Nitrogen use efficiency for wheat in semiarid region of Buenos Aires (Argentina): effects of the dose and timing application

En las regiones semiáridas, la erraticidad de las precipitaciones dificulta la optimización de la fertilización. El objetivo fue analizar la influencia de la variabilidad climática sobre la respuesta a diferentes dosis y momentos de fertilización en la productividad del trigo y en la eficiencia en el uso del nitrógeno en un sitio de la región semiárida bonaerense. Durante cinco años se realizaron ensayos de fertilización con trigo, combinando dosis de N (0, 25, 50 y 100 kg ha-1) y momentos de fertilización: siembra (Ns) y macollaje (Nm). Se evaluó la eficiencia agronómica en el uso del fertilizante aplicado (EUF) para la producción de materia seca (MS) y de grano, así como la recuperación aparente del nitrógeno (RAN). Se detectaron interacciones entre variables y las eficiencias. Para Nm se encontraron correlaciones significativas de todos los parámetros con las precipitaciones de octubre. La proteína en ambos momentos estuvo significativa e inversamente correlacionada con las precipitaciones del ciclo. Se observaron correlaciones significativas de EUF de MS y grano siguiendo el orden: Prec. Ciclo completo>Prec. primavera> Prec. Oct > Prec. Set. La variabilidad climática interanual demostró la mayor influencia sobre las eficiencias en el uso del N, independientemente del momento de aplicación.In semiarid regions optimal fertilization is difficult due to erratic rainfall. The aim of this study was to analyze the influence of climate variability on the response to different rates and timing of fertilization on wheat productivity and on efficiencies in the use of nitrogen in a site of the semiarid region of the province of Buenos Aires, Argentina. For five years, fertilization trials were conducted in wheat combining N rates (0, 25, 50 y 100 kg ha-1) and times of fertilization: Seeding (Ns) and tillering (Nm). Agronomic efficiency (EUF) for dry matter (MS) and grain, and apparent recovery of nitrogen (RAN) were evaluated. Interactions between variables (year, rates and times) and efficiencies were found. In Nm, significant correlations of all parameters were found with October rainfall. Protein for Ns and Nm was significantly and inversely correlated with full cycle rainfall. Significant correlations were found in EUF of MS and grain in this order: Full cycle rainfall> Spring rainfall> Oct rainfall> Set rainfall. Interannual climate variability showed the greatest influence on the nitrogen use efficiencies, regardless the application timing.Fil: Martinez, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida(i); Argentina. Universidad Nacional del Sur; ArgentinaFil: Galantini, J. A.. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida(i); Argentina. Universidad Nacional del Sur; ArgentinaFil: Landriscini, Maria Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida(i); Argentina. Universidad Nacional del Sur; Argentin

Soil quality assessment based on soil organic matter pools under long‐term tillage systems and following tillage conversion in a semi‐humid region

A field study was conducted to assess the long-term effects of no-tillage (NT) and conventional tillage (CT), and the short-term effects following tillage conversion -from CT to NT (NTn) and from NT to CT (CTn) on soil quality (SQ) indicators in a semi-humid climate. First, plots of a long-term tillage experiment on a Luvic Phaeozem initiated in 1986, were split into two subplots in 2012, yielding four treatments: NT, CT, NTn and CTn. In 2015, composite soil samples were collected from each treatment and from a natural site (Ref) at depths 0-5, 5-10, 10-20 and 0-20 cm. Several indicators were determined: soil organic carbon (SOC) and nitrogen (SON); particulate organic C (POM-C) and N (POM-N); potential N mineralization (PMN) and soil respiration (Rs). Moreover, bulk density was determined in long-term tillage systems. Different ratios between indicators were calculated, with emphasis on its function in the agroecosystem, i.e. functional indicators. Significant differences in SOC, SON and PMN were found between CT and NT at most depths. In contrast, three years after tillage conversion, only a part of the SQ indicators studied were modified mainly at the 0-10 cm depth. The functional indicators showed differences between tillage systems in the long-term and after short-term tillage conversion depending on the depth; however, the PMN/SON ratio demonstrated differences at all depths. Under these conditions, this ratio -related to easily mineralizable N fraction- proved to be a promising indicator for assessing SQ under contrasting tillage systems regardless of the sampling depth.Fil: Martinez, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Galantini, Juan Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Duval, Matias Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; ArgentinaFil: López, Fernando Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin

Molecular insights into the behaviour of bile salts at interfaces: a key to their role in lipid digestion

Hypotheses. Understanding the mechanisms underlying lipolysis is crucial to address the ongoing obesity crisis and associated cardiometabolic disorders. Bile salts (BS), biosurfactants present in the small intestine, play key roles in lipid digestion and absorption. It is hypothesised that their contrasting functionalities – adsorption at oil/water interfaces and shuttling of lipolysis products away from these interfaces – are linked to their structural diversity. We investigate the interfacial films formed by two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), differing by the presence or absence of a hydroxyl group on their steroid skeleton. Experiments. Their adsorption behaviour at the air/water interface and interaction with a phospholipid monolayer – used to mimic a fat droplet interface – were assessed by surface pressure measurements and ellipsometry, while interfacial morphologies were characterised in the lateral and perpendicular directions by Brewster angle microscopy, X-ray and neutron reflectometry, and molecular dynamics simulations. Findings. Our results provide a comprehensive molecular-level understanding of the mechanisms governing BS interfacial behaviour. NaTC shows a higher affinity for the air/water and lipid/water interfaces, and may therefore favour enzyme adsorption, whereas NaTDC exhibits a higher propensity for desorption from these interfaces, and may thus more effectively displace hydrolysis products from the interface, through dynamic exchange

Production and quality of different cover crops in soybean monoculture

Los cultivos de cobertura (CC) son una alternativa para mejorar la materia orgánica del suelo, capturar nutrientes lábiles minimizando su lixiviación durante largos períodos de barbecho, típicos de sistemas agrícolas con alta participación de soja (Glycine max L. Merr.). El objetivo del trabajo fue evaluar durante dos años (2009 y 2010) la producción y composición nutricional de diferentes CC en un sistema simplificado (monocultivo soja) bajo siembra directa. Los CC utilizados fueron: (T) trigo pan (Triticum aestivum L.), (A) avena (Avena sativa L.), (V) Vicia (Vicia sativa L.) y (A+V) avena+vicia. Al momento del secado de los CC se determinó: producción de materia seca (MS), composición bioquímica (celulosa, hemicelulosa y lignina), macro y micro nutrientes. La producción de MS en T y A osciló entre 7,2 y 11,1 Mg ha-1, diferenciándose significativamente de V con valores entre 4,1 y 4,6 Mg ha-1. La concentración de C no presentó diferencias entre CC (43-45% C). La cantidad de N acumulado en la biomasa aérea varió entre 102 y 212 kg N ha-1, destacando los mayores aportes en V, presentando diferencias únicamente entre años. La concentración de polímeros estructurales diferenció claramente entre especies de CC, donde T y A presentaron mayores concentraciones de celulosa y hemicelulosa con respecto a V. Inversamente, V presentó mayores concentraciones de carbohidratos no estructurales y lignina que las gramíneas. Las gramíneas de invierno como CC fueron más eficientes en producir MS y por consiguiente más eficaces para contribuir al potencial aumento de la materia orgánica del suelo, favoreciendo el reciclado de macro y micronutrientes, evitando el lixiviado de aquellos más lábiles.Cover crops (CC) are an alternative to improve soil organic matter and to capture labile nutrients by minimizing their loss by leaching during the long-term fallows typical of agricultural systems with high frequency soybean (Glycine max L. Merr.). The objective of this work was to evaluate the production and nutrient content of different CC in a simplified system (soybean monoculture) under no-tillage for two years (2009-2010). The CC used were: (T) bread wheat (Triticumaestivum L.), (A) oat (Avena sativa L.), (V) vetch (Vicia sativa L.), and (A+V) oat + vetch. Upon drying the CC we determined: production of total aerial dry matter (MS), biochemical composition (cellulose, hemicellulose and lignin), and macro- and micronutrients. Dry matter production in T and A ranged from 7.2 to 11.1 Mg ha-1, differing significantly from V which reached values between 4.1 and 4.6 Mg ha-1. Carbon concentration did not differ among CC (43-45% C). The amount of N accumulated in aboveground biomass ranged from 102 to 212 kg N ha-1, with the highest inputs recorded in V, which showed differences only between years. The concentration of structural polymers clearly differed between CC species, with T and A showing higher concentrations of cellulose and hemicellulose than V. Conversely, V showed higher concentrations of nonstructural carbohydrates and lignin than grasses. Winter grasses as CC were more efficient in producing MS and therefore more effective to contribute to potential increased soil organic matter, promoting the recycling of macro- and micronutrients, and preventing the leaching of the most labile ones.Centro de Recursos Naturales Renovables de la Zona Semiárida (Cerzos), Dpto. Agronomía, UNS-CONICET, Bahía Blanca, ArgentinaComisión de Investigaciones Científicas (CIC), CERZOS-UNS, Bahía Blanca, ArgentinaAER INTA Cañada de Gómez, ArgentinaInstituto de Suelos, INTA Castela

Soil organic matter dynamics and quality during a wheat-clover rotation in a semiarid haplustoll

Several studies have reported modifications in soil chemical and physical parameters under rotations with legume inclusion. This modification had the potential of improving soil fertility and grain production. The objective of this research was to evaluate changes in the distribution and quality of soil organic fractions during a 3 year wheat (Triticum aestivum) - 3 year red clover (Trifolium pratense) rotation. Soil samples at 0 - 0.15 m depth were taken in five of the six year rotation. Organic fractions, physically (particulate organic carbon, COP) and chemically (humic and fulvic acids, AH and AF, respectively) separated were determined and chemically and spectrometrically characterised. The quantity and distribution of the organic fractions were different along the rotation. The more labile soil organic matter fractions, COP and AF, were higher during legume phase and diminished during wheat phase. This decrease of labile relative to recalcitrant organic matter resulted in significative differences in COP:total organic carbon (COT) and AH:AF ratios between wheat and clover phase. The COP:COT ratios were lower than 19 under wheat and higher than 21 under clover. The AH presented higher nitrogen and lower sulphur contents during clover phase, while the opposite was observed during wheat phase. This compositional changes were clearly reflected by the N:S and C:S atomic ratios. Total acidity in AH was slightly increased during the legume phase, as a consequence of the significative increase in -OH phenolic groups. Infrared and fluorescence spectra of the AH from soils under wheat and clover were similar among them, probably due to the short rotation period that produce only minor changes in the AH molecular structure. Legume inclusion in the rotation increased labile organic matter fractions and modified the composition of the recalcitrant ones. Both changes would improve soil fertility and grain production

El cultivo de trigo en la región semiárida bonaerense: impacto sobre algunas propiedades químicas del suelo

The intensification of the agriculture in the Semiarid Region was characterized by a decrease of the area destined for pastures, in favour of the surface with monoculture of wheat. In this context, crop rotation, fertilization, and the residue management and soil water are fundamental to increasing the productivity of wheat in this region. The objective was to quantify the qualitative and quantitative changes in production systems on some properties of a semiarid soil from Buenos Aires after 22 years of production. The study was conducted in the EEA INTA Bordenave. We studied the following crop sequences: WW CT (wheat monoculture with conservation tillage (CT), 1983-2006), WW NT (wheat monoculture with CT, 1983-1999, and no-till (NT), 1999-2006) and WG (conventional management, wheat and grazing of natural grasses, alternatively one year each). Total organic carbon (TOC), total nitrogen (Nt), extractable phosphorus (Pe) and pH in water were measured. Fractionation was performed by particle size, which was determined the OC and N. In general, TOC levels showed a significant effect of rotation, fertilization and tillage. In not fertilized treatments, conventional management presented higher levels of TOC and monoculture the greatest losses. In fertilized plots, TOC levels were significantly higher in NT accumulated mainly in the first 5 cm of soil, without differences in soil tillage. In 0-20 cm showed higher concentrations of POC in monoculture than in conventional management. Nt was significantly higher in conventional management respect of wheat monoculture without fertilizer. The NT was the only system that produced significant differences by effect of fertilization. Fertilization was a tendency for accumulation of Pe versus non-fertilized in depth (5-10 and 10-20 cm), remained significant in the monoculture treatment. For the conditions of soil and climate of the region, including the NT as management practices improved soil organic status only when combined with the use of fertilizers.La intensificación de la agricultura en la región semiárida se caracterizó por una disminución del área destinada a pasturas, a favor de la superficie con monocultivo de trigo. En este contexto, la rotación de cultivos, la fertilización, el manejo de los residuos y el agua edáfica son aspectos fundamentales para el aumento de la productividad del trigo en esta región. Se planteó como objetivo cuantificar los cambios cuali y cuantitativos en sistemas de producción sobre algunas propiedades de un suelo de la región semiárida bonaerense, luego de 22 años de producción. El trabajo se realizó en la EEA del INTA Bordenave. Se estudiaron las siguientes secuencias de cultivos: TT LC (monocultivo de trigo con labranza conservacionista (LC), 1983-2006); TT SD (monocultivo de trigo con LC, 1983-1999, y con siembra directa (SD), 1999-2006) y TP (manejo tradicional, un año trigo y un año alternativamente con pastoreo de los rastrojos, 1983-2006). En cada uno se evaluó el carbono orgánico total (COT), el nitrógeno total (Nt), el fósforo extraíble (Pe) y el pH en agua. Se realizó un fraccionamiento por tamaño de partícula, en las que se determinó el CO y N. En general, los niveles de COT mostraron un efecto significativo de la rotación, fertilización y la labranza. En los tratamientos no fertilizados, el manejo tradicional presentó los niveles más altos de COT y el monocultivo las mayores pérdidas. En las parcelas fertilizadas, los niveles de COT fueron significativamente más altos en SD, principalmente en los primeros 5 cm del suelo, mientras que en los suelos con labranza no se observaron diferencias. En 0-20 cm se observó mayor concentración de COP en monocultivo que en manejo tradicional. El Nt fue significativamente más alto en el manejo tradicional respecto del monocultivo de trigo sin fertilizante. La SD fue el único sistema que produjo diferencias significativas por efecto de la fertilización. A su vez, la fertilización produjo una tendencia a la acumulación del Pe frente a los no fertilizados en la profundidad (5-10 y 10-20), que fueron significativos en los tratamientos con monocultivo. Para las condiciones edafo-climáticas de la región, la inclusión de la SD como práctica de manejo mejoró la condición orgánica del suelo sólo cuando se combinó con el uso de fertilizantes