Volumen 20, Número 2 (Diciembre, 2002)
Approaches to assessing sustainable agricultura
Enfoques para evaluar la agricultura sostenible
JA Zinck, JL Berroterán, A Farshad, A Moameni, S Wokabi & E Van Ranst
Pág. 55-68
This paper brings together several case studies in which different methodological approaches and techniques mobilizing single or composite indicators were applied to assess agricultural sustainability at four hierarchical levels, including the land management system, the cropping system, the farming system, and the agricultural sector system. The first case study (Iran) focuses on the land management system at the level of individual soil units, using statistical quality control charting to assess the soil fertility status and its effect on agricultural sustainability. Statistical limits are adequate to monitor the behavior of a data population over time, but must be replaced by acceptance/sufficiency standards for sustainability assessment. A relevant limitation of control charting is that large data sets are needed to allow for random sample data selection from the whole population and check for normal distribution of the data. The second case (Kenya) concentrates on the cropping system at parcel level, using yield gap analysis to evaluate sustainable crop productivity. Although yield gap analysis does not indicate by itself what yield level is sustainable, it points at levels of crop productivity higher than farmers’ yields, which could be achievable with additional inputs and improved management practices. If the farmer can raise the yield to a higher level, his/her farming activity will become more profitable and therefore more sustainable. The third study (Iran) refers to the farming system at the production unit level, using the energy balance analysis to compare the sustainability of traditional and modern agricultural systems. Energy balance analysis has the advantage of expressing all input and output parameters in the same unit. The approach allows us to establish input/output ratios and compare different farming systems in quantitative terms for assessing their sustainability, but it must be combined with complementary techniques to cover the many facets of the sustainability concept. The last case study (Venezuela) addresses the agricultural sector as a whole, using an aggregated index to monitor the sustainability of the farming activity at regional/national level. Component indicators must be chosen according to data availability, data sensitivity to temporal changes and the capacity of the data to describe quantitatively the behavior of the agricultural activity. The index needs refinement by integrating additional indicators and by allocating differential weights to the indicators to properly reflect their relevance and dynamics. Much effort is still needed to integrate the methodological approaches in one coherent framework allowing to navigate through the hierarchical levels of the agricultural macro-system and to take into account the many requirements involved in a holistic model of sustainability.
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Tamaño y estabilidad de agregados y su relación con la conductividad hidráulica saturada en suelos bajo labranza convencional y praderas
Size and stability of soil aggregates and their relationships with saturated hydraulic conductivity in soils under conventional tillage and prairies
F Cabria, M Calandroni & G Monterubbianesi
Pág. 69-80
When organic matter is the major stabilizing agent and aggregate structure is hierarchical, different types of aggregates are being formed and turned over at different rates related to the turnover rates of their organomineral binding agents. Consequently, soil aggregation and organic matter storage are intimately associated with each other. Changes in either of these processes often result in feedbacks on the other. These feedbacks are mediated through organomineral associations, which function as aggre- gate binding and stabilizing agents. The nature of these organomineral associations and their special locations within the aggregate hierarchy determine the degree to which soil organic carbon is physi- cally protected from decomposition and, consequently, result in organic pools with various input and turnover rates. In degrading systems, the disruption of aggregate exposes previously protected but relatively labile organic matter to decomposers, resulting in a loss of soil organic matter and further destabilization of aggregates. We used this conceptual frame to examine the relationship between aggregation state of three soil series and saturated flow of water (ks). Aggregate stability and size distribution, geometric particle-size diameter (DGPag) and structural stability index (IE) were quan- tified. The result showed that conventional tillage modified IE, DGPag and aggregate stability and size distribution. This management system did not affect stability of aggregates menor que 0.059 mm in diameter. Stability of aggregates > 0,059 mm in diameter decreased 58%, 39% and 28% and declined DGPag 51%, 52% and 57% in El Cruce, Azul and Mar del Plata soil respectively. Contrary to what happened with IE, the lower the position of soils on the landscape, the higher the effect of conventional tillage on DGPag. When were considered variables that take part in the formation and stability of aggregate hierarchy, aggregates stability and size distribution could be justified. The effects that management system exerted on the size and stability of aggregates allowed for the understanding of the relationship between ks and DGPag.
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Formas de fósforo en suelos altamente meteorizados del sur de la Provincia de Misiones
Phosphorus forms in highly weathered soils of south Misiones Province
C Fernández López, S Vazquez & HC Dalurzo
Pág. 81-87
The low phosphorus availablility of Oxisols, Ultisols, and Alfisols of Misiones is an important limitation for agricultural production, though their high total phosphorus content. Our objectives were to determine the distribution of organic- (Po) and inorganic (Pi) phosphorus forms in these soils and to determine the relationships between phosphorus fractions and edaphic properties. Phosphorous fractions were determined by means of the Hedley‘s modified extraction method. Results showed that residual phosphorous forms were the highest in all studied soils (293 mg kg-1 in Ultisols, 230 mg kg- 1 inOxisolsand128mgkg-1 inAlfisols),anditshowedanincreasewithsoildepth.Negativecorrelations were obtained between Al and H and residual phosphorus. Phosphates were transformed into secondary forms (the inorganic and organic NaOH and NaOH sonicated extracted phosphates) which predominated over the labile phosphate forms in agreement with an increase of the amorphous Al and Fe contents. Organic NaOH extracted phophates followed the residual phosphates in accumulation amounts, and also showed decreases with depth: Oxisols and Ultisols contained 28% at soil surface and 10% at the bottom, while Alfisols showed similar amounts at both depths (26% and 14%, respectively). The bicarbonate organic extracted phosphorus varied between 18 to 28 mg kg-1 in all soil types. The NaHCO3 and NaOH extracted organic phosphates were positively correlated with organic carbon. Though all studied soils were developed on basaltic materials, the HCl soluble phosphates were very low (less than 1% of total P) probably because they went lost during pedogenesis process. Alfisols located at lower relief positions showed lowest phosphate contents than other studied soils.
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Prácticas de rehabilitación de Aridisoles y Entisoles del norte de la Patagonia afectados por la apertura de líneas sísmicas
Rehabilitation practices of Aridisols and Entisols affected by seismic lines in Patagonia, Argentina
A Apcarian, C Aruani , P Schmid, P Broquen & PA Imbellone
Pág. 88-97
The north Patagonian region of Argentina is affected by desertification processes. The combination of petroleum activity and the existence of seismic lines across of this arid area increases desertification. The purpose of this study was to evaluate the application of different soil rehabilitation practices. Five soils, representative of the most important landscape units were selected: Typic Torripsamment, Argic Petrocalcid, Natric Petrocalcid, Calcic Petrocalcid, and Argic Petrocalcid. Four treatments were applied on each soil: control, tillage, tillage + transplantation of native vegetation species, and tillage + sowing of native vegetation species. Five indicators were measured to assess the effectiveness of each treatment during three years: vegetation cover, accumulation and denudation of soil material, diversity of vegetation species, and tillage perdurability. Results showed that tillage + transplantation of native vegetal species was the most effective practice in all studied soils to achieve an effective vegetation regeneration. In the Argic Petrocalcid vegetation cover increased from 13 % to 45 %, species diversity varied from 6 to 16, and no soil denudation was detected. Tillage was also effective in the moderately deep Argic Petrocalcid but this practice is not recommended in shallow and very shallow or sandy soils. Human intervention through adequate management practices make plant regeneration possible over seismic lines, however the effectiveness of each practice can be different at different landscape units.
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Distribución y disponibilidad de elementos potencialmente tóxicos en suelos representativos de la Provincia de Buenos Aires enmendados con biosólidos
Distribution and availability of potentially toxic elements in representative soils of Buenos Aires Province as a result of biosolid application
SI Torri & RS Lavado
Pág. 98-109
Sewage sludge can be applied to cropland to supply and recycle nutrients and organic carbon. Potentially toxic elements (EPT) in the sludge, however, are of environmental concern. A pot experiment was performed to study the effects of the application of biosolid (BIO) or biosolid containing 30% (P/ P) of its own incineration ash (BCEN) on soil properties and chemical extractability of Cd, Cu, Pb and Zn on three pristine soils (Typic Hapludoll, Typic Natracuoll and Typic Argiudoll). Potentially toxic elements were sequentially fractionated into exchangeable, organically bound, carbonate-associated and remnant fractions. Soil organic matter content, pH, CE and total Cd, Cu, Pb and Zn significantly increased in the three soils as a result of the application of the amendments. At day 1, the elements of the treated soils were mainly found in the remnant fraction. A year after biosolid application, redistribution towards carbonate-associated (62-92% for Pb, 41-76% for Zn) or carbonate-associated and organically bound fraction (25-48 % and 30-46% respectively for Cu) was observed. These results confirm the reports made by other authors in similar studies (Walter, Cuevas 1999). The distribution pattern of the studied elements could not be associated with soil texture or organic matter content. Soil pH (Cu, Zn), organic matter reactivity (Cu) or insoluble components (Pb, Cd) explained the partition of the elements among the different fractions. Zn and Cu were the only elements found in the exchangeable fraction. For each soil, no significant differences were observed between the exchangeable fraction of the BIO or BCEN treatments. The elements were mainly found in the less available forms, indicating a protective effect of the inorganic or organic matrix of the biosolid.
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Fertilización fosfatada prolongada y contenido de elementos traza en un Argiudol Típico de la Pampa Ondulada
Long term phosphate fertilization and trace element contents in a Typic Argiudoll of the Rolling Pampas
MS Zubillaga & RS Lavado
Pág. 110-113
The application of phosphorus fertilizers can produce an accumulation of trace elements (TE) in soils. Little is known about the input of TE from commercial P fertilizers in Argentina. Our objective was to evaluate the total and bioavailable content of TE of a Typic Argiudoll fertilized with diammonia phosphate for 20 years. The work was performed on the Rolling Pampas, Argentina. The treatments were: 1) pristine plot, with no history of fertilization; 2) rotation plot (alfalfa non fertilized, but fertilized previous corn) and 3) continuous corn plot, fertilized with diammonia phosphate. Total (aqua regia) and bioavailable (DTPA) TE in soils were determined with IPC. Other soil properties were also determined. The soil total micronutrient concentrations were lower in the continuous corn plot, which could be accredited to crop exportation. On the other hand, bioavailable form of Cu, Mn y Zn were higher in this treatment, and it was related to acidification and changes in organic C in those soils. There were no evidences of changes in the total and the bioavailable contents of heavy metals in the soil. It was concluded that TE accumulation due to continuous phosphorous fertilization is not relevant in the studied area.
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Uso del modelo fractal para caracterizar la distribución de tamaño de partículas en suelos
The use of the fractal model to characterize particle-size distribution in soils
RR Filgueira, MG García, MF Roggiero, CI Cerisola, A Aragón & GO Sarli
Pág. 114-117
The objective of this study was to characterize the particle-size distribution of a soil by means of fractal geometry using the accumulated mass fraction and the particle diameter. In order to fit the experimental data the accumulated mass and the particle diameter were related by a power law relation, as a result of considering the fragmentation process as fractal. The samples were taken from a Typic Argiudoll, near La Plata City, Buenos Aires Province, at depths ranging from 0 to 400 mm. The fit of experimental results was satisfactory, with fragmentation fractal dimensions, D, ranging from 2.403 to 2.679 and coefficients of correlation, R2, ranging from 0.879 to 0.999. The values obtained in the present study differ considerably from the universal parameter D = 2.8 suggested by other researchers. However, our results were in agreement with other studies with soils of similar clay contents. The conclusions emerged from the study confirmed that mass distribution versus particle diameter followed a power law relation, consistent with a probabilistic fractal model of fragmentation, and that the fractal dimension increased with the increasing clay content and soil depth.
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Superficie específica de un Hapludult Típico. Efectos de la aplicación de materia orgánica
Specific surface area of a Typic Hapludult as affected by the addition of organic matter
LL Fournier, RR Filgueira, LJ Sikora, WJ Rawls & YA Pachepsky
Pág. 118-121
Beneficial effects of amending soils with organic by-products includes improvement of chemical and physical properties. Very few papers have studied changes in soil specific surface area after amendments with manures or composts. Soil samples were taken from a Typic Hapludult under a corn (Zea mays L)-soybean (Glycine max Merr) rotation, before and after four years of manures, composts and inorganic nitrogen fertilizer application. Soil samples were tested for changes in soil surface area using nitrogen gas adsorption at 78 K. The specific surface area significantly increased in all treatments, excepting in the fertilized treatment. With the addition of organic amendments the specific surface varied between 0.73 m2/g and 0.91 m2/g by one percent of soil C increase.
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Biomasa y acumulación de nitrógeno en trigo bajo dos sistemas de labranza y fertilización nitrogenada
Biomass and nitrogen accumulation in wheat under two tillage systems and nitrogen fertilization
SI Golik & HO Chidichimo
Pág. 122-124
The aim of this work was to analyze shoot and root biomass production and nitrogen accumulation on wheat, under different tillage systems and treatments of nitrogen fertilization. In 1997, two tillage systems were analyzed: conventional system (mouldboard plow ) and reduced tillage system (chisel) under three fertilization treatments: control (N0), 90 kg N ha-1 in a single dose at sowing (N90) and 45 kg N ha-1 at sowing + 45 kg N ha-1 at the end of tillering (N45+45). There were not significant effects of tillage systems on shoot and root-biomass and N-accumulation but of fertilization treatments. Root/shoot ratio of fertilized treatments had a similar behavior than the control, probably in associa- tion to the the fenological stage considered. Roots length were affected by fertilization under reduced tillage system. Positive correlations between root N and shoot N (r =0,48, P less than 0,05) and between root N and grain N (r =0,48, P less than 0,05) were found.
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