The use of fertigation, coupled with micro-irrigation, has continued to increase since it was first introduced in horticultural cropping systems. This combination provides a technical solution whereby nutrients and water can be supplied to the crop with high precision in terms of time and space, thereby allowing high nutrient use efficiency. However, the correct estimation of crop nutrient and water needs is fundamental to obtaining precise plant nutrition and high nutrient use efficiency in fertigated cropping systems. This paper illustrates the state-of-the-art and new perspectives for optimal nutrient management of vegetable crops cultivated under fertigation regimes. An overall description is reported for the most valuable technologies and techniques based on simulation models, soil testing, plant testing, and related decision support systems that can be adopted for efficient fertigation. However, it should be highlighted that only a few of the above technologies and techniques are practically available and/or easy to use by growers. Therefore, much more attention should be paid in the future to the transfer of research knowledge to farmers and technical advisors.

New Trends in the Fertigation Management of Irrigated Vegetable Crops

In intensive vegetable production, N fertiliser applications often contribute to a supply of N that appreciably exceeds crop N requirements resulting in the loss of N to the environment which can result in NO3− contamination of water bodies. There is a range of tools and strategies that can assist vegetable growers to improve N management. These include various methods based on soil analysis or estimation of the soil N supply, N balance calculations, methods based on plant analysis, methods based on monitoring crops with optical sensors, and the use of computerised decision support systems based on simulation models or data bases. Use of these tools has been demonstrated to appreciably reduce fertiliser N application and N losses while maintaining production. The selection of tools to be used by a grower will be influenced by factors such as availability, the grower’s technical level, and economic considerations. For fertigation systems with high frequency N application, a combination of a planning method such as a decision support system with a monitoring method is recommended. Additional tools that can assist in demonstrating to stakeholders the benefit of improved N management are simulation models that provide scenario analysis. Fundamental strategies for improving N fertiliser management are to consider all N sources such as root zone soil mineral N and N mineralised from organic materials, and to partition N application so that it coincides with crop N demand.

Tools and Strategies for Sustainable Nitrogen Fertilisation of Vegetable Crops

Monitoring nitrogen status of vegetable crops and soils for optimal nitrogen management

Fertigation in combination with drip irrigation is being increasingly used in vegetable crop production. From a nutrient management perspective, this combination provides the technical capacity for precise nitrogen (N) nutrition, both spatially and temporally. With these systems, N and other nutrients can be spoon-fed to crops, through frequent applications of small amounts, to the immediate root zone as required by the crop. In commercial farming practice, management of combined drip/fertigation systems generally does not take advantage of this potential for precise N management. As is common in commercial farming, management of both irrigation and N with drip/fertigation systems is generally based on growers' experience, with the objective of avoiding deficiencies that may limit production. Because of frequent N application, the established improved nutrient management strategies, based on infrequent soil testing, pre-plant and one or two side-dress applications, are of limited value. With drip/fertigation, dynamic N management approaches are required so that the capacity for frequent small applications can be fully exploited to provide (a) site and season specific management and (b) dynamic responses to temporal N requirements. Dynamic irrigation management is required for the same reasons. Modelling and monitoring approaches and combinations of the two enable exploitation of the technical capacity for precise N and irrigation management. Decision support systems (DSS) based on simple simulation models with limited data inputs can provide crop specific plans of daily N and irrigation requirements. The use of soil moisture sensors is an effective and proven monitoring approach for irrigation management. For monitoring of soil/crop N status, soil monitoring through regular sampling of soil-water extracts and soil solution is being used, and crop/plant monitoring approaches such as with proximal optical sensors and petiole sap analysis are promising methods.

Sustainable irrigation and nitrogen management of fertigated vegetable crops.

Agriculture consumes maximum water of up to 70% of the total fresh water withdrawn in the world for consumptive purposes Rapid population growth is further driving fresh water demand and putting tremendous stress on limited fresh water resources This increasing demand can only be met by improving the current water use efficiency and by creating new water sources Desalination could therefore play a significant role in creating a new water source by using unlimited saline water sources However, current desalination technologies are energy intensive and energy has a significant impact on climate change If low cost desalination technologies were made available, their impact on agriculture sector would be significant for many water stressed regions of the world
Recently, forward osmosis (FO) has been recognised as one of the most promising low energy processes for desalination The FO process is based on the principle of natural osmotic process driven by the concentration gradient and not by hydraulic pressure like the reverse osmosis (RO) process and hence requires significantly lower energy In the FO process, a concentrated draw solution (DS) extracts fresh water from the saline water using special membranes The issue of membrane fouling in FO process is less challenging than the RO process where fouling constitutes a major operating issue However, the lack of a suitable DS has limited the application of FO desalination for potable water The separation of draw solutes from the diluted DS after desalination requires additional post-treatment processes that still consume energy, making FO uncompetitive with the already established RO desalination technology
The FO process offers novelty for those applications where the complete separation of draw solutes is not necessary and where the final diluted DS can be used directly if the presence of draw solutes adds value to the end use Fertiliser drawn forward osmosis (FDFO) desalination for fertigation is therefore proposed based on this concept When fertilisers are used as the draw solutes in the FDFO desalination process, the diluted fertiliser solution after desalination can be directly applied for fertigation because fertilisers are essential for plants This concept avoids the need for an additional post-treatment process for the separation and recovery of draw solutes The objective of this study is therefore to investigate the performance of the FDFO desalination process for fertigation, identify its limitations and investigate options to overcome these limitations The study has been presented in eleven chapters that include a definition of the detailed concept and an assessment of the performance of eleven selected fertilisers as the DS under various conditions, through both simulation and bench-scale experiments
The energy required for FDFO for direct fertigation was estimated to be less than 024 kW/m3 of fertigation water, which is comparatively lower than the most efficient current desalination technologies As such, FDFO can also be easily powered…

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A novel fertiliser drawn forward osmosis desalination for fertigation

Efficient fertilizer and water use is becoming increasingly important in greenhouse vegetable production in Greece. To improve greenhouse irrigation and fertilization practices, a fertilization management program developed in The Netherlands was tested in plasticulture under Mediterranean conditions in Greece. Soil was analyzed according to the 1:2 volume water extract method, and recommendations for preplant fertilization, and the amount and concentration of fertigation determined. Calcareous soils, high in clay content, absorbed potassium. Soils low in organic matter content were also low in water holding capacity. Due to these low water contents at field capacity, and the standard ratio of soil:water in the 1:2 volume water extractions, soil solution was diluted 6-13 times, which was higher than in soils with high water holding capacity at higher organic matter contents. It was concluded that the fertilizer recommendations developed under Dutch glasshouse conditions were useful under plasticul...

Development of Fertigation for Trickle Irrigated Vegetables Under Mediterranean Conditions

Responses of young olive (‘Koroneiki’) plants treated with organic and inorganic fertilizers

The application of nutrient solutions to the foliage of plants is an alternative means to fertilise crops. Foliar fertilisation is used to overcome the disadvantages of soil applications. Variable plant responses to these foliar fertilisation spray solutions have often been described in the literature. However, knowledge about the penetration mechanisms, the role of a leaf-applied inorganic or organic solution, and the results obtained by its application is still limited. The complex character of the factors determining the effects of sprays hinders the development of suitable foliar fertilisation strategies, applicable under variable local conditions and for various plant types. This review describes some basic factors involved in the penetration process of foliar sprays in olive (Olea europaea L.) trees. Chemistry, leaf penetration, and plant nutrition principles will be merged with the aim of clarifying the constraints, opportunities, and future perspectives of sprays to cure olive tree nutrient deficiencies and, hence, both increase the yield and improve the fruit quality. 

V. Kavvadias

Papers

Development of Fertigation for Trickle Irrigated Vegetables Under Mediterranean Conditions

Responses of young olive (‘Koroneiki’) plants treated with organic and inorganic fertilizers

Inorganic and organic foliar fertilization in oliveS