Explore the vast range of titles available.

La zonificación del área cafetera mexicana se realiza de forma geográfica, pero dada la diversidad climática de esta, dicha clasificación difícilmente capta la homogeneidad ambiental y no representa las condiciones adaptativas del cultivo. Con la evapotranspiración se pretende identificar la salida de humedad regional y, aunque es aceptada por la academia, es estimada y la calidad de la información generada depende de la capacidad predictiva del algoritmo o de la eficiencia del modelo empleados. Por ello, se propuso un indicador evaluativo del balance hídrico (BH) del área cafetera de Oaxaca, Puebla y Veracruz, con los periodos húmedos y secos definidos por su pluviosidad. Se colectaron datos mensuales de precipitación y evaporación del área estudiada (1921-2018), cuyo cociente se denominó “déficit de evaporación (DE)” (DE > 1.0: exceso, DE < 1.0: déficit). La estación húmeda (PH = junio: septiembre) y seca (PS = noviembre: abril) fueron delimitadas con PH; el mes más lluvioso anual se concretó con zonas con pluviosidad homogénea (PP6 = junio, PP7 = julio, PP8 = agosto, PP9 = septiembre); con el cálculo del DE y su modificación, el DEP1 (cociente del DE en PS vs. DE anual y su relación con el DE en enero) se delimitaron zonas con humedad homogénea, y se validó DEPH con la tendencia en PS y el cálculo del DE por mes y sitio específicos. DEP1 es un índice climático que detecta variaciones temporales y espaciales del BH de áreas cafeteras (R2 = 0.92), y contribuirá a gestionar los recursos hídricos y evaluar la adaptación ambiental del cultivo.

Growth and water use were measured in wheat (Triticum aestivum L.) grown in northern Syria in a typical Mediterranean climate over five seasons 1991/92-1995/96. Water use was partitioned into transpiration (T) and soil evaporation (E-s) using Ritchie's model, and water-use efficiency (WUE) and transpiration efficiency (TE) were calculated. The aim of the study was to examine the influence of irrigation and nitrogen on water use, WUE and TE. By addition of 100 kg N ha(-1), E-s was reduced from 120 mm to 101 mm under rain-fed conditions and from 143 mm to 110 mm under irrigated conditions, and T was increased from 153 mm to 193 mm under rain-fed conditions and from 215 mm to 310 mm under irrigated conditions. Under rain-fed conditions, about 35% of evapotranspiration (ET) may be lost from the soil surface for the fertilized crops and 44% of ET for the unfertilized crops. Transpiration accounted for 65% of ET for the fertilized crops and 56% for the unfertilized crops under rain-fed. As a result of this, WUE was increased by 44% for dry matter and 29% for grain yield under rain-fed conditions, and by 60% for dry matter and 57% for grain yield under irrigated conditions. Transpiration efficiency for the fertilized crops was 43.8 kg ha(-1) mm(-1) for dry matter and 15 kg ha(-1) mm(-1) for grain yield, while TE for the unfertilized crops was 33.6 kg ha(-1) mm(-1) and 12.2 kg ha(-1) mm(-1) for dry matter and grain yield, respectively. Supplemental irrigation significantly increased post-anthesis water use, transpiration, dry matter and grain yield. Water-use efficiency for grain yield was increased from 9.7 to 11.0 kg ha(-1) mm(-1) by supplemental irrigation, although WUE for dry matter was not affected by it. Irrigation did not affect transpiration efficiency for grain yield, but decreased transpiration efficiency for dry matter by 16%. This was associated with higher harvest index as a result of good water supply in the post-anthesis period and increased transpiration under irrigated conditions.

The mechanisms by which a porous windbreak modifies airflow, microclimates and hence crop yields are addressed, based upon recent wind tunnel experiments, field observations and numerical modelling. This paper is thus an update to the excellent reviews in Brandle (1988). It shows how a turbulent mixing layer initiated at the top of the windbreak dominates the airflow behind a windbreak. This mixing layer spreads vertically as it moves downwind, growing at a rate determined by the turbulence in the approach flow and the windbreak's 'permeability'. The roughness of the terrain and land-cover upwind, windbreak height and porosity are thus the main controls on the amount and extent of shelter provided by a windbreak. The changes in temperature, humidity, heat and evaporation fluxes given these changes in turbulence are then described. Based on the turbulent mixing layer model, the highly sheltered 'quiet zone' will be typically warmer and more humid while further downwind in the 'wake zone', cooler and drier conditions would be expected. The careful experimental studies needed to verify these theoretical predictions have not yet been published. Shade is also shown to modify the heating in the quiet zone and, depending on the orientation of the windbreak, can offset the warming in the quiet zone. Lastly, the mechanisms affecting plant productivity are described in light of these airflow and microclimate changes. A major effect of a windbreak is to reduce the incidence of low frequency, high magnitude damage events such as sandblasting or lodging. Microclimate effects, however, do not always improve productivity. For example, while shelter may improve water-use efficiency in irrigated crops by increasing yields and reducing water-use, this may not be the case in dryland agriculture.[PUBLICATION ABSTRACT]

Field experiments were conducted at the Agricultural Engineering Experimental Farm of The Federal University of Technology, Akure, during 2006/2007 and 2007/2008 seasons to investigate the response of cassava under drip irrigation. The experiment was laid out in a randomised complete block design (RCBD) with three replications. The treatments were based on four different water regimes; with T100 receiving 100% available water (AW), T50 and T25 receiving 50% and 25% of AW and T0 with zero irrigation (control treatment). Disease free stems of the cassava cultivar TMS 91934 were planted at a spacing of 1 m by 1 m. The results indicated that T100 full treatment produced the highest average total dry matter yield of 49.12 and 37.62 t/ha in 2006/07 and 2007/08 cropping seasons, respectively. However, the average total dry matter production in T50, T25, and T0 showed significant differences in their values. Low total dry matter yields of 7.12 and 5.92 t/ha, respectively, were associated with T0 for the two cropping seasons. The total water use of 1491.75 and 1701.13 mm was recorded for T100, while total water use of 729.00 and 651.13 mm were obtained for T0 in the two cropping seasons. The water use efficiency determined for the two cropping seasons ranged between 7.38 kg/ha and 32.93 kg/ha. The percentages of total water applied from total water use for T100 were 51.11% and 61.72%, while 14.83% and 17.85% were recorded for T25 for 2006/07 and 2007/08 cropping seasons, respectively.

El presente trabajo muestra una comparativa de estudios realizados a torres de enfriamiento húmedas a contraflujo para sintetizar aportes, estudios y metodologías que permitan dar un contexto reciente al estado actual de la investigación en este campo. Este trabajo parte desde los fundamentos básicos en torres de enfriamiento, sus secciones de estudio y problemáticas a resolver, con un enfoque hacia el consumo de agua en los procesos evaporativos por transferencia de calor en gotas de agua para calcular las pérdidas de agua por evaporación y arrastre. Se revisan y discuten los fundamentos de torres de enfriamiento y aplicaciones generales, los métodos comunes de investigación en torres de enfriamiento utilizados, con énfasis en las características particulares según el tipo de estudio, ya sea desde el punto de vista de diseño de la torre de enfriamiento, las características que afectan su funcionamiento o desempeño, los fundamentos de análisis energético, las sugerencias en la realización de estudios numéricos y simulaciones por CFD, además de su validación correspondiente mediante estudios experimentales. La información recopilada en este trabajo proporciona una visión general y simplifica los avances esenciales en la reducción de las pérdidas por evaporación y arrastre en torres de enfriamiento a contraflujo, las características y tendencias en el desarrollo de modelos matemáticos computacionales y recomendaciones para llevar a cabo estudios teóricos y experimentales para comprender más ampliamente los mecanismos de transferencia de calor y masa.

Regional model experiments for the drought period of May-June-July (MJJ) 1988 and the flood period of MJJ 1993 over the Central Plains of the United States are conducted to study the contribution of local versus nonlocal processes to the maintenance and/or enhancement of the conditions. It is found that the effect of local recycling of evaporated water is not important for the overall development of these two extreme climatic regimes as compared to the effect of large-scale moisture fluxes and synoptic cyclonic activity. In fact, sensitivity experiments indicate that in the Upper Mississippi Basin (UMB) the main effect of decreased evaporation associated with dry soil conditions at the beginning of the simulated periods is to increase buoyancy, dynamically sustain convection, and increase precipitation, thereby providing a negative feedback mechanism for the drought-flood conditions. Overall, the model shows a reasonably good performance in simulating various characteristics of surface climatology over the region during these two extreme periods, with total simulated precipitation being close to observed in MJJ 1988 and lower than observed by about 25% in MJJ 1993. The simulated surface hydrologic budgets and different precipitation statistics over the UMB are also analyzed

Responses of stomata to environment have been intensively studied, but little is known of genetic effects on stomatal conductance or their consequences. In Pima cotton (Gossypium barbadense L.), a crop that is bred for irrigated production in very hot environments, stomatal conductance varies genetically over a wide range and has increased with each release of new higher-yielding cultivars. A cross between heat-adapted (high-yielding) and unadapted genotypes produced F2 progeny cosegregating for stomatal conductance and leaf temperature. Within segregating populations in the field, conductance was negatively correlated with foliar temperature because of evaporative cooling. Plants were selected from the F2 generation specifically and solely for differing stomatal conductance. Among F3 and F4 populations derived from these selections, conductance and Md cooling were significantly correlated with fruiting prolificacy during the hottest period of the year and with yield. Conductance was not associated with other factors that might have affected yield potential (single-leaf photosynthetic rate, leaf water potential). As breeders have increased the yield of this crop, genetic variability for conductance has allowed inadvertent selection for \"heat avoidance\" (evaporative cooling) in a hot environment

In the tropics, the water potential of a region cannot be adequately assessed from precipitation alone due to the seasonal character of rainfall and even more so owing to the changing climate scenario. It is therefore necessary that in any agro-climatological program, there must be a clear understanding of the actual amount of water that evaporates and transpires (AET), and the amount of water that would evaporate and transpire if water were always readily available (PET). This could be done through the method of the water balance. The present work examines the water budget of parts of the Imo river basin and its implications for improved crop production through supplementary irrigation schedules. It was observed, that the study area is already facing moisture-stress. This is because even during rainy months supplementary irrigation is required to compensate for the occasionally moisture deficit due to increased evapotranspiration. The study showed that cultivation of maize, rice and tomatoes can be carried out on an all-year round basis under a scientific irrigation scheme. Thus the study provided farmers with guideline on the period and quantity of water required for supplementary irrigation, a development which will prevents wilting of plants before the application of needed water.

Endotherms dissipate heat to the environment to maintain a stable body temperature at high ambient temperatures, which requires them to maintain a balance between heat dissipation and water conservation. Birds are relatively small, contain a large amount of metabolically expensive tissue, and are mostly diurnal, making them susceptible to physiological challenges related to water balance and heat dissipation. We compiled total evaporative water loss (TEWL) measurements for 174 species of birds exposed to different temperatures and used comparative methods to examine their relationships with body size, ambient temperature, precipitation, diet, and diel activity cycle. TEWL in the thermoneutral zone (TNZ) was associated primarily with body mass and activity phase. Larger and more active-phase birds, with their higher metabolic rates, lost more water through evaporation than smaller, resting-phase birds, particularly at higher thermal exposures. However, maximum temperature of the natural habitat became an important determinant of TEWL when birds were exposed to temperatures exceeding the TNZ. Species from hotter climates exhibited higher TEWL. Adaptation to arid climates did not restrict evaporative water loss at thermal conditions within the TNZ, but promoted evaporative water loss at exposures above the TNZ. The TEWL of granivores, which ingest food with low water content, differed little from species with other food habitats under all thermal conditions. The effects of environmental covariates of TEWL were dissimilar across thermal exposures, suggesting no evidence for a tradeoff between water conservation in the TNZ and heat dissipation at exposure to higher temperatures. Thus, birds may be able to acclimate when climate change results in the need to increase heat dissipation due to warming, except perhaps in hot, arid environments where species will need to depend heavily upon evaporative cooling to maintain homeothermy.