• Authors:
    • Drinkwater, L. E.
    • David, M. B.
    • Tonitto, C.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 112
  • Issue: 1
  • Year: 2006
  • Summary: The availability of Haber-Bosch nitrogen (N) has permitted agricultural intensification and increased the productive capacity of agroecosystems; however, approximately 50% of this applied fertilizer N is lost from agricultural landscapes. Extensive efforts have been devoted to improving the N use efficiency of these systems. Diversified crop rotations using cover crops to provide a variety of ecosystem functions, including biological N fixation (BNF), could maintain yields while reducing N losses. Although leguminous plants used as green manures are capable of fixing N in quantities which exceed cash crop demand, the prospect of replacing significant quantities of Haber-Bosch N with BNF is widely viewed as impractical due to yield reductions. Likewise, the practice of replacing bare fallows with non-leguminous cover crops in systems receiving Haber-Bosch N is generally deemed not economically viable. We conducted a quantitative assessment of cash crop yields and N retention in rotations that implemented these practices. We performed a meta-analysis on experiments comparing crop yield, nitrate leaching, or soil nitrate between conventional (receiving inorganic fertilizer with a winter bare fallow) and diversified systems managed using either a non-legume over-wintering cover crop (amended with inorganic fertilizer) or a legume over-wintering cover crop (no additional N fertilizer). Only studies with rotations designed to produce a cash crop every year were included in our analysis. Many yield comparisons were found in the literature, but only a limited number of nitrate leaching or soil inorganic N studies met the criteria for inclusion in a meta-analysis. Long-term studies were also uncommon, with most data coming from experiments lasting 2-3 years. Yields under non-legume cover crop management were not significantly different from those in the conventional, bare fallow systems, while leaching was reduced by 70% on average. Relative to yields following conventional N-fertilization, the legume-fertilized crops averaged 10% lower yields. However, yields under green manure fertilization were not significantly different relative to conventional systems when legume biomass provided >=110 kg N ha-1. On average, nitrate leaching was reduced by 40% in legume-based systems relative to conventional fertilizer-based systems. Post-harvest soil nitrate status, a measure of potential N loss, was similar in conventional and green manure systems suggesting that reductions in leaching losses were largely due to avoidance of bare fallow periods. These results demonstrate the potential for diversified rotations using N- and non-N-fixing cover crops to maintain crop yields while reducing the anthropogenic contributions to reactive N fluxes.
  • Authors:
    • Varvel, G. E.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 2
  • Year: 2006
  • Summary: Sequestration and storage of carbon (C) by agricultural soils has been cited as one potential part of the solution to soil degradation and global climate change. However, C sequestration in soils is a slow and dynamic process. The objective of this study was to evaluate the effects of crop rotation and N fertilizer management on soil organic C (SOC) levels at several points in time during 18 yr of a long-term study in the Western Corn Belt. Seven cropping systems (three monoculture, two 2-yr, and two 4-yr rotations) with three levels of N fertilizer were compared. Soil samples were taken in the spring in 1984, 1992, 1998, and 2002 to a depth of 30 cm in 0- to 7.5-, 7.5- to 15-, and 15- to 30-cm increments. No differences were obtained in SOC levels in 1984 at the beginning of the study. After 8 yr, rotation significantly increased SOC 449 kg ha-1 across all cropping systems. From 1992 to 2002, SOC levels in the 0- to 7.5-cm depth decreased by 516 kg ha-1 across all cropping systems. Soil organic C levels in the 7.5- to 15-cm depths in 1992 and 2002 demonstrated similar rotation effects to those in the surface 0- to 7.5-cm, being not significantly affected from 1984 to 1992 but being significantly decreased from 1992 to 2002 (568 kg SOC ha-1 across all cropping systems). Many of the SOC gains in the surface 30 cm measured during the first 8 yr of the study were lost during the next 10 yr in all but the 4-yr cropping systems after 18 yr. The loss of SOC in this latter period occurred when depth of tillage was increased by using a tandem disk with larger-diameter disks. These results demonstrate that more than one point-in-time measurement from long-term experiments is necessary to monitor SOC changes when several management variables, such as cropping system and N fertilizer, are being used. They also indicate that apparent small changes in cultural practices, such as in depth of tillage in this experiment, can significantly change SOC dynamics in the soil. Subtle changes in cultural practices (e.g., tillage depth) can have significant long-term results, but long-term experiments are required to quantify their impact under variable climatic conditions.
  • Authors:
    • Bullock, D. G.
    • Hao, X.
    • Robertson, G. P.
    • Kravchenko, A. N.
  • Source: Agronomy Journal
  • Volume: 98
  • Issue: 6
  • Year: 2006
  • Summary: Lack of information about the spatial variability of soil C in different management systems limits accurate extrapolation of C sequestration findings to large scales. The objectives of this study were to: (i) describe and quantify variability of total C in three management systems, chisel-plow (CT) and no-till (NT) with conventional chemical inputs and a chisel-plow organic management practice with cover crops (CT-cover) 15 yr after conversion from conventional management; (ii) assess the strengths of spatial correlation in the three studied systems; and (iii) evaluate contributions of topography and texture to the overall total C variability and its spatial components. The data were collected at 12 60 by 60 m plots at the Long Term Ecological Research site, Kellogg Biological Station, MI. The data consisted of elevation measurements taken on a 2 by 5 m grid and a total of 1160 measurements of total C, sand, silt, and clay contents taken from the 0- to 5-cm depth. Overall variability of total C in NT was more than four times greater than in CT, and in CT-cover the variability was more than two times greater than CT. Spatial correlation of total C was the strongest in NT, followed by CT-cover, and then by CT. Stronger spatial structures in NT and CT-cover were found to form in response to topographical and texture gradients. Effects of texture were largely associated with topographical effects; however, even when topography was controlled for, texture still substantially contributed to explaining total C variability.
  • Authors:
    • Perez, A.
    • Ali, M.
    • Pollack, S.
    • Lucier, G.
  • Year: 2006
  • Summary: The U.S. fruit and vegetable industry accounts for nearly a third of U.S. crop cash receipts and a fifth of U.S. agricultural exports. A variety of challenges face this complex and diverse industry in both domestic and international markets, ranging from immigration reform and its effect on labor availability to international competitiveness. The national debate on diet and health frequently focuses on the nutritional role of fruit and vegetables, and a continued emphasis on the benefits of eating produce may provide opportunities to the industry. In the domestic market, Americans are eating more fruit and vegetables than they did 20 years ago, but consumption remains below recommended levels. In terms of per capita consumption expressed on a fresh-weight basis, the top five vegetables are potatoes, tomatoes, lettuce, sweet corn, and onions while the top five fruit include oranges, grapes (including wine grapes), apples, bananas, and pineapples. The industry also faces a variety of trade-related issues, including competition with imports. During 2002-04, imports accounted for 21 percent of domestic consumption of all fresh and processed fruit and vegetables, up from 16 percent during 1992-94.
  • Authors:
    • Wander, M.
    • Marriott, E. E.
  • Source: Soil Biology and Biochemistry
  • Volume: 38
  • Issue: 7
  • Year: 2006
  • Authors:
    • Wander, M. M.
    • Marriott, E. E.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 3
  • Year: 2006
  • Summary: Even though organic management practices are intended to enhance soil performance by altering the quantity or quality of soil organic matter (SOM), there is no consensus on how to measure or manage SOM status. We investigated the veracity of common perceptions about SOM quantity in organically and conventionally managed soils by evaluating the relative responsiveness to organic management of particulate organic matter (POM) and the Illinois Soil N Test (IL-N), which has been proposed as a direct measure of labile N. Soil samples were obtained from nine farming systems trials in the USA. Soil organic C (SOC), total N (TN), POM-C, POM-N, and IL-N were compared among manure + legume-based organic, legume-based organic, and conventional farming systems. The organic systems had higher SOC and TN concentrations than conventional systems whether or not manure was applied. The POM-C, POM-N, and IL-N concentrations did not differ between manure + legume- and legume-based organic systems. The amount of N recovered in POM and IL-N was similar. Organic management enriched soil POM-C and -N by 30 to 40% relative to the conventional control and this level of enrichment was two to four times greater than that in any other fraction. The IL-N fraction was not a good measure of labile N as it was less enriched than POM and included recalcitrant components. This is evidenced by the strong correlation between IL-N and SOC, TN, climate and textural characteristics. Particulate organic matter provided clearer evidence of SOM and labile N accrual under organic management. Direct links between POM status and soil N supply and physical condition are being pursued to help farmers manage biologically based fertility.
  • Authors:
    • Kumar, P.
    • Yadav, S. K.
    • Kumar, M.
    • Rinwa, R . S.
  • Source: Haryana Journal of Horticultural Sciences
  • Volume: 35
  • Issue: 3/4
  • Year: 2006
  • Summary: An experiment was conducted during 2003-04 and 2004-05 to study the nitrogen, phosphorus and potassium uptake by different cropping systems in semiarid tract of Haryana, India. The experiment comprised 7 cropping systems, viz., pearl millet-wheat, pearl millet-mustard, soyabean-wheat-cowpea, sorghum-wheat, pearl millet-potato-green gram, pearl millet-field pea-maize, and cotton-wheat. The uptake of nitrogen, phosphorus and potassium by the crops varied among different cropping systems. The nutrient uptake was higher in high yielding cropping systems. The nutrients uptake was highest in pearl millet-potato-green gram cropping system.
  • Authors:
    • Spiridon, C.
    • Rotarescu, M.
    • Raranciuc, S.
    • Guran, M.
    • Popov, C.
    • Vasilescu, S.
    • Gogu, F.
  • Source: Probleme de Protectia Plantelor
  • Volume: 34
  • Issue: 1/2
  • Year: 2006
  • Summary: This paper summarizes the harmful pests and pathogens infecting cereals and legumes (grown for grain, industrial purposes and fodder production) in Romania in 2005. The soil and seed pathogens include: Tilletia spp. and Fusarium spp. in wheat; Ustilago nuda [ U. segetum var. nuda] and Pyrenophora graminea in barley; Pythium spp. and Fusarium spp. in maize; Sclerotinia sclerotiorum, Botrytis cinerea, Plasmopara helianthi [ Plasmopara halstedii] and Orobanche cumana in sunflower; and Fusarium spp. and Pythium spp. in pea, bean and soyabean. Foliar and ear diseases include: Erysiphe spp., Septoria spp., Pyrenophora graminea, Puccinia spp. and Fusarium spp. in wheat and barley; U. maydis [ U. zeae], Helminthosporium turcicum [ Setosphaeria turcica], Fusarium spp. and Nigrospora oryzae [ Khuskia oryzae] in maize; Sclerotinia sclerotiorum, Botrytis cinerea, Alternaria spp. and Phomopsis spp. in sunflower; and Erysiphe spp. and Septoria spp. in rape. Soil pests included: Zabrus tenebrioides and Agriotes spp. in spiked cereals; Tanymecus dilaticollis and Agriotes spp. in maize and sunflower; Delia platura in beans; Phyllotreta atra in rape and mustard; Aphthona euphorbiae in linseed; and Sitona spp. and Agriotes spp. in lucerne and clover. Pests that attack aerial parts and seeds include: Eurygaster integriceps, Lema melanopa [ Oulema melanopus] and Anisoplia spp. in wheat, barley and oats; Ostrinia nubilalis and Diabrotica virgifera virgifera in maize; Thrips linarius in linseed; Athalia rosae, Meligethes aeneus and Brevicoryne brassicae in rape and mustard; Hypera variabilis [ H. postica], Semiothisa clathrata, Bruchophagus roddi and Subcoccinella vigintiquattuorpunctata in lucerne and clover.
  • Authors:
    • Healy, K.
    • Reichstein, I.
    • Murray, B.
  • Source: 9th International Working Conference on Stored Product Protection -- New Chemicals and Food Residues PS3-2-6324
  • Year: 2006
  • Summary: The National Residue Survey (NRS) is an operational unit of the Australian Government Department of Agriculture, Fisheries and Forestry. NRS has managed and operated residue testing programs (including meat products and grains) for over 40 years. The NRS Grains Residue Testing Program is fully industry funded via a 0.015% ad valorem levy on grain growers. This Residue Testing Program complements that undertaken by grain marketers/handlers from grower receivals to bulk storage. Noting that NRS does not have a regulatory role, the Grains Program is viewed as providing independent verification of the residue status of Australian grain at the point of out-turn for export and for receival at grain processors such as flour mills. The Grains Program covers wheat, barley, oat, sorghum, canola, field pea, chickpea and lupin. By 2007, it is expected to extend to all tradeable grains including lentil, soybean, maize, triticale, sunflower, mung bean and faba/broad bean. Each year, the Grains Program is independently reviewed and a prospective monitoring plan circulated to the Grains Council of Australia and State affiliates, and peak grain industry bodies for endorsement. The Grains Program monitoring plan specifies that approximately 5,500 grain samples are collected per annum from export shipments and containers, flour mills, feedmills, feedlots and maltsters. About 4,000 samples are collected from export shipments where every hatch of every ship from every Australian grain export terminal is sampled during loading. The monitoring plan stipulates that samples be sent to an accredited proficiency-tested laboratory and residue testing results reported to the grain marketer/handler within 14 days of sample collection. Grain samples are subjected to a chemical screen covering a range of insecticides, fungicides and environmental contaminants. These residue testing results are reported against Australian MRLs established by Food Standards Australia and New Zealand.
  • Authors:
    • Wojciak, H.
    • Adamiak, J.
    • Rychcik, B.
  • Source: Plant, Soil and Environment
  • Volume: 52
  • Issue: Special Issue
  • Year: 2006
  • Summary: A field experiment was conducted during 1992-2004 on Luvisols (formed from silty light loam) at the Experimental Station at Bacyny to investigate the response of the most important plants cultivated in Poland to monocultural cultivation. Twelve plant species were cultivated in crop rotations: (A) potato-oats-flax-winter rye-faba bean-winter triticale; (B) sugarbeet-maize-spring barley-pea-winter rape-winter wheat, and (C) each of the species in monocultures. The organic matter content in the soil plough layer (0-250 mm) in 1992, 1998 and 2004 is presented. Fractionation of humus was carried out with the Duchaufour and Jacquin method. Under the conditions of the crop rotations, organic matter content slightly increased; similar tendencies were observed in most monoculture fields. The lowest content of organic C was recorded under the conditions of continuous cultivation of pea, maize and faba bean. Humins and humus compounds (extraction II and III) had a dominant share among the determined fractions. Humic acids prevailed over fulvic acids in the crop rotation cultivations and in the most monoculture fields. However, the prevalence of fulvic acids was found under the conditions of continuous cultivation of sugarbeet, potato and winter rye.