The objective of the Hortimed RTD project was to develop a context sensitive strategy for managing irrigation and nutrient supply to protected crops, under constraint conditions on the quantity and quality of the water supply. The economical (quality and quantity of crop yield/ the producer side) and the ecological (sustainability, contamination risks of water table, and healthy vegetables/ the consumer side) factors, affecting the strategic and operational decisions, have been the focal points of the research. The research activities of the project have advanced our knowledge on plant response to salinity and water stress. These new findings, together with actions on:
system analysis and validation experiments on salinity buildup in closed irrigation systems
integrated manipulation of aerial and root environment to increase plants’ tolerance to salinity
cascaded cropping systems to increase utility of salinity water
were bound in a number of hardcopy deliverables of the project. The acquired new knowledge was delineated into rules, models and suggested “good practices” and combined with new management techniques into developing a Decision Support System for growers and consultants; a valuable source for students and educators as well.
The work has been organized into four work packages, as follows:
This work package analyses the present situation, both resources and
expected requirements, in the most important horticultural areas in the
Mediterranean basin. Water and nutrient requirements are coupled to the
development of realistic fertigation recipes for the major horticultural
crops, and management procedures are developed to match water and nutrient
delivery with the desired level. The work package is broken down into two
Determine environmental impact for selected protected horticultural crops,
for different root media and salt content of available water.
Task 1.2. Develop irrigation/fertigation recipes for
main vegetables under protectedconditions based on soil fertility, growth
stage and yield quality targets.
Task 1.2. Develop irrigation/fertigation recipes (ARI, Cyprus)
Fertigation was studied as a means to increase yield and improve quality of drip irrigated greenhouse crops (Deliverable 2: Fertigation recipes for selected crops in the Mediterranean region). A model was developed for fertigation of selected greenhouse crops, to be used at farmers level.
Seasonal irrigation requirement for greenhouse tomato and cucumber was 450 and 350 mm, respectively. Reduced irrigation and irrigation with saline water, both increased salinity of the root zone, due to accumulation of chlorides, and decreased tomato and cucumber yields. Application of higher amounts of water for leaching purposes was beneficial. Fertigation of phosphorus proved to be superior, compared to incorporation of P in the soil at planting, as it increased leaf P content and yield of greenhouse tomato and cucumber.
Studies using N15 urea fertilizer with greenhouse tomato and cucumber, indicated that the rate of N-uptake was lower during the initial growth cycle, and increased as the growing season progressed. Irrigation with saline water reduced total N-uptake and fertilizer N utilization, and increased for both crops the amount of N requirement per unit of yield produced.
Irrigation requirement of open field pepper over the entire growing season totaled to 540 mm. Fertigation of nitrogen increased vegetative growth and yield, in comparison to incorporation of N in the soil at planting. Nitrogen uptake and fertilizer N utilization were also higher with fertigation, while increasing N concentration in the irrigation water, total N-uptake increased and fertilizer N utilization decreased.
In Deliverable 2, fertigation equipment, fertilizers, practices and recommendations are discussed. The model calculates for a target yield of tomato, pepper, cucumber and melon N, P and K recipes for the preflowering and fruiting cycles. Calculations are based on crop water and nutrient requirements, soil type and soil fertility. Nutrient concentrations in the irrigation water are also converted to concentrations of the selected fertilizers in the stock solution.
Irrigation requirement was determined for drip-irrigated greenhouse and open field vegetables. Reduced irrigation and irrigation with saline water both decreased yields, while the application of excess water for leaching of salts was beneficial. Fertigation of N and P increased yields, compared to application of fertilizers in the soil at planting. The rate of N-uptake was lower during the initial growth cycle. N-uptake and fertilizer N utilization decreased with saline water and increased with fertigation. Increasing nitrogen concentration in the irrigation water, N-uptake increased while fertilizer N utilization decreased. Crop water and nutrient requirements, soil type and soil fertility are important parameters to be considered in fertigation scheduling.
Abbreviations: EC electrical conductivity, VPD vapor pressure deficit
The work package deals with ways to
mitigate the deleterious effects of salinity on horticultural crops by
exploiting the climate control, crop succession and irrigation management
capability of greenhouses. In task 2.1, a literature survey scaled
yield response sensitivity
of strawberry (very sensitive), roses (sensitive), cucumber,
pepper, melon (moderately sensitive) and tomato (moderately tolerant). A
model for predicting the salt accumulation in closed-loop irrigation was
developed. The survey and the model will serve to develop a strategy for
crop successions in closed-loop systems. Three experiments, tomato in
Northern Spain, tomato in Southern Spain and
rose in Israel investigated the relation between transpiration,
salinity level of the nutrient solution and climate control obtained by
evaporating free water in the confined space of the greenhouse.
The main findings were:
1) The evaporation treatment lowered transpiration and delayed the accumulation of solutes in the re-circulated irrigation water.
2) The increased salinity of the irrigation water did not affect significantly production of tomato
3) Increased salinity in the course of a closed-loop irrigation cycle lowered transpiration.
4) The electrical conductivity (EC) of the collected nutrient solutions was higher than that of the originally prepared nutrient solutions.
The second year’s effort focused on examination of the incidence of water re-circulation strategies. The management variables are volume of irrigation solution, its initial solute load (salt and nutrients), application frequency, leaching fraction, salinity set point for bleeding, bleeding volume, and fresh solution influx volume. Four groups participated in the experiments:
IMAG studied the response of tomato to fluctuating EC adopting a partial bleeding strategy to maintain the salinity of the root medium between 6 and 9 dS m‑1 in its brackish water treatment. Yield was similar to that expected from exposure to constant salinity at the weighted average of the treatment. The salinity had no significant effect on nutrient uptake. Another experiment was aimed at minimizing salt accumulation by reducing the volume of irrigation to zero leaching fraction. The normal irrigation solution of 3 dS m‑1 of sweet pepper was replaced with a 1 dS m‑1 solution when EC in the root medium exceeded 3 dS m‑1. The reduced volume treatment had the same performance as the traditional drain collecting closed-loop system, but saved nutrient and water.
UNIPI completed the salt accumulation model when the irrigation solution is re-circulated. Experimental validations on tomato irrigated using solutions containing 10 and 20 mM NaCl agreed well with predictions. Another experiment on sweet pepper attempted to reduce exposure to salt accumulation by using subsurface irrigation, assuming that salts would redistribute by capillary rise of the solution near the surface layer of the substrate, but lower vigor and lower water consumption of the subirrigated treatment by comparison with regular drip irrigation dictates a redesign of the experiment.
CIFA-IRTA extended the study of yield response of tomato to salinity when fogging systems operate when the vapor pressure deficit exceeds 2.5 kPa, with EC treatments ranging from 2 to 6 dS m‑1. Salinity decreases the yield in high VPD treatments. Under low VPD high occurrence of blossom end rot reduced marketable yield. The group’s contribution to the study of salt accumulation was to parameterize a simplified transpiration model that accounts for the effect of VPD control, and nutrient uptake functions.
ARO-ISWES studied the effect of controlled humidity increase using a wet pad and fan system and of its consequent decrease of transpiration on salinity stress of roses. Increasing the humidity slowed salt accumulation in the closed-loop system, and increased leaf water potential. Salinity decreased stomatal conductance. The decrease of leaf area due to salinity was not significant.
Third year research activity for WP-2 continued to rely heavily on experimental work to provide more data on short and long-term the response of crops to the increased salinity resulting from the use of closed-loop fertigation. Evapotranspiration causes nutrient and sodium chloride accumulation in the irrigation solution. To manage the water and nutrient supply, UNIPI developed a salt accumulation model in Deliverable 6. UNIPI also experimented the use of subirrigation on the grounds that capillary rise would lead to salt accumulation in the top layer of the substrate where roots do not grow. The treatment resulted in lower leaching requirements and a reduction of nutrient solution loss. Climate control operations lowering the water requirements of crops to extend the tolerable level of recycled water deterioration were investigated by CIFA-IRTA and AROISWES. CIFA showed that shading had no significant effect on tomato production or quality, but reduced water consumption, increasing the water use efficiency in the high EC treatment from 19.3 to 28.6 g of fruit per liter of water used. The corresponding water use efficiency increased in the low EC treatment was from 23.0 to 37.2 g per liter. IRTA experimented the use of fogging to increase salinity tolerance of sweet pepper. Salinity depressed vegetative growth but had no significant effect on production. CIFA-IRTA checked a transpiration model for development of the management strategy and found good agreement with measurements in normal operation and under shade. The experiment at AROISWES on roses involved both shading and humidity modification by an evaporative wet pad in closed-loop irrigation with leaching set at 2.7, 4.0 and 5.5 dS m-1. The wet pad operation improved production and quality in the 2.7 and 4.0 dS m-1 treatments, but the highest productivity was achieved in wet pad - 4.0 dS m-1 treatment. Productivity deteriorates at a salinity of 5.5 dS m-1. Recirculation of the nutrient solution increased the concentration of major nutrient as well as that of NaCl.
Work package 3 deals with means to ensure that irrigation water of the lowest possible quality is used, within the constraints of an economic management of the farm. The final result of the work package is a set of rules that must form a decision support for the grower, about application of the available water resources. In fact, a grower must take “optimal” decisions about water management, within three time-horizons:
1. Long-term (strategic), that is to choose the fitting of his farm (such as rain collection; desalinisation; disinfecting), in view of local conditions;
2. Medium-term (tactic), that is to select the cropping plan in view of the fitting of the farm and of the available water;
3. Daily management (operational). That is to select which (of possibly many) water sources to use to re-fill the irrigation tank.
We have compiled the information necessary for the cost-benefit analysis at strategic level, in the form of a database containing the required information (climate, crops and economics) as is presently available in the partner countries (Task 3.1, Deliverable 7)).
We have developed and validated a model suitable for the decision-making at operational level. The model calculates accumulation of non-useful salts in a closed system and evaluates costs of discharging ions vs yield loss caused by salinity (Task 3.2, Deliverable 8).
Both the operational and the tactic level involve primarily knowledge about crop response to salinity, for which we have largely drawn from the work performed in Work Package 2, and the compilation in Deliverable 2. An additional element considered in this Work Package has been studying the feasibility of mixed cropping systems, whereby drain water from one is used as input to the other (Task 3.3, Deliverable 9).
The initial actions planned into the project were the development of two Decision Support Systems (DSS):
DSS1: A decision support for on-line water and nutrient management. This system will be based on the models developed by the actions described above and will provide an output usable by modern greenhouse computers.
DSS2: A decision support system for off-line consultation on appropriate investments for improving the water situation at the farm level, for growers’ use.
To support the implementation of models needed for the DSS2, the following tools were developed (ready for publication):
An irrigation control algorithm for accurate water use, based on transpiration model tuning on-line.
An analytical tool for using time integrated variable measurements for fitting models of Transpiration vs Environmental conditions and Nutrient Uptake vs Transpiration.
Results from WP1-3 were used to develop and compile the off-line DSS for advising the grower for appropriate investments in infrastructure of water supply and the management of it and the on-line DSS, coupled to Greenhouse Control Systems, for better management of available water sources at each specific instant along the crop life. The developed DSS combines all the works of the project and becomes the major means of project dissemination and demonstration. A working prototype of DSS1 is delivered with this final report (D12). In addition to the DSS dissemination means a number of booklets assist the dissemination on paper (D10, D14, D15, D16). Dissemination seminars have been successfully completed in several places of greenhouse interest in Greece, like Nafplion and Ierapetra.
The work has delivered a good number of conference and journal articles as well as growers’ journals and seminars. In addition to these regular dissemination publications the work is consolidated:
in a volume of Deliverables (D1-D15), all important sources of information for hydroponic cultivations in the Mediterranean region. It will be further processed and published as a book. The acquired new knowledge was delineated into rules, models and suggested “good practices” and combined with new management techniques into developing a Decision Support System (D12, D13) for growers and consultants; a valuable source for students and educators as well.
Dissemination activities such as workshops and seminars were conducted in all participating countries with major events organized
in the University of PISA (ISHS International conference, which delivered proceedings [Acta Horticulturae Νο 609, Alberto.Pardossi@agr.unipi.it], and
CIFA-Almeria 5 days’ International workshop, which delivered a textbook in Spanish [firstname.lastname@example.org].
A spinoff company [GEOMATIONS SA] has been established [www.geomations.com] and given access to the results for immediate exploitation.
Hortimed results bring new knowledge in the field of hydroponic production, which is gaining a growing importance for Med and other developing countries around the world. This is evidenced by the advances in greenhouse fertigation technologies and it is enforced by water scarcity and chemical restrictions (i.e. methyl bromide ban).
This work has aslo led to 4 MSc and 10 PhDs.