• Authors:
    • Weise, S. F.
    • Swanton, C. J.
  • Source: Weed Technology
  • Volume: 5
  • Issue: 3
  • Year: 1991
  • Summary: A growing awareness of environmental issues in Canada has had a major influence on government policies. An initiative was launched by the government of Ontario to promote research toward the development of an integrated weed management (IWM) system. Research in IWM must take all aspects of the cropping system into consideration and evolve in a progressive manner. This approach must encompass the role of conservation tillage, knowledge of the critical period of weed interference, alternative methods of weed control, enhancement of crop competitiveness, modeling of crop-weed interference, influence of crop rotation and seed bank dynamics, and education and extension of the findings. The complexity involved in addressing these issues requires a multi-disciplinary approach.
  • Authors:
    • Lafond, G. P.
    • Zentner, R. P.
    • Biederbeck, V. O.
    • Campbell, C. A.
  • Source: Canadian Journal of Soil Science
  • Volume: 71
  • Issue: 3
  • Year: 1991
  • Summary: The effects of crop rotations and various cultural practices on soil organic matter quantity and quality in a Rego, Black Chernozem with a thin A horizon were determined in a long-term study at Indian Head, Saskatchewan. Variables examined included: fertilization, cropping frequency, green manuring, and inclusion of grass Jegume hay crop in predominantly spring wheat (Triticum aestiyum L.) production systems. Generally, fertilizer increased soil organic C and microbial biomass in continuous wheat cropping but not in fallow-wheat or fallow-wheat-wheat rotations. Soil organic C, C mineralization (respiration) and microbial biomass C and N increased (especially in the 7.5- to l5-cm depth) with increasing frequency of cropping and with the inclusion of legumes as green manure or hay crop in the rotation. The influence of treatments on soil microbial biomass C (BC) was less pronounced than on microbial biomass N. Carbon mineralization was a good index for delineating treatment effects. Analysis of the microbial biomass C/N ratio indicated that the microbial suite may have been modified by the treatments that increased soil organic matter significantly. The treatments had no effect on specific respiratory activity (CO2-C/BC). However, it appeared that the microbial activity, in terms of respiration, was greater for systems with smaller microbial biomass. Changes in amount and quality of the soil organic matter were associated with estimated amount and C and N content of plant residues returned to the soil.
  • 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.
  • Authors:
    • Deibert, E. J.
  • Source: Agronomy Journal
  • Volume: 81
  • Issue: 4
  • Year: 1989
  • Summary: Information on response of soybean [Glycine max (L.) Merr.] cultivars to reduced tillage systems in northern dryland areas is limited. A 4-yr field study (1984 to 1987) was conducted to evaluate the effect of tillage system, weed control method, and cultivar maturity on soybean seed yield variables. An early and a late-maturing soybean cultivar were grown on a Fargo clay (fine, montmorillonitic frigid Vertic Haplaquoll) on established tillage plots. Tillage systems included conventional (moldboard plow) and three reduced tillage systems (sweep, intertill, and no-till) with herbicides or herbicides plus cultivation for weed control. Climatic conditions resulted in differences among years in seed yield, seed weight, seed moisture, seed oil concentration, and seed oil yield. These seed variables were not significantly influenced by tillage system, weed control method, or cultivar maturity when grown in rotation with barley (Hordeum vulgare L.), but showed significant interactions. Cultivation for weed control depressed seed yield and weight of only the early cultivar. Early plant water stress (June and July) lowered yield of the early cultivar more than the late cultivar. Early cultivar no-till yields (1240 kg ha−1) were greater than tilled system yields (average 1070 kg ha−1). while late cultivar yields were similar among systems (average 1420 kg ha−1). An early maturing cultivar performed similarly to a late-maturing cultivar irrespective of tillage system unless early plant water stress was encountered. Fall application of granular herbicide provided good weed control, but cultivation for weed control was not beneficial for the yields parameters measured.
  • Authors:
    • Ojima, D. S.
    • Cole, C. V.
    • Schimel, D. S.
    • Parton, W. J.
  • Source: Soil Science Society of America Journal
  • Volume: 51
  • Issue: 5
  • Year: 1987
  • Summary: We analyzed climatic and textural controls of soil organic C and N for soils of the U.S. Great Plains. We used a model of soil organic matter (SOM) quantity and composition to simulate steady-state organic matter levels for 24 grassland locations in the Great Plains. The model was able to simulate the effects of climatic gradients on SOM and productivity. Soil texture was also a major control over organic matter dynamics. The model adequately predicted aboveground plant production and soil C and N levels across soil textures (sandy, medium, and fine); however, the model tended to overestimate soil C and N levels for fine textured soil by 10 to 15%. The impact of grazing on the system was simulated and showed that steady-state soil C and N levels were sensitive to the grazing intensity, with soil C and N levels decreasing with increased grazing rates. Regional trends in SOM can be predicted using four site-specific variables, temperature, moisture, soil texture, and plant lignin content. Nitrogen inputs must also be known. Grazing intensity during soil development is also a significant control over steady-state levels of SOM, and since few data are available on presettlement grazing, some uncertainty is inherent in the model predictions.
  • Authors:
    • Miller, M.
    • O'Halloran, I.
    • Arnold, G.
  • Source: Canadian Journal of Soil Science
  • Volume: 66
  • Issue: 2
  • Year: 1986
  • Summary: In 1981, phosphorus absorption by young corn plants was greater from no-till than from plowed plots with similar NaHCO 3-extractable P (Ext P) concentrations. A series of growth room studies was conducted to explain this difference. Corn plants grown on cores from the no-till plots had a higher P concentration than plants grown on soil from the plowed plots, in spite of a lower root growth and a lower Ext P content. Disturbance of the no-till soil eliminated the effect. A parameter, accessible P (Acc-P), was calculated from root length and Ext P assuming P was absorbed from a cylinder of soil around each root. Shoot P content at a given Acc-P content was always higher with the undisturbed no-till soil than with either the disturbed no-till or the plowed soil. Irradiation (gamma-ray) of the no-till soil reduced P absorption by a similar degree to disturbance, indicating that a biological factor was involved. Disturbance of soil had no influence on P content of canola ( Brassica napus L.), a nonmycorrhizal crop. Soil disturbance reduced the intensity of mycorrhizal infection in corn roots. It is hypothesized that disturbance of the no-till soil reduced P absorption by reducing the effectiveness of the mycorrhizal symbiosis.
  • Authors:
    • Sommerfeldt, T. G.
    • Freeze, B. S.
  • Source: Canadian Journal of Soil Science
  • Volume: 65
  • Issue: 4
  • Year: 1985
  • Summary: The economics of hauling manure as a substitute for commercial fertilizer in the production of cultivated crops was investigated using a computer model that accommodates variables such as hauling distance, machinery complement, hauling speed, labor use, spreading time, and crop response. Machinery complement and labor requirements were defined and budgeted for three farm-feedlot scenarios, namely: a very large farm-feedlot (> 1000 head capacity), a large farm-feedlot (500–1000 head capacity), and a small farm-feedlot (< 500 head capacity). Results indicate that manure, valued for its N and P2O5 nutrient content, is generally an economical substitute for commercial fertilizer when hauled up to 15 km from feedlot sources. Large farm-feedlots, hauling manure less frequently and employing a farm tractor with front-end loader and single axle truck with a manure box, can haul manure up to 15 km and recover all costs. Small farm-feedlots employing a farm tractor with front-end loader and pull-type manure spreader can economically haul manure up to 15 km if non-cash costs and labor charges are disregarded. Alternatively, custom corral cleaners can be hired to haul manure up to 18 km in competition with commercial fertilizer on an N and P2O5 nutrient value basis. The yield benefits of manure increased the breakeven hauling distances dramatically for some crops. A need for more research to determine economic optimum manure application rates for various crops is identified. Key words: Fertilizer, feedlot manure, fertilizer economics, animal wastes
  • Authors:
    • Doran, J. W.
    • Linn, D. M.
  • Source: Soil Science Society of America Journal
  • Volume: 48
  • Issue: 4
  • Year: 1984
  • Summary: Surface soils from long-term tillage comparison experiments at six U.S. locations were characterized for aerobic and anaerobic microbial populations and denitrification potential using an in situ acetylene blockage technique. Measurements of soil water content, bulk density, and relative differences in pH, NO-3-N, water-soluble C, and total C and N contents between tillage treatments were also determined at the time of sampling. Numbers of aerobic and anaerobic microorganisms in surface (0-75 mm) no-till soils averaged 1.35 to 1.41 and 1.27 to 1.31 times greater, respectively, than in surface-plowed soils. Bulk density, volumetric water content, water-filled pore space, and water-soluble C and organic C and N values were similarly greater for surface no-till soils compared to conventionally tilled soils. Deeper in the soil (75-300 mm), however, aerobic microbial populations were significantly greater in conventionally tilled soils. In contrast, below 150 mm, the numbers of anaerobic microorganisms differed little between tillage treatments. In no-till soils, however, these organisms were found to comprise a greater proportion of the total bacterial population than in conventionally tilled soils. Measurements of the denitrification potential from soils at three locations generally followed the observed differences in anaerobic microbial populations. Denitrifying activity, after irrigation with 15 mm of water, was substantially greater in surface 0- to 75-mm no-till soils than in conventionally tilled soils at all locations. At the 75- to 150-mm soil depth, however, the denitrification potential in conventionally tilled soils was the same or higher than that of no-till soils. In surface no-till soils, increased numbers of anaerobic microorganisms and a substantially greater denitrification potential, following irrigation, indicate the presence of less-aerobic conditions in comparison to conventionally tilled soils. This condition appears to result from greater soil bulk densities and/or water contents of no-till soils, which act to increase water-filled porosity and the potential for water to act as a barrier to the diffusion of oxygen through the soil profile.
  • Authors:
    • Kohl, D. H.
    • Shearer, G.
    • Lockeretz, W.
  • Source: Science
  • Volume: 211
  • Issue: 4482
  • Year: 1981
  • Summary: A small minority of farmers in the Midwest produces crops on a commercial scale without using modern fertilizers and pesticides. On the basis of a 5-year study, it appears that these farmers have more in common with the majority of farmers in the region than with certain stereotypes of organic farmers. Their farming practices (other than chemical use), the size and labor requirements of their farms, and the production and profitability they achieve differ from those of conventional farmers by considerably less than might be expected on the basis of the fundamental importance of chemicals in modern agricultural production. Compared to conventional methods, organic methods consume less fossil energy and cause less soil erosion, but have mixed effects on soil nutrient status and grain protein content.
  • Authors:
    • Moore, R. A.
    • Krueger, C. R.
    • White, E. M.
  • Source: Agronomy Journal
  • Volume: 68
  • Issue: 4
  • Year: 1976
  • Summary: Cultivated Williams loam (Typic Argiboroll, fine-loamy, mixed) soils in north-central South Dakota were sampled after pastures were established and 8 years later so that the effect of the pastures on soils could be studied from analysis in the laboratory. Pastures were seeded to Russian wildrye (Elymus junceus Fisch.), crested wheatgrass (Agropyron desertorum (Fisch.) Schult.), or a mixture smooth bromegrass (Bromus inermis Leyss.), intermediate wheatgrass (Agropyron intermedium (Host) Beauv.), a pasture alfalfa (Medicago sativa L.). Soil N and bulk densities increased as available P decreased in the 8 years. The soil organic matter increased under all pastures, but it was small. The increases in organic matter, decreases in available P, and increases in saturated-clod bulk densities were different in the various pastures. Total N and organic matter increased about 0.001 and 0.02% per year, respectively, which is slower than the rate of decrease caused by cultivating the original grassland soils.