• Authors:
    • Scow, K. M.
    • Shennan, C.
    • Horwath, W. R.
    • Clark, M. S.
  • Source: Agronomy Journal
  • Volume: 90
  • Issue: 5
  • Year: 1998
  • Summary: Soil chemical properties during the transition from conventional to organic and low-input farming practices were studied over 8 yr in California's Sacramento Valley to document changes in soil fertility status and nutrient storage. Four fanning systems differing in crop rotation and external inputs were established on land previously managed conventionally. Fertility in the organic system depended on animal manure applications and winter cover crops; the two conventional systems received synthetic fertilizer inputs; the low-input system used cover crops and animal manure during the first 3 yr and cover crops and synthetic fertilizer for the remaining 5 yr. At 4 and 8 yr after establishment, most changes in soil chemical properties were consistent with predictions based on nutrient budgets. Inputs of C, P, K, Ca, and Mg were higher in the organic and low-input systems as a result of manure applications and cover crop incorporations. After 4 yr, soils in the organic and low-input systems had higher soil organic C, soluble P, exchangeable K, and pH. Ceasing manure applications in the low-input system in Year 4 resulted in declining levels of organic C, soluble P, and exchangeable K. Crop rotation (the presence or absence of corn) also had a significant effect on organic C levels. Differences in total N appeared to be related in part to inputs, but perhaps also to differing efficiency of the farming systems at storing excess N inputs: the low-input system appeared to be most efficient, and the conventional systems were least efficient. Electrical conductivity (EC), soluble Ca, and soluble Mg levels were tightly linked but not consistently different among treatments. Relatively stable EC levels in the organic system indicate that animal manures did not increase salinity. Overall, our findings indicate that organic and low input farming in the Sacramento Valley result in small but important increases in soil organic C and larger pools of stored nutrients, which are critical for long-term fertility maintenance.
  • Authors:
    • McCarl, B. A.
    • Adams, D. M.
    • Alig, R. J.
  • Source: Journal of Agricultural and Applied Economics
  • Volume: 30
  • Issue: 2
  • Year: 1998
  • Summary: The forest and agriculture sectors are linked by having a portion of their land bases suitable for use in either sector. A substantial part of the southern land base is suitable for either forestry or agriculture use, with most of forestation on U.S. agriculture land in the South. We examine how land exchanges between forestry and agriculture are influenced by specific federal conservation and farm support policies, including changes in the Conservation Reserve Program. Reallocation of land is a significant part of the sectors' responses to the policies, along with intensification of timber management on existing southern forests.
  • Authors:
    • Myers, R.
    • Pullins, E.
  • Source: American Journal of Alternative Agriculture
  • Volume: 13
  • Issue: 3
  • Year: 1998
  • Summary: The agronomic and economic performance of five alternative crops was assessed in comparison to the no-till wheat-soyabean double-cropping system prevalent in the southern Corn Belt of the USA. A field site was established in 1992 at the University of Missouri-Columbia and two further sites in Missouri were added in 1993. Amaranth, buckwheat, sunflower, and pearl millet were planted after the harvest of canola [rape] or wheat, or after fallow. Alternative double-crop grain yield, production costs, and net returns were compared with those of double-crop soyabean. Wheat yielded more than canola. Sunflower grain yields did not differ significantly after winter-crop treatments at any site. Yields of amaranth, buckwheat, soyabean, and pearl millet differed after winter crops at some sites. At three study yield levels, net returns were positive and greatest for double-crop wheat-amaranth, canola-amaranth, wheat-sunflower, and canola-sunflower systems. All double-crop systems except canola-pearl millet had positive net returns at median study yield levels. Low or negative net returns resulted from the combination of low yield and low price for some double crops. Canola was shown to be an economically feasible alternative to wheat in a double-cropping system for central and southern Missouri. Buckwheat and sunflower were shown to be agronomically and economically competitive alternatives to soyabean following either canola or winter wheat, with buckwheat most valuable in late-season planting conditions.
  • Authors:
    • Mitchell, C. C.,Jr.
    • Reeves, D. W.
    • Hubbs, M. D.
  • Source: Proceedings 21st Annual Southern Conservation Tillage Conference for Sustainable Agriculture/Arkansas Agricultural Experiment Station Special Report 186
  • Issue: 186
  • Year: 1998
  • Summary: Investigations were conducted on a Typic Hapludult in USA, to assess the effects of a 3 year rotation (cotton-grain crops plus a winter legume cover crop), a 2 year rotation (cotton-grain crops-winter legume), and 3 continuous cropping systems on soil quality after 100 years. Soil quality was better in the 3 year rotation plus legume cover crop. This was attributed to higher soil C, cation exchange capacity, water retention and water stable aggregates, and reduced surface soil strength. Under continuous cotton, soil strength was increased down to 5 in depth. N fertilizer and/or legume cover crop within continuous cotton increased soil C over the past 100 years. Because of continuous tillage over the 100 years the rotation treatments had little effect on soil extractable nutrients. The semi-quantitative assessment of the USDA-Soil Quality Kit gave higher variability of parameters relative to standard procedures. The Kit should therefore be used only to evaluate trends and comparisons.
  • Authors:
    • Doran, J. W.
    • Koerner, P. T.
    • Power, J. F.
    • Wilhelm, W. W.
  • Source: Soil Science Society of America Journal
  • Volume: 62
  • Issue: 5
  • Year: 1998
  • Summary: Returning crop residue improves water conservation and storage, nutrient availability, and crop yields, We have little knowledge, however, er, of the residual impacts of crop residues on soil properties and crop production. We hypothesized that residual impacts of crop residues vary with the amount of residues used. A 10-yr study near Lincoln, NE, evaluated the residual effects of an earlier 8-yr study of various crop residue amounts on crop growth and selected soil properties. From 1978 through 1985, crop residues were returned at 0, 50, 100, and 150% of the quantity produced by the previous crop (averaging 0 to approximate to 6 Mg ha(-1) yr(-1)). Continuous corn (Zea mays L.) was produced 1986 through 1995 on these plots, except sorghum [Sorghum bicolor (L.) Moench] was substituted in several years. To study management effects on residual responses, plots were subdivided with or without tillage, N fertilizer (60 kg N ha(-1)), and hairy vetch (Vicia villosa L.) cover crop. Residual effects of the 150% residue amount increased grain production 16% compared with the 0% amount (4900 vs. 4250 kg ha(-1), respectively), and were not affected by time or other management practices. Increasing previous residue amount did enhance soil N availability (from 73.0 to 82.3 kg autoclave-mineralizable N ha(-1)) and Bray soil P (16.7 to 20.3 kg ka(-1)). These results are among the first to show that residual effects of crop residue are prolonged (half-life of approximate to 10 yr) and probably result from changes in soil properties that enhance soil nutrient availability.
  • Authors:
    • Kolberg, R. L.
    • Rouppet, B.
    • Westfall, D. G.
    • Peterson, G. A.
  • Source: Soil Science Society of America Journal
  • Volume: 61
  • Issue: 2
  • Year: 1997
  • Summary: Direct quantitative measurement of soil net N mineralization in agricultural soils under field conditions has not been widely used. A potential method of in situ net N mineralization was investigated in the fallow phase of a 3-yr no-till crop rotation at two sites. Undisturbed soil cores (5 by 15 cm) with anion- and cation-exchange resins (Sybron Ionac ASB-1P and C-249) at the bottom were incubated in situ. Nitrate-N plus NH4+-N extracted from soil was added to extracted amounts from resin bags to determine net N mineralized during each of three incubation periods (3-4 wk each). Total net N mineralization was 33.7 and 26.5 kg N ha(-1) during 84 and 75 d of incubation at Sterling and Stratton, respectively. Relative amounts of resin did not affect N captured but cores placed midway between old corn (Zea Mays L.) rows tended to accumulate more (P > F = 0.13) N than cores placed in rows. This in situ method appears to be a reliable method for measuring net N mineralization in the field; however, variation is large and many observations are required to obtain net N mineralization rates within an acceptable confidence interval.
  • Authors:
    • Peterson, G. A.
    • Westfall, D. G.
    • McGee, E. A.
  • Source: Journal of Soil and Water Conservation
  • Volume: 52
  • Issue: 2
  • Year: 1997
  • Summary: Wheat-fallow (W-F) is the predominant cropping system in the Great Plains, but the percent of precipitation stored as soil water (WSE) during fallow is frequently less than 25% with conventional tillage. No-till technology has improved potential WSE. Our objectives were to determine the effects of cropping system, landscape position (soil), and evaporative gradient (location) on WSE during inter-crop periods in intensified no-till cropping systems. Water storage efficiency was 48% during the wheat to corn fallow period in the 3- or 4-year rotational systems, contrasting sharply with the 22% WSE for the W-F system. The 3-year system, with a shorter fallow period (11 months), was just as effective in storing water as the long fallow period (14 months) in the WF system. Water storage efficiency was the lowest at the southern location, which had the highest potential evapotranspiration, but the contrasts among cropping systems remained. Toeslope soils had the highest WSE compared to summit or sideslope positions because of their opportunity to catch runoff water. The possibility exists for using even move intensive cropping systems than those examined in this study and this may mean that summer fallow could be eliminated with no-till practices.
  • Authors:
    • Norwood, C.
    • Currie, R.
  • Source: Journal of Production Agriculture
  • Volume: 10
  • Issue: 1
  • Year: 1997
  • Summary: Dryland crop yields in the U.S. Great Plains are limited by low precipitation and high potential evapotranspiration. In western Kansas wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] are grown commonly, whereas corn (Zea mays L.) is believed to lack sufficient drought and heat tolerance for dryland production. A study was conducted near Garden City, KS, from 1991 through 1995 to determine whether corn could be grown successfully. No-till (NT) and conventional-till (CT) corn and grain sorghum were compared. In the driest year, sorghum yielded 137% more than corn with CT and 85% more with NT, but in 3 of 5 yr, NT corn yielded from 34% to 112% more than NT sorghum. In the remaining year, CT sorghum yielded more than CT corn, but NT yields did not differ. Overall, NT increased corn yields by 28% and net return by 69%, but increased sorghum yields by only 11% add had no effect on net return. No-till corn yielded 28% more than NT sorghum and produced 169% more net return, whereas CT corn yielded 11% more than CT sorghum and produced 48% more net return. Dryland corn can be grown in western Kansas if lower yields and returns are accepted in dry years in exchange for yields and returns considerably higher than those of sorghum in favorable years. No tillage will substantially increase yields in most years and is essential to assure adequate corn yields in dry years.
  • Authors:
    • Rubin, A. B.
    • Southworth, R. M.
    • Walker, J. M.
  • Source: Agricultural Uses of By-Products and Waste
  • Volume: 668
  • Year: 1997
  • Summary: More than one billion tons of agriculturally recyclable waste organic and inorganic by-products are generated each year in the United States. A large number of Federal and state guidances, policies and rules govern the processing, distribution, and agricultural use or disposal of organic and inorganic by-product materials. Important opportunities exist for tailor-making these by-products and wastes to enhance their benefits when used separately and/or together with conventional fertilizer and soil conditioning materials. This paper discusses the need for stewardship and the implementation of a strategy that makes use of by-products and wastes in a holistic and safe manner, minimizes nuisances, and optimizes the opportunities for sustained agricultural use.
  • Authors:
    • Lyon, D. J.
    • Peterson, G. A.
    • Halvorson, A. D.
    • Leavitt, S. W.
    • Follett, R. F.
    • Paul, E. A.
  • Source: Soil Science Society of America Journal
  • Volume: 61
  • Issue: 4
  • Year: 1997
  • Summary: The size and turnover rate of the resistant soil organic matter (SOM) fractions were measured by 14C dating and 13C/12C measurements. This involved soils archived in 1948, and recent samples, from a series of long-term sites in the North American Great Plains. A reevaluation of C dates obtained in the 1960s expanded the study scope. The 14C ages of surface soils were modern in some native sites and near modern in the low, moist areas of the landscape. They were much older at the catena summits. The 14C ages were not related to latitude although this strongly influenced the total SOM content. Cultivation resulted in lower C contents and increased the 14C age by an average of 900 yr. The 10- to 20-cm depths from both cultivated and native sites were 1200 yr older than the 0- to 10-cm depth. The 90- to 120-cm depth of a cultivated site at 7015 yr before present (BP) was 6000 yr older than the surface. The nonhydrolyzable C of this depth dated 9035 yr BP. The residue of 6 M HCl hydrolysis comprised 23 to 70% of the total soil C and was, on the average, 1500 yr older. The percentage of nonhydrolyzable C and its 14C age analytically identify the amount and turnover rate of the old resistant soil C.