HORTIMED
High-cash horticultural crops in the Mediterranean depend on irrigation. Typically, surface waters supply only a small fraction (10 to 20%) of the applied volume. The rest comes from groundwater, often exploited at a much larger rate than recharge. For instance, in the leading horticultural area of Morocco (the Souss Valley), the annual deficit of the aquifer is estimated at some 40% of the total irrigation water use (780 million m3), and a yearly drop of 2m in the level of the aquifer has been measured. In addition to depletion, quality of underground water resources deteriorates. Salinisation and nitrate/pesticide pollution have been reported in almost every horticultural area in the Mediterranean basin. Indeed, the salinity (EC) of available groundwater in most horticultural areas in the Mediterranean region is around (or above) 3 dS/m and increasing, often with an imbalance of cations (higher SAR, sodium adsorption ratio) and relatively high content of anions (carbonates). In order to prevent salt accumulation in the root zone (soil or substrate), water is applied in excess, thus increasing production costs and causing severe environmental pollution. The use of closed substrate systems (i.e. with re-use of the drainage, or wastewater) with proper management of the nutrient solution supply can reduce substantially both pollution and water use. However, the salinity of the supply water and the unused fertilisers in the drain, cause a gradual build-up in osmotic pressure and in the concentration of toxic ions (sodium chloride, sulphate) with a consequent depression in plant growth and crop yield (both quantity and quality). These effects are further increased by the interaction of salinity with the high-temperature stress in the root zone and the related risks of salt-related disorders
Given the potentially positive aspects of protected cultivation (water- and land-use efficiency, enormous economic impact), constraints of water supply, water quality and pollution of water resources should not hinder their ongoing growth, particularly in the developing countries in the Mediterranean region. Means that an individual grower can use for reducing consumption of fresh water are:
Match irrigation/nutrients supply to plants’ needs. Methods for estimating crop water and nutrients requirement suited for horticultural crops and to modern application techniques are still wanting. Trickle, minisprinkler and sprinkler irrigation, which are highly efficient methods of water application, are also ideally suited for fertigation (combined irrigation and fertilisation), which constitutes the best means for controlling timing, placement, and supply of water-soluble fertilisers. A method for on line model tuning of water uptake model, versus climatic variables, has been reported, capable of very accurately controlling water supply to real plant needs.
Maximise value of lower-quality water. Adverse climatic factors (namely high temperature) and the hardness and salinity of marginal water represent one of the major agronomic constraints to its use in greenhouse horticulture. The response to salinity has been investigated in many crops, particularly in tomato as far as Mediterranean species are concerned. Nevertheless less attention has been paid to salinity effects on other vegetable species which are important in horticultural industry in the Mediterranean regions. The development of an integrated approach to overcome the problem of increasing soil and water salinity needs the knowledge of the degree of salt tolerance of various species which can be adopted for feasible crop combinations. On the other hand an increased salinity level or restricted water supply may improve product quality. Climatic control (e.g. light intensity, humidity, carbon dioxide injection) in protected horticultural crops affects directly their hydric demand, possibly contributing to mitigate the effects of salinity upon yield and increasing overall water use efficiency. Although ionic concentration in the xylem is lower than in the root zone solution, mineral accumulation in the plant depends on the climate driven transpiration.
Increase supply of marginal water. For instance, the use of closed substrate systems (i.e. with re-circulating nutrient solution) with proper management can reduce substantially both yield depression and need for crop protection. The potential for rain harvesting, even in semi-arid regions is huge: for instance, estimated the potential for protected cultivations in the West Bank to be 3 million m3/year out of an actual water use of some 9 million m3/year.
Recycling, recirculating or treating nutrient- and pesticide-enriched greenhouse and nursery nutrient drainage and runoff reduce environmental impact. Conventional wetland disposal is a cost effective, low maintenance alternative for treating greenhouse wastewater. Successive re-use on species of increasing salt tolerance could lessen waste water volume and chemical release, emulating an idea put forth for open field crops. In these systems salt-tolerant crops would be cultivated with salt-enriched nutrient solutions flushed out of growing systems with less tolerant species. The concentrated saline solution is finally discarded when the salinity is too high for cropping, but its nutrient content is low and therefore environmentally safe. Producers have recognised the recoverable value of refuse released to the air, water or landfill. Production with no negative environmental impact is called zero-pollution manufacturing or closed-loop manufacturing.
Expert Systems, like human experts, perform generic tasks on the basis of the problem type, regardless of the application area. Problem types predominating the role of expert systems are diagnosis and interpretation followed by planning, control and selection. Leading areas, in terms of number of applications, are business, manufacturing and medicine followed by engineering and agriculture. The breadth of the applications is remarkable. We have seen it applied from controlling life support systems in space to helping farmers avoid pest infestations.
To help peanut and cotton growers make the best decisions about managing their crops, researchers at Virginia Tech created a Peanut/Cotton Info-Net. The bulletin board system (BBS) provides daily crop advisories and weather information to growers , extension agents and companies. In another example, an expert system designed to diagnose disease in soybean crops proved to be more reliable than the human experts who supplied the sample diagnoses.
Today, expert systems are built to merge with the mainstream of information processing and are well attuned to the requirements for integration posed by real business applications. A system developed to manage the greenhouse environment and save energy has an embedded a Knowledge Based System in the form of low level "smart functions" for on-line control, as well as in the form of a native fuzzy expert shell, that seamlessly communicates with the control functions.
With a DSS to support them in selecting among these means, growers know what they can do to decrease consumption/depletion of water resources in their holding, and the associated costs. However, they will be prepared to bear the additional costs only if they perceive the common (and their own) interest. That is, advisory services and authorities must be able to prove that their policies are in the growers’ interest, in order to ensure the co-operation of growers, if any hope of success is to be retained. That requires that policies selected are best suited to the particular conditions of each region, and that methods and results are disseminated among growers.