• Authors:
    • Beckie, H. J.
    • Zand, E.
  • Source: Canadian Journal of Plant Science
  • Volume: 82
  • Issue: 2
  • Year: 2002
  • Summary: The competitiveness of three hybrid and three open-pollinated canola cultivars against two wild oat populations was determined under controlled environment conditions at two plant densities and five canola:wild oat ratios (100:0, 75:25, 50:50, 25:75, 0:100). Analysis of replacement series and derivation of relative crowding coefficients (RCC), based on shoot dry weight or leaf area, indicated that hybrid canola cultivars were twice as competitive than open-pollinated cultivars when weed interference was relatively high (i.e., high plant density and vigorous wild oat growth). Little difference in competitiveness among cultivar types was apparent when weed interference was lower. The results of this study suggest that hybrid canola cultivars may be best suited for use in an integrated weed management program, particularly for farmers of organic or low input cropping systems.
  • Authors:
    • Blackshaw, R. E.
    • Anderson, R. L.
    • Derksen, D. A.
    • Maxwell, B.
  • Source: Agronomy Journal
  • Volume: 94
  • Issue: 2
  • Year: 2002
  • Summary: Cropping systems in the northern Great Plains (NGP) have evolved from wheat Triticum aestivum L.)-fallow rotations to diversified cropping sequences. Diversification and continuous cropping have largely been a consequence of soil moisture saved through the adoption of conservation tillage. Consequently, weed communities have changed and, in some cases, become resistant to commonly used herbicides, thus increasing the complexity of managing weeds. The sustainability of diverse reduced tillage systems in the NGP depends on the development of economical and effective weed management systems. Utilizing the principle of varying selection pressure to keep weed communities off balance has reduced weed densities, minimized crop yield losses, and inhibited adverse community changes toward difficult-to-control species. Varied selection pressure was best achieved with a diverse cropping system where crop seeding date, perennation, and species and herbicide mode of action and use pattern were inherently varied. Novel approaches to cropping systems, including balancing rotations between cereal and broadleaf crops, reducing herbicide inputs, organic production, fall-seeded dormant canola (Brassica napus and B. rapa), and the use of cover crops and perennial forages, are discussed in light of potential systems-level benefits for weed management.
  • Authors:
    • Samson, R. A.
    • Girouard, P.
    • Fyles, J. W.
    • Zan, C. S.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 86
  • Issue: 2
  • Year: 2001
  • Summary: The conversion of relatively undisturbed ecosystems such as forests and grasslands to intensively managed agroecosystems has had major impacts on global carbon (C) cycling largely as a result of land clearing, cultivation, and replacement of perennial vegetation by annual crops. Numerous studies have demonstrated the ability of fast-growing perennial plant species dedicated to bioenergy production to sequester substantial amounts of C. Thus, the conversion of conventionally managed agricultural land to perennial bioenergy crops can be expected to increase C stored in above- and belowground biomass and in soil organic matter because of their perennial nature and greater root biomass. In this study, C storage was compared among five ecosystems in southwestern Quebec including two perennial crops, switchgrass (Panicum virgatum L.), and willow (Salixalbaxglatfelteri L.), and an annual corn (Zea mays L.) crop at two sites of differing soil fertility, a 20-year-old abandoned field, and a mature hardwood forest. After 4 years of production, corn had significantly higher levels of aboveground C than willow at the less fertile site, but no significant differences were detected at the more fertile site. Both perennial systems had significantly higher root C than the corn system but switchgrass had significantly higher root C levels below 30 cm compared with willow and corn. Soil organic C under willow at the more fertile site was higher than under the other managed or unmanaged systems, including willow at the less fertile site. The results of this study suggest that perennial energy crops grown on relatively fertile soils, have the potential to increase substantially soil C levels compared with conventional agricultural systems or unmanaged systems.
  • Authors:
    • Halvorson, A. D.
    • Wienhold, B. J.
    • Black, A. L.
  • Source: Agronomy Journal
  • Volume: 93
  • Issue: 5
  • Year: 2001
  • Summary: Spring wheat (Triticum aestivum L.) is generally produced in the northern Great Plains using tillage and a crop-fallow system. This study evaluated the influence of tillage system [conventional-till (CT), minimum-till (MT), and no-till (NT)] and N fertilizer rate (0, 22, and 45 kg N ha(-1)) on grain N, grain N removal from cropping system, and changes in residual postharvest soil NO3-N during six rotation cycles of a dryland spring wheat-fallow (SW-F) cropping system. Grain N concentration increased vith increasing N rate and was higher with CT (33-3 g kg(-1)) than with NT (32.3 g kg-1) at 45 kg ha(-1) N rate. Grain N removal per crop was greater with CT (70 kg N ha (1)) and MT (68 kg N ha(-1)) than with NT (66 kg N ha (1)) and tended to increase with increasing N rate, but varied with rotation cycle. Total grain N removal in six rotation cycles was in the order: CT > MT > NT. Total grain N removal by six SW crops was increased by N fertilization, with only 21 and 17% of the applied N removed in the grain for the 22 and 45 kg ha(-1) N rates, respectively. Postharvest soil NO3-N levels in the 150-cm profile varied with N rate and rotation cycle, with residual NO3-N increasing during consecutive dry crop cycles. In contrast, some leaching of NO3-N below the SW root zone may have occurred during wetter crop cycles. Soil profile NO3-N levels tended to be greater with CT and MT than with NT. Variation in precipitation during rotation cycles and N fertilization impacted grain N removal and residual soil NO3-N levels more than tillage system within this SW-F cropping system.
  • Authors:
    • Stuedemann, J. A.
    • Franzluebbers,A. J.
    • Sanderson, M. A.
    • Stout, W. L.
    • Schnabel, R. R.
  • Source: The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect
  • Year: 2001
  • Authors:
    • Skaggs, R. K.
  • Source: Agricultural Water Management
  • Volume: 51
  • Issue: 2
  • Year: 2001
  • Summary: The possibility that drip irrigation technology could increase yields, reduce the incidence of crop diseases, and improve fruit quality has been identified as a critical research issue for the New Mexico chile pepper industry. Numerous hypotheses have been expressed regarding the low incidence of drip irrigation usage among New Mexico farmers. A survey of farmers was conducted in 1999 to assess commercial chile pepper producers' attitudes toward and knowledge of drip irrigation technology. The survey data were used in logistic regression models that predict current high-tech irrigation system usage, drip irrigation usage, and plans for future drip irrigation adoption by chile pepper producers. The results of this research provide information useful to extension personnel, other researchers, and chile industry members. Results also raise questions about the impact of widespread drip irrigation adoption on multi-user irrigation systems, such as those found in New Mexico.
  • Authors:
    • Lal, R.
    • Kimble, J. M.
    • Follett, R. F.
  • Year: 2001
  • Summary: Grazing lands represent the largest and most diverse land resource-taking up over half the earth's land surface. The large area grazing land occupies, its diversity of climates and soils, and the potential to improve its use and productivity all contribute to its importance for sequestering C and mitigating the greenhouse effect and other conditions brought about by climate change. The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect gives you an in-depth look at this possibility.
  • Authors:
    • Wagoner, P.
    • Drinkwater, L. E.
    • Douds, D. D.
    • Galvez, L.
  • Source: Plant and Soil
  • Volume: 228
  • Issue: 2
  • Year: 2001
  • Summary: Low-input agricultural systems that do not rely on fertilizers may be more dependent on vesicular-arbuscular mycorrhizal [VAM] fungi than conventionally managed systems. We studied populations of spores of VAM fungi, mycorrhiza formation and nutrient utilization of maize (Zea mays L.) grown in moldboard plowed, chisel-disked or no-tilled soil under conventional and low-input agricultural systems. Maize shoots and roots were collected at four growth stages. Soils under low-input management had higher VAM fungus spore populations than soils under conventional management. Spore populations and colonization of maize roots by VAM fungi were higher in no-tilled than in moldboard plowed or chisel-disked soil. The inoculum potential of soil collected in the autumn was greater for no-till and chisel-disked soils than for moldboard plowed soils and greater for low-input than conventionally farmed soil. The effects of tillage and farming system on N uptake and utilization varied with growth stage of the maize plants. The effect of farming system on P use efficiency was significant at the vegetative stages only, with higher efficiencies in plants under low-input management. The effect of tillage was consistent through all growth stages, with higher P use efficiencies in plants under moldboard plow and chisel-disk than under no-till. Plants grown in no-tilled soils had the highest shoot P concentrations throughout the experiment. This benefit of enhanced VAM fungus colonization, particularly in the low-input system in the absence of effective weed control and with likely lower soil temperatures, did not translate into enhanced growth and yield.
  • Authors:
    • McGill, W. B.
    • Izaurralde, R. C.
    • Robertson, J. A.
    • Juma, N. G.
    • Grant, R. F.
  • Source: Soil Science Society of America Journal
  • Volume: 65
  • Issue: 1
  • Year: 2001
  • Summary: Soil C contents can be raised by land use practices in which rates of C input exceed those of C oxidation. Rates of C inputs to soil can be raised by continuous cropping, especially with perennial legumes, and by soil amendments, especially manure. We have summarized our understanding of the processes by which changes in soil C content are determined by rates of soil C input in the mathematical model ecosys. We compared model output for changes in soil C with those measured in a Gray Luvisol (Typic Cryoboralf) at Breton, Alberta, during 70 yr of a 2-yr wheat (Triticum aestivum L.)-fallow rotation vs. a 5-yr wheat-oat (Avena sativa L.)-barley (Hordeum vulgare L.)-forage-forage rotation with unamended, fertilized, and manured treatments. Model results indicated that rates of C input in the 2-yr rotation were inadequate to maintain soil C in the upper 0.15 m of the soil profile unless manure was added, but that those in the 5-yr rotation were more than adequate. Consequent changes of soil C in the model were corroborated by declines of 14 and 7 g C m-2 yr-1 measured in the control and fertilized treatments of the 2-yr rotation; by gains of 7 g C m-2 yr-1 measured in the manured treatment of the 2-yr rotation; and by gains of 4, 14, and 28 g C m-2 yr-1 measured in the control, fertilized, and manured treatments of the 5-yr rotation. Model results indicated that soil C below 0.15 m declined in all treatments of both rotations, but more so in the 2-yr than in the 5-yr rotation. These declines were corroborated by lower soil C contents measured between 0.15 and 0.40 m after 70 yr in the 2- vs. 5-yr rotation. Land use practices that favor C storage appear to interact positively with each other, so that gains in soil C under one such practice are greater when it is combined with other such practices.
  • Authors:
    • Baldock, J. A.
    • Drury, C. F.
    • Gregorich, E. G.
    • Greaves, Travis
  • Source: Canadian Journal of Soil Science
  • Volume: 81
  • Issue: 1
  • Year: 2001
  • Summary: Legume-based cropping systems could help to increase crop productivity and soil organic matter levels, thereby enhancing soil quality, as well as having the additional benefit of sequestering atmospheric C. To evaluate the effects of 35 yr of maize monoculture and legume-based cropping on soil C levels and residue retention, we measured organic C and 13C natural abundance in soils under: fertilized and unfertilized maize (Zea mays L.), both in monoculture and legume-based [maize-oat (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa] rotations; fertilized and unfertilized systems of continuous grass (Poa pratensis L.); and under forest. Solid state 13C nuclear magnetic resonance (NMR) was used to chemically characterize the organic matter in plant residues and soils. Soils (70-cm depth) under maize cropping had about 30-40% less C, and those under continuous grass had about 16% less C, than those under adjacent forest. Qualitative differences in crop residues were important in these systems, because quantitative differences in net primary productivity and C inputs in the different agroecosystems did not account for observed differences in total soil C. Cropping sequence (i.e., rotation or monoculture) had a greater effect on soil C levels than application of fertilizer. The difference in soil C levels between rotation and monoculture maize systems was about 20 Mg C ha-1. The effects of fertilization on soil C were small (~6 Mg C ha-1), and differences were observed only in the monoculture system. The NMR results suggest that the chemical composition of organic matter was little affected by the nature of crop residues returned to the soil. The total quantity of maize-derived soil C was different in each system, because the quantity of maize residue returned to the soil was different; hence the maize-derived soil C ranged from 23 Mg ha-1 in the fertilized and 14 Mg ha-1 in the unfertilized monoculture soils (i.e., after 35 maize crops) to 6-7 Mg ha-1 in both the fertilized and unfertilized legume-based rotation soils (i.e., after eight maize crops). The proportion of maize residue C returned to the soil and retained as soil organic C (i.e., Mg maize-derived soil C/Mg maize residue) was about 14% for all maize cropping systems. The quantity of C3-C below the plow layer in legume-based rotation was 40% greater than that in monoculture and about the same as that under either continuous grass or forest. The soil organic matter below the plow layer in soil under the legume-based rotation appeared to be in a more biologically resistant form (i.e., higher aromatic C content) compared with that under monoculture. The retention of maize residue C as soil organic matter was four to five times greater below the plow layer than that within the plow layer. We conclude that residue quality plays a key role in increasing the retention of soil C in agroecosystems and that soils under legume-based rotation tend to be more "preservative" of residue C inputs, particularly from root inputs, than soils under monoculture.