The Almeria greenhouses are located in a region declared by the EU to be a Zone Vulnerable to Nitrate Contamination (ZNV)The company also has regional legislation in place to reduce both nitrogen fertilizer inputs to crops and associated environmental pollution.

This is the context in which the AGR224 Intensive Horticultural Systems Research Group and Ciaimbital, the University of Almeria's own Center for Research in Agri-Food Biotechnology. Specifically, and focused on the greenhouse cucumber crop, they have studied its response to the inputs of this fertilizer (N), knowing, from previous studies, that farmers follow standard recipes in the planning of fertilization, which means not taking into account the residual nitrogen present in the soil from previous seasons or the mineralized from manure or other organic matter inputs. That said, in the greenhouses of Almeria, N inputs are high in relation to crop needs.

The fieldwork was carried out in the UAL-Anecoop Experimental Station with three trials, each in a different growing season: autumn-winter, early spring and late spring. In all of them commercial cucumber varieties were used and in the late spring trial three different varieties were compared. In each of these trials, increasing doses of N were applied in fertigation. The study concludes that for a cucumber crop in a greenhouse with a usual cycle of 70-84 days, an N input of 230 kg ha-1 is recommended, but that, if there is residual mineral N or previous organic matter inputs, it is advisable to estimate these amounts and subtract them from the given recommendation, making up the difference. To perform these calculations, it is recommended to use the VegSyst-DSS software application developed by the working group. The transfer of the results of the study concludes that the N limits of 4 kg N t-1 (ton of fresh fruit) recommended in the regional action plans of the Junta de Andalucía, designed to implement the nitrate directive, are excessive and could be reduced by approximately half, to values around 2 kg N t-1.

This study has been prepared by Marisa Gallardo, Francisco Padilla, Teresa Peña-Fleitas, Romina de Souza, Alejandra Rodriguez and Rodney B. Thompsonand has been published in the magazine European Journal of Agronomya highly prestigious, titled '.Crop response of greenhouse soil-grown cucumber to total available N in a Nitrate Vulnerable Zone.'. It is part of a line of research by the group to determine the optimum amounts of this nitrogen fertilizer.

Nutrient associated with aquifer contamination

The group has chosen N because it is the nutrient applied in greater quantities and is associated with aquifer contamination, and this research is trying to provide solutions that optimize production and minimize nitrate losses to the environment. It should be added that the recommended amounts of fertilizer do not change between crop cycles nor between varieties, and given that in the greenhouses of Almeria nutrients are applied in nutrient solutions, the fertilizer recommendations of 230 kg ha-1, assuming that there is no residual N in the soil and that there have been no contributions of organic matter (soil = inert substrate), would correspond to nutrient solutions with N concentrations of 11.9 mm L-1 for the autumn cycle, 9 mm L-1 for the spring cycle and 6.5 mm L-1 for the late spring cycle.