Volumen 21, Número 1 (Junio, 2003)
Cuantificación de las fracciones orgánicas e inorgánicas de fósforo en suelos de la Mesopotamia Argentina
Quantification of organic and inorganic phosphorus fractions in soils of the argentinean Mesopotamia
NG Boschetti , CE Quintero, RA Benavidez & L Giuffré
Pág. 1-8
Surface horizon samples of 13 uncultivated and nonfertilized soils of the Argentinean Mesopotamia, with differing weathering stages, were analyzed for organic and inorganic phosphorus forms to evalu- ate the effects of different soil development on phosphorous composition. Results indicated that absolute contents of total phosphorus varied from 125 mg P kg-1 in Entisols, to 700 mg P kg-1 in Oxisols and Ultisols. The distribution stable and available phosphorus forms, as well as the inorganic and organic forms, depended on the genesis and of the evolution state of soils. Available phosphorus for plants represented less than 10% of total phosphorus in moderate and highly developed soils, and 20 to 30 % in less developed soils (Entisols and Inceptisol). The most developed soils (Oxisols and Ultisols) had 50 to 70 % of P in unreactive forms while the less developed (Molisols, Entisols and Inceptisols) had 30 to 40 %. Inorganic P extracted with the Anionic Exchange Membrane was closely related to soil organic carbon contents (r = 0,90 p menor que 0.01) and the fraction extracted with 1M HCl was related to the exchangeable calcium (r=0,85 p menor que 0.01). Organic P extracted with OHNa was positively related to amorphous Fe and Al contents of soils (r=0,86 p menor que 0.01). In all soils, labile and moderately labile organic fractions prevailed with respect to the inorganic, fractions being higher in the highly weathered soils.
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Utilización de formaldehido para la erradicación de hongos micorríticos arbusculares de muestras de suelo
The use of formaldehyde for eliminating arbuscular mycorrhizal fungi from soil samples
F Covacevich & HE Echeverría
Pág. 9-17
A limitation for mycorrhizal research is the adequate control of arbuscular mycorrhizal fungi (AMF) which normally colonizes roots plants. For manipulating mycorrhizal population, it is necessary to develop an appropriate substrate free of AMF when they could be latter propagated. The substrate, however, should not be different from the used soil in the most of the characteristics that influence mycorrhizal development and activity. The aim of this work was to determine the formaldehyde ability to eliminate AMF, without affecting plant growth, mycorrhizal development and mycorrhizal benefit on the host plant. The effects of formaldehyde supply in a soil-sand (1:1) mixture were evaluated in three pot assays: the appropriate concentration was selected, the propagation of two AMF isolates was performed, and the effects of disinfecting and inoculating soil on colonization and growth of tall fescue (Festuca arundinacea Schreb.) and wheatgrass (Thinopyrum ponticum Podp = Agropyron elongatum Beauv.) were evaluated. The soil Bray-P (15,2 ± 1,56 mg kg-1 ), pH (5,60 ± 0,29) and organic matter (7,07 ± 0,20 %) content were not affected by formaldehyde supply. Formaldehyde soil application at concentrations higher than 10 ul.g1 impeded plants emergency. The concentration range of 3,33-10 ul.g-1 effectively eliminated indigenous mtycorrhizal colonization without deterring plant growth. Concentrations lower than 10 ul.g-1, however, allowed fungal development of non- mycorrhizal fungi. Mycorrhizal development of Acaulospora longula and Glomus claroideum isolates, as a result of maize inoculation, was possible after disinfecting soil with 10 ul formaldehyde g-1. Colonization of G.claroideum in tall fescue inoculated plants growing within the formaldehyde disinfected soil reached about 30 %, being three fold higher than native mycorrhizal plants. Formaldehyde did not negatively affect tall fescue and wheatgrass growth. In addition, it showed both indigenous and G. claroideum mycorrhizal benefit. Formaldehyde fumigated soil can be used for propagation of AMF inoculum. More research on formaldehyde effects on the development of soil microorganisms other than mycorrhizal must be further developed.
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Respuesta del cultivo de maíz bajo siembra directa a la fuente y al método de aplicación de nitrógeno
Response of corn under no-tillage to nitrogen source and placement meted
PA Barbieri, HE Echeverría & HR Sainz Rozas
Pág. 18-23
Nitrogen fertilization is a common practice in no-tillage (NT) corn. However, when fertilizers like urea are broadcasted on soil surface, volatilization losses could decrease crop nitrogen availability. Two experiments were carried out at INTA Experimental Station, Balcarce, Argentina (37o45′ S; 58o18′ W), during 1998/99 and 1999/00 growing seasons. In 1998/99 treatments were: 1) without nitrogen, 2) urea broadcasted, 3) calcareous ammonium nitrate (CAN) broadcasted and 4) urea incorporated (4 cm). In 1999/00 the same treatments were evaluated except CAN. Nitrogen rate (70 kg N ha-1) was applied at six leaves corn growing stage (V6). In both years volatilization losses, chlorophyll content at flowering, aboveground biomass, accumulated nitrogen and grain yield at physiological maturity were evaluated. Both years, volatilization losses from broadcasted urea were not higer than 7% of applied nitrogen. Volatilization losses from incorporated urea were lower than 0,1%. Averaged through the years, grain yield was significantly increased by nitrogen fertilization (7480 and 9980 kg ha-1, control versus fertilizer treatments, respectively), but it was not different between nitrogen source or placement methods. Chlorophyll content was increased by nitrogen fertilization in both years, regardless of nitrogen source or placement methods. Nitrogen recovery (kg N uptake from fertilizer/kg N applied) as determined by difference method was not different between CAN and urea incorporated (0,90, average years) and this value was greater than broadcasted urea (0,75, average years). There were no differences in nitrogen use efficiency (kg grain/kg N applied) between urea placement methods or nitrogen sources, because physiological efficiency was greater for urea broadcasted than incorporated urea or CAN. Therefore, the incorporation of urea below residues would not be advantageous practice for Balcarce area, because volatilization losses were not high under theses conditions.
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Incubación anaeróbica del suelo como diagnóstico de la respuesta a nitrógeno del maíz bajo siembra directa
Soil anaerobic incubation as an aid for predicting nitrogen fertilizer response of maize under no-tillage
PA Calviño & HE Echeverría
Pág. 24-29
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Rugosidad y cobertura superficial de un Argiudol Vértico de la Pampa Ondulada (Buenos Aires, Argentina) sometido a lluvias naturales
Soil surface roughness and surface cover of a Vertic Argiudoll from the Rolling Pampa subjected to natural rainfalls
F Peleretegui, R Plaza de Ayala & C Chagas
Pág. 30-33
Soil surface random roughness strongly infuences its hydrologic response. The aim of this work was to quantify the dynamics of the surface roughness for a Vertic Argiudoll which was subjected to natural rainfall and was kept in a rough, bare or covered surface condition. For that purpose, 0,25 m2 square microplots containing 20 kg of a topsoil devoted to 8 years of conventional agriculture were prepared. Plant residues were hand removed but soil clods were kept undisturbed. The period of measurements included a four months summer fallow, in which rainfall and surface roughness were periodically monitored. The relative roughness (roughness measured after rainfalls / initial roughness measured immediately after tillage) from the covered treatment was significantly higher than that of the uncovered treatment. This confirmed the influence of rainfall kinetic energy on the obtained results because cumulative rainfall was the same for both treatments. This influence was explained with the following equations for the covered treatment Relative Roughness=10-6 PP2 – 7 10- 4 PP + 1 (R2=0.63) and for the bare treatment Relative Roughness= 2 10-6 PP2 – 1,7 10-3 PP + 1 (R2=0,83) where PP is cummulative rainfall (mm)
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