• Authors:
    • Searchinger,Timothy D.
    • Sehy,Ulrike
    • Ruser,Reiner
    • Munch,Jean Charles
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 99
  • Issue: 1
  • Year: 2003
  • Summary: Nitrous oxide emissions and selected soil properties in a high and a low yielding area of a maize field were monitored weekly over a 1-year period. In both the high and the low yielding area, N2O emissions from a treatment subject to site-specific N-fertilization were compared to a conventionally fertilized control. Emission peaks were measured following N fertilization, rainfall, harvest, tillage and freeze-thaw cycles from all treatments in conditions favorable for denitrification. Between 80 and 90% of annual emissions were released between April and September. A value of 60% WFPS was identified as a threshold for the induction of elevated N2O emissions (>50 mug N2O-N m(-2) h(-1)). A significant relationship (r(2) = 0.41) between N2O flux rates and WFPS was found when neither soil nitrate contents nor temperature were limiting for microbial denitrification. Mean cumulative N2O emissions from the control treatments in the high yielding area, located in a footslope position and thus receiving lateral water and nutrient supply, more than doubled those from the control treatments in the low yielding area in a shoulder position (8.7 and 3.9 kg N2O-N ha(-1), respectively). Higher average WFPS in the high yielding area was identified as responsible for this difference. The site-specific fertilized treatments in the low yielding area were supplied with 125 kg N fertilizer ha-1 as compared to 150 kg N fertilizer ha(-1) (control treatments). This reduction resulted in 34% less N2O released in roughly 10 months following differentiated fertilization while crop yield remained the same. In the high yielding area, N fertilizer supply in the site-specific fertilized treatment was 175 kg N ha(-1) as compared to 150 kg N ha(-1) in the control. Neither crop yield nor N2O emissions were significantly affected by the different fertilizer rates. (C) 2003 Elsevier Science B.V. All rights reserved.
  • Authors:
    • Ahuja, L. R.
    • Westfall, D. G.
    • Peterson, G. A.
    • Sherrod, L. A.
  • Source: Soil Science Society of America Journal
  • Volume: 67
  • Issue: 5
  • Year: 2003
  • Summary: Soil organic C (SOC) has decreased under cultivated wheat (Triticum aestivum)-fallow (WF) in the central Great Plains.We evaluated the effect of no-till systems of WF, wheat-corn (Zea Mays)-fallow (WCF), wheat-corn-millet (Panicum miliaceum)-fallow, continuous cropping (CC) without monoculture, and perennial grass (G) on SOC and total N (TN) levels after 12 yr at three eastern Colorado locations. Locations have long-term precipitation averages of 420 mm but increase in potential evapotranspiration (PET) going from north to south. Within each PET location, cropping systems were imposed across a topographic sequence of summit, sideslope, and toeslope. Cropping intensity, slope position, and PET gradient (location) independently impacted SOC and TN to a 5-cm soil depth. Continuous cropping had 35 and 17% more SOC and TN, respectively, than the WF system. Cropping intensity still impacted SOC and TN when summed to 10 cm with CC > than WF. Soil organic C and TN 20% in the CC system compared with WF in the 0- to 10-cm depth. The greatest impact was found in the 0- to 2.5-cm layer, and decreased with depth. Soil organic C and TN levels at the high PET site were 50% less than at the low and medium PET sites, and toeslope soils were 30% greater than summit and sideslopes. Annualized stover biomass explained 80% of the variation in SOC and TN in the 0- to 10-cm soil profile. Cropping systems that eliminate summer fallowing are maximizing the amount of SOC and TN sequestered.
  • Authors:
    • Angers, D. A.
    • Gregorich, E. G.
    • VandenBygaart, A. J.
  • Source: Canadian Journal of Soil Science
  • Volume: 83
  • Issue: 4
  • Year: 2003
  • Summary: To fulfill commitments under the Kyoto Protocol, Canada is required to provide verifiable estimates and uncertainties for soil organic carbon (SOC) stocks, and for changes in those stocks over time. Estimates and uncertainties for agricultural soils can be derived from long-term studies that have measured differences in SOC between different management practices. We compiled published data from long-term studies in Canada to assess the effect of agricultural management on SOC. A total of 62 studies were compiled, in which the difference in SOC was determined for conversion from native land to cropland, and for different tillage, crop rotation and fertilizer management practices. There was a loss of 24 ± 6% of the SOC after native land was converted to agricultural land. No-till (NT) increased the storage of SOC in western Canada by 2.9 ± 1.3 Mg ha–1; however, in eastern Canada conversion to NT did not increase SOC. In general, the potential to store SOC when NT was adopted decreased with increasing background levels of SOC. Using no-tillage, reducing summer fallow, including hay in rotation with wheat (Triticum aestivum L.), plowing green manures into the soil, and applying N and organic fertilizers were the practices that tended to show the most consistent increases in SOC storage. By relating treatment SOC levels to those in the control treatments, SOC stock change factors and their levels of uncertainty were derived for use in empirical models, such as the United Nations Intergovernmental Panel on Climate Change (IPCC) Guidelines model for C stock changes. However, we must be careful when attempting to extrapolate research plot data to farmers fields since the history of soil and crop management has a significant influence on existing and future SOC stocks.
  • Authors:
    • Shapouri, H.
    • Gauthier, W.
    • Wailes, E.
    • Fritz, J.
    • Dikeman, M.
    • Gallagher, P. W.
  • Source: Environmental and Resource Economics
  • Volume: 24
  • Issue: 4
  • Year: 2003
  • Summary: The components of social costs included in the supply analysis are cash outlays and opportunity costs associated with harvest and alternative residue uses, potential environmental damage that is avoided by excluding unsuitable land, and costs in moving residues from farms to processing plants. Regional estimates account for the growing conditions and crops of the main agricultural areas of the United States. Estimates include the main U. S. field crops with potential for residue harvest: corn, wheat, sorghum, oats, barley, rice and cane sugar. The potential contribution of residues to U. S. energy needs is discussed.
  • Authors:
    • Fick, G. W.
    • Hwang, J. T. G.
    • Gauch, H. G.
  • Source: Agronomy Journal
  • Volume: 95
  • Issue: 6
  • Year: 2003
  • Summary: The appropriateness of a statistical analysis for evaluating a model depends on the model's purpose. A common purpose for models in agricultural research and environmental management is accurate prediction. In this context, correlation and linear regression are frequently used to test or compare models, including tests of intercept a = 0 and slope b = 1, but unfortunately such results are related only obliquely to the specific matter of predictive success. The mean squared deviation (MSD) between model predictions X and measured values Y has been proposed as a directly relevant measure of predictive success, with MSD partitioned into three components to gain further insight into model performance. This paper proposes a different and better partitioning of MSD: squared bias (SB), nonunity slope (NU), and lack of correlation (LC). These MSD components are distinct and additive, they have straightforward geometric and analysis of variance (ANOVA) interpretations, and they relate transparently to regression parameters. Our MSD components are illustrated using several models for wheat (Triticum aestivum L.) yield. The MSD statistic and its components nicely complement correlation and linear regression in evaluating the predictive accuracy of models.
  • Authors:
    • Vigil,M. F.
    • Nielsen,D. C.
    • Benjamin,J. G.
  • Source: Geoderma
  • Volume: 116
  • Issue: 1-2
  • Year: 2003
  • Summary: Soil management decisions often are aimed at improving or maintaining the soil in a productive condition. Several indicators have been used to denote changes in the soil by various management practices, but changes in bulk density is the most commonly reported factor. Bulk density, in and of itself, gives little insight on the underlying soil environment that affects plant growth. We investigated using the Least Limiting Water Range (LLWR) to evaluate changes in the soil caused by soil management. The LLWR combines limitations to root growth caused by water holding capacity, soil strength and soil aeration into a single number that can be used to determine soil physical improvement or degradation. The LLWR appeared to be a good indicator of plant productivity when the full potential of water holding capacity on available water can be realized, such as with wheat (Triticum aestivum, L.) grown in a no-till system when the wheat followed a fallow period. A regression of wheat yield to LLWR gave an r(2) of 0.76. The LLWR was a poorer indicator of plant productivity when conditions such as low total water availability limited the expression of the potential soil status on crop production. Dryland corn (Zea mays, L.) yields were more poorly correlated with LLWR (r(2)=0.18), indicating that, under dryland conditions, in-season factors relating to water infiltration may be more important to corn production than water holding capacity. An improved method to evaluate in-season soil environmental dynamics was made by using Water Stress Day (WSD). The WSD was calculated by summing the differences of actual water contents in the field from the limits identified by the LLWR during the growing season. A regression of irrigated corn yield with LLWR as the soil indicator of the soil environment resulted in an r(2) of 0.002. A regression of the same yield data with WSD as the indicator of the soil environment resulted in an r(2) of 0.60. We concluded that the LLWR can be a useful measure of management effects on soil potential productivity. Soil management practices that maximize the LLWR can maximize the potential of a soil for crop production. Knowledge of the LLWR for a soil can help the farm manager optimize growing conditions by helping schedule irrigation and for making tillage decisions. The WSD, calculated from the LLWR and in-season water dynamics, allows us to evaluate changes in the soil caused by differing soil management practices and identify critical periods of stress on the plant that can reduce production.
  • Authors:
    • Yang, H.
    • Walters, D. T.
    • Dobermann, A.
    • Cassman, K. G.
  • Source: Annual Review of Environment and Resources
  • Volume: 28
  • Issue: 1
  • Year: 2003
  • Summary: Agriculture is a resource-intensive enterprise. The manner in which food production systems utilize resources has a large influence on environmental quality. To evaluate prospects for conserving natural resources while meeting increased demand for cereals, we interpret recent trends and future trajectories in crop yields, land and nitrogen fertilizer use, carbon sequestration, and greenhouse gas emissions to identify key issues and challenges. Based on this assessment, we conclude that avoiding expansion of cultivation into natural ecosystems, increased nitrogen use efficiency, and improved soil quality are pivotal components of a sustainable agriculture that meets human needs and protects natural resources. To achieve this outcome will depend on raising the yield potential and closing existing yield gaps of the major cereal crops to avoid yield stagnation in some of the world's most productive systems. Recent trends suggest, however, that increasing crop yield potential is a formidable scientific challenge that has proven to be an elusive goal.
  • Authors:
    • Merrill, S.
    • Tanaka, D.
    • Anderson, R.
  • Source: Agricultural Water Management
  • Volume: 58
  • Issue: 3
  • Year: 2003
  • Summary: The predominate crops grown in the northern Great Plains of the United States are cereal grains, which are well adapted to the region's semiarid climate and short growing season. However, rotations are changing because minimum- and no-till production systems improve precipitation-use-efficiency. Therefore, producers are seeking diversity in crop choices to improve the design of their rotations. Our objective with this study was to examine water relations and agronomic performance of seven broadleaf crops that may be suitable for a semiarid climate. Dry pea ( Pisum sativum L.), dry bean ( Phaseolus vulgaris L.), and sunflower ( Helianthus annuus L.) were the most favorable for this region considering crop yield and water-use-efficiency (WUE). Soybean ( Glycine max L.), crambe ( Crambe abyssinica Hochst), canola ( Brassica rapa L.), and safflower ( Carthamus tinctorius L.) were less successful. Water use for grain production ranged from 23 to 37 cm among crops whereas water-use-efficiency varied three-fold. Soil water extraction patterns differed between sunflower and dry pea, with sunflower extracting more water as well as accessing water deeper in the soil profile. Integrating oilseed and legume crops with cereal grains in a cycle-of-four rotation will aid producers in managing diseases and weeds, as well as improve grain yield due to the rotation effect.
  • Authors:
    • McDonald, C.
    • Stevenson, F.
    • Zentner, R.
    • McConkey, B.
    • Miller, P.
    • Gan, Y.
  • Source: Agronomy Journal
  • Volume: 95
  • Issue: 2
  • Year: 2003
  • Summary: Crops grown in previous years impact the amounts of residual soil water and nutrients available for subsequent plant growth. Appropriate sequences allow efficient use of the available soil resources by the crop to increase yields at a system's level. This study was conducted to determine whether the grain yield and grain crude protein concentration (GCPC) of durum wheat ( Triticum turgidum L.) were related to crops grown in the previous 2 yr. Durum was grown following pulses [chickpea ( Cicer arietinum L.), lentil ( Lens culinaris Medik.), and dry pea ( Pisum sativum L.)], oilseed [mustard ( Brassica juncea L.) or canola ( B. napus L.)], and spring wheat ( Triticum aestivum L.) in southwest Saskatchewan from 1996 to 2000. Durum increased grain yields by 7% and GCPC by 11% when grown after pulse crops rather than after spring wheat. Durum after oilseeds increased grain yield by 5% and GCPC by 6%. Pulse and oilseed crops grown for the previous 2 yr increased durum grain yield 15% and GCPC 18% compared with continuous wheat systems. Fall residual soil NO 3-N and available soil water accounted for 3 to 28% of the increased durum yield in two of five site-years, whereas those two factors accounted for 12 to 24% of the increased GCPC in three of five site-years. Durum grain yield was negatively related to GCPC. The relationship was stronger when durum was preceded by oilseeds compared with pulses. Broadleaf crops in no-till cropping systems provide significant rotational benefits to durum wheat in the semiarid northern Great Plains.
  • Authors:
    • Diffey, S.
    • Good, A.
    • Mead, J.
    • Hocking, P.
  • Source: Australian Journal of Experimental Agriculture
  • Volume: 43
  • Issue: 11
  • Year: 2003
  • Summary: Land preparation for canola (oilseed rape; Brassica napus L.) by conventional cultivation can involve a number of workings, resulting in soil degradation and reduced crop growth. Minimum-tillage systems may help overcome these problems, but the placement of fertiliser at sowing must avoid chemical injury to germinating seed. The responses of canola cultivars to tillage and fertiliser placement were studied for 2 seasons at high (Breakfast Creek, 1997; Harden, 1998) and low (Ardlethan, 1997-98) rainfall sites. The tillage treatments were conventional cultivation, one-pass, and no-till (direct drill). The fertiliser treatments were 200 kg/ha 'starter' fertiliser (a compound fertiliser supplying 30 kg N, 26 kg P and 22 kg S/ha) either placed with the seed, or broadcast, or banded to the side and 3 cm below the seed. In 1997 the canola was sown after wheat, and in 1998 after pasture. Plant establishment of all cultivars was reduced by 40-65% when fertiliser was placed with the seed; tillage treatment did not alter this response. Placing fertiliser with the seed reduced dry matter/m 2 by up to 40% in plants at flowering, but by physiological maturity, there were no differences in dry matter/m 2 due to fertiliser placement. Analysis of the combined seed yields for both years showed that although plants in the with-seed placement compensated by producing more seed/plant, this compensation was sufficient only at Breakfast Creek for yields to be comparable to those of the other fertiliser placements. Tillage had little effect on seed yields. In 1997, no-till yielded more than one-pass at Ardlethan, but in 1998 at Ardlethan no-till yielded less than the other tillage systems. Fertiliser placement and tillage had no effect on seed oil concentration and meal protein content. Cone penetrometer measurements (1998) showed no differences in soil strength between tillage treatments at Ardlethan; while at Harden, one-pass had less soil strength than the other tillage treatments. Crop water extraction was not affected by tillage at any site. It is concluded that a conservation-farming system involving no-till or one-pass tillage, and separation of seed and fertiliser has the potential for producing high yielding canola crops, reducing the risk of soil degradation, as well as saving time and land-preparation costs.