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Browsing Faculty Publications by Author "American Society of Agronomy, publisher"

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    Corn root effects on the nitrogen-supplying capacity of a conditioned soil
    (Colorado State University. Libraries, 2002-05) Harwood, Richard R., author; Smeenk, Jeffrey, author; Willson, Thomas C., author; Paul, Eldor A., author; Sanchez, Jose E., author; American Society of Agronomy, publisher
    The design of sustainable N management strategies requires a better understanding of the processes influencing the ability of soils to supply N to a growing crop. Although commonly ignored, the release of C by plant roots may have a tremendous impact on soil organic matter turnover under certain soil conditions. The main objective of this study was to determine if living corn (Zea mays L.) roots would increase the N-supplying capacity of a soil with an enhanced mineralizable N pool. A rotation of corn–corn–soybean [Glycine max (L.) Merr.]–wheat (Triticum aestivum L.) in combination with cover crops and the application of composted manure were used to increase the mineralizable N pool. The N-supplying capacity of bare soil and soils planted with corn and wheat was calculated, and changes in N and C pool sizes were determined by laboratory incubations. Living corn roots increased the inorganic N–supplying capacity of the conditioned soil by >50%. We suggest that this increase is caused by an increase in net N mineralization. This is supported by the considerable size reduction of the 70-d N pool in the soil planted with corn. No significant increase in the soil N-supplying capacity was observed when wheat was planted, indicating the possibility that this effect may vary dramatically among plant species. The contribution of corn and wheat root rhizodeposition to the active C pool and as energy source to enhance microbial activity and organic matter turnover is discussed.
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    Fate of legume and fertilizer nitrogen-15 in a long-term cropping systems experiment
    (Colorado State University. Libraries, 1994-09) Janke, Rhonda R., author; Peters, Steven E., author; Paul, Eldor A., author; Hesterman, Oran B., author; Harris, Glendon H., author; American Society of Agronomy, publisher
    Relying more on biological N2 fixation has been suggested as a way to meet one of the major challenges of agricultural sustainability. A 15N study was conducted to compare the fate of applied legume and fertilizer N in a long-term cropping systems experiment. Nitrogen-15-1abeled red clover (Trifolium pratense L.) and (NH4)2SO4 ere applied microplots within the low-input and conventional cropping systems of the Farming Systems Trial at the Rodale Institute Research Center in Pennsylvania. The 15SN was applied to soil and traced into corn (Zea mays L.) in 1987 and 1988. Residual 15SN was also traced into second-year spring barley (Hordeum vulgare L.). Legume and fertilizer 15SN remaining in soil was measured and loss of N was calculated by difference. More fertilizer than legume N was recovered by crops (40 vs. 17% of input), more legume than fertilizer N was retained in soil (47 vs. 17% of input), and similar amounts of N from both sources were lost from the cropping systems (39% of input) over the 2-yr period. More fertilizer than legume N was lost during the year of application (38 vs. 18% of input), but more legume than fertilizer N was lost the year after application (17 vs. 4% of input). Residual fertilizer and legume 15SN was distributed similarly among soil fractions. Soil microbial biomass was larger in the legume-based system. A larger, but not necessarily more active, soil microbial biomass was probably responsible for the greater soil N supplying capacity in the legume-based compared with fertilizer-based system.
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    Gaseous nitrogen losses from soils under zero-till as compared with conventional-till management systems
    (Colorado State University. Libraries, 1984-01) Paul, Eldor A., author; Rennie, D. A., author; Aulakh, M. S., author; American Society of Agronomy, publisher
    The gaseous losses of N from conventional-till (CT) and zero-till (ZT) crop fields were 3 to 7 and 12 to 16 kg N ha−1 y−1, respectively. In contrast, losses from CT and ZT fallow were severalfold higher, namely, 12 to 14 and 34 kg N ha−1, respectively. The more dense surface soil and consistently higher moisture content (lower air-filled porosity) were identified as major factors affecting increased denitrification under ZT. The potential denitrification rates were markedly higher under ZT, and the population of denitrifiers was up to six times higher than in CT soil samples. The contribution of lower soil horizons towards gaseous N losses was found to be low on both CT and ZT fields, and this finding was confirmed from a survey carried out on three other widely differing soils. Volumetric soil moisture and air temperature were the only two of several factors that accounted for a significant portion of the variations in gaseous N fluxes under field conditions. The average mole fraction of N2O ranged from almost 100% to as low as 28% of the total gaseous products and showed a negative relationship with soil moisture.
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    Managing soil carbon and nitrogen for productivity and environmental quality
    (Colorado State University. Libraries, 2004-05) Robertson, G. Philip, author; Knezek, Bernard D., author; Paul, Eldor A., author; Parker, Elaine, author; Smeenk, Jeffrey, author; Kizilkaya, Kadir, author; Willson, Thomas C., author; Harwood, Richard R., author; Jose E., Sanchez, author; American Society of Agronomy, publisher
    In this study, we investigated the impact of cropping system management on C and N pools, crop yield, and N leaching in a long-term agronomic experiment in Southwest Michigan. Four management types, conventional (CO), integrated fertilizer (IF), integrated compost (IC), and transitional organic (TO) were applied to two crop sequences, a corn (Zea mays L.)–corn–soybean [Glycine max (L.) Merr.]–wheat (Triticum aestivum L.) rotation and continuous corn, which were grown with and without cover crops in the IF, IC, and TO managements. Using compost as a fertility source and reducing the use of herbicides and other chemicals resulted in long-term changes in soil organic matter pools such TO ≥ IC > IF ≥ CO for total C and N and for the labile C and N measured through aerobic incubations at 70 and 150 d. Mineralizable N varied within the rotation, tending to increase after soybean and decrease after corn production in all systems. Corn yield was closely associated with 70-d N mineralization potential, being greatest for first-year corn with cover and least for continuous corn without cover under all management types. Although the TO and IC systems produced the lowest yield for second-year or continuous corn, the combination of soybean and wheat plus red clover (Trifolium pratense L.) always supported high yield for first-year corn. Fall nitrate level and nitrate leaching were higher for commercially fertilized corn than for any other crop or for compost-amended corn.
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    Response of mycorrhizal and P-fertilized soybeans to nodulation by Bradyrhizobium or ammonium nitrate
    (Colorado State University. Libraries, 1986-01) Paul, Eldor A., author; Pacovsky, R. S., author; Bethlenfalvay, G. J., author; American Society of Agronomy, publisher
    Management of N2-fixing bacteria or P-scavenging endomycorrhizae may lead to decreased fertilizer use on extensively cropped lands. To measure the effectiveness of these microsymbionts, soybean [Glycine max (L.) Merr. cv. Amsoy 71] plants were grown in a growth chamber in a soil [Josephine silty clay loam (mesic Typic Haploxerult)] low in plant-available N and P. Plants were inoculated with different Bradyrhizobium strains or received nutrient solutions of different N concentrations (0.0, 1.0, 2.0, 4.0 mM N) and P adequate for maximum plant growth under these conditions. Other plants were infected with a vesicular-arbuscular mycorrhizal (VAM) fungus and a Bradyrhizobium strain and received no N or P in the nutrient solution. The purpose of this study was to determine the growth response of soybean to N fertilization or nodulation by B. japonicum under conditions of high P availability or V AM-assisted P uptake. Nodulated non-VAM soybean plants had dry weights and development similar to that of the 4.0 mM N fertilizer treatment. Total N and Mn, leaf area, and leaf P of nodulated plants were higher than in the comparable N-fertilized plants in the absence of P stress. Soybeans infected with both the VAM fungus and Bradyrhizobium were similar in total dry weight, leaf area, and development to plants that received 1.0 or 2.0 mM N. They, however, contained more leaf N, more root Cu and Zn, and less Mn and P than the 2.0 mM N treatment. It is concluded that a number of host characteristics of nodulated plants are due to the altered functional aspects of the symbiosis and not N input alone. The presence of the VAM fungus can decrease nutrient stress in environments limited in P, Zn and Cu, elements essential in N2 fixation.