eight studies reported that net returns were greater from a more intensive crop rotation than from WF when reduced-tillage (RT) or no-till (NT) were used following wheat harvest and prior to the summer crop planting, With government program payments, WF was more profitable with conventional tillage (CT) than with NT. Production costs increased as cropping intensity increased and tillage decreased. Economic risk analysis showed that wheat-sorghum-fallow (WSF) was less risky than WF in Kansas. Cropping systems using more intensive rotations with less tillage had higher production costs than WF, but also had increased net returns and reduced financial risk, while remaining in compliance with 1990 Farm Bill provisions.
  • 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:
    • Mosier, A. R.
    • Delgado, J. A.
  • Source: Journal of Environmental Quality
  • Volume: 25
  • Issue: 5
  • Year: 1996
  • Summary: Nitrous oxide (N2O) and methane (CH4) are greenhouse gases that are contributing to global warming potential. Nitrogen (N) fertilizer is one of the most important sources of anthropogenic N2O emissions. A field study was conducted to compare N-use efficiency and effect on N2O and CH4 flux, of urea, urea plus the nitrification inhibitor dicyandiamide (U + DCD), and a control release fertilizer, polyolefin coated urea (POCU) in irrigated spring barley (Hordeum vulgare L.) in northeastern Colorado. Each treatment received 90 kg urea-N ha(-1) and microplots labeled with N-15-fertilizer were established. Average N2O emissions were 4.5, 5.2, 6.9, and 8.2 g N ha(-1) d(-1) for control, U + DCD, POCU, and urea, respectively. During the initial 21 d after fertilization, N2O emissions were reduced by 82 and 71% in the U + DCD and POCU treatments, respectively, but continued release of N fertilizer from POCU maintained higher N2O emissions through the remainder of the growing season. No treatment effect on CH4 oxidation in soils was observed. Fertilizer N-15 found 50 to 110 cm below the soil surface was lower in the POCU and U + DCD treatments. At harvest, recovery of N-15-fertilizer in the plant-soil system was 98, 90, and 85% from POCU, urea, and U + DCD, respectively. Grain yield was 2.2, 2.5, and 2.7 Mg ha(-1) for POCU, urea, and U + DCD, respectively. Dicyandiamide and POCU showed the potential to be used as mitigation alternatives to decrease N2O emissions from N fertilizer and movement of N out of the root zone, but N release from POCU does need to be formulated to better match crop growth demands.
  • Authors:
    • Franzluebbers, A. J.
    • Arshad, M. A.
  • Source: Soil Science Society of America Journal
  • Volume: 60
  • Issue: 5
  • Year: 1996
  • Summary: Changes in soil organic matter (SOM) pools during adoption of reduced (RT) or zero tillage (ZT) can influence soil physical properties, nutrient cycling, and CO2 flux between soil and atmosphere. We determined soil organic C (SOC), soil microbial biomass C (SMBC), basal soil respiration (BSR), and mineralizable N to a depth of 200 mm at the end of 3, 5, and 6 yr after implementation of tillage management on a Falher clay (fine, montmorillonitic, frigid Typic Natriboralf) near Rycroft, Alberta, in a canola (Brassica campestris L.)-wheat (Triticum Aestivum L.)-barley (Hordeum vulgare L.)-fallow cropping system. At the end of 6 yr, SOC was not different among tillage regimes and averaged 8.6 kg m−2. At the end of 3 and 5 yr, SMBC was not significantly different among tillage regimes, but at the end of 6 yr SMBC was 7% greater in RT and 9% greater in ZT than in conventional tillage (CT). Basal soil respiration and mineralizable N at the end of 6 yr were not different among tillage regimes following barley and averaged 2.7 g CO2-C m−2 d−1 and 5.0 g inorganic N m−2 24 d−1, respectively. However, BSR following fallow was 2.2, 2.5, and 2.6 g CO2-C m−2 d−1 in CT, RT, and ZT, respectively. Mineralizable N following fallow was 5.8 g inorganic N m−2 (24 d)−1 in RT and ZT and 7.3 g inorganic N m−2 (24 d)−1 in CT. At 0 to 50 mm, there was no significant increase in SOC at the end of 6 yr, a 17 to 36% increase in SMBC, and a 12 to 69% increase in BSR with ZT compared with CT, depending on rotation phase. Relatively small changes in SOM pools with adoption of conservation tillage may be attributable to the large amount of SOM initially present and the cold, semiarid climate that limits SOM turnover.
  • Authors:
    • Lyon, D. J.
    • Baltensperger, D. D.
  • Source: Journal of Production Agriculture
  • Volume: 8
  • Issue: 4
  • Year: 1995
  • Summary: Downy brome (Bromus tectorum L.), Jointed goatgrass (Aegilops cylindrica Host), and volunteer cereal rye (Secale cereale L.) are winter annual grass weeds that are increasingly troublesome in the winter wheat (Triticum aestivum L. emend. Thell.)-fallow rotation areas of the western USA. Six dryland cropping systems-continuous no-till winter wheat, winter wheat-fallow with fall tillage, winter wheat-fallow with fail applied herbicide, winter wheat-fallow-fallow, winter wheat-sunflower-fallow, and winter wheat-prose millet-fallow-were compared for their effect on winter annual grass densities in winter wheat. Winter annual grass densities averaged 145, 4.4, and 0.4 plants/sq yard for the 1-, 2-, and 3-yr systems, respectively. Eradication of the winter annual grasses was not achieved with any of the systems. Dockage and foreign material levels in wheat grain were lower in 3-yr than in 2-yr cropping systems. Jointed goatgrass was the most persistent annual grass investigated.
  • Authors:
    • Li, C.
  • Source: Soil Management and Greenhouse Effect
  • Year: 1995
  • Authors:
    • Rowell, A. L.
    • Weinrich, K. B.
    • Barnwell, T. O.
    • Jackson, R. B.,IV
    • Patwardhan, A. S.
    • Donigian, A. S.
  • Source: Soil Management and Greenhouse Effect
  • Year: 1995
  • Authors:
    • Porter, P.
  • Source: Journal of Production Agriculture
  • Volume: 8
  • Issue: 2
  • Year: 1995
  • Summary: A study was conducted on an Orangeburg loamy sand (fine-loamy, siliceous, thermic Typic Paleudults) near Blackville, South Carolina in 1990-92 to determine the effect of deep tillage on both canola [rape] and wheat, the subsequent response of doublecropped soyabeans, and response of wheat grown following the soyabean crop when controlled traffic and minimum tillage practices were used. Canola yields averaged 37.8 bu/acre in 1991 and 43.2 bu/acre in 1992, whereas wheat yields were 58.0 and 72.5 bu/acre, respectively. In both years, deep tillage (chiselling to 11 in) had no effect on wheat yields when compared with discing. Deep tillage increased canola yields by 12.5% in the drier of the two growing seasons. Soyabean yields were not significantly affected by the tillage used for the previous crops. Subsoiled soyabeans yielded 33.7 vs. 31.9 bu/acre for no-till soyabeans in 1991, and 22.6 vs. 19.4 bu/acre in 1992. In 1992, soyabean tillage following wheat did not affect soyabean yield but following canola, in-row subsoiling resulted in greater soyabean yields than no-till. Wheat following soyabeans was not affected by the tillage practice used for the previous winter crops, and the 1992 wheat yields were unaffected by previous winter crop or soyabean tillage. In 1993, soyabean tillage did not affect subsequent wheat yield but following canola, in-row subsoiling resulted in greater wheat yields than no-till. It is suggested that canola has no adverse effect on either soyabeans or wheat when grown in sequence on a Coastal Plain soil.