• Authors:
    • Rich, J.
    • Wiatrak, P.
    • Katsvairo, T.
    • Marois, J.
    • Wright, D.
  • Source: Proceedings of the 26th Southern Conservation Tillage Conference for Sustainable Agriculture, Raleigh, North Carolina, USA, 8-9 June, 2004
  • Year: 2004
  • Summary: Soils in the southeast have low organic matter content, low native fertility, and low water holding capacity which has resulted in stagnant yields. Long term studies across the country (Morrow, Sanborn, Magruder, Old Rotation [Auburn]) have shown that land coming out of long term perennial grasses often has an organic matter content of over 4% and decreases as it stays in continuous annual cropping and levels off after 80-100 years once the level reaches about 1 1/2% with use of conservation tillage, cover crops, proper rotation, and modern fertility practices. Years of research in the southeast have shown that perennial grasses such as bahiagrass can help improve soil structure and reduce pests such as nematodes and increase crop yields, sometimes dramatically. Research in the southeast with this perennial grasses grown in rotation with crops has shown higher yields (50% more groundnuts than under conventional annual cropping systems), increased infiltration rates (more than 5 times faster), higher earthworm numbers (thousands per acre vs. none in many cases), and a more economically viable (potential for 3-5 times more profit) cropping system. Diversification into livestock can add another dimension to the farming system making it more intensive and provide a readily available use for perennial grasses.
  • Authors:
    • Bunce, J. A.
  • Source: Oecologia
  • Volume: 140
  • Issue: 1
  • Year: 2004
  • Summary: Reductions in leaf stomatal conductance with rising atmospheric carbon dioxide concentration ([CO 2]) could reduce water use by vegetation and potentially alter climate. Crop plants have among the largest reductions in stomatal conductance at elevated [CO 2]. The relative reduction in stomatal conductance caused by a given increase in [CO 2] is often not constant within a day nor between days, but may vary considerably with light, temperature and humidity. Species also differ in response, with a doubling of [CO 2] reducing mean midday conductances by 50% in others. Elevated [CO 2] increases leaf area index throughout the growing season in some species. Simulations, and measurements in free air carbon dioxide enrichment systems both indicate that the relatively large reductions in stomatal conductance in crops would translate into reductions of
  • Authors:
    • Schimmelpfennig, D. E.
    • McCarl, B. A.
    • Chen, C. C.
  • Source: Climatic Change
  • Volume: 66
  • Issue: 1/2
  • Year: 2004
  • Summary: One of the issues with respect to climate change involves its influence on the distribution of future crop yields. Many studies have been done regarding the effect on the mean of such distributions but few have addressed the effect on variance. Furthermore, those that have been done generally report the variance from crop simulators, not from observations. This paper examines the potential effects of climate change on crop yield variance in the context of current observed yields and then extrapolates to the effects under projected climate change. In particular, maximum likelihood panel data estimates of the impacts of climate on year-to-year yield variability are constructed for the major U.S. agricultural crops. The panel data technique used embodies a variance estimate developed along the lines of the stochastic production function approach suggested by Just and Pope. The estimation results indicate that changes in climate modify crop yield levels and variances in a crop-specific fashion. For sorghum, rainfall and temperature increases are found to increase yield level and variability. On the other hand, precipitation and temperature are individually found to have opposite effects on corn yield levels and variability.
  • Authors:
    • Owen, M. D. K.
    • Felix, J.
  • Source: Weed Technology
  • Volume: 18
  • Issue: 1
  • Year: 2004
  • Summary: In 1998, 1,260 soil samples were collected from 63 of 99 Iowa counties to characterize the weed seedbanks in fields under the conservation reserve program (CRP) and adjacent fields under continuous cultivation. Five annual grass and 13 broadleaf weed species were identified in both the CRP and adjacent cultivated fields. Seedbank differences between CRP and adjacent cultivated fields were evident only for foxtails, common lambsquarters, pigweeds, and sweetclover, with the average of 3.288, 10,681, 38, and 1,709 seeds/m(2), respectively; the corresponding seed population in adjacent CRP fields was 59, 57, 1,924, and 74%, respectively. However, weed species diversity was not significantly different between fields in CRP and continuous cultivation. Only CRP fields in the northwest Iowa crop-reporting district had a higher foxtail species seed population (4,915 seeds/m2) than the adjacent cultivated fields (1,782 seeds/m2). Land under CRP in northern (N), eastern, and southern (S) districts had 58% (4,158 seeds/m(2)), 6% (312 seeds/m(2)), and 18% (594 seeds/m(2)) of the continuously cultivated foxtail species seedbank. Common lambsquarters seed populations were 4,128 and 3,801 seeds/m2 in the cultivated fields of the N and central (C) districts, compared with 772 and 252 seeds/m2 in adjacent CRP fields, respectively. Pigweed species seeds were more numerous in the cultivated fields than in adjacent CRP fields in the northeast, C, and S Iowa districts. Sweetclover seed population was consistently higher in CRP land because it was included as part of the CRP covers seeding. Overall, broadleaf weed seeds comprised 90% of the seedbanks in both CRP and adjacent cultivated land. A competitive cover crop canopy in CRP probably reduced weed seedbanks by suppression of weeds and seed production. Also, annual seed production, differences in weed biology, and differential herbicide performance in cultivated fields may have contributed to higher seed populations.
  • Authors:
    • Sanders, D. C.
    • Paullier, J.
    • Maeso, D.
    • Arboleda, J.
    • Gilsanz, J. C.
    • Hoyt, G. D.
    • Behayout, E.
    • Lavandera, C.
  • Source: Proc. XXVI IHC – Sustainability of Horticultural Systems Eds. L. Bertschinger and J.D. Anderson Acta Horticulturae 638, ISHS 2004
  • Issue: 638
  • Year: 2004
  • Summary: Seven rotational systems were evaluated for vegetable crops in USA and Uruguay. Rotational systems that include both winter and summer cover crops and vegetable crops were used. Treatments comprised: continuous cropping system, T1; multiple vegetable system, T2; green manure system, T3; chicken manure system, T4; fallow system, T5; strip tillage system, T6; and no-tillage system, T7. The crops used were sweet potato, squash, oat or triticale winter cover crop, sorghum or Sudan grass summer cover crop, sweetcorn, garlic, carrot with chicken manure and fallow. Different insects, diseases and weed infestations were recorded in the systems. The study began in spring 1999 in Uruguay and spring 2000 in North Carolina, USA. This paper reports only results from Uruguay. The yields obtained were good compared to the national average in most cases. The average yield is 7 t/ha for sweet potato and 3.5 t/ha for garlic. T6 had the highest soil macrofauna (70 worms/m 2 compared to 4.2 in T1). Soil biomass was sampled for four times: 13 April, 26 May, 17 August and 08 November 2000. T7 system had greater soil biomass during the period of observation than T1 or T4 systems. T6 and T7 treatments had the lowest nitrate levels in the soil among all treatments. T4 was enough for garlic growth. T6, T7 and T4 systems had less sclerotia (from Sclerotium rolfsii [ Corticium rolfsii]) than T1 and T2 systems.
  • Authors:
    • Giles, J.
  • Source: Nature
  • Volume: 428
  • Issue: 6985
  • Year: 2004
  • Summary: For the past five years, global sales of organic produce have increased by 20% per year. How much more of the market share will go to organic food depends on how that standard is defined and whether evidence supports claims that "organic" is better for human health and beneficial to the environment and whether organic farming can produce yields sufficient to meet demand.
  • Authors:
    • Porter, G. A.
    • Griffin, T. S.
  • Source: Biology and Fertility of Soils
  • Volume: 39
  • Issue: 5
  • Year: 2004
  • Summary: Information is needed on the ability of different crop management factors to maintain or increase soil C and N pools, especially in intensively tilled short crop rotations. Soil samples from field experiments in Maine were used to assess the effect of cover crop, green manure (GM) crop, and intermittent or annual amendment on soil C and N pools. These field experiments, of 6-13 years' duration, were all characterized by a 2-year rotation with either sweet corn (Zea mays L.) or potato (Solanum tuberosum L.), and primary tillage each year. Total, particulate organic matter (POM), and soil microbial biomass (SMB)-C and -N pools were assessed for each experiment. Total C and N stocks were not affected by red clover (Trifolium pratense L.) cover crop or legume GM, but were increased by 25-53% via a single application of papermill sludge or an annual manure and/or compost amendment. With the exception of continuous potato production which dramatically reduced the SMB-C and SMB-N concentration, SMB-C and -N were minimally affected by changes in cropping sequence, but were quite sensitive to amendments, even those that were primarily C. POM-C and -N, associated with the coarse mineral fraction (53-2,000 mum), were more responsive to management factors compared to total C and N in soil. The change in soil C fractions was a linear function of increasing C supply, across all experiments and treatments. Within these intensively tilled, 2-year crop rotations, substantial C and N inputs from amendments are needed to significantly alter soil C and N pools, although cropping sequence changes can influence more labile pools responsible for nutrient cycling.
  • Authors:
    • Nelson, L. A.
    • Baltensperger, D. D.
    • Eskridge, K. M.
    • Russell, W. K.
    • Guillen-Portal, F. R.
    • D'Croz-Mason, N. E.
    • Johnson, B. E.
  • Source: Crop Science
  • Volume: 44
  • Issue: 5
  • Year: 2004
  • Summary: Dryland maize ( Zea mays L.) production in the U.S. western High Plains is hampered by variable yields because of substantial environmental variation in this region. This study was conducted to determine the degree to which the ranking of superior maize hybrids for dryland production in the western High Plains was predictable from performance of the same hybrids in highly productive, irrigated environments in the same region. Forty-five maize hybrids were evaluated for grain yield performance under different water regimes in western Nebraska, eastern Wyoming, and northeastern Colorado in 1998 and 1999. The value of genotypic variance was by far larger in fully irrigated test environments (0.70) than in nonirrigated test environments (0.01-0.17). The genotypic mean repeatability in fully irrigated test environments (0.63) compared with that in nonirrigated test environments (0.18-0.69, respectively), and it showed correspondence with yield performance. The genetic correlation between fully and nonirrigated environments (0.72) was lower than that observed between all-nonirrigated environments (0.78-1.02). Thus, the proportion of direct advance in the former case (0.63) was generally lower than in the latter (0.41-0.97). However, an environmental similarity ratio (ESR) derived from crossover interaction indicated that water-contrasting environments were as similar (ESR=0.53) as nonirrigated environments (ESR=0.49) in ranking the maize hybrids. Selective identification of maize hybrids in irrigated environments for production under nonirrigated environments in the western High Plains might be a useful surrogate to direct selection in the latter environments.
  • Authors:
    • Sherrod,L. A.
    • Shaver,T. M.
    • Peterson,G. A.
  • Source: Geoderma
  • Volume: 116
  • Issue: 1-2
  • Year: 2003
  • Summary: Great Plains dryland agriculture is a risky venture because of large annual fluctuations in precipitation and high evaporation potentials. Water capture is limited by low water infiltration rates because many of our soils have relatively small aggregate size distributions, which limit infiltration, and are also susceptible to crusting and sealing. No-till management has permitted cropping intensification, which via improved water storage, has increased crop residue returned to the soil, decreased surface bulk density, and increased surface soil porosity. Our objective was to quantify the relationship between crop residue biomass generated by cropping system intensification and the physical properties of the surface soil (0-2.5-cm depth). This study was conducted within an existing long-term dryland experiment consisting of three sites in eastern Colorado that transect an evapotranspiration gradient. Each site transects a soil catena with three distinct soils arranged along a slope gradient. Only soils at the summit and toe slopes were sampled for this study. Soils are Argiustolls and Ustochrepts. Three no-till cropping systems, Wheat-Fallow (WF), Wheat-Corn-Fallow (WCF), and Continuous Cropping (CC), were sampled in the summer of 1998 after the cropping systems had been in place for 12 years. Bulk density, effective porosity, aggregate size distribution, sorptivity, and soil aggregate organic C content were measured at the surface 2.5 cm of the soil in each cropping system at the two soil positions at each site. Bulk density was reduced by 0.01 g cm(-3) for each 1000 kg ha(-1) of residue addition over the 12-year period. Each 1000 kg ha(-1) of residue addition increased effective porosity by 0.3%. Increases in macroaggregation were associated with linear increases in the C content of the aggregates; each g kg(-1) of organic C in the macroaggregates increased the proportion of macroaggregates by 4.4%. Implementation of no-till intensive cropping systems under this semiarid environment increased, residue biomass, which has ultimately increased effective porosity, and thus water capture potential was increased.
  • Authors:
    • Turvey, C. G.
    • Kay, B. D.
    • Joseph, S.
    • Weersink, A.
  • Source: CAFRI: Current Agriculture, Food and Resource Issues
  • Volume: 4
  • Year: 2003
  • Summary: The objective of the 1997 Kyoto agreement was to limit greenhouse gas (GHG) emissions among signatory countries and thereby slow global warming. Under the agreement, Canada has committed itself to reduce GHGs over the next decade by 6 percent from estimated 1990 levels. Debate has now begun on the appropriate government policies that will induce the desired GHG reductions. Regulations could be in the form of direct controls or economic incentives, such as a subsidy/tax system or an emission trading system. The success of the U.S. emission market for SO2 (Schmalenseeet al., 1998) has generated growing interest in the use of a similar market mechanism for carbon (Holmes and Friedman, 2000). The existence of a carbon credit market presents the agricultural sector with another potential revenue source (Sandor and Skees, 1999). While agriculture contributes approximately 10 percent of Canada’s greenhouse gas emissions, it also has the potential to sequester carbon through strategies such as zero tillage, reduced summer fallow and improved grazing. These sequestration activities could be incorporated into an emission trading system and create a “carbon credit” for each unit of CO2 that is removed from the atmosphere. Firms with high emission reduction costs could then buy these credits rather than bear the large abatement costs associated with reducing their GHG emission levels. The perception is that the marginal cost of abatement for agriculture is less than that for other sectors (McCarl and Schneider, 2000). Thus, farmers may be able to profit by selling credits for activities that sequester carbon. An example of such a transaction was the purchase of carbon credits from Iowa farmers who adopted no-till by a consortium of Canadian energy companies (GEMCO) (Lessiter, 1999). Whether the development of a carbon credit market will affect the management decisions of an Ontario crop farmer is the focus of this study.