Mariateresa Cardarelli

Effects of Drought on Nutrient Uptake and Assimilation in Vegetable Crops

Scarcity of water is a severe environmental limit to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Nutritional imbalance under drought conditions depresses plant growth and therefore productivity by affecting nutrient uptake, transport, and distribution. Despite contradictory reports on the effects of nutrient supply on plant growth under drought conditions, it is generally accepted that an increased nutrient supply will not improve plant growth when the nutrient is already present in sufficient amounts in the soil and the drought is severe. A better understanding of the role of mineral nutrients in plant resistance to drought will contribute to improve fertilizer management in arid and semiarid areas and in regions suffering from temporary drought. Considering that vegetables are concentrated in semiarid zones where water stress is frequent, it is important to ascertain how this type of stress affects the nutrient uptake and assimilation of these crops. This chapter starts with an overview of the recent literature on plant nutrition of vegetables under drought conditions, stressing mainly the effects of drought on nutrient availability, uptake, transport, and accumulation in plants, and also the interactions between nutrient supply and drought response; it then proceeds to identify the means to increase nutrient availability under drought conditions through breeding, grafting, and fertilization.

Modelling Evapotranspiration of Container Crops for Irrigation Scheduling

Irrigation is now recognized as an important component in the agriculture economy of Mediterranean regions. As practiced by many growers, it is often based on traditional application methods that fail to measure the supply of water needed to satisfy the variable requirements of different crops. In order to achieve more profitable and sustainable cropping systems, it is essential to modernize existing irrigation systems and improve irrigation water use efficiency (WUE). Up-to-date methods of irrigation should likewise be based on sound principles and techniques for attaining greater control over the soil-cropwater regime and for optimizing irrigation in relation to all other essential agricultural inputs and operations. Accurate predictions of crop water requirements are necessary for an efficient use of irrigation water in container crops cultivated both outdoors and in greenhouse. Irrigation scheduling (IS) has conventionally aimed to achieve an optimum water supply for productivity, with soil or container water content being maintained close to field capacity. Different approaches to IS have been developed, each having both advantages and disadvantages but despite the number of available systems and apparatus, not entirely satisfactory solutions have been found to rationalize IS, assuring optimal plant growth with minimal water use (Jones, 2004). Many growers, especially in the Mediterranean regions, use simple timers for automated irrigation control of containerized crops and scheduling is based on their own experience. Evapotranspiration (ET) is the primary process affecting crop water requirements and, therefore, its knowledge is essential for efficient irrigation management. ET is the combined process of evaporation from soil or substrate and leaf transpiration. Evapotranspiration requires two essential components: a source of energy and a vapour transport mechanism. Energy is needed for phase change from liquid to vapour in sub-stomatal cavities whereas the leaf-to-air vapour pressure gradient ensures that water vapour crosses leaf stomata. In container-grown plants, ET is affected by many factors, both environmental (e.g. air temperature, radiation, humidity, wind speed) and plant related characteristics (e.g. growth