• Authors:
    • Lindwall, C. W.
    • Roman, E. S.
    • Moyer, J. R.
    • Blackshaw, R. E.
  • Source: Crop Protection
  • Volume: 13
  • Issue: 4
  • Year: 1994
  • Summary: Soil erosion by wind or water is a serious problem in North and South America. When no-till or reduced tillage is used to control erosion, the density of certain annual and perennial weeds can increase and new weed control techniques are usually required. The effects of conservation tillage on annual and perennial weeds, weeds that are spread by wind, plants from rangelands and pasture as weeds and volunteer plants as weeds arc reviewed. Current weed control methods with minimum tillage, herbicides, cover crops and other cultural practices in conservation tillage systems in North and South America are described. Some producers are successfully controlling weeds in continuous summer cropping systems in North America and in double cropping systems that include wheat in the winter and soybean or corn in the summer in Brazil, Argentina and southeastern United States. Successful conservation tillage systems usually involve cropping sequences of three or more crop types and several herbicides. In these cropping sequences, the ground is covered with a crop during most of the period in which the climate is favourable for weed growth. Perennial weeds are a problem in all tillage systems and there is a general dependence on glyphosate for perennial weed control. In successful conservation tillage systems, the amount and cost of herbicides used is similar to that for herbicides used in conventional tillage systems.
  • Authors:
    • Sweeney, D. W.
    • Moyer, J. L.
  • Source: Soil Science Society of America Journal
  • Volume: 58
  • Issue: 5
  • Year: 1994
  • Summary: With increased emphasis on conservation tillage, information is needed on the use of spring- or fall-seeded legumes as green manures for eastern Great Plains grain sorghum [Sorghum bicolor (L.) Moench] production. This study was conducted to determine whether legumes can be beneficial to subsequent grain sorghum crops grown in conservation tillage systems on prairie soil. Comparisons included the effects of (i) red clover (Trifolium pratense L.) and hairy vetch (Vicia villosa Roth) before grain sorghum vs. continuous grain sorghum, (ii) reduced or no-tillage, and (iii) fertilizer N rates on grain sorghum grown on two sites of a Parsons silt loam (fine, mixed, thermic Mollic Albaqualf). Surface soil at Site 1 was higher in pH (7.2 vs. 6.2), P (12 vs. 4 mg kg(-1)), and K (80 vs. 60 mg kg(-1)) than at Site 2. Yield of the first sorghum crop after legume kill-down in 1987 ranged from 79 to 131% more than for continuous grain sorghum. At the higher fertility Site 1, red clover residual increased yields to 3.7 from 2.7 Mg ha(-1) with continuous grain sorghum in the third year; at the lower fertility Site 2, the legume residual did not influence yield after the first year. First-year grain sorghum yielded 1.1 to 1.6 Mg ha(-1) more with reduced tillage than with no-tillage, but the difference was less in subsequent years. In 1987, yield was not affected by fertilizer N even following grain sorghum, but the response was significant in subsequent years. Low N response on this high organic matter prairie soil contributed to uncertain fertilizer N equivalencies and suggested other non-N benefits from the legumes.
  • Authors:
    • Hernandez, C. F.
    • Casanova, M. R.
  • Source: Avance Agroindustrial
  • Volume: 14
  • Issue: 57
  • Year: 1994
  • Summary: In field trials on degraded or fertile soils at 2 sites in Tucuman in 1991-93, maize was sown directly or following a range of cultivations as part of a rotation with wheat and soyabeans, or in a system of continuous cultivation, and with or without application of N and P. Application of 60-80 kg N as urea was recommended under trial conditions; P had no further beneficial effect. The importance is stressed of maintaining the water balance by reducing disturbance of the soil and of increasing N use efficiency through management of stubble and cover crops. Production systems based on direct sowing, rotations, green manures, and sowing into stubble with application of complementary fertilizer were recommended to give the highest grain yields.
  • Authors:
    • Raimbult, B. A.
    • Vyn, T. J.
  • Source: Agronomy Journal
  • Volume: 85
  • Issue: 5
  • Year: 1993
  • Summary: Tillage systems need to be compared over an extended period of time to determine their transitional and long-term impacts on crop growth and soil properties. A 15-yr experiment established in 1976 compared reduced tillage systems with conventional fall moldboard plowing for production of continuous corn (Zea mays L.) on a Maryhill silt loam soil (Typic Hapludalf). Corn plant growth and yield and soil properties were compared for five tillage systems: fall plow (fall mold-board plow + spring secondary tillage), fall chisel plow (fall chisel plow + spring secondary), spring plow, spring plow/secondary (spring plow + secondary), and no-till. No-till consistently resulted in slower plant growth than most or all of the other tillage systems. The fall plow and spring plow/secondary treatments resulted in grain yields averaging 5% more than fall chisel plow, 9% more than spring plow, and 16% more than no-till yields. From 1976 to 1983, no-till yields tended to increase relative to fall plow; from 1988 to 1990, however, no-till yields were much less than fall plow. No-till resulted in the lowest proportion of aggregates < 5 mm in diameter, highest bulk density, and greatest penetrometer resistance. Penetrometer resistance of the spring plow plots increased at a slower rate with depth than the fall chisel plow system. Among soil properties measured, the proportion of aggregates < 5 mm in diameter was most often significantly correlated with yield.
  • Authors:
    • Liu, R.
    • Phillips, D. L.
    • Lee, J. J.
  • Source: Water, Air, & Soil Pollution
  • Volume: 70
  • Issue: 1
  • Year: 1993
  • Summary: The EPIC model was used to simulate soil erosion and soil C content at 100 randomly selected sites in the US corn belt. Four management scenarios were run for 100 years: (1) current mix of tillage practices maintained; (2) current trend of conversion to mulch-till and no-till maintained; (3) trend to increased no-till; (4) trend to increased no-till with addition of winter wheat cover crop. As expected, the three alternative scenarios resulted in substantial decreases in soil erosion compared to the current mix of tillage practices. C content of the top 15 cm of soil increased for the alternative scenarios, while remaining approximately constant for the current tillage mix. However, total soil C to a depth of 1 m from the original surface decreased for all scenarios except for the no-till plus winter wheat cover crop scenario. Extrapolated to the entire US corn belt, the model results suggest that, under the current mix of tillage practices, soils used for corn and/or soybean production will lose 3.2 x 10^6 tons of C per year for the next 100 years. About 21% of this loss will be C transported off-site by soil erosion; an unknown fraction of this C will be released to the atmosphere. For the base trend and increased no-till trend, these soils are projected to lose 2.2 x 10^6 t-C yr-1 and 1.0 x 10^6 t-C yr-1, respectively. Under the increased no-till plus cover crop scenario, these soils become a small sink of 0.1 x 10^6 t-C yr-1. Thus, a shift from current tillage practices to widespread use of no-till plus winter cover could conserve and sequester a total of 3.3 x 10^6 t-C yr-1 in the soil for the next 100 years.
  • Authors:
    • Luna, J. M.
    • Laub, C. A.
    • Pimentel, D.
  • Source: Environmental Entomology
  • Volume: 21
  • Issue: 1
  • Year: 1992
  • Summary: Rye, Secale cereale L., used as a winter cover crop was killed by the herbicide paraquat or by mowing with a rotary mower. In subsequent no-ill corn, Glyptapanteles militaris (Walsh) (Hymenoptera: Braconidae) and Periscepsia laevigata (Wulp) (Diptera: Tachinidae) were the most abundant of twelve species of parasitoids that emerged from field-collected larvae of the armyworm, Pseudaletia unipuncta (Haworth). No effects of cover crop suppression practices were detected for parasitism rates for any individual species or for total armyworm parasitism. Seasonal parasitism rates ranged from 32 to 45%. HIgher numbers of Pterostichus spp. and Scarites spp. (Coleoptera: Carabidae), and wolf spiders (Araneae: Lycosidae) occurred early in the corn season in the mowed cover crop treatment compared with the herbicide killed cover crop treatment. Subsequent reduction oflarval densities of armyworm in mowed plots following higher predator densities suggests the role of these generalist predators in biological control of armyworm.
  • Authors:
    • Anderson, G. W.
    • Shaw, J. E.
    • Swanton, C. J.
    • Eadie, A. G.
  • Source: Weed Technology
  • Volume: 6
  • Issue: 3
  • Year: 1992
  • Summary: The acceptance of no-till crop production systems has been limited due to expected problems with weed management. Field experiments were established at two locations in Ontario in 1988 and one location in 1989. Band or broadcast applications of preemergence (PRE) combinations of high or low label rates of atrazine with or without metolachlor or inter-row cultivation, were evaluated for their effectiveness in controlling annual weeds in no-till corn. At each location, different herbicide and cultivation combinations were required to achieve adequate weed control. Corn grain yield was equivalent regardless of whether herbicides were applied as a band or broadcast treatment at all three sites. At two of the three sites, one cultivation combined with herbicides applied as a band was adequate to maintain weed control and corn grain yields. Selective application of herbicides in bands represented an approximate 60% reduction in total herbicide applied into the environment. The integration of a shallow post-plant inter-row cultivation combined with the soil conservation attributes of no-till, would enhance the sustainability of a modified no-till corn production system.
  • Authors:
    • Bishnoi, S. R.
    • Mosier, A. R.
    • Bronson, K. F.
  • Source: Soil Science Society of America Journal
  • Volume: 56
  • Issue: 1
  • Year: 1992
  • Summary: Nitrous oxide and N2 are the major denitriflcation products in irrigated corn (lea mays L.). In addition, N2O is considered a gas that contributes to global warming and stratospheric O3 depletion. Minimizing NjO emissions in cropping systems is therefore an economic as well as an important environmental concern. In a 1989 field experiment, the nitrification inhibitor encapsulated calcium carbide (ECC) (0,20, or 40 kg CaC2 ha-') or nitrapyrin (0.5 L a.i. ha-1) was banded with urea (218 kg N ha-') 7 wk after planting com. Between 1 and 14 wk after fertilization in 1989, N2O losses of 3226, 1109,1017, and 1005 g N2O-N ha-' from urea alone, urea plus nitrapyrin, urea plus 20 kg ECC ha-1, and urea plus 40 kg ECC ha-1, respectively, were measured from vented chambers. Nitrous oxide fluxes were positively correlated with soil NO, levels, indicating that the nitrification inhibitors indirectly controlled N2O emissions by preventing NO3 from accumulating in the soil. Carbon dioxide emissions from the root zone were generally not affected by ECC or nitrapyrin. In 1990, losses of N2O were less than in 1989 (1651 g N ha-' with urea alone), probably because there were fewer irrigations. Nitrapyrin and ECC addition to urea resulted in 980 and 459 g N ha-1 N2O being emitted the second year. Nitrification inhibitors appear to be a useful tool in mitigating N2O emissions in agricultural systems.
  • 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:
    • Kitchen, N. R.
  • Source: Dissertation Abstracts International. B, Sciences and Engineering
  • Volume: 51
  • Issue: 8
  • Year: 1990
  • Summary: A long-term study was conducted at 2 sites in E. Colorado to study the influence of N fertilizer rate and source/placement/timing (NSP), and crop rotation wheat/fallow (WF), and wheat, maize or sorghum/fallow (MSF) on no-tillage dryland cropping systems. Grain yield and vegetative biomass increased linearly with fertilizer N rate up to 84 kg/ha for wheat and 101 kg/ha for maize indicating that current N recommendations at Colorado State University may be insufficient for meeting N needs of no-tillage crops. N fertilizer recovery efficiency (NFRE) decreased with N fertilizer rate. Production increased more with N fertilizer additions in the MSF than in the WF rotation system. If differences occurred with NSP treatments, banding gave greater production and NFRE than broadcast application. In 1989 at one location, wheat production from the MSF rotation was greater than from the WF rotation. The av. annual grain and vegetative production from MSF was approx. double that produced in the WF cropping system. Water conservation with no-tillage systems allowed more intense cropping than a WF rotation. N loss from the MSF rotation was significant, increased with N rate and was attributed to N loss in both inorganic- and organic-N pools. Nitrate leaching in the no-tillage MSF rotation was unlikely since NO 3 decreased with soil depth.