Soil fertility management in organic greenhouse crops; a case study on fruit vegetables

In the EU regulation, confirmed by IFOAM, soil is considered to be connected to the subsoil, therefore soil-less culture is not included in the scope of this paper. Soil fertility is a complex matter, since this term is related to soil physics, minerals and biological characteristics and each of these parameters is important. One of the key issues in organic production is the approach to soil and soil fertility. This is evident in the EU regulation on fertilisers and organic soil amendments used in organic food production, which details restrictions on crop production. The goal in organic production is equilibrium between the production capacity of the soil and other production factors, rather than maximising yields, and the input of manure, compost and mineral fertilisers is constrained by regulations. Conversely, greenhouse crops are characterised by high production levels which are considered necessary to recoup investment costs, and consequently require high nutrient inputs, which conflicts with the basic organic intentions. Leaching in open field production is of concern, but in greenhouse horticulture, it can be fully controlled, since precipitation is excluded. The growing period for fruit vegetable crops is too long for all nutrients to be supplied by base dressings alone, as adding the amount of fertiliser required to supply season-long nutrients would result in excessive levels of soil nutrients and electrical conductivity (EC) values would be too high. Soil N-dynamics must also be considered, as N-immobilisation will result in poor N supply to the crop, and rapid N-mineralisation creates a risk of N losses through leaching and too much vegetative development. Therefore, top dressings in the form of rapid mineralising fertilisers are indispensable. Over-fertilisation and leaching of N and P should be negative, but also can be avoided by fine-tuning nutrient supply and demand, in combination with advanced irrigation scheduling. Therefore, the fertilisation plan should have a balanced approach, taking into account the ratios of all individual macro-nutrients, as well as considering the inputs of undesirable residual salts like Na, Cl and SO4 and using predictive models for crop demand and N delivery. Additional regulations on mandatory restrictions for top dressings will soon come into effect, making balanced fertilisation complicated and possibly leading to undesirable lower nutrient use efficiencies