Science and technologies for the efficient use of water in agriculture
Food production capacity is closely linked to the availability of water to meet the water needs of crops. In most cases, it is associated with the amount of water transpired by plants. On a global level, agriculture faces the challenge of satisfying a high increase in the demand for food (from 60-80% to 2050), while the cultivated area and available water resources are limited and limiting (FAO, 2009 ). To address this situation, it will be necessary to promote the efficient use of water in agriculture.
This analysis, which is very relevant worldwide, acquires special importance at the level of the Mediterranean countries because, in general, water availability is scarce and climate change will negatively affect the resources available not only because of the increase in temperatures, but, especially, due to the irregularity in the temporal distribution of rainfall. Drought periods and torrential rains will alternate with the result of a very considerable reduction of water resources for all uses, and especially for agricultural uses. In this scenario, being efficient with the water resource becomes an imperative need that we must face immediately and very rigorously, becoming a strategic aspect of economic, environmental and food availability sustainability for our society.
"In the coming decades, the efficient management of irrigation water will be essential to guarantee food security for humanity"
Improving efficiency (water productivity) in our agricultural systems is a possible challenge. For example, based on the R&D work and the observations of what happens in the irrigated productive plantations of the Lleida area in the last 20 years, it is evidenced how irrigation technification allows to reduce the volume of water that it is required to produce an apple (Fig. 1). According to the water footprint data (volume of water required to produce a unit of product) from FAO, to produce an apple of about 200 g, 70 liters of water are required. Figure 1 shows how this data is very close to what we have observed in traditional irrigated areas (69 liters), but at the same time we detect that as we introduce localized irrigation systems (63 liters) and we learn to manage these systems properly (hydraulically and agronomically) These water requirements decrease until reaching 31 liters of water to produce this same apple. So that putting into practice technology and knowledge (technification), this figure decreases progressively. Something similar happens with all crops. Therefore, research on water use in agriculture pursues the objective of producing more with less water.
Figure 1. Effect of irrigation technification on the water footprint of an apple (Girona et al., 2012).
Irrigation, due to its complexity, is probably one of the cultural techniques that most worries the producer, and although some advanced irrigators already achieve a very efficient application, in general there is still a wide potential for improvement, given that the user / producer is not able to control all the parameters involved. In this context, it is interesting to consider the facilitating role that some technologies can provide, among which we highlight:
- Irrigation supervision and automation systems.
- Simulation models of crop water relations.
- Remote sensing of the water status of crops.
Figure 2. Loop between the digital world and the real world in the optimization of irrigation management.
It should be noted that, in practice, the technical limitations facing irrigation optimization are not usually found in the digital world but in the real world. For example, having monitoring systems at an acceptable cost, or having an irrigation facility that allows optimized decisions to be implemented.
Irrigation agronomy
The correct application of the technification, in the terms that we have used before, part of the knowledge of the determination of the water requirements of the crops, and how these should be applied through irrigation systems, as well as seasonal sensitivity to water deficit. Managing water to cover crop needs and applying it so that the plant can use it would be the first objective of efficient irrigation. In the event that we do not have all the water that a crop requires, knowing at what times and under what circumstances to apply it is essential to be efficient and effective in the productive management of water.
“To reduce the gap between scientific-technical knowledge and its application, technologies such as the IoT will be of great help”
From the IRTA Program Efficient Water Use in Agriculture we have been working for more than 35 years to determine the water requirements of the crops with the use of the most relevant technologies, in the development of methodologies and systems that allow it, in the characterization of the seasonal sensitivity of crops to the water deficit, in the response of crops to different water contributions, and in the management of woody crops in periods of drought. In all these works, both the productive and qualitative aspects have been evaluated, in which the vineyard for wine production should be highlighted as a reference example. All this has allowed us to design efficient irrigation strategies, many of them based even on applying moderate water deficits (in intensity and duration), known by the generic name of controlled deficit irrigation (DRC) strategies, which represent in a very evident way the concept of Smart Irrigation Strategies. However, this knowledge would be of little use if we were not able to standardize it, and move from the punctual result of an essay to the globalization of a concept, and that is why for more than 20 years we are working on the development of models that predict the response of crops to different water and agronomic scenarios. Model availability is a basic element for irrigation technification.
The irrigation agronomy should not only take into account the aspects related to the water we manage, but also how this application of irrigation is interrelated with the meaningful management, the application of mineral nutrients (fertilizers) must be closely linked to the management of the irrigation, since the complementarity of irrigation and fertilizers is so great that it is impossible not to think about them together, why fertirrigation is a very important area of work in our research group.
"IRTA works on the elaboration of models that predict the response of crops to different water and agronomic scenarios"
Digital irrigation support tools
The precise adjustment of the irrigation doses to the daily needs of each plot implies a chain of operations that would be unfeasible to address them manually. From the data collection in the field, its processing and integration with the meteorology and with a coherent strategy for the whole campaign, to the communication with the irrigation automatons installed in the field. IRRIX is a web platform, developed at IRTA, which performs all these operations in an automated way, which allows to apply efficient irrigation strategies almost without assistance. The system has been tested on a wide range of crops, which includes tomato, pepper, apple, plum, nectarine, almond and olive.
Figure 3. IRRIX, web tool for automated irrigation programming using sensors.
Remote sensing applied to precision irrigation
The application of uniform irrigation, based on general estimates of crop water needs, may result in over-irrigation of some plots -Or part of them- while, with the same doses, others may be under water deficit. Remote sensing provides a fast and comprehensive monitoring method for the entire length of a crop, which also allows us to know its intraparcel variability. Among the parameters that it provides for irrigation management, the Crop Water Stress Index (CWSI) stands out, based on the temperature of the vegetation cover, which allows quantitatively mapping the water state and from it, being able to apply a differential irrigation. Also, by combining multispectral and thermal remote sensing, it is possible to monitor crop evapotranspiration, which is a key parameter for planning and managing irrigation. In this sense, the IRTA team participates in the development of the European Space Agency (ESA) evapotranspiration product, using images from Sentinel 2 and Sentinel 3 satellites.
Figure 4. Instant evapotranspiration map of the Lleida area, the day 13 / 07 / 2018 at noon, calculated by thermal balance models from images of Sentinel 2 and Sentinel 3 satellites.
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