• Authors:
    • Owensby, C. E.
    • Parton, W. J.
    • Schimel, D. S.
    • Ojima, D. S.
  • Source: Biogeochemistry
  • Volume: 24
  • Issue: 2
  • Year: 1994
  • Summary: Fires in the tallgrass prairie are frequent and significantly alter nutrient cycling processes. We evaluated the short-term changes in plant production and microbial activity due to fire and the long-term consequences of annual burning on soil organic matter (SOM), plant production, and nutrient cycling using a combination of field, laboratory, and modeling studies. In the short-term, fire in the tallgrass prairie enhances microbial activity, increases both above-and belowground plant production, and increases nitrogen use efficiency (NUE). However, repeated annual burning results in greater inputs of lower quality plant residues causing a significant reduction in soil organic N, lower microbial biomass, lower N availability, and higher C:N ratios in SOM. Changes in amount and quality of below-ground inputs increased N immobilization and resulted in no net increases in N availability with burning. This response occurred rapidly (e.g., within two years) and persisted during 50 years of annual burning. Plant production at a long-term burned site was not adversely affected due to shifts in plant NUE and carbon allocation. Modeling results indicate that the tallgrass ecosystem responds to the combined changes in plant resource allocation and NUE. No single factor dominates the impact of fire on tallgrass plant production.
  • 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:
    • Polley, H. W.
    • Mayeux, H. S.
    • Johnson, H. B.
    • Gebhart, D. L.
  • Source: Journal of Soil and Water Conservation
  • Volume: 49
  • Issue: 5
  • Year: 1994
  • Summary: ABSTRACT The land use change from cropland to perennial grass cover associated with The Conservation Reserve Program (CRP) may sequester atmospheric CO, back into the soil carbon pool, thereby changing formerly cultivated soils from sources to sinks,for atmospheric carbon. To evaluate the effect of CRP on soil organic carbon (SOC] levels, samples from adjacent cropland, native pasture, and five year old CRP sites in Texas, Kansas, and Nebraska were analyzed. Across all locations, SOC levels for cropland, CRP, and native pasture were 59.2, 65.1, and 90.8 metric tons c-1 ha-1 in the surface 300 cm, respectively. CRP lands gained an average of 1.1 tons C ha-1 yr-1 suggesting that the 17 million hectares of land enrolled in CRP may have the potential to sequester about 45% of the 38. 1 million tons of carbon released annually into the atmosphere from US agriculture. These findings illustrate that agricultural CO2 emissions may be effectively controlled through changes in land use and management systems.
  • Authors:
    • Copeland, S. M.
    • Tanaka, D. L.
    • Power, J. F.
    • Allmaras, R. R.
  • Source: Conservation Tillage in Temperate Agroecosystems
  • Year: 1994
  • Authors:
    • Black, A. L.
    • Bauer, A.
  • Source: Soil Science Society of America Journal
  • Volume: 58
  • Issue: 1
  • Year: 1994
  • Summary: The positive effects of soil organic matter (OM) on soil properties that influence crop performance are well documented. But definitive and quantitative information of differential effects of soil OM contents is lacking for the northern Great Plains. The objective of this study was to quantify the contribution of a unit quantity of soil OM to productivity. Experiments were conducted on Williams loam (fine-loamy, mixed, Typic Argiboroll) for 4 yr in the same field. The variables were soil OM content of the upper 30.5 cm together with all combinations of three postplanting soil available N levels (55, 90, and 125 kg N ha-1 as NO3-N to 1.2 m) and three water levels. Water levels were uniformly maintained with a trickle system that independently metered water to each plot for each soil available N level. Pretillering spring wheat (Triticum aestivum L.) plant population decreased as soil OM content decreased in 3 of 4 yr. On an annual basis, highest total aerial dry matter and grain yields were associated with highest OM contents. The contribution of 1 Mg OM ha-1 to soil productivity, across the range of 64 to 142 Mg OM ha-1, was calculated as equivalent to 35.2 kg ha-1 for spring wheat total aerial dry matter and 15.6 kg ha-1 for grain yield. Loss of productivity associated with a depletion of soil OM in the northern Great Plains is primarily a consequence of a concomitant loss of fertility.
  • 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:
    • Grisso, R. D.
    • Jasa, P. J.
    • Dickey, E. C.
  • Source: Journal of Production Agriculture
  • Volume: 7
  • Issue: 4
  • Year: 1994
  • Summary: In Nebraska, early adopters of conservation tillage, especially those using no-till planting, had some concerns regarding planter performance, early season weed control, and possible yield reductions. Selected tillage and planting systems were used long term to evaluate effects on soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] yield, soil properties, and residue cover in a nonirrigated rotation. The six tillage and planting systems selected for evaluation were: no-till, no-till with row-crop cultivation, disk, double disk, chisel, and plow. In 1981, two sets of field plots were established near Lincoln, NE, on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls) so that both crops could be evaluated each year. Measurements were not taken until completion of one crop rotation cycle. After this cycle, for the first 3 yr of yield measurements, no differences occurred in grain yield among the tillage and planting systems. After five additional years, differences in yield were measured, with no-till tending to have the greatest yield for both crops. Row-crop cultivation of no-till soybean did not result in any measurable yield differences, but for grain sorghum, row-crop cultivation resulted in an average yield decrease of 6 bu/acre. Soil organic matter tended to be greatest for the continuous no-till system and lowest for the plow system. The plow system had slightly less penetration resistance within the 4- to 8-in. depth than the other treatments, whereas, the double-disk system was slightly greater within the 2- to 6-in. depth. Draft and power requirements for planting in the selected tillage and planting systems were not different. The major difference among the tillage and planting systems was residue cover remaining after planting. No-till had the most residue cover, but there was no appreciable accumulation of residue over the 10 yr of continuous use of the tillage and planting systems. For the last 5 yr, no-till tended to have the greatest yield for both crops. Thus, for the soil and conditions evaluated, no-till yields were as good as the other systems during early years, and were better after 5 yr of continuous use. Thus, producers adopting no-till and other residue management practices have the opportunity to enhance profitability because of the same or greater yields and reduced production costs by eliminating tillage operations.
  • Authors:
    • Zentner, R. P.
    • Campbell, C. A.
  • Source: Soil Science Society of America Journal
  • Volume: 57
  • Issue: 4
  • Year: 1993
  • Summary: Few studies conducted in western Canada have assessed how crop rotations and fertilization influence soil organic matter content on land that has been cropped for many years. We monitored soil organic matter in the 0- to 0.15- and 0.15- to 0.3-m depths of a 24-yr crop rotation experiment conducted on a medium-textured Aridic Haploboroll in southwestern Saskatchewan. Prior to the study, the land had been in a hard red spring wheat (Triticum aestivum L.)-fallow rotation for {approx}50 yr. Only the 0- to 0.15-m segment showed significant treatment effects. Due to good weather and crop yields in the first 15 yr, soil organic matter had increased under well-fertilized annually cropped rotations, and it remained constant under fallow-containing rotations and under continuous wheat receiving inadequate N fertilizer. Because of several dry years in the final 9 yr of the study, all rotations except a well-fertilized, fallow-winter cereal-wheat system lost organic matter. Changes in organic matter were directly related to the amount of crop residues produced by these systems and their ease of eroding. Soil organic matter was inversely related to apparent N deficit (i.e., N exported in grain minus N applied as fertilizer). The fallow-flax (Linum usitatissimum L.)-wheat rotation receiving N and P fertilizer had the lowest soil organic matter, partly due to low production of crop residues by flax, partly to greater leaching of NO3, and partly due to some loss of flax residues blown from the plots. Soil organic matter in the well-fertilized fallow-winter cereal-wheat rotation remained constant because its shorter fallow period reduced soil erosion, and due to its more efficient use of N, as evidenced by minimal leached NO3-N.
  • 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.