Traditional and New Approaches to Irrigation Scheduling in Vegetable Crops

Intensive vegetable cropping systems use large amounts of water and nutrients. Excess application of water and nutrients results in economic losses (higher fertilizers and pumping costs) and contributes to nutrient: leaching and environmental degradation. Increasing nutrient use efficiency (NUE) and water use efficiency (WUE) should be a priority for sustainable horticulture. This increased NUE, WUE, or both depend on the utilization of efficient irrigation technology, including appropriate methods for irrigation scheduling (IS). Various methods are available for IS based on determination of crop water balance (weather-based method), soil/substrate moisture level, or plant water relations. Rather than discussing the physical and biological basis of irrigation management, this article focuses on currently available irrigation control devices for open-field and greenhouse production systems, with particular emphasis on soil moisture sensors (SMSs). SMS regulates the frequency of irrigation and, possibly, the water dose by continuously monitoring volumetric water content (theta) or matrix potential (psi(m)) of the growing media. A new generation of dielectric SMS has been developed to measure both theta and the electrical conductivity (EC) of pore water in soil and artificial media. This provides the possibility of controlled fertigation based on measured EC. Despite the development in IS, in most regions worldwide, especially in less developed countries, many growers still rely on personal experience for determining crop water requirements and the timing of irrigation. Therefore, the main constraints to the improvement of irrigation efficiency are related to the overall cost of these technologies and to the policies adopted for their dissemination and transfer to professional growers.