El suelo es uno de los componentes principales de los agro-ecosistemas (capital natural), que junto a las demás formas de capital, brindan servicios ecológicos (SE) destinados a las necesidades y bienestar humanos. La Región Semiárida Pampeana (RCP), en la Provincia de La Pampa, posee suelos poco desarrollados, recibe escasas lluvias y vientos de moderados a fuertes. Estas condiciones son propicias para el proceso de erosión eólica potencial, es decir la pérdida de suelo por acción del viento. Esta pérdida implica la reducción de la fertilidad física y química, con la consecuente reducción en el flujo de los SE. Las condiciones de manejo del suelo, definen la erosión eólica actual, la cual puede cuantificarse experimentalmente. Adicionalmente, se puede determinar la composición química de estos residuos. El avance de la agricultura, la intensificación de los sistemas productivos y prácticas de laboreo tradicionales inapropiados, hacen de este fenómeno un proceso irreversible, cuando se supera valores umbrales considerados moderados. Se expresa en toneladas por hectárea (t/ha). El productor no considera entre sus costos de producción, los SE del suelo que esta utilizando, los que toma de un stock inicial y sobre los que tampoco existe un precio de mercado de referencia. Una de las hipótesis de trabajo fue que las pérdidas por erosión actual, en rotaciones y en el ciclo de los cultivos agrícolas, pueden alcanzar niveles moderados a severos. La incorporación en los costos directos de cultivos agrícolas, del nitrógeno (N) y fósforo (P) involucrados en el material erosionado, por su magnitud puede causar niveles de quebranto en el margen bruto (MB) final. El costo de reemplazo de estos nutrientes se lo denominó Indicador Ambiental (IA) y se estimó, monetariamente, a través de su equivalente en nutrientes de fertilizantes. Otra hipótesis planteada, sugiere que es posible plantear actividades tecnológicamente superadoras, que reduzcan los niveles de erosión, mejoren el balance de algunos nutrientes esenciales y que se integren en un sistema productivo ambiental y económicamente sustentable. Para estimar la tasa de erosión eólica, se utilizó el modelo empírico identificado en castellano con las siglas EWEQ (Wind Erosion Equation), el cual fue cargado con secuencias de cultivos reales (rotaciones), con longitud de tiempo variables y para 6 sitios de la estepa pampeana: 3 sitios de la denominada Subzona Castex (Castex Norte, Castex Sur-Santa Rosa y Castex Sur-Anguil); 2 sitios de la Subzona Pico (Pico Norte y Pico Sur) y 1 sitio de la Subzona Guatrache. El modelo devuelve la tasa de erosión promedio anual de toda la rotación, como también la tasa de erosión del ciclo de cada cultivo agrícola (t/ha ciclo), aprovechando el detalle en las fecha precisas entre operaciones. Con estos registros, se estimaron los costos directos de todos los ciclos disponibles de trigo, girasol, soja y maíz. Utilizando los precios de insumos y productos de Febrero de 2008, se calculó la incidencia del IA, en los costos directos y sus efectos en el MB final. El plan de optimización se realizó para las condiciones agroclimáticas, dimensiones y caracterización de sistemas productivos del Sitio Castex Norte (Subzona Castex), a través de una matriz de programación lineal (PL). Se diseñaron previamente los planteos técnicos basados en tecnologías disponibles, los resultados económicos (MB) y el balance de N, P y carbono orgánico (CO) de cada actividad. La tasa de erosión eólica estimada para cultivos en siembra convencional (SC) en la primera parte, fue un insumo directo de la matriz, utilizada como restricción ambiental. Las pérdidas de N y P involucradas por esta vía, formaron parte de los egresos, dentro del balance de nutrientes. Fue necesario simular en el EWEQ, aquellas alternativas tecnológicamente mejoradas, no disponibles entre los registros reales y donde predominó la siembra directa (SD) y estrategias de fertilización. También se estimaron los índices para algunos de los recursos forrajeros de la actividad ganadera (invernada). Se puso énfasis en las restricciones ambientales, mientras que desde lo técnico-agronómico no hubo limitaciones en las restricciones de capital de trabajo ni diferenciación en el tipo de suelo. Para esta segunda etapa, se utilizaron precios de insumos de 2006 y las cotizaciones del disponible 2007 para los productos. Se detectaron menores tasas de erosión eólica en SD que en SC. En el Sitio Guatraché se redujo de 10,0 t/ha en una rotaciones en SC a 5,6 t/ha en SD (44% menos). También se redujo en más de un 50% entre ciclos de cultivos, dentro de una misma rotación, al utilizar SD. En todos los casos, significó un pasaje del grado de erosión de moderado/severo a erosión ligera. El costo de reemplazo del IA, fue variable entre cultivos, entre sistema de siembra (SD vs SC) e influenciado por el nivel de costos directos totales. En los cultivos conducidos en SC, con tasas de erosión eólica cercanas y levemente superiores a 8 t/ha ciclo, la participación del IA fue de 20 a 40 % en trigo; 15 a 25% en maíz; 20 a 35% en girasol y de 20 a 30% en soja. Con tasas de erosión 4 a 6 t/ha ciclo en SD, el IA tuvo una participación del 8% en maíz; del 8 a 16 % en trigo y del 8 a 21% en girasol. Respecto al efecto sobre el MB inicial, solo se produjeron quebrantos cuando los rendimientos de trigo fueron inferiores a 1t/ha y un caso de maíz, con una producción de 1,4 t/ha. Las actividades propuestas en la matriz de PL permitieron detectar déficits generalizados en el balance de nutrientes, en aquellos cultivos conducidos con esquemas tradicionales de manejo tecnológico y/o de escaso nivel de fertilización. Por el contrario, la actividad ganadera mostró todos los índices positivos. Sobre una explotación de 506 ha, la mejor solución de la matriz de PL quedo integrada por 143 ha de trigo en SC con aplicación de fertilizante apuntando a máximo rendimiento (TrSCDMR); 170 ha de maíz en SD y de alta producción (MaSDAP) y 193 ha de girasol en SD con fertilización de máxima respuesta (GiSDFER). Este sistema agrícola alcanzó el máximo margen bruto total (MBT) con una erosión eólica promedio anual de 4,9 t/ha. Los beneficios ambientales de la ganadería no se aprovecharon frente a un precio promedio de 2,70 $/kg de carne. Sin embargo, los costos de sustitución indicaban que la invernada podía participar con un precio de 3,46 $/kg de carne (+28%). Siendo un valor esperable dentro de la volatilidad de precios de la serie 2007/2008, se simuló un escenario mixto, donde la invernada participó con 245 ha, la misma alternativa de girasol en SD con 153 ha, y el mismo maíz de alta producción con 143 ha. Entre el sistema agrícola y el mixto, el MBT se redujo solo el 1% ($ 390.660 vs. $386.795 respectivamente). Palabras clave: erosión eólica, servicios ecológicos, programación lineal, balance de nutrientes, nitrógeno, fósforo. / Soil is one of the main components of agro-ecosystems (natural capital). Together with other forms of capital, provides ecological services (ES) for human needs and welfare. The Semi-Arid Pampas Region (SPR) has poorly developed soils, receives little rain and moderate to strong winds. These conditions are favourable for the process known as potential wind erosion, namely the loss of soil by wind action. This loss implies a reduction of both physical and chemical fertility, with consequent reduction in the flow of those ES, mentioned above. The conditions of soil management, define the current wind erosion, which can be quantified experimentally. Additionally, chemical composition of these residues can be determined. It is expressed in tons per hectare (t/ha).The advancement of agriculture, the intensification of production systems and traditional inappropriate tillage practices, generates an irreversible phenomenon, when it exceeds threshold values, considered moderate. Farmers do not consider among their production costs, the ES they are using, which they take from an initial stock. In addition, there is no price market reference. One of the working hypothesis was that losses caused by current wind erosion, in both rotations and crops cycle, can achieve moderate to severe levels. The incorporation into crops direct costs of nitrogen (N) and phosphorus (P) involved in the eroded material might produce actual gross margin (GM) losses. The replacement cost of these nutrients was named in this research as Environmental Index (EI) and it was considered, in money terms, through its equivalent in nutrients from fertilizer. Another hypothesis suggests that it is possible to raise productive activities technologically enhanced that reduces the levels of erosion, improve the balance of some essential nutrients and can be integrated into a production system, environmentally and economically sustainable. The empirical model Wind Erosion Equation (EWEQ) was used to estimate wind erosion rate. Its inputs were farmers real data, including crops seasonal sequences (rotations). Records varied in lengths of time and came from six places in the Pampas Steppe: three places in the so-called Sub-Zone "Castex" (North Castex site, South-Castex- Santa Rosa site and South Castex-Anguil site), two in the Sub-Zone "Pico" (North Pico site and South Pico site) and one site of Sub-Zone "Guatraché". The model returns the average annual erosion rate of the entire rotation, and the cycle crop erosion rate (t/ha cycle). This last rate takes advantage of the detail in the precise date information between machinery operations, within the model. These records, also allowed estimating direct costs of all the available crops cycles of: wheat, sunflower, soybeans and corn. Using inputs and commodities prices of February 2008, the incidence of EI in direct costs and its impact on the final GM, was calculated. The optimization plan was carried out for agro-climatic conditions, farm size and production systems patterns of North Castex Site (Sub-Zone "Castex"), through a matrix of linear programming (LP). Previously, technical set up approaches were designed, based on available technology, also the economic performance (GM) and the balance of N, P and organic carbon (OC) of each activity. The estimated wind erosion rate estimated for crops in the first part of the study and involving conventional tillage (CT) sowing system was a direct input for the matrix, used as environmental constraints. The concentration of N and P involved in this losses, were part of discharges within the balance of nutrients. It was necessary to use the EWEQ, to simulate those alternatives technologically enhanced, witch no records were available, and where no-tillage (NT) and fertilization strategies have been used. It was also estimated rates for some of the forage resources of livestock activity (fattening steers). Emphasis was placed on the environmental constraints, while no limitations were set from those technical-agronomic constraints such as working capital or differentiation in the type of soil. For this second stage is used pricing of inputs, 2006 and 2007 current prices of commodities. Wind erosion rates resulted lower in NT than in CT. In Site Guatraché the index varied from 10.0 t/ha year-1 in a CT rotation, to 5.6 t/ha year-1 in NT rotation (44% less). It also declined by over 50% between cycles of crops, within a single rotation, by using NT. In all cases, it was an overtaking from a moderate/severe degree of erosion to light erosion rate. The replacement cost of EI, varied between crops, between sowing system (NT vs CT) and highly influenced by the level of total direct costs. Those crops conducted in CT, with wind erosion rates nearby and slightly higher than 8 t/ha cycle-1, the EI share in costs was 20 to 40% in wheat, 15 to 25% in corn, 20 to 35% in sunflower and 20 to 30% in soybeans. With erosion rates of 4 to 6 t/ha cycle-1, in NT cycle, the EI had an 8% share of corn costs, from 8 to 16% in wheat and from 8 to 21% in sunflower. Concerning to the effect on initial GM, economic losses occurred only when the yields of wheat were lower than 1t/ha and in the case of corn, one case was found when production reached 1,4 t/ha. The proposed activities in the matrix of LP helped to detect widespread deficits in the balance of nutrients in crops those conducted with traditional patterns of technological management and/or low levels of fertilization. By contrast, livestock activity showed all positive indexes. On a farm of 506 hectares, the best solution of the matrix of LP resulted in 143 ha of CT wheat with fertilizer application aimed at maximum performance (TrSCDMR); 170 ha of NT corn and high production (MaSDAP) and 193 ha of NT sunflower with the highest expected fertilization response (GiSDFER). This "grain cropping system reached a maximum total gross margin (TGM) with an average annual wind erosion rate of 4.9 t/ha year-1. The environmental benefits of livestock are not exploited, facing an average price of 2,70 $/kg of live weight. However, the "shadow price" indicated that livestock activity might take part of the solution with a price of 3,46 $/ kg of live weight (+28%). Since this was an expected value along 2007/2008 meat market prices series, it was simulated a "crop and beefs mixed system where livestock participated with 245 ha, along with 153 ha of former NT sunflower alternative, and 143 ha of the same high production corn. When comparing the "grain cropping and "crop and beefs mixed systems, TGM decreased only 1% ($ 390,660 vs. $ 386,795, respectively).

Os impactos do manejo intensivo sobre a sustentabilidade da produção florestal dependem da manutenção da fertilidade dos solos. A contribuição dos resíduos florestais e a ciclagem de nutrientes nesse processo são determinantes. Os objetivos desse trabalho foram: (i) quantificar a biomassa e o estoque de nutrientes na parte aérea e no sistema radicular de um povoamento de Pinus taeda aos 16 anos de idade; (ii) caracterizar o potencial de liberação de nutrientes dos minerais primários e secundários, e o estoque de nutrientes de um Cambissolo Húmico; (iii) quantificar a exportação de nutrientes via colheita de madeira e dos componentes florestais; (iv) avaliar potencial da sustentabilidade da produtividade de madeira com base no balanço de nutrientes, sob diferentes cenários de manejo florestal. Avaliouse uma plantação de Pinus taeda na idade de 16 anos em um Cambissolo Húmico Alumínico léptico de textura argilosa, relevo ondulado no meio-sul catarinense. Amostraram-se dez árvores de cinco classes diamétricas em função da distribuição dos diâmetros à altura do peito. Para cada árvore mensurou-se a biomassa de acículas, galhos, casca, madeira e raízes. Além da biomassa vegetal, amostrou-se serapilheira acumulada e solo nas camadas 0-20, 20-40, 40-60, 60-100, 100-140, 140-180 e 180-190 cm. Equações entre a área seccional a 1,30 m e a biomassa de cada componente foram ajustadas para estimar a biomassa das árvores inventariadas. Equações entre o conteúdo de nutriente e a biomassa do componente também foram ajustadas para estimar a quantidade de cada nutriente em todos os componentes da árvore. As equações permitiram estimar para as demais árvores do talhão a biomassa de cada componente e o seu respectivo estoque de nutrientes. Nas amostras de solo e de serapilheira se determinou a concentração e o estoque de nutrientes, além de no solo realizar-se a caracterização mineralógica. Simularamse três cenários de manejo florestal, retirada da madeira (A), da madeira + casca (B) e da madeira + casca + copa (C) do sistema florestal. A soma de todos os componentes da biomassa foi de 313 Mg ha-1, sendo a madeira o mais representativo (62%). O estoque dos nutrientes na árvore foi N > Ca > K > S > Mg > P. A madeira foi o componente que acumulou as maiores quantidades de nutrientes (210 N, 33 P, 85 K, 91 Ca, 31 Mg e 65 S, kg ha-1). A mineralogia do Cambissolo demonstrou predominância do quartzo nas frações areia, silte e argila, com pequenos traços de vermiculita na fração de silte. A argila é a principal fração que contribui com o intemperismo do solo, devido à transformação da vermiculita-ilita, liberando K. Para os três cenários de manejo, o esgotamento de nutrientes do sistema solo-biomassa foi: P > S > N > K > Mg > Ca. O P e o S permaneceram como mais limitantes no cenário A decorrente de seus baixos estoques disponíveis no solo. No cenário B, o número de rotações florestais se alterou para N, K e S. O cenário C resultou na maior diminuição de produtividade, possibilitando para o P duas rotações e para o Mg 14. Desta forma, evidenciou-se, pelo número potencial de rotações de cultivo, que os diferentes cenários de manejo podem em curto prazo comprometer a sustentabilidade do P. taeda. / The impacts of intensive management on the sustainability of forest production depends on the maintenance of soil fertility. The contribution of forest residues and nutrient cycling in this process are crucial. The objectives of this study were: (i) quantify the biomass and nutrient stocks in the shoot above and belowground and root system of a stand of 16-years-old Pinus taeda, (ii) characterize the potential release of nutrients from primary and secondary minerals, and the stock of nutrients in a Humic Cambisol (iii) quantify the export of nutrients through wood harvesting and forest components, (iv) evaluate the potential of sustainability in wood based on the balance of nutrients under different forest management scenarios. We evaluated a 16-years-old plantation of Pinus taeda in a Humic Cambisol, undulating relief in the middle-south of Santa Catarina. Ten trees were sampled from five diameter classes according to the distribution of diameter at breast height. Biomass of the needles, twigs, bark, wood and roots were measured for each tree. Besides the biomass and litter soil samples were collected from the layers 0-20, 20-40, 40-60, 60-100, 100- 140, 140-180 and 180-190 cm. Equations which has the sectional area of 1.30 m as independent variable and the biomass of each component as the dependent variable were adjusted to estimate the biomass of the entire studied forest. Furthermore, equations which has the nutrient content of the component as the dependent variable and the biomass as independent variable were adjusted to estimate the amount of each nutrient in all parts of the tree.The concentration and stock of nutrient were determined from the soil sample collected. In addition, a mineralogical characterization was performed for the soil and litters. Three scenarios simulated forest management, removal of wood (A), the wood and bark (B) and wood + bark + cup (C) of the forest system. The sum of all components of biomass was 313 mg h-1 being the most representative of the wood (62%). The stock of nutrients in the tree was N> Ca> K> S> Mg> P. The wood was the largest exporter of nutrients (210 N, 33 P, 85 K, 91 Ca, 31 Mg and 65 S, kg ha-1). The mineralogy of the Cambisol showed the predominance of quartz sand, silt and clay, with small traces of vermiculite in the silt fraction. Clay is the main fraction which contributes to the weathering of the soil due to the transformation of illite-vermiculite, releasing K. The depletion of nutrients from the soil-biomass was: P> S> N> K> Mg> Ca and S. The P and S remained as the most limiting at the scenario A due to its low inventories in the soil. At the scenario B, the number of rotations forest changed to N, K, S. The scenario C resulted in the greatest reduction in productivity, allowing for P two rotation and for Mg 14. It was evident by the number of potential crop rotations, the different management scenarios in the short term may jeopardize the sustainability of P. taeda.

Os impactos do manejo intensivo sobre a sustentabilidade da produção florestal dependem da manutenção da fertilidade dos solos. A contribuição dos resíduos florestais e a ciclagem de nutrientes nesse processo são determinantes. Os objetivos desse trabalho foram: (i) quantificar a biomassa e o estoque de nutrientes na parte aérea e no sistema radicular de um povoamento de Pinus taeda aos 16 anos de idade; (ii) caracterizar o potencial de liberação de nutrientes dos minerais primários e secundários, e o estoque de nutrientes de um Cambissolo Húmico; (iii) quantificar a exportação de nutrientes via colheita de madeira e dos componentes florestais; (iv) avaliar potencial da sustentabilidade da produtividade de madeira com base no balanço de nutrientes, sob diferentes cenários de manejo florestal. Avaliouse uma plantação de Pinus taeda na idade de 16 anos em um Cambissolo Húmico Alumínico léptico de textura argilosa, relevo ondulado no meio-sul catarinense. Amostraram-se dez árvores de cinco classes diamétricas em função da distribuição dos diâmetros à altura do peito. Para cada árvore mensurou-se a biomassa de acículas, galhos, casca, madeira e raízes. Além da biomassa vegetal, amostrou-se serapilheira acumulada e solo nas camadas 0-20, 20-40, 40-60, 60-100, 100-140, 140-180 e 180-190 cm. Equações entre a área seccional a 1,30 m e a biomassa de cada componente foram ajustadas para estimar a biomassa das árvores inventariadas. Equações entre o conteúdo de nutriente e a biomassa do componente também foram ajustadas para estimar a quantidade de cada nutriente em todos os componentes da árvore. As equações permitiram estimar para as demais árvores do talhão a biomassa de cada componente e o seu respectivo estoque de nutrientes. Nas amostras de solo e de serapilheira se determinou a concentração e o estoque de nutrientes, além de no solo realizar-se a caracterização mineralógica. Simularamse três cenários de manejo florestal, retirada da madeira (A), da madeira + casca (B) e da madeira + casca + copa (C) do sistema florestal. A soma de todos os componentes da biomassa foi de 313 Mg ha-1, sendo a madeira o mais representativo (62%). O estoque dos nutrientes na árvore foi N > Ca > K > S > Mg > P. A madeira foi o componente que acumulou as maiores quantidades de nutrientes (210 N, 33 P, 85 K, 91 Ca, 31 Mg e 65 S, kg ha-1). A mineralogia do Cambissolo demonstrou predominância do quartzo nas frações areia, silte e argila, com pequenos traços de vermiculita na fração de silte. A argila é a principal fração que contribui com o intemperismo do solo, devido à transformação da vermiculita-ilita, liberando K. Para os três cenários de manejo, o esgotamento de nutrientes do sistema solo-biomassa foi: P > S > N > K > Mg > Ca. O P e o S permaneceram como mais limitantes no cenário A decorrente de seus baixos estoques disponíveis no solo. No cenário B, o número de rotações florestais se alterou para N, K e S. O cenário C resultou na maior diminuição de produtividade, possibilitando para o P duas rotações e para o Mg 14. Desta forma, evidenciou-se, pelo número potencial de rotações de cultivo, que os diferentes cenários de manejo podem em curto prazo comprometer a sustentabilidade do P. taeda. / The impacts of intensive management on the sustainability of forest production depends on the maintenance of soil fertility. The contribution of forest residues and nutrient cycling in this process are crucial. The objectives of this study were: (i) quantify the biomass and nutrient stocks in the shoot above and belowground and root system of a stand of 16-years-old Pinus taeda, (ii) characterize the potential release of nutrients from primary and secondary minerals, and the stock of nutrients in a Humic Cambisol (iii) quantify the export of nutrients through wood harvesting and forest components, (iv) evaluate the potential of sustainability in wood based on the balance of nutrients under different forest management scenarios. We evaluated a 16-years-old plantation of Pinus taeda in a Humic Cambisol, undulating relief in the middle-south of Santa Catarina. Ten trees were sampled from five diameter classes according to the distribution of diameter at breast height. Biomass of the needles, twigs, bark, wood and roots were measured for each tree. Besides the biomass and litter soil samples were collected from the layers 0-20, 20-40, 40-60, 60-100, 100- 140, 140-180 and 180-190 cm. Equations which has the sectional area of 1.30 m as independent variable and the biomass of each component as the dependent variable were adjusted to estimate the biomass of the entire studied forest. Furthermore, equations which has the nutrient content of the component as the dependent variable and the biomass as independent variable were adjusted to estimate the amount of each nutrient in all parts of the tree.The concentration and stock of nutrient were determined from the soil sample collected. In addition, a mineralogical characterization was performed for the soil and litters. Three scenarios simulated forest management, removal of wood (A), the wood and bark (B) and wood + bark + cup (C) of the forest system. The sum of all components of biomass was 313 mg h-1 being the most representative of the wood (62%). The stock of nutrients in the tree was N> Ca> K> S> Mg> P. The wood was the largest exporter of nutrients (210 N, 33 P, 85 K, 91 Ca, 31 Mg and 65 S, kg ha-1). The mineralogy of the Cambisol showed the predominance of quartz sand, silt and clay, with small traces of vermiculite in the silt fraction. Clay is the main fraction which contributes to the weathering of the soil due to the transformation of illite-vermiculite, releasing K. The depletion of nutrients from the soil-biomass was: P> S> N> K> Mg> Ca and S. The P and S remained as the most limiting at the scenario A due to its low inventories in the soil. At the scenario B, the number of rotations forest changed to N, K, S. The scenario C resulted in the greatest reduction in productivity, allowing for P two rotation and for Mg 14. It was evident by the number of potential crop rotations, the different management scenarios in the short term may jeopardize the sustainability of P. taeda.