Protected crops have become widely extended due to their integral optimization potential of the production system. The control processes in greenhouses (climate, irrigation and fertilization) is a prerequisite for the agriculture of precision, with aims not only to increase productivity but also, to improve work conditions and assure the best management of resources to reduce detrimental effects into the environment.
    Soilless crop technique crop provides an important tool to optimize water and mineral supplies. In soilless crops, the roots grow in a well-known substrate of limited volume and low water retention that requires high frequency fertigation regimes, on the minute scale.
    It is well known that the roots take up water and nutrients in a selective and variable way. Climate variation shapes involve changes on evapotranspiration demands that could generate salt accumulation in the substrate and even damage the roots. In order to avoid this situation, in open soilless systems, growers irrigate at high frequency, providing an excess nutrient solution volumes which generates lixiviates that are wasted off. Consequently, the low efficiency of the use of water and nutrients seriously and negatively spoils the environment.
    To minimize the problem there is a trend towards reusing lixiviates. In a short terms basis, water plant demands are being used to implement the algorithms of predictive models which integrate both climatic and physiological parameters. Nevertheless, at the moment, the knowledge of plant nutrient demand in a short-term basis is scarce, in particular that of nitrate. Consequently, it becomes necessary to study water and nitrate plant demands separately.
    Nitrate uptake requires energy consumption which is provided by the assimilates that are translocated to the roots from the aerial organs. Carbohydrates availability in the root depends on the whole plant distribution of carbohydrates and is related to environmental parameters, in special to global radiation. In a mature plant, in our case the rose plant, we need to know the degree of these environmental relationships and also the interactions between growing organs, which are the sinks of the assimilates, such as the growing flower shoots and buds against the roots which take up the nutrients. Moreover, woody pluriannual plants are able to develop morphological adaptations as a response to changes in the environment, such as those in leaves when radiation levels vary. These morphological changes vastly affect the source-sink relations. The study of leaf morphology and its association with source-sink relationships arouses great interest when the affected plant species has  economical interest for its flowers or fruits.
    To study these aspects regarding rose crop for cut flowers we set the following goals :
- To devise and validate nitrate uptake models based on hourly kinetics keeping in mind easily measurable climatic variables such as radiation, temperature and air humidity andut also easily calculable ones such as water uptake rate.
- To develop seasonal models to estimate the yield of flower shoots based on radiation and temperature and to analyze the seasonal differences on flower shoot quality and quantity, in connection with the specific leaf area of the flower shoot and the flower bud sizes.
- To study the effect of radiation on C/N relation by means of the evaluation of seasonal biomass, nitrogen and total non-structural carbohydrates between roots, arched stems and flower shoots.
- To study the flower shoot sink effects both on mineral uptake and on carbohydrate and nitrogen distribution during the flower shoot development cycle in two seasons with different radiation levels.
    All the experiments carried out in this Thesis are performed on rose plants (Rosa x hybrida) growing continuously, under closed soilless system using perlite as substrate, in a greenhouse with automatised heating (air, substrate), fog and ventilation. Roses are harvested all year round. Bending technique has been used to manage the plant. Global radiation (outside and inside the greenhouse), air temperature (outside and inside the greenhouse), substrate and nutrient solution temperatures and air humidity are measured by means of sensors every 5 seconds and registered in a data acquisition system.
    The study of water and nitrate uptake kinetics in a hourly basis requires sampling hourly in a 24-hour cycle. An independent pure hydroponic system inside the greenhouse, with 30 plants and with precision scales has allowed to record water volume every 15 seconds and the hourly water balance is taken into account. An automatic sampling equipment has allowed to take nutrient solution samples every hour. Hourly mineral uptake rates of the 30 plants are deduced from the mineral concentration measures of the nutrient solution samples associated with the hourly water balance.
    To devise and validate the nitrate uptake rate model in a mature woody crop, it is needed to collect information that could affect its production and harvesting under growing conditions. Four data base are built up ( climate measurements, hourly net water and nitrate uptake rates,..) corresponding to four climatic conditions that represent the annual cycle (summer, autumn, winter, spring). Empirical relationships for net nitrate uptake rate (dependent variable) have been obtained using, as regressor variables, measurements of radiation, temperature, vapour pressure deficit and net water uptake rates. The prediction capability of these relationships depends on the diurnal/nocturnal period of the 24-hour cycle, and on the season. These models have been validated with independent samples.
    To study the relationships between seasonal carbohydrate and nitrogen distributions and the production and, between the radiation and the temperature conditions and the flower shoot quality, both flower shoot production and quality have been screened through the year. Four whole plant samples per season have been sampled. Biomass and total non structural carbohydrates and nitrogen content distributions among roots, arched stems and flower shoots are calculated. In general, roots contain more nitrogen than arched stems and, flower shoot nitrogen content depends on growth rate. Soluble sugars are more concentrated in the aerial part of the plants than in roots and more in flower shoots than in arched stems. With regard to starch, the highest concentration is found in winter in all plant parts considered. Concentration level decreases in spring and continues decreasing in the summer being lowest values in the autumn. While plant biomass is not altered by plant management practices, biomass and carbon and nitrogen assimilate distribution between the three organs is maintained all through the year. However, the impending renewal of arched stems once a year - which is practised at the end of the spring - induces the relocation of resources in order to make the suitable nitrogen and carbon nutrients available to the whole plant. The quantity and quality of flower shoots, with regard to the specific leaf area and the flower bud size, can be related to the intercepted radiation per leaf area unit and to temperature. The results  led to proposals for the improvement of management.
    The effect of the flower shoot as a sink on mineral uptake and carbon and nitrogen distribution is studied by means of experiments based on flower shoot basal pruning as an initial plant growth stage. Total non-structural carbohydrate and nitrogen contents and distribution as well as water and mineral uptake kinetics are followed from the initial stage to harvest , allowing to distinguish between metabolic and environmental components that affect mineral uptake. This experiment has been performed separately in two seasons, spring and summer, both with a high growth rate but differing in radiation level interception by the plant.
    The results showed the relevancy of the flower shoots as the main sink of the plant, from pruning to visible bud stage and the source condition of the flower shoot leaves from the visible bud stage to harvest. The influence of temperature both on how long it takes to obtain harvesting flower shoots and on their quality are also remarked upon.
    As a result of this study it is proposed, on the one hand, modifications of plant management practices that allows to improve the quantity and quality of cut roses and, on the other hand, the incorporation of algorithms to the nutrient management control systems that might reduce water and nutrients consumption, particularly of nitrate, limiting it to the quantity that plant demands at each time of growth.