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Araujo A.S.F.,Federal University of Piaui | Leite L.F.C.,Embrapa Mid North | De Freitas Iwata B.,Embrapa Mid North | De Andrade Lira Jr. M.,University of Pernambuco | And 2 more authors.
Agronomy for Sustainable Development | Year: 2012

Soils around the world are degraded due to inappropriate management practices. There is thus the necessity to find more conservationist agricultural systems. Agroforestry system is an alternative system that helps prevent land degradation while allowing continuing use of land to produce crops and livestock on a sustainable basis. Agroforestry system is a form of sustainable land use that combines trees and shrubs with crops and livestock in ways that increase and diversify farm and forest production while also conserving natural resources. This system enhances organic carbon accumulation in soils by the inclusion of cover crops and permanent vegetation, which is expected to increase the soil microbial biomass. The use of microorganisms aims at improving nutrient availability for plants. Currently, there is an emerging demand to decrease the dependence on chemical fertilizers and achieve sustainable agriculture and agroforestry. Arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria, and the association of rhizobia with leguminous plants are mutualistic symbioses of high economic importance for increasing agricultural production. The biological nitrogen fixation (BNF) process is an economically attractive and ecologically sound method to reduce external nitrogen input and improve the quality and quantity of internal resources. BNF by associative diazotrophic bacteria is a spontaneous process where soil nitrogen is limited and adequate carbon sources are available. However, the ability of these bacteria to contribute to increased crop yields is only partly a result of BNF. The successful use of legumes is dependent upon appropriate attention to the formation of effective symbioses with root nodule bacteria. An essential component for increasing the use of legumes is the integration of plant breeding and cultivar development, with appropriate research leading to the selection of elite strains of root nodule bacteria. An expansion of the utility of inoculants is also necessary to develop a broad conceptual framework and methodology that is supported by scientific arguments; it is destined to impact assessment of the use of new biological products in agriculture. © INRA and Springer Science+Business Media B.V. 2011.

Buch A.C.,Federal University of Fluminense | Niemeyer J.C.,Federal University of Santa Catarina | Fernandes Correia M.E.,Embrapa Agrobiology | Silva-Filho E.V.,Federal University of Fluminense
Ecotoxicology and Environmental Safety | Year: 2016

Mercury (Hg) is a highly toxic nonessential trace metal. Despite its natural occurrence in the Earth's Crust, its concentrations have been steadily increasing in the environment due to anthropogenic sources. Recent studies have showed great concern about soil fauna, once the potential adverse effects of mercury concentrations in the environment of these invertebrates are still poorly understood, especially when linked to forest soils and tropical biota. Different collembolan species can show distinct toxicity effects to the contaminants, impairing its developing lifelong and affecting its diversity and abundance in the environment. Laboratory studies were performed to evaluate the ecotoxicity of Hg(II) to collembolan species collected in Brazil, Proisotoma minuta (autochthonous) and Folsomia candida (allochthonous), as a tool to predict effects in ecological risk assessment of tropical regions. Behavioral, acute and chronic tests were carried under temperatures of 20°C and 24°C using two test soils, natural and artificial, spiked with increasing mercury concentrations. F. candida was more sensitive to mercury contamination than P. minuta, presenting the most restrictive values of EC50 and LC50. Reproduction was a considerably more sensitive endpoint than avoidance and mortality. The 28-day lower EC50 values were found in chronic tests for F. candida in natural soil to 24°C (3.32 mg Hg kg-1), while for P. minuta was in tropical artificial soil to 20°C (4.43 mg Hg kg-1). There were similarity for each collembolan species to respond at the Hg(II) effects when exposed at 20°C and 24°C. F. candida can be suitable as a bioindicator species to mercury ecotoxicity tests in tropical forest soils. © 2016 Elsevier Inc.

Jantalia C.P.,Embrapa Agrobiology | Halvorson A.D.,U.S. Department of Agriculture
Agronomy Journal | Year: 2011

Conventional plow tillage (CT) is a common soil management practice under irrigated continuous corn (Zea mays L.) in the semiarid central Great Plains that requires a relatively high N fertilizer rate to optimize grain yield and economic returns. This study investigated how four rates of N input (0, 67, 101, and 224 kg N ha-1) under irrigated CT management affects aboveground corn production, stover characteristics, and crop biomass. We also examined soil quality parameters under these treatments, including total soil carbon (TSC) and soil particulate organic matter (POM), soil organic carbon (SOC) and total soil nitrogen (TSN) stocks in the 0- to 7.6-, 0- to 15.2-, and 0- to 30.4-cm soil depths of a clay loam soil. Nitrogen fertilization significantly increased corn grain, stalks, cob and stover yields as well as C and N content of the biomass. The C/N ratios of stalks and stover decreased with increasing N rate, but cob C/N ratios did not change. Increasing N rate increased TSN concentration in 0- to 7.6- and 7.6- to 15.2-cm depths and decreased C/N ratio in all soil layers between 1999 and 2008. We found no significant change in SOC and POM-C stocks under increasing N fertilizer addition aft er 10 yr of irrigated, CT continuous corn despite higher stover yields, and the stover C and N returned to the soil aft er harvest with increasing N rate. The lack of increased SOC storage with increasing residue C inputs suggests that decomposition processes controlled the SOC stocks. © 2011 by the American Society of Agronomy.

Halvorson A.D.,2150 Center Ave | Jantalia C.P.,Embrapa Agrobiology
Agronomy Journal | Year: 2011

Converting to no-till (NT) production can affect N requirements for optimizing corn (Zea mays L.) yields while enhancing soil organic carbon (SOC) and N levels. Nitrogen fertilization impacts on irrigated, NT continuous-corn grain, stalk, cob, and stover yields, stover C and N uptake, and C/N ratios were evaluated for 11 yr on a clay loam soil. Changes in SOC and total soil nitrogen (TSN) were also monitored. Grain, stalk, cob, and stover yields increased with increasing N rate, as did N and C uptake. The C/N ratio of stalk residue declined with increasing N rate, but cob C/N ratio was not affected, with an average stover C/N ratio of 68 at the highest N rate. Nitrogen fertilization increased SOC and TSN levels with average SOC and TSN mass rate gains with N application of 0.388, 0.321, and 0.160 Mg SOC ha -1 yr -1 and 0.063, 0.091, and 0.140 Mg TSN ha -1 yr -1 in the 0- to 7.6-,0- to 15.2-, and 0- to 30.4-cm soil depths, respectively. The SOC and TSN mass rate changes were lower without N application. Increases in TSN appeared to be more rapid than SOC, resulting in a decline in the soil C/N ratio with time. Under irrigated, NT continuous corn production, N fertilization optimized grain and residue yields, with the enhanced benefit of increased SOC and TSN levels in the semiarid central Great Plains. Removal of cobs or partial stover residue as a cellulosic feedstock for ethanol production appears possible without negative effects on soil quality under irrigated, NT corn production. © 2011 by the American Society of Agronomy.

Sagrilo E.,Embrapa Mid North | Rittl T.F.,Wageningen University | Hoffland E.,Wageningen University | Alves B.J.R.,Embrapa Agrobiology | And 2 more authors.
Geoderma Regional | Year: 2015

Soil amendment with biochar has been claimed as an option for carbon (C) sequestration in agricultural soils. Most studies on biochar/soil organic carbon (SOC) interactions were executed under laboratory conditions. Here we tested the stability of biochar produced in a traditional kiln and its effects on the stocks of native SOC under field conditions. The biochar was characterized using pyrolysis-gas chromatography-mass spectrometry, and then added to an Oxisol under savannah climate. This soil was amended with 0, 5, 10, 20 and 40 Mg ha- 1 of biochar in a randomized complete block design with four replications and cultivated with soybean over four cropping seasons (CSs; 120 days each). Soil samples from the 0-10 cm top layer were collected at the end of the first and fourth CSs and analyzed for CO2 emissions, isotopic C abundance (13C/12C ratio) and enzymatic activity (fluorescein diacetate and dehydrogenase). The biochar showed a low degree of thermal modification. Its relative decomposition rate was higher (k = 0.32-1.00 year- 1) than generally claimed (k = 0.005-0.0005 year- 1), and higher than the decomposition of native SOC (k = 0.22 year- 1). Addition of biochar did not affect the stocks of native SOC. Our findings highlight the need for critically reviewing the potential of locally produced biochar to sequester C. © 2015 Elsevier B.V.

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