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Simple Summary: Agroindustrial by-products serve as an alternative source of livestock feed, significantly contributing to the sustainability of livestock systems. A very interesting by-product is dehydrated orange pulp (DOP), generated by the industrial production of orange juice, Spain being the largest producer of it in Europe. The DOP could be used as food for ruminants, replacing cereals. We have shown that DOP could replace up to 80% of the cereals in diets without detrimental effects on milk production during complete lactation and the growth of the kids. Furthermore, the milk quality improved from the perspective of human health. As a continuation of that trial, and given the current consumer interest in the healthy properties of animal products, the present study examined the replacing cereal with DOP in the diet of dairy goats, and focused on the antioxidant compounds and fatty acid contents of artisanal cheeses made from raw milk. The vitamin E content, total phenols, and total antioxidant activity in the cheeses increased as the amount of dehydrated orange pulp in the diet rose. In summary, the use of dehydrated orange pulp contributes to both sustainable livestock practices and the quality of goat cheese. Agroindustrial by-products constitute an alternative source of feed livestock, and their use contributes to the sustainability of livestock systems and the circular bioeconomy. The effects of replacing cereal (0%, 40%, and 80%) with dehydrated orange pulp (DOP) in the diet of goats on the antioxidant and fatty acid (FA) contents of cheeses were evaluated. For a more suitable understanding of the role of coagulant enzymes in establishing the properties of the cheese, the effect of milk-clotting with animal and vegetable rennet was also analysed. The rennet did not substantially affect the FA or the antioxidant compounds, and the use of DOP did not affect the FA contents. However, the α-tocopherol levels, total phenolic compounds (TPC), and total antioxidant capacity (TAC) in cheeses increased as the percentage of DOP replacing cereals increased. Moreover, the high correlation obtained between the TAC and the TPC (r = 0.73) and α-tocopherol (r = 0.62) contents indicated the important role played by these compounds in improving the antioxidant capacity of the cheese. In conclusion, DOP is a suitable alternative to cereals in the diet of goats and improves the antioxidant status of the cheese produced. [ABSTRACT FROM AUTHOR]

The reset control is a simple nonlinear control approach where the states of the controller are conducted to zero when a particular condition is satisfied. The PI+CI is a controller that mixes the simplicity of PI controllers with the benefits of a reset action to mitigate the fundamental limitations of linear control. However, the tuning of this kind of controller, with three parameters, two for the linear part and one for the nonlinear one, is not trivial. In this paper, simple tuning rules for PI+CI are proposed for both tracking and regulation problems, assuming first-order dynamics for the plant. The resulting control scheme, for which the reset coefficient is computed from exponential functions, is simulated and compared with an ideal PI+CI where the reset coefficient is obtained using rules available in the literature. Similar results are obtained for the tracking problem, and optimal performance based on the Integral Absolute Error (IAE) is also obtained for the regulation problem. These new rules, in contrast to those already existing in the literature, depend only on closed-loop specifications. Furthermore, the framework based on the minimization of IAE, used to obtain the proposed rules, makes it possible to consider for the first time the tracking and regulation problems simultaneously, i.e., cases where setpoint changes and disturbance arrivals can occur at the same time before reaching a new steady state. The results are validated using a set of study cases. [ABSTRACT FROM AUTHOR]

The industrial production of microalgae is a process as sustainable as it is interesting in terms of its diverse applications, especially for wastewater treatment. Its optimization requires an exhaustive knowledge of the system, which is commonly achieved through models that describe its dynamics. Although not widely used in this field, artificial neural networks are presented as an appropriate technique to develop this type of model, having the ability to adapt to complex and nonlinear problems solely from the process data. In this work, neural network models have been developed to characterize the pH dynamics in two different raceway reactors, one with freshwater and the other with wastewater. The models are able to predict pH profiles with a prediction horizon of up to eleven hours and only using available measurable process data, such as medimum level, CO 2 injection, and solar radiation. The results demonstrate the potential of artificial neural networks in the modeling of continuous dynamic systems in the field of industry, obtaining accurate, fast-running models that can adapt to different circumstances. Moreover, these models open the field to the design of data-driven model-based control algorithms to account for the nonlinear dynamics of this biological system. [ABSTRACT FROM AUTHOR]

The present paper investigates the optimal control of the photosynthetic growth process in an artificial light photobioreactor operated in batch mode, the objective being to find an optimal incident light intensity for which the consumption of light energy, for any amount of newly formed biomass, is minimal. By using a simple and reliable model for the photosynthetic growth of microalgae of microalgae, predictions can be made on the quantity of produced biomass and on the amount of light consumed, whose ratio gives the biomass yield on light energy. This variable is unimodal on the allowed range of incident light intensities and has been used as objective function. An improved objective function is proposed by using the specific growth rate and a weighing factor that allows obtaining the desired amount of biomass while the light energy consumption is optimal. A closed-loop control structure has been designed based on the developed optimization algorithm. The optimal controller has been validated in simulation, comparing different lengths of the optimization horizon and the sampling period. It was found that a bigger sampling period, for the cases where there is no online information on the biomass concentration, does not significantly affect the productivity. The optimization algorithm can be used either online or offline, being useful for various experimental setups. [ABSTRACT FROM AUTHOR]

Our aim was to characterize the organoleptic and nutritional properties of meat from suckling (one-month-old) and light (around three-months-old) lambs in local breeds on the Spanish Mediterranean islands, using meat from male lambs of the Mallorquina and Roja Mallorquina breeds. The lambs were kept with their mother at all times under an extensive management system and fed on mother's milk until naturally weaned. In the Mallorquina breed, suckling lambs (n = 20) were slaughtered after weaning and the light lambs were bred using natural pasture (n = 20) or concentrate (n = 20), and the Roja Mallorquina light lambs were fed pasture and concentrate (n = 20). The pH, colour, texture, water-holding capacity, fatty acids, volatile compounds and sensorial attributes of the meat were analyzed. No differences in meat colour or texture were observed. The highest levels of non-desirable fatty acids were observed in lambs raised using concentrate. Light lambs showed a higher aldehydes content than suckling lambs. High notes of lactic acid and milk flavour were detected. Regardless of access to pasture or concentrate, continued access to mother's milk during rearing influences the sensorial meat traits of these lambs, so we consider this type of management an optimal way of obtaining the traditional 'Mediterranean lamb meat'. [ABSTRACT FROM AUTHOR]

Testosterone Concentrations, Odor, Scrotal Circumference, and Sexual Interactions with... Time had a marked effect on the plasma testosterone concentration ( I p i < 0.01), as did the interaction of time × buck photoperiod treatment ( I p i < 0.01), the interaction of time × agonist ( I p i < 0.01), and the interaction of time × buck photoperiod treatment × agonist ( I p i < 0.01) (Figure 4A,B). In Experiment 1, the results demonstrate that contact with females induces a rapid rise in the testosterone concentrations of the bucks exposed to a natural photoperiod; however, this contact did not modify the testosterone concentrations of the photostimulated bucks. In general, the testosterone concentration of both groups, used or not, was similar for the entire experiment, except when the bucks were introduced to the females (25 March), at which time the testosterone concentrations of the bucks used increased and decreased rapidly (Figure 1B). Testosterone Concentrations and Sexual Behavior Time had a marked effect on the plasma testosterone concentration ( I p i < 0.001), as did the interaction of time × buck photoperiod treatment ( I p i < 0.001) (Figure 1A). [Extracted from the article]

Microalgae-bacteria consortia have been proposed as alternatives to conventional biological processes to treat different types of wastewaters, including animal slurry. In this work, a microalgae-bacteria consortia (ABACO) model for wastewater treatment is proposed, it being calibrated and validated using pig slurry. The model includes the most relevant features of microalgae, such as light dependence, endogenous respiration, and growth and nutrient consumption as a function of nutrient availability (especially inorganic carbon), in addition to the already reported features of heterotrophic and nitrifying bacteria. The interrelation between the different populations is also included in the model, in addition to the simultaneous release and consumption of the most relevant compounds, such as oxygen and carbon dioxide. The implementation of the model has been performed in MATLAB software; the calibration of model parameters was carried out using genetic algorithms. The ABACO model allows one to simulate the dynamics of different components in the system, and the relative proportions of microalgae, heterotrophic bacteria, and nitrifying bacteria. The percentage of each microbial population obtained with the model was confirmed by respirometric techniques. The proposed model is a powerful tool for the development of microalgae-related wastewater treatment processes, both to maximize the production of microalgal biomass and to optimize the wastewater treatment capacity. [ABSTRACT FROM AUTHOR]

Electricity load forecasting, optimal power system operation and energy management play key roles that can bring significant operational advantages to microgrids. This paper studies how methods based on time series and neural networks can be used to predict energy demand and production, allowing them to be combined with model predictive control. Comparisons of different prediction methods and different optimum energy distribution scenarios are provided, permitting us to determine when short-term energy prediction models should be used. The proposed prediction models in addition to the model predictive control strategy appear as a promising solution to energy management in microgrids. The controller has the task of performing the management of electricity purchase and sale to the power grid, maximizing the use of renewable energy sources and managing the use of the energy storage system. Simulations were performed with different weather conditions of solar irradiation. The obtained results are encouraging for future practical implementation. [ABSTRACT FROM AUTHOR]

In this paper, measurable disturbance compensation techniques are analyzed, focusing the problem on the input-output and disturbance-output time delays. The feedforward compensation method is evaluated for the common structures that appear between the disturbance and process dynamics. Due to the presence of time delays, the study includes causality and instability phenomena that can arise when a classical approach for disturbance compensation is used. Different feedforward configurations are analyzed for two feedback control techniques, PID (Proportional-Integral-Derivative) and MPC (Model Predictive Control) that are widely used for industrial process-control applications. The specific tuning methodology for the analyzed process structure is used to obtain improved disturbance rejection performance regarding classical approaches. The evaluation of the introduced disturbance rejection schemes is performed through simulation, considering process constraints in order to highlight the advantages and drawbacks in common scenarios. The performance of the analyzed structure is expressed with different indexes that allow us direct comparisons. The obtained results show that the proper design and tuning of the feedforward action helps to significantly improve the overall control performance in process control tasks. [ABSTRACT FROM AUTHOR]

Simple Summary: Dried orange pulp can conveniently replace cereals in ruminant diets; however, no published reports have considered a similar substitution for the goat diet throughout lactation. Therefore, in this study, we evaluated the effects of cereal replacement (40% and 80%) by dried orange pulp in the diet of Payoya breed goats during the entire lactation period (180 days) on milk yield and composition, blood metabolites and production economics. Also evaluated, in mid-lactation, were the nutrient utilisation and ruminal fermentation of the dried orange pulp diets. Milk production and gross composition did not change in goats fed diets that included dried orange pulp. A decrease in nitrogen availability and retention was observed, while an increase detected in the digestibility of cellulose likely boosted rumen microbial protein synthesis. No pathological effects of dried orange pulp supplementation were detected in blood metabolites. The partial substitution of cereals for dried orange pulp reduced costs and raised economic profits. In conclusion, the partial replacement of cereals by dried orange pulp is a profitable and healthy nutritional strategy in dairy goats that does not compromise their productivity and is suitable for the entire lactation period. Dried orange pulp (DOP) can be incorporated into ruminant diets, but no reports have considered this strategy during the entire lactation period in goats. Two experiments were performed using lactating Payoya goats. In experiment 1, to study the effect, over 180 days, of DOP on milk yield and composition, blood metabolites and economic values, 44 primiparous goats were allocated into three groups: control diet (concentrate plus lucerne) and DOP40 and DOP80 diets, in which DOP replaced 40% and 80%, respectively, of the cereals. Nutrient digestibility and rumen fermentation were also studied (experiment 2). The DOP diets did not affect milk yield and composition. DOP triggered lower intake and digestibility of ether extract and crude protein. Ruminal fermentation was unaffected by DOP, except for a decrease in butyrate for DOP80. The energy balance was unaltered by diet while the balance and retention of nitrogen decreased. Regarding plasma biochemistry, DOP supplementation caused changes that could indicate an improvement in hepatic function and reduced muscular damage and oxidative muscular stress. Moreover, DOP80 provided a profit increase of EUR 3.27/goat. In conclusion, the partial replacement of cereals by DOP is a profitable and healthy nutritional strategy in dairy goats and is suitable for the entire lactation period without compromising productivity. [ABSTRACT FROM AUTHOR]

Simple Summary: Spain is a major global producer of both goats and oranges. The orange juice industry produces high levels of organic waste that could be used as alternative feedstock for ruminants, enhancing dairy farm sustainability by lowering feed costs and reducing the environmental impact. An example of such organic waste is dried orange pulp (DOP), which has been proven beneficial as a 40% or 80% replacement for cereal in the diet of goats at an early lactation stage; therefore, it is pertinent to study these by-products over a longer period, such as the complete lactation cycle of 180 days. This study evaluated the Payoya dairy breed and the resultant milk's antioxidant composition and fatty acid (FA) content in terms of saturated, monounsaturated, and polyunsaturated FAs (SFA, MUFA, and PUFA, respectively). The levels of vitamin E, total phenolic compounds, and antioxidant capacity in milk increased as the percentage of DOP replacing cereals increased. Moreover, the inclusion of DOP improved the nutritional value of the milk for human health (according to the thrombogenicity index, MUFA/SFA, and PUFA/SFA ratios), especially at the end of lactation, leading to the conclusion that DOP might be an appropriate alternative to cereals in the diets of goats. Although dried orange pulp (DOP) as a short-term dietary supplementation has been proven an effective substitute for cereals in goat diets–without impairing milk quality–there have been no studies considering its use over the full lactation period. This study evaluated replacing cereal with DOP in goat diets for the full 180-day lactation period on milk's fatty acid (FA) and antioxidant composition. Payoya goats were assigned to three diet groups: a control group consuming a commercial concentrate with alfalfa hay as forage; a DOP40 or DOP80 group, wherein 40% or 80% of the cereal in the concentrate was replaced by DOP. The α-tocopherol and phenolic compounds levels and the antioxidant capacity in the milk increased as the DOP percentage increased. Including DOP might improve the FA indices of milk in the context of human health, especially when included at the end of lactation because it contributes to reducing the thrombogenicity index and increasing both the monounsaturated/saturated FA and polyunsaturated/saturated FA indices and the amounts of indispensables α-C18:3 n-3 and C18:2 n-6 cis. Ultimately, DOP presents a plausible alternative to cereals in the diet of goats throughout lactation to improve the nutritional milk quality, especially the healthy antioxidant capacity. [ABSTRACT FROM AUTHOR]

One of the most critical variables in microalgae-related processes is the pH; it directly determines the overall performance of the production system especially when coupling with wastewater treatment. In microalgae-related wastewater treatment processes, the adequacy of pH has a large impact on the microalgae/bacteria consortium already developing on these systems. For cost-saving reasons, the pH is usually controlled by classical On/Off control algorithms during the daytime period, typically with the dynamics of the system and disturbances not being considered in the design of the control system. This paper presents the modelling and pH control in open photobioreactors, both raceway and thin-layer, using advanced controllers. In both types of photobioreactors, a classic control was implemented and compared with a Proportional–Integral (PI) control, also the operation during only the daylight period and complete daily time was evaluated. Thus, three major variables already studied include (i) the type of reactors (thin-layers and raceways), (ii) the type of control algorithm (On/Off and PI), and (iii) the control period (during the daytime and throughout the daytime and nighttime). Results show that the pH was adequately controlled in both photobioreactors, although each type requires different control algorithms, the pH control being largely improved when using PI controllers, with the controllers allowing us to reduce the total costs of the process with the reduction of CO2 injections. Moreover, the control during the complete daily cycle (including night) not only not increases the amount of CO2 to be injected, otherwise reducing it, but also improves the overall performance of the production process. Optimal pH control systems here developed are highly useful to develop robust large-scale microalgae-related wastewater treatment processes. [ABSTRACT FROM AUTHOR]

Simple Summary: On the extensive and semi-extensive goat farms of the Mediterranean region, the induction of the male effect is a common reproductive management practice in spring mating (seasonal anoestrous). The sexual activity displayed by the bucks is one of the main factors that determines the reproductive performance of this practice and, for that reason, it is essential to photostimulate the bucks prior to using it. However, the effectiveness of this photostimulation and the male effect could depend on the seasonality of the breed of buck used. Thus, the present work aimed to compare the efficiency of the male effect, in terms of doe reproductive response and reproductive performance, as induced by bucks made sexually active via photostimulation, from breeds with different reproductive seasonality (Murciano–Granadina, low reproductive seasonality vs. Blanca Andaluza, high reproductive seasonality). The results demonstrated that the Blanca Andaluza bucks subjected to a natural photoperiod and used for the male effect induced a lower percentage of females into oestrus and ovulation, resulting in lower productivity. This suggests that photoperiod-treated bucks efficiently induce the male effect, but photostimulation may be more necessary for breeds with deep seasonality. This study examines the effectiveness of the photoperiod treatment (extra light for 88 days) to render the bucks sexually active during the seasonal anoestrous in order to induce a male effect, depending on the reproductive seasonality of the breed of the bucks used. In April, 57 anoestrous Blanca Andaluza does were distributed into four groups with three males each: 13 were exposed to control Murciano–Granadina bucks (lower seasonality); 15 were exposed to photostimulated Murciano–Granadina bucks; 14 were exposed to control Blanca Andaluza bucks (higher seasonality), and 15 were exposed to photostimulated Blanca Andaluza bucks. After male introduction, the sexual behaviour of the bucks was assessed, and harness marks recorded doe oestrous behaviour. Ovulation was confirmed from plasma progesterone, and the ovulation rate was assessed by transrectal ultrasonography. Fecundity, fertility, prolificacy and productivity were also determined. All of the does in all of the groups showed ovulation. Interaction between both sources of variation was observed: the percentage of females showing oestrous (p < 0.01) and productivity (p < 0.05) was the lowest in the Blanca Andaluza control group (50% and 0.36 ± 0.17 goat kids born/female, respectively). In conclusion, photoperiod-treated bucks efficiently induce a male effect, but photostimulation could be more necessary for breeds with deep seasonality. [ABSTRACT FROM AUTHOR]

We conducted the first nutritional analysis of dairy products from the traditional Roja Mallorquina sheep breed. Samples of bulk raw milk were taken twice a month from December 2015 to March 2016 from sheep fed using a part-time grazing system, and fresh soft (FC, n = 8) and ripened (RC, n = 8) cheeses were made. The variability in vitamins, total phenolic compounds (TPC), total antioxidant capacity (TAC), and fatty acid (FA) content was influenced by the cheese-making process (differences between the cheese and the original milk) and by the type of cheese-making technology (mainly related to heating, the use of starter culture, and ripening). The most notable physicochemical characteristic of the cheeses was low fat content (24.1 and 29.6 g/100 g for FC and RC). Milk and RC were characterised by major concentrations of retinol (211.4 and 233.6 μg/100 g dry matter (DM), respectively) and TPC (18.7 and 54.6 μg/100 g DM, respectively), while FC was characterised by major concentrations of retinol (376.4 μg) and α-tocopherol (361.7 μg). The fat-soluble components of the FC generally exhibited better nutritional value for human health than those of the milk and RC, with a higher level of retinol and α-tocopherol; lower values for saturated FA, atherogenic, and thrombogenic indices; and higher levels of monounsaturated FA, polyunsaturated FA, n-3, and n-6. Acids, alcohols, and ketones comprised almost 95% of the volatile compounds detected. Acetoin and products of lactose and citrate metabolism played an important role in the development of the aromatic attributes of both kinds of cheese. This preliminary study can contribute to add value to these traditional products according to healthy nutritional criteria and supports the implementation of strategies to promote their commercialisation and obtain product labelling as "pasture-fed" or specific marks. [ABSTRACT FROM AUTHOR]

The increased use of concentrates to reduce pasture as a feed source in productive systems like Payoya breed goat farms has made it necessary to decrease feeding costs. The inclusion of agro-industry by-products such as dry orange pulp pellets in goat diets has been suggested as a sustainable alternative to cereal-based concentrates. The aim of this work was to assess the influence of diets including dry orange pulp pellets on the quality of cheeses traditionally made from Payoya breed goat milk. We analysed the physicochemical characteristics, sensory properties and volatile compound profiles of 18 artisanal cheeses made from raw Payoya milk. In this study, goats were fed with different concentrations of dry orange pulp; and cheeses were curdled with animal and vegetable coagulants. Slight differences were detected between some cheeses. However, the use of citrus by-products in the Payoya goat diets did not substantially affect the cheeses' physicochemical properties, olfactory attributes, or volatile profiles. Therefore, dried citrus pulp can be used as a substitute for cereal concentrates without affecting the distinct properties of these ripened raw goat milk cheeses. [ABSTRACT FROM AUTHOR]

In this work, simple tuning rules for feedforward compensators were applied to design a control strategy to regulate the inside air temperature of a greenhouse during daytime by means of a natural ventilation system. The developed control strategy is based on a PI (Proportional-Integral) controller combined with feedforward compensators to improve the performance against measurable external disturbances such as outside air temperature, solar radiation, and wind velocity. Since the greenhouse process dynamics is very complex and physical non-linear models are mathematically complicated, a system identification methodology was proposed to obtain simpler models (high-order polynomial and low-order transfer functions). Thus, an easier procedure was completed to tune the PI controller parameters and to obtain the feedforward compensators expressions by following a series of modern and simple tuning rules. Simulations with real data were executed to compare the control performance of a PI controller with or without the addition of feedforward compensators. Moreover, real tests for the developed control strategy were carried out in an experimental greenhouse. Results demonstrate an enhanced control performance with the presence of the feedforward compensators under different weather conditions. [ABSTRACT FROM AUTHOR]

Simple Summary: Spain is a major global producer of both goats and citrus fruits on the world. Using by-products of the orange industry for feeding ruminants has environmental advantages. In this work, we analysed how replacing cereal concentrates with dehydrated orange pulp (DOP) in the diet of mother goats affects the meat quality of suckling kids. We evaluated the following characteristics of the meat of suckling kids of the dairy Payoya breed: chemical composition; texture; water holding capacity; colour; saturated, monounsaturated, and polyunsaturated fatty acids (SFA, MUFA, and PUFA, respectively); volatile compounds; and sensorial appraisal. The inclusion of DOP in goat feed did not affect the proximal composition, texture, colour, or juiciness of the kids' meat. However, the inclusion of DOP improved the indices of the nutritional value of the meat for human health (thrombogenicity index, PUFA/SFA ratio, and n-6/n-3 ratio). The inclusion of DOP in goat feed reduced MUFA content in the kids' meat. An increase in aromatic compounds, including ethyl furan, dimethyl disulphide, and heptane, was observed in the grilled meat of kids from goats that were fed DOP. The use of DOP in goat feed improved consumers' sensory appreciation of the suckling kids' meat. We analysed how replacing cereal concentrates with dehydrated orange pulp (DOP) in the diet of mother goats affects the meat quality of suckling kids. Three experimental diets for mother goats were designed. The DOP-0 diet contained commercial concentrates and alfalfa hay. In the DOP-40 and DOP-80 diets, 40% and 80% (respectively) of the cereal in the concentrate was replaced with pellets of DOP (the alfalfa hay component was unchanged). We evaluated the chemical composition, texture, water holding capacity, colour, fatty acids (FAs) profile, volatile compounds, and sensorial appraisal of the meat from 30 male suckling kids (cold carcass weight 4.74 kg, 4.82 kg, and 4.65 kg for DOP-0, DOP-40, and DOP-80, respectively) of the Payoya breed (n = 10 for each diet). Meat from kids in the DOP-40 and DOP-80 groups exhibited characteristics favourable for human health, including the meat's thrombogenicity index, PUFA/SFA ratio (0.60 index), and n-6 PUFA/n-3 PUFA ratio (approximately 7.50). The meat also exhibited reduced MUFA content (around 460 mg/100 g fresh meat). An increase in ethyl furan, dimethyl disulphide and heptane was observed in grilled meat from goats that were fed using DOP. The inclusion of DOP in goat feed improved consumers' sensory appreciation of the kid's meat. [ABSTRACT FROM AUTHOR]

In this paper, a new solution to improve the traditional control operation of raceway microalgae reactors is presented. The control strategy is based on an event-based method that can be easily coupled to a classical time-driven proportional-integral controller, simplifying the design process approach. The results of a standard Proportional-Integral (PI) controller, as well as of two event-based architectures, are presented in simulation and compared with each other and with traditional On/Off control. It is demonstrated that the event-based PI controller—operating during the whole day instead of only during daytime—achieves a better performance by reducing the actuator effort and saving costs related to gas consumption. [ABSTRACT FROM AUTHOR]

Monitoring the greenhouse transpiration for control purposes is currently a difficult task. The absence of affordable sensors that provide continuous transpiration measurements motivates the use of estimators. In the case of tomato crops, the availability of estimators allows the design of automatic fertirrigation (irrigation + fertilization) schemes in greenhouses, minimizing the dispensed water while fulfilling crop needs. This paper shows how system identification techniques can be applied to obtain nonlinear virtual sensors for estimating transpiration. The greenhouse used for this study is equipped with a microlysimeter, which allows one to continuously sample the transpiration values. While the microlysimeter is an advantageous piece of equipment for research, it is also expensive and requires maintenance. This paper presents the design and development of a virtual sensor to model the crop transpiration, hence avoiding the use of this kind of expensive sensor. The resulting virtual sensor is obtained by dynamical system identification techniques based on regressors taken from variables typically found in a greenhouse, such as global radiation and vapor pressure deficit. The virtual sensor is thus based on empirical data. In this paper, some effort has been made to eliminate some problems associated with grey-box models: advance phenomenon and overestimation. The results are tested with real data and compared with other approaches. Better results are obtained with the use of nonlinear Black-box virtual sensors. This sensor is based on global radiation and vapor pressure deficit (VPD) measurements. Predictive results for the three models are developed for comparative purposes.