257 research outputs found

    Growth and nutritive value of pastures under climate extremes

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    The main aim of this thesis was to investigate the impacts of future climate extreme scenarios, including increased temperatures and severe droughts, on the nutritive value of key pasture grassland species. My research involved the evaluation of changes in forage nutritional composition and digestibility under contrasting climate regimes. In addition, I looked at possible explanations for the observed changes in forage nutritive value associated with plant growth and morphological traits, including productivity and structural allocation (e.g. dead material and leaf:stem biomass ratios). In order to improve the understanding of climate change impacts on forage nutritive value of future pasture systems, I conducted a series of experiments (short- and long-term) at the Pastures and Climate Extremes experimental field facility and a glasshouse facility at the Hawkesbury Campus of Western Sydney University, Richmond, New South Wales, Australia. I predicted that both forage production and nutritive value would be adversely impacted by extreme scenarios of warming and drought. I further predicted that the combination of these scenarios would have a more pronounced negative impact on forage than the single climate treatments. I found that the impacts on pasture production and forage nutritive value were greater under severe drought than under warming, and their combination resulted in effects that were not always greater than those associated with warming or drought treatments on their own. In addition, I observed that climate extremes strongly impact pasture productivity, resulting in low forage production and increased dead biomass, with the magnitude varying by species. The effects of climate treatments on forage nutritive value (including nutritional composition and digestibility) were mixed, including both marginal increases and declines and null effects. The outcomes of this thesis show the importance of exploring species-specific nature in response to seasonal droughts and elevated temperatures to better understand climate change impacts on pasture systems and inform future planting decisions and breeding programmes. Further, this thesis provides insights for grazing industries in Australia and abroad about the potential impacts of extreme events on pasture management and animal production

    Use of inert markers to predict diet composition, forage intake, digestibility and passage rate in sheep.

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    Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.The mechanisms that regulate intake and composition of selected diets in ruminants are complex and vary among animals of the same species and cross species. These are governed by highly variable aspects, which range from animal factors to physio-chemical properties of feeds. Understanding how ruminants select their diets is imperative to improve their utilisation of feed resources regarding the diversity of plant species that can be used as their sources of feed. The objectives of the study were to: (1) determine the effect of group feeding and removal of dietary ingredient (Sorghum bicolor) on diet selection, nutrient and total dry matter intake, and digestibility in choice-fed sheep; (2) asses the effect of animal stocking rate on dry matter and nutrient intake, botanical composition, nutrients selected, total tract digestibility and passage rate of diet consumed by sheep; and (3) predict dry matter and nutrient intake, botanical composition, nutrients selected and total tract digestibility using inert markers. Twelve sheep (mean weight: 29.7 ± 4.63 kg) were assigned to three treatments. In treatment one, five feeds were fed to sheep fed as a group of 9 sheep (G). In the second treatment, five feeds were fed to sheep penned in isolation (I) and in the last treatment, four feeds with sorghum stover (SS) removed were fed to sheep penned in isolation (R). There were five experimental feeds: veld hay (VH), sorghum stover (SS) and maize stover (MS) fed ad-libitum, and Lucerne hay (LH) and bean straw (BS) fed at restriction levels of 0.15 and 0.35 kg/day per sheep, respectively, in a group or individually fed sheep. Diet compositions were similar (p >0.05) between sheep fed individually with or without SS. Similarity in proportion of these dietary ingredients consumed between R and I may be due to less selection of SS; therefore, its removal did not significantly influence consumption and selection of other dietary ingredients. Group feeding of sheep relative to individual feeding with similar dietary ingredients influenced selection of SS. Sheep fed individually had lower intake levels of SS. Establishment of a dominance hierarchy in group-fed sheep may have caused dominant animals to feed on poor quality stovers just to prevent sheep lower in the hierarchy from eating resulting in high consumption of stovers. Fifteen sheep (mean body weight 46.5 ±3.3 kg) were blocked by weight into four groups and each sheep was randomly allocated to four stocking rates (treatments) of 1, 2, 4 and 8 sheep per pen and fed: MS, SS, and VH. All feeds were fed on separate feeding troughs ad-libitum. To evaluate the effect of animal stocking rate (SR) on passage rate of digesta, one sheep each from stocking rates one (SR1) and two (SR2) animals per pen and two sheep each pair from stocking rates of four (SR4) and eight (SR8) animals per pen were randomly selected and dosed with Ytterbium (particulate) and cobalt-ethylenediamine tetraacetic acid (Co-EDTA; liquid) markers. An optimisation procedure was used to predict diet selection by minimising the sum of the squared discrepancies between the proportional concentration of markers (acid insoluble ash: AIA, modified acid detergent fibre: MADF, and acid detergent lignin: ADL) in faeces (A) and their proportional concentration in dietary components (E) (MS, SS and VH), corrected for faecal recoveries of markers. Fractional passage rate (liquid and particulate) from both the rumen and in the hind gut, mean retention time, and total mean retention times across treatments were similar (p >0.05). Similarly, intake of dietary ingredients, nutrients (crude protein: CP, neutral detergent fibre: NDF and acid detergent fibre: ADF), total dry matter intake and composition of diets selected were not different across treatments. Selectivity index factors of diets selected were all within the range of 1.56-3.80, which reflected that animals were able to retain the diets they selected long enough in the gastro intestinal tract (GIT) for efficient digestion. Total tract digestibility and mineral intake (Ash) differed (p <0.05) in relation to animal stocking rate. Sheep in SR2 had the highest digestibility and consequently increased dry matter intake. Predicted dry mater intake and total tract digestibility of a diet selected by sheep were less sensitive to correction of incomplete faecal recovery of the markers and they tended to be similar to observed dietary parameters. Therefore, inert markers can be used to predict several components of a diet selected by grazing sheep and other classes of ruminants

    Enhancing on-farm fodder availability and utilization for sustainable dairy production in the smallholder farming systems of western usambara highlands, Tanzania

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    A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Life Sciences of the Nelson Mandela African Institution of Science and Technology, Arusha, TanzaniaDairy cattle farmers in Tanzania experience a huge decline in milk production due to insufficient feed supply to their animals particularly during the dry seasons. This poses a great challenge to sustainability of smallholder dairy farming systems (SHDFSs) in the country. The aim of this study was to evaluate fodder resources availability, utilization practices and seasonal variations; as well as to assess potentials for improving pasture production and utilization in the SHDFSs of Western Usambara Highlands (WUHs), Tanzania. Integrated approaches were used in this study including review of literature, household and farm surveys, planting and evaluating suitability of four Pennisetum purpureum Schumach varieties (local Napier, Bana, Ouma and Kakamega 2) in improving ruminant feed availability. In addition, an experiment was conducted during a dry season to assess the potential of graded levels of homemade supplementary ration (HSR) consisting of Calliandra calothyrsus leaf-meal, maize bran, molasses and mineral-vitamin premixes on dairy cattle milk productivity. Results indicated that fodder scarcity was the major challenge during the dry season (July-October). On-farm fodder resources contributed most of the cattle diet. Natural pasture and Napier grass were the most important feeds in wet season and maize stover in dry seasons. Processing and supplementation of poor roughages with protein-energy concentrates were unpopular. Milk yields were 5.57 and 3.01 litres/cow/day in the wet and dry seasons respectively. The findings also demonstrated that Ouma and Kakamega 2 can be promoted in the WUHs for forage use due to higher biomass production. HSR improved the dry season milk yields significantly (P<0.001). Nonetheless, simulated year-round daily milk yields indicated that 4 and 6 kg HSR/cow/day would double the milk yields. There was overall significant difference (P=0.02) in the income to cost ratios (ICR) across the HSR levels. However, the ICR for 4 and 6 kg HSR/cow/day did not differ significantly (P<0.05). In conclusion, the supplementation level of 4 kg HSR/cow/day to the fibrous basal diets is suitable for profitable milk yields in the WUHs. It is therefore, recommended to increase fodder production and adopt proper supplementation practices to meet sustainable dairy production in the WUHs and elsewhere with similar environment

    COVER CROPPING: SENSOR-BASED ESTIMATIONS OF BIOMASS YIELD AND NUTRIENT UPTAKE AND ITS IMPACT ON SUGARCANE PRODUCTIVITY

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    Sugarcane in Louisiana can be harvested for up to three years from one planting. Soil cultivation along sides of established beds is done for weed control and improve fertilizer use efficiency which increases the risk of soil degradation and yield decline. Planting cover crops (CC) is a soil conservation practice and an effective strategy to improve soil health and nutrient recycling. Limited work has been done on remote sensor-based evaluation of the potential nutrient benefits from cover crops and its effect on nutrient cycling on sugarcane systems. This study was conducted to evaluate the effect of two planting methods (broadcast and drilling) and three seeding rates (100%, 50%, and 25% of NRCS recommendation) of a mix of three legumes and two brassicas CC species and a control without CC, on sugarcane yield and quality parameters, and on soil nutrients levels. This study was also used for the acquisition of normalized difference vegetation index (NDVI), collected using GreenSeeker® and multispectral camera (MicaSense® - RedEdge-M) mounted on an unmanned aerial vehicle, to correlate with CC biomass and nutrient uptake. The NDVI readings and CC biomass clippings, using the quadrat frame method, were collected a week before CC termination. Tissue analysis was carried out by C:N dry combustion analyzer and nitric acid digestion-hydrogen peroxide for multi-element analysis. Cane yield was acquired with a chopper harvester and a dump billet wagon. Quality components were obtained by a SpectraCane® automated near infrared (NIR) analyzer for quality parameters. Soil inorganic nitrogen (N) content (NH4+ + NO3-) was quantified using KCl extraction procedure and flow injection analysis. Other soil nutrients content was determined based on Mehlich-3 extraction procedure followed by ICP. A strong positive correlation between the GreenSeeker NDVI (NDVI-GS) and aerial images derived NDVI (NDVI-AI) was obtained with a coefficient of determination (R2) value of 0.63. Adjustment of NDVI with, number of days, cumulative growing degree days, and number of days with positive growing degree days, from planting to sensing increased the R2 values up to 0.76, 0.76 and 0.73, respectively. The NDVI-GS obtain a stronger linear relationship with CC dry biomass and N content than NDVI-AI. Good positive correlations (0.48 \u3e R2 \u3e 0.12) were found between NDVI and some macronutrients (P and K) and micronutrients (Mn and Cu). Overall, there was no significant effect of planting method and seeding rate observed on cane yield and quality parameters. Moreover, there was no statistical difference on CC nutrient removal rate among the treatments (p\u3e0.05). For plant cane, the average cane and sugar yield across sites was 96 Mg ha-1 and 10794 kg ha-1, respectively. Lower yield was attained by the ratoon crops averaging only at 71 Mg ha-1 cane yield and 7197 kg ha-1 sugar yield. Remote sensing is a promising and viable technique to estimate CC biomass and nutrient uptake. Finally, this study corroborates the long-term effect of CC on nutrient management and their effect on cane yield and quality parameters

    Carbono orgánico en suelos agrícolas y agroforestales: Efecto de las diferentes prácticas de gestión

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    Soil is a global resource that has the capacity to contain large amounts of organic carbon. In fact, soils contain more carbon than plants and the atmosphere combined. However, in recent decades human activities such as land-use change, deforestation, biomass burning, and environmental pollution have accelerated the release of terrestrial carbon into the atmosphere, increasing the greenhouse effect. The study of soil organic carbon cycle was recognized in the last decades as a necessary step for controlling future increases in atmospheric CO2, as well as necessary to simultaneously ensure the sustainability agricultural activities. A better comprehension of the he dynamics of soil organic carbon (SOC) in different agricultural systems will allow an improvement of soil quality and soil organic carbon storage under different climate and soil conditions. However, despite of decade’s long research on this subject, there is still the need for a better appraisal of soil carbon dynamics in specific agricultural systems based on robust in field empirical studies. So, relevant contributions to a better understanding of the impact of land use on the global carbon cycle is of great importance. The present research, framed in the context of a PhD specialization on soil carbon in agricultural areas, is aimed to generate new information on the effect of different factors (climate, land use, management, altitude, and soil type) that influence the sequestration and accumulation of organic carbon along the profile in the soil in different agricultural and forest systems across contrasting edaphoclimatic conditions. This research includes not only new quantitative information on soil organic carbon, but also innovative studies on its distribution among different soil carbon compartments and on the use of near infrared spectroscopy (NIR) on soil organic carbon determination. The first study (Chapter 2) is an analysis of the effect of different agricultural uses in a subtropical climate, in the area of the Carrizal River valley in the province of Manabí Ecuador, based on the analysis of 64 soil profiles. In each profile simples were taken in the soil profile horizons to obtain the concentration of organic carbon up to a maximum depth of 150 cm in different agricultural management (permanent, intensive rotation and abandoned crops), In this study twenty-one different agricultural uses were identified. As expected, the highest concentrations of soil organic carbon happened in the A horizon, which has an average thickness of 40 cm. A trend towards a higher carbon sequestration potential was observed in the grass, intercropping like cocoa with banana and corn area management with an average value of 1.7% C, much higher than the area under mechanized agriculture, which presented lower carbon concentration, with an average value of 0.26% C. Regarding the total soil organic carbon stock, the first horizon accumulated more carbon compared to the other (B and C) soil profiles, with an average value of 41.32±20.97 t C ha−1 and 15.06±15.61 t C ha−1, respectively. The second study (Chapter 3) evaluated the effect of forest management in a temperate climate. For this study, soil samples were taken in a managed environment of forest species (Alnus incana, Fagus sylvatica, Picea abies and Mixed: stands containing beech and spruce) in an elevation range from 1100 m a.s.l. from the Babia Góra National Park in southern Poland. Sampling points were taken up to a maximum depth of 100 cm. The results in this study revealed that the SOC reserves in the mountain soils of the Babi Góra National Park are characterized by their great variability (from 50.10 t ha−1 to 905.20 t ha−1). In the conditions of this study, the type of soil is the dominant factor determining soil organic carbon stock, which coupled with topographic factors influence soil and vegetation conditions. This explains such diversity in the accumulation of soil organic carbon in different mountain soils in the areas. The largest carbon stock was recorded in histosols (>550 t C ha−1), which are located in the lower part of the national park. The third block of the research focused on two field studies in one of the most important agroforestry systems across the Mediterranean, dehesa. The first study (Chapter 4) is located in a dehesa in Hinojosa del Duque in Córdoba, Spain: Dehesa is an agro-silvo-pastoral system which combines open land and low density trees (holm oaks). In this first study we investigated two adjacent dehesas on the same soil type but different characteristics. One was a pastureland with young holm oaks (planted in 1995 with a density of 70 trees ha−1 at 12 m x 12 m spacing. The area had been grazed by Merino sheep since 2000, at a grazing rate of 3 sheep per hectare. The second, adjacent area is a cultivated pasture with mature oaks with a minimum age of 90-100 years widely spaced (1.2 trees ha−1). Every three years, a mixture of peas and oats is grown for hay. Tillage is used for the preparation of this seeding except in the immediate vicinity (about 0.3-0.4 m) of the tree trunk. The first dehesa at higher tree density was part of this second dehesa, and so both had the same characteristics until year 1995. Both dehesas were sampled simultaneously in 2017. Sampling points were taken under and outside the canopy projection up to a maximum depth of 100 cm divided into 8 sections (0-2 cm, 2-5 cm, 5-10 cm, 10-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, and 80- 100 cm). The results showed that a change in dehesa type from an old low density dehesa combining pasture with seeding every 3 years to a one only pastured with increased tree growth (70 trees ha), showed no significant differences in carbon concentration after 22 years’ sicen implanting the more dense dehesa. A clear stratification of carbon was observed in the soil profile, particularly in the top 10 cm of the soil, as well as an effect of the adult tree which resulted in a higher concentration under the tree canopy in the middle soil depth section (20-40 cm) in the mature dehesa. Significant difference in carbon stock was only observed in the top 0-2 cm (5.86±0.56 t ha1 vs 3.24±0.37 t ha1, been higher in the newly planted dehesa. To our knowledge this is the first study evaluating in dehesa the distribution of soil organic carbon into this four (unprotected and physically, chemically and biochemically protected) fractions. Our results showed how most of the carbon in the two dehesas was stored in the unprotected fraction, been its relative contribution higher in the top 0-2 cm o the pastured dehesa and in the below canopy area of the mature trees in the cropped dehesa. This indicates that much of the fraction contained in these soils is particularly vulnerable to hypothetical changes to less sustainable managements. The second study in dehesa (Chapter 5) was located in the municipality of Pozoblanco in the north of the province of Cordoba. In this area three areas of continuous extensive grazing for more than 50 years with cattle, sheep, and pigs were identified, and three areas with different intensity were studied. These areas were: I) Intensive grazing management. II) moderate grazing management and III) no grazing (area excluded for more than 20 years). Sampling points were taken at each of the three areas up to a maximum depth of 30 cm divided into 5 sections (0-2 cm, 2-5 cm, 5-10 cm, 10-20 cm, and 20-30 cm). Concentrations at different grazing intensities showed, as expected, higher carbon concentrations at the surface soil layer (0-2 cm) average of 1.59±0.44%, decreasing to 0.48±0.15% in the deeper section of the soil profile at 20-30 cm. Contradicting our initial hypothesis, no differences in soil organic carbon concentration were detected among the three areas with different grazing intensities, The total carbon stock was analyzed in the whole soil profile (0-30 cm), indicating non significant differences among the two grazed areas, average value of 27 t ha−1, or the area without grazing 26 t ha−1. As in the previous dehesa, the dominant fraction was the unprotected carbon. However, in this case the relative differences in the soil organic carbon concentration between the unprotected fraction and the physically and the chemically protected fractions was larger than in the first dehesa, particularly because the protected fractions tended to show a higher concentration than in the dehesa studied in Chapter 4. Using the empirical results from the study of the second dehesa, we developed a spectral library and predictive equations of concentration of soil organic carbon using Vis-NIR (Chapter 6) from this dataset. The accuracy of the SOC predictive models was very good, with R2 higher than 0.95 and residual predictive deviation (RPD) higher than 4.54, respectively. Refinement of VIS-NIR techniques, such as the one discussed in Chapter 6, could increase our ability to provide more affordable and robust technologies to measure large numbers of samples with the required accuracy, although it is less clear how to address other important sources of variability, such as soil depth, soil type, bulk density, and rock content. To reduce this uncertainty will be of great relevance to continue performing detailed experiments to better quantify on the effect of land use and cropping systems on soil organic carbon content, such as those described in chapters 3, 5 and 5. To date, these experiments are irreplaceable to test specific hypothesis relevant at local level (like the time to increase soil organic carbon stock after planting at higher density, Chapter 4), but also to create a corpus of available data which could improve, or lead to new ones, conceptual or numerical simulation models that can systematize our understanding of the soil organic carbon cycle and eventually reduce the need for large-scale sampling to verify the evolution of soil organic carbon in agricultural systems.El suelo es un recurso mundial que tiene la capacidad de contener grandes cantidades de carbono orgánico. De hecho, los suelos contienen más carbono que las plantas y la atmósfera juntas. Sin embargo, en los últimos decenios, las actividades humanas, como el cambio de uso de la tierra, la deforestación, la quema de biomasa y la contaminación ambiental, han acelerado la liberación de carbono terrestre en la atmósfera, aumentando el efecto invernadero. El estudio del ciclo del carbono orgánico del suelo ha sido reconocido en las últimas décadas como un paso necesario para controlar los futuros incrementos del CO2 atmosférico, y también para asegurar la sostenibilidad de la producción agrícola. Una mejor comprensión de la dinámica del carbono orgánico del suelo (SOC) en los diferentes sistemas agrícolas permitirá mejorar la calidad del suelo y el almacenamiento de carbono orgánico del suelo en diferentes condiciones edafoclimáticas. Sin embargo, a pesar de décadas de investigaciones sobre este asunto, sigue siendo necesaria una mejor evaluación de la din´[a]mica del carbono del suelo en sistemas agrícolas específicos, basada en estudios empíricos de campo sólidos. Una mejor comprensión del impacto del uso de la tierra en el ciclo mundial del carbono es de gran relevancia. La presente investigación, enmarcada en el contexto de una especialización de doctorado sobre el carbono del suelo en las zonas agrícolas, tiene por objeto generar nueva información sobre el efecto de los diferentes factores (clima, uso de la tierra, ordenación, altitud y tipo de suelo) que influyen en el secuestro y la acumulación de carbono orgánico a lo largo del perfil en el suelo en diferentes sistemas agrícolas y forestales condiciones edafoclimáticas muy diversas. Esta investigación incluye no sólo nueva información cuantitativa sobre el carbono orgánico del suelo, sino también estudios innovadores sobre su distribución entre diferentes compartimentos y sobre el uso de la espectroscopia del infrarrojo cercano (NIR) en la determinación del carbono orgánico del suelo. El primer estudio (Capítulo 2) es un análisis del efecto de los diferentes usos agrícolas en un clima subtropical, en la zona del valle del río Carrizal en la provincia de Manabí, Ecuador basado en el análisis de 64 perfiles de suelo. En cada perfil se tomaron muestras en los horizontes de los perfiles de suelo para obtener la concentración de carbono orgánico hasta una profundidad máxima de 150 cm en diferentes manejos agrícolas (permanentes, rotación intensiva y cultivos abandonados). En esta zona se identificaron veintiún usos agrícolas diferentes. Como era de esperar, las mayores concentraciones de carbono orgánico en el suelo se produjeron en el horizonte A, que tiene un espesor medio de 40 cm. Se observó una tendencia hacia un mayor potencial de secuestro de carbono en zonas pastos, cultivo intercalado como cacao con plátano y maíz con un valor promedio de 1.7% C, mucho mayor que las zonas de agricultura mecanizada que presentó una menor concentración de carbono con un valor promedio de 0. 26% C. El contenido total de carbono, el primer horizonte (A) fue mucho mayor en comparación con los otros perfiles de suelo (B y C), con un valor medio de 41,32±20,97 t C ha1 y 15,06±15,61 t C ha1, respectivamente. El segundo estudio (Capítulo 3) evaluó el efecto de la ordenación forestal en un clima templado. Para ello, se tomaron muestras de suelo en un entorno de gestión de especies forestales (Alnus incana, Fagus sylvatica, Picea abies, y Mixto: rodales que contienen hayas y abetos) en un rango de elevación de 1100 m s.n.m. del Parque Nacional de Babia Góra en el sur de Polonia. El suelo se muestreó hasta una profundidad máxima de 100 cm. Los resultados de este estudio en Polonia revelaron que las reservas SOC en los suelos de montaña del Parque Nacional de Babi Góra se caracterizan por su gran variabilidad (de 50,10 t ha1 a 905,20 t ha1). En las condiciones de este estudio, el tipo de suelo es fue el factor dominante que determina el contenido total de carbono orgánico del suelo, que junto con los factores topográficos determina las condiciones del suelo y la vegetación. Esto explica tal diversidad en la acumulación de carbono orgánico del suelo en diferentes suelos de montaña en las zonas La mayor reserva de carbono se registró en los histosoles (>550 t C ha1), que están situados en la parte baja del parque nacional. El tercer bloque de la investigación se centró en dos estudios de campo en uno de los sistemas agroforestales más importantes del Mediterráneo, la dehesa. El primer estudio (Capítulo 4), se investigó una dehesa en Hinojosa del Duque en Córdoba, España: La dehesa es un sistema agro-silvo-pastoril que combina zona de cultivo y/o pastoreo con árboles a baja densidad (encinas). En este estudio localizamos dos dehesas adyacentes en el mismo tipo de suelo pero de características diferentes. Una era una dehesa con encinas jóvenes (plantadas en 1995 con una densidad de 70 árboles ha1 a 12 m x 12 m de distancia. La zona había sido pastoreada por ovejas merinas desde el año 2000, a una tasa de pastoreo de 3 ovejas por hectárea. La segunda zona, adyacente a la primera, es un pastizal cultivado con robles maduros con una edad mínima de 90-100 años ampliamente espaciados (1,2 árboles ha1). Cada tres años se cultiva una mezcla de guisantes y avena para el heno. La parcela se labra para la preparación del terreno para siembra excepto el suelo en las inmediaciones (alrededor de 0,3-0,4 m) del tronco del árbol. La primera dehesa con mayor densidad de árboles formaba parte de esta segunda dehesa, por lo que ambas tuvieron las mismas características hasta el año 1995. Ambas dehesas fueron muestreadas simultáneamente en 2017. Los puntos de muestreo se tomaron bajo y fuera del dosel vegetal hasta una profundidad máxima de 100 cm divididos en 8 secciones (0-2 cm, 2-5 cm, 5-10 cm, 10-20 cm, 20-40 cm, 40-60 cm, 60-80 cm y 80- 100 cm). Los resultados mostraron que un cambio en el tipo de dehesa de una antigua dehesa de baja densidad que combinaba el pastoreo con la siembra cada 3 años a una dehesa única con un mayor crecimiento de los árboles (70 árboles ha), no resultó en diferencias significativas en la concentración de carbono después de 22 años de pecado implantando la dehesa más densa. Se observó una clara estratificación del ca bono en el perfil del suelo, en particular en los 10 cm superiores del suelo, así como un efecto del árbol adulto que dio lugar a una mayor concentración de carbono bajo el dosel de los árboles en la profundidad intermedia (20-40 cm) en la dehesa madura. Sólo se observó una diferencia significativa en la reserva de carbono en los 0-2 cm superiores (5,86±0,56 t ha1 vs 3,24±0,37 t ha1, siendo mayor en la dehesa recién plantada. Hasta donde sabemos, este es el primer estudio que ha evaluado en dehesa la distribución del carbono orgánico del suelo estas cuatro fracciones (desprotegida, física, química y bioquímicamente protegidas). Nuestros resultados mostraron cómo la mayor parte del carbono en las dos dehesas se almacenaba en la fracción no protegida, siendo su relevancia relativa particularmente alta en la profundidad superior de 0-2 cm de la dehesa sólo pastoreada y en la zona de la copa de los árboles maduros en la dehesa cultivada. Esto indica que gran parte de la fracción contenida en estos suelos es particularmente vulnerable a hipotéticos futuros cambios en los manejos menos sostenibles. El segundo estudio en dehesa (Capítulo 5) se efectuó en el municipio de Pozoblanco, al norte de la provincia de Córdoba. En esta zona se identificó una dehesa que de manera continuada se ha pastoreada desde hace más de 50 años de manera extensiva extensivo con ganado vacuno, ovino y porcino. En la misma se delimitaron tres zonas con diferente densidad de pastoreo. Estas zonas fueron:. I) Manejo de pastos intensivos. II) Manejo moderado del pastoreo y III) no pastoreo (área excluida durante más de 20 años). Se tomaron puntos de muestreo en cada zona hasta una profundidad máxima de 30 cm divididos en 5 secciones (0-2 cm, 2-5 cm, 5-10 cm, 10-20 cm y 20-30 cm). Los resultados mostraron, como era de esperar, mayores concentraciones de carbono en la superficie (0-2 cm) 1,59±0,44% disminuyendo a 0,48±0,15% en la última sección del perfil del suelo a 20-30 cm. Contra nuestra hipótesis de partida no se detectaron diferencias en concentración de carbono en el suelo entre las tres zonas. Se analizó la cantidad total de carbono en todo el perfil del suelo (0-30 cm), indicando diferencias no significativas entre las dos áreas de pastoreo, valor promedio de 27 t ha1, o el área sin pastoreo 26 t ha1. Al igual que en la dehesa estudiada en el Capítulo 4, la fracción dominante fue el carbono no protegido. Sin embargo, en este caso las diferencias relativas en la concentración de carbono orgánico del suelo entre la fracción no protegida y las fracciones física y químicamente protegidas fue mayor que en la primera dehesa, particularmente debido a que las fracciones protegidas tendían a mostrar una mayor concentración de carbono orgánico que en la dehesa estudiada anteriormente en el Capítulo 4. Utilizando los resultados experimentales de este último estudio„ desarrollamos una biblioteca espectral y para desarrollar ecuaciones predictivas de concentración de carbono orgánico utilizando Vis-NIR (Capítulo 6) para este set de datos. La precisión de los modelos SOC fue muy buena, con R2 mayor de 0.95 y la desviación predictiva residual (RPD) superior a 4,54. El perfeccionamiento de las técnicas Vis-NIR, como la que se analiza en el Capítulo 6, podría aumentar nuestra capacidad de proporcionar tecnologías más asequibles y robustas para medir un gran número de muestras con la precisión necesaria, aunque no resulta claro cómo abordar otras fuentes importantes de variabilidad, como son la profundidad del perfil y el tipo de suelo, la densidad aparente y el contenido de material grueso superior a 2mm. Para reducir esta incertidumbre será de gran relevancia continuar realizando experimentos bien diseñados para cuantificar mejor el efecto del uso de la tierra y los sistemas de cultivo en el contenido de carbono orgánico del suelo, como los descritos en los capítulos 3, 4 y 5. Estos experimentos son irreemplazables para validar hipótesis relevantes a nivel local (como el momento de aumentar las reservas de carbono orgánico del suelo después de la plantación a una mayor densidad, Capítulo 4), pero también para crear un corpus de información disponible que podría mejorar, o conducir a nuevos, modelos de simulación conceptual o numérica que pueden sistematizar nuestra comprensión del ciclo del carbono orgánico del suelo y eventualmente reducir la necesidad de muestreo a gran escala para verificar la evolución del carbono orgánico del suelo en los sistemas agrícolas

    Nonlinear multiple regression methods for spectroscopic analysis: application to NIR calibration

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    Chemometrics has been applied to analyse near-infrared (NIR) spectra for decades. Linear regression methods such as partial least squares (PLS) regression and principal component regression (PCR) are simple and widely used solutions for spectroscopic calibration. My dissertation connects spectroscopic calibration with nonlinear machine learning techniques. It explores the feasibility of applying nonlinear methods for NIR calibration. Investigated nonlinear regression methods include least squares support vec- tor machine (LS-SVM), Gaussian process regression (GPR), Bayesian hierarchical mixture of linear regressions (HMLR) and convolutional neural networks (CNN). Our study focuses on the discussion of various design choices, interpretation of nonlinear models and providing novel recommendations and insights for the con- struction nonlinear regression models for NIR data. Performances of investigated nonlinear methods were benchmarked against traditional methods on multiple real-world NIR datasets. The datasets have differ- ent sizes (varying from 400 samples to 7000 samples) and are from various sources. Hypothesis tests on separate, independent test sets indicated that nonlinear methods give significant improvements in most practical NIR calibrations

    Multivariate analysis for quality control of agrifood materials using near infrared spectroscopy

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    Seguridad y calidad alimentaria son uno de los conceptos más demandados actualmente en la industria agroalimentaria. La mayoría de análisis de control de los productos alimentarios se lleva a cabo mediante métodos tradicionales (vía húmeda). Los principales problemas relacionados con este tipo de análisis son el consumo de tiempo para la obtención de los resultados de una sola muestra, el coste del análisis, así como la limitación en cuanto a su implantación en la línea de producción o en el campo, entre otros. Paralelamente al desarrollo e innovación tecnológica, numerosos métodos han sido implementados para la determinación, evaluación y control de la calidad de los productos agroalimentarios en las últimas décadas. Estos métodos están basados en la detección de varias propiedades tanto físicas como químicas correlacionadas con ciertos factores cualitativos de los productos. Uno de los métodos más difundido y aún en desarrollo debido a su gran aplicabilidad, es la espectroscopía de infrarrojo cercano (tecnología NIRS, Near Infrared Spectroscopy). Han pasado más de 20 años desde su primera introducción como potente herramienta hecha por Karl Norris en el análisis de la composición de los cereales. El planteamiento de esta tesis nace de la necesidad, cada vez mayor, del control de los parámetros de calidad de los productos agroalimentarios de manera rápida y precisa. La categorización del trigo en función de su calidad o el valor añadido que adquiere la soja según el porcentaje de proteína o grasa presente en una determinada variedad ha llevado al estudio de la aplicación de la espectroscopía de infrarrojo cercano en dichos productos. El objetivo general de la investigación ha consistido en la aplicación de la tecnología NIRS para la determinación de parámetros de calidad en muestras de...Food safety and quality are currently the most popular concepts in the food industry. Usually, most control analyses of food products are carried out by conventional methods (wet chemistry). However, some of the main negative issues of these methods are: they are time consuming in order to obtain the results of a single sample, the raising price and the limitation on its implementation in the production line or in the field, among others. At the same time to the technological innovation and development, during the last decades many methods have been implemented for the identification, assessment and quality control of food products. These methods are based on the detection of various physical and chemical properties correlated with certain product quality factors. One of the most widespread due to its wide applicability is the near-infrared spectroscopy (NIRS technology, Near Infrared Spectroscopy). It has been over 20 years since its first introduction as a powerful tool made by Karl Norris in the analysis of the composition of the grains. The approach of this thesis arises from the increasing need of fast and accurate analyses of quality parameters control on food products. The categorization of wheat in terms of quality and the added value acquired by the percentage of soy protein or fat in a particular variety has led to the study of the application of near infrared spectroscopy in these products. The general objective of the research has been the application of NIRS technology for the determination of quality parameters in wheat and soybean samples. As a result, this study has led to the development of four chapters: - "Development of robust soybean NIR Calibration Models with temperature compensation and high variability in the data basis." This chapter was focused on the development of robust calibrations by adding in the group of samples instrumental and environmental variability..

    Food, Nutrition and Agrobiodiversity Under Global Climate Change

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    Available evidence and predictions suggest overall negative effects on agricultural production as a result of climate change, especially when more food is required by a growing population. Information on the effects of global warming on pests and pathogens affecting agricultural crops is limited, though crop–pest models could offer means to predict changes in pest dynamics, and help design sound plant health management practices. Host-plant resistance should continue to receive high priority as global warming may favor emergence of new pest epidemics. There is increased risk, due to climate change, to food and feed contaminated by mycotoxin-producing fungi. Mycotoxin biosynthesis gene-specific microarray is being used to identify food-born fungi and associated mycotoxins, and investigate the influence of environmental parameters and their interactions for control of mycotoxin in food crops. Some crop wild relatives are threatened plant species and efforts should be made for their in situ conservation to ensure evolution of new variants, which may contribute to addressing new challenges to agricultural production. There should be more emphasis on germplasm enhancement to develop intermediate products with specific characteristics to support plant breeding. Abiotic stress response is routinely dissected to component physiological traits. Use of transgene(s) has led to the development of transgenic events, which could provide enhanced adaptation to abiotic stresses that are exacerbated by climate change. Global warming is also associated with declining nutritional quality of food crops. Micronutrient-dense cultivars have been released in selected areas of the developing world, while various nutritionally enhanced lines are in the release pipeline. The high-throughput phenomic platforms are allowing researchers to accurately measure plant growth and development, analyze nutritional traits, and assess response to stresses on large sets of individuals. Analogs for tomorrow’s agriculture offer a virtual natural laboratory to innovate and test technological options to develop climate resilience production systems. Increased use of agrobiodiversity is crucial to coping with adverse impacts of global warming on food and feed production and quality. No one solution will suffice to adapt to climate change and its variability. Suits of technological innovations, including climate-resilient crop cultivars, will be needed to feed 9 billion people who will be living in the Earth by the middle of the twenty-first century
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