• Authors:
    • Follett, R. F.
    • Paustian, K.
    • Sperow, M.
    • Eve, M. D.
  • Source: Environmental Pollution
  • Volume: 116
  • Issue: 3
  • Year: 2002
  • Summary: Average annual net change in soil carbon stocks under past and current management is needed as part of national reporting of greenhouse gas emissions and to evaluate the potential for soils as sinks to mitigate increasing atmospheric CO2. We estimated net soil C stock changes for US agricultural soils during the period from 1982 to 1997 using the IPCC (Intergovernmental Panel on Climate Change) method for greenhouse gas inventories. Land use data from the NRI (National Resources Inventory; USDA-NRCS) were used as input along with ancillary data sets on climate, soils, and agricultural management. Our results show that, overall, changes in land use and agricultural management have resulted in a net gain of 21.2 MMT C year-1 in US agricultural soils during this period. Cropped lands account for 15.1 MMT C year-1, while grazing land soil C increased 6.1 MMT C year-1. The land use and management changes that have contributed the most to increasing soil C during this period are (1) adoption of conservation tillage practices on cropland, (2) enrollment of cropland in the Conservation Reserve Program, and (3) cropping intensification that has resulted in reduced use of bare fallow.
  • Authors:
    • FAO
    • FAO
  • Year: 2002
  • Authors:
    • Cross, A. F.
    • Engle, D. M.
    • Tunnell, T. R.
    • Zhang, H.
    • Fuhlendorf, S. D.
  • Source: Restoration Ecology
  • Volume: 10
  • Issue: 2
  • Year: 2002
  • Summary: A comparative analysis of soils and vegetation from cultivated areas reseeded to native grasses and native prairies that have not been cultivated was conducted to evaluate restoration of southern mixed prairie of the Great Plains over the past 30 to 50 years. Restored sites were within large tracts of native prairie and part of long-term grazing intensity treatments (heavy, moderate, and ungrazed), allowing evaluation of the effects of grazing intensity on prairie restoration. Our objective was to evaluate restored and native sites subjected to heavy and moderate grazing regimes to determine if soil nutrients from reseeded cultivated land recovered after 30 years of management similar to the surrounding prairie and to identify the interactive influence of different levels of grazing and history of cultivation on plant functional group composition and soils in mixed prairies. For this mixed prairie, soil nitrogen and soil carbon on previously cultivated sites was 30 to 40% lower than in uncultivated native prairies, indicating that soils from restored sites have not recovered over the past 30 to 50 years. In addition, it appears that grazing alters the extent of recovery of these grassland soils as indicated by the significant interaction between grazing intensity and cultivation history for soil nitrogen and soil carbon. Management of livestock grazing is likely a critical factor in determining the potential restoration of mixed prairies. Heavy grazing on restored prairies reduces the rate of soil nutrient and organic matter accumulation. These effects are largely due to changes in composition (reduced tallgrasses), reduced litter accumulation, and high cover of bare ground in heavily grazed restored prairies. However, it is evident from this study that regardless of grazing intensity, restoration of native prairie soils requires many decades and possibly external inputs to adequately restore organic matter, soil carbon, and soil nitrogen.
  • Authors:
    • Jackson, R. B.
    • Maherali, H.
    • Anderson, L. J.
    • Johnson, H. B.
    • Polley, H. W.
    • Gill, R. A.
  • Source: Nature
  • Volume: 417
  • Issue: 6886
  • Year: 2002
  • Summary: Carbon sequestration in soil organic matter may moderate increases in atmospheric CO2 concentrations (C-a) as C-a increases to more than 500 mumol mol(-1) this century from interglacial levels of less than 200 mumol mol(-1) (refs 1- 6). However, such carbon storage depends on feedbacks between plant responses to Ca and nutrient availability(7,8). Here we present evidence that soil carbon storage and nitrogen cycling in a grassland ecosystem are much more responsive to increases in past Ca than to those forecast for the coming century. Along a continuous gradient of 200 to 550 mumol mol(-1) (refs 9, 10), increased C-a promoted higher photosynthetic rates and altered plant tissue chemistry. Soil carbon was lost at subambient C-a, but was unchanged at elevated C-a where losses of old soil carbon offset increases in new carbon. Along the experimental gradient in C-a there was a nonlinear, threefold decrease in nitrogen availability. The differences in sensitivity of carbon storage to historical and future C-a and increased nutrient limitation suggest that the passive sequestration of carbon in soils may have been important historically, but the ability of soils to continue as sinks is limited.
  • Authors:
    • Reule, C. A.
    • Peterson, G. A.
    • Halvorson, A. D.
  • Source: Agronomy Journal
  • Volume: 94
  • Issue: 6
  • Year: 2002
  • Summary: Winter wheat (Triticum aestivum L.)-fallow (WF) using conventional stubble mulch tillage (CT) is the predominant production practice in the central Great Plains and has resulted in high erosion potential and decreased soil organic C (SOC) contents. This study, conducted from 1990 through 1994 on a Weld silt loam (Aridic Argiustoll) near Akron, CO, evaluated the effect of WF tillage system with varying degrees of soil disturbance [no-till (NT), reduced till (RT), CT, and bare fallow (BF)] and crop rotation [WF, NT wheat-corn (Zea mays L.)-fallow (WCF), and NT continuous corn (CC)] on winter wheat and corn yields, aboveground residue additions to the soil at harvest, surface residue amounts at planting, and SOC. Neither tillage nor crop rotation affected winter wheat yields, which averaged 2930 kg ha-1. Corn grain yields for the CC (NT) and WCF (NT) rotations averaged 1980 and 3520 kg ha-1, respectively. The WCF (NT) rotation returned 8870 kg ha-1 residue to the soil in each 3-yr cycle, which is 2960 kg ha-1 on an annualized basis. Annualized residue return in WF averaged 2520 kg ha-1, which was 15% less than WCF (NT). Annualized corn residue returned to the soil was 3190 kg ha-1 for the CC (NT) rotation. At wheat planting, surface crop residues varied with year, tillage, and rotation, averaging WCF (NT) (5120 kg ha-1) > WF (NT) (3380 kg ha-1) > WF (RT) (2140 kg ha-1) > WF (CT) (1420 kg ha-1) > WF (BF) (50 kg ha-1). Soil erosion potential was lessened with WCF (NT), CC (NT), and WF (NT) systems because of the large amounts of residue cover. Levels of SOC in descending order in 1994 were CC (NT) [>=] WCF (NT) [>=] WF (NT) = WF (RT) = WF (CT) > WF (BF). Although not statistically significant, the CC (NT) treatment appeared to be accumulating more SOC than any of the rotations that included a fallow period, even more rapidly than WCF (NT), which had a similar amount of annualized C addition. Reduced tillage and intensified cropping increased SOC and reduced soil erosion potential.
  • Authors:
    • Carter, M. R.
  • Source: Agronomy Journal
  • Volume: 94
  • Issue: 1
  • Year: 2002
  • Summary: Soil quality concepts are commonly used to evaluate sustainable land management in agroecosystems. The objectives of this review were to trace the importance of soil organic matter (SOM) in Canadian sustainable land management studies and illustrate the role of SOM and aggregation in sustaining soil functions. Canadian studies on soil quality were initiated in the early 1980s and showed that loss of SOM and soil aggregate stability were standard features of nonsustainable land use. Subsequent studies have evaluated SOM quality using the following logical sequence: soil purpose and function, processes, properties and indicators, and methodology. Limiting steps in this soil quality framework are the questions of critical limits and standardization for soil properties. At present, critical limits for SOM are selected using a commonly accepted reference value or based on empirically derived relations between SOM and a specific soil process or function (e.g., soil fertility, productivity, or erodibility). Organic matter fractions (e.g., macro-organic matter, light fraction, microbial biomass, and mineralizable C) describe the quality of SOM. These fractions have biological significance for several soil functions and processes and are sensitive indicators of changes in total SOM. Total SOM influences soil compactibility, friability, and soil water-holding capacity while aggregated SOM has major implications for the functioning of soil in regulating air and water infiltration, conserving nutrients, and influencing soil permeability and erodibility. Overall, organic matter inputs, the dynamics of the sand-sized macro-organic matter, and the soil aggregation process are important factors in maintaining and regulating organic matter functioning in soil.
  • Authors:
    • Riveland, N.
    • Lafond, G.
    • Nielsen, D.
    • Brandt, S.
    • Miller, P.
    • Tanaka, D.
    • Johnston, A.
  • Source: Agronomy Journal
  • Volume: 94
  • Issue: 2
  • Year: 2002
  • Summary: Oilseed crops are grown throughout the semiarid region of the northern Great Plains of North America for use as vegetable and industrial oils, spices and birdfeed. In a region dominated by winter and spring wheat ( Triticum aestivum), the acceptance and production of another crop requires that it both has an agronomic benefit to the cropping system and improve the farmers' economic position. In this review, we compare the adaptation and rotational effects of oilseed crops in the northern Great Plains. Rape ( Brassica sp. [ Brassica napus var. oleifera]), mustard ( B. juncea and Sinapis alba), and flax ( Linum usitatissimum) are well adapted to cool, short-season conditions found on the Canadian prairies and northern Great Plains border states of the USA. Sunflower ( Helianthus annuus) and safflower ( Carthamus tinctorius) are better adapted to the longer growing season and warmer temperatures found in the northern and central Great Plains states. Examples are presented of how agronomic practices have been used to manipulate a crop's fit into a local environment, as demonstrated with the early spring and dormant seeding management of rape, and of the role of no-till sowing systems in allowing the establishment of small-sown oilseed crops in semiarid regions. Continued evaluation of oilseed crops in rotation with cereals will further expand our understanding of how they can be used to strengthen the biological, economic and environmental role of the region's cropping systems. Specific research needs for each oilseed crop have been recommended.
  • Authors:
    • Li, X. Y.
    • Zhao, H. L.
    • Gao, C. Y.
    • Li, F. R.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 91
  • Issue: 1-3
  • Year: 2002
  • Summary: Winter wheat (Triticum aestivum L.) monoculture is common in wheat-growing areas of the Loess Plateau of northwest China. This system is characterized by nearly 3-month summer fallow from wheat harvest at the end of June or early July to sowing in late September. It not only lowers the overall precipitation-use efficiency because of the large amount of evaporation from the bare soil surface during the fallow period but also entails high risk of erosion by summer rainstorms. There is a need to develop more effective cropping systems to replace the current production system. Seven alternative rotations, mainly using wheat, rapeseed, corn, potato, pearl millet, linseed, alfalfa and sweetclover, were established and their use of environmental resources, production performance, energy efficiency, soil fertility sustainability, and soil conservation effectiveness were compared with continuous wheat cropping. The rotations had greater potential use of environmental resources. Despite showing no clear advantage in grain yields, all rotations were significantly higher in total above-ground biomass production and more efficient in energy transformation compared with continuous wheat cropping. After a 3-year cycle, the rotations did not adversely affect soil bulk density but some rotations significantly increased soil water-stable aggregates compared with the initial measurement. For the rotations based on the inclusion of legumes, the availability of N was apparently improved but the total P was substantially reduced compared with the initial measurement and continuous wheat cropping. An assessment of soil conservation effectiveness with a weighted soil conservation effectiveness index (WSCEI) indicated that the rotations performed much better than continuous wheat cropping in conserving soil and water resources. This study also strongly recommend that it is feasible to cultivate winter wheat followed by a 3-month legume fallow crop in year I and then a summer crop cultivation in the next. This system provides a soil cover during both erosion-prone rainy periods while leaving the soil bare for about 7 months (October-April) every 2 years. Another alternative is to cultivate winter wheat followed by a 15-month legume crop cultivation in years I and 2 and then a summer crop in year 3. This system allows the soil to be covered during three rainy periods while leaving the soil bare for about 7 months every 3 years. As most of this 7-month period is winter with low rainfall (snow) and temperatures below 0degreesC, not only is soil evaporation very low but the risk of erosion is also low. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Authors:
    • Haqqani, A. M.
    • Munir, M.
    • Mann, R. A.
  • Source: Pakistan Journal of Agricultural Research
  • Volume: 18
  • Issue: 1
  • Year: 2002
  • Summary: Rice-wheat cropping system is the most important one in Pakistan. The system provides food and livelihood for more than 15 million people in the country. The productivity of the system is much lower than the potential yields of both rice and wheat crops. With the traditional methods, rice-wheat system is not a profitable one to many farmers. Hence, Cost of cultivation must be reduced and at the same time, efficiency of resources like irrigation water, fuel, and fertilizers must be improved to make the crop production system more viable and ecofriendly. Resource conserving technology (RCT) must figure highly in this equation, since they play a major role in achieving the above goals. The RCT include laser land leveling, zero-tillage, bed furrow irrigation method and crop residue management. These technologies were evaluated in irrigated areas of Punjab where rice follows wheat. The results showed that paddy yield was not affected by the new methods. Direct seeding of rice crop saved irrigation water by 13% over the conventionally planted crop. Weeds were the major problem indirect seeded crop, which could be eliminated through cultural, mechanical and chemical means. Wheat crop on beds produced the highest yield but cost of production was minimum in the zero-till wheat crop. Planting of wheat on raised beds in making headway in lowlying and poorly drained areas. Thus, resource conserving tillage technology provides a tool for making progress towards improving and sustaining wheat production system, helping with food security and poverty alleviation in Pakistan in the next few decades.
  • Authors:
    • Chanasyk, D. S.
    • Mathison, M. N.
    • Naeth, M. A.
  • Source: Canadian Journal of Soil Science
  • Volume: 82
  • Issue: 2
  • Year: 2002
  • Summary: The longevity of deep ripping effects on Solonetzic soils was investigated at 11 field sites in east-central Alberta after a period of 15 to 20 yr. Select soil properties and crop yield of deep-ripped and non-ripped control plots were analyzed. Dryland yield data of wheat, barley, oats and canola were assessed for 10 of the 11 sites over a 16-yr time period. Select soil properties were analyzed once in 1998 with penetration resistance (PR) evaluated again in 1999. A significant difference in penetration resistance was found between the deep ripped versus control treatments ( P≤0.05). There were no significant treatment differences for soil texture, bulk density (Db), pH, electrical conductivity (EC) or sodium adsorption ratio (SAR). A significant yield difference between the deep ripping and control treatments (for all crop species) was found for 6 of 10 sites ( P≤0.10), with all sites having an increase in mean yield for the majority of years evaluated. Generally, sites in the drier ecoregions had smaller yield increases than those in the wetter ones. Hence some beneficial effects from deep ripping remain for a long time period.