Overcoming the salinity and nitrate leaching paradox in soil-grown pepper in mediterranean greenhouses

The salinity-nitrate (NO3-) leaching paradox is an increasingly important issue in soil-grown intensive vegetable production systems in drier regions. Traditional management of either salinity or NO3- leaching promotes the other. This is an issue in the greenhouse vegetable production system of Almeria where legislation requires reduced NO3- leaching and on-going salinisation of aquifer water, used for irrigation, is an increasingly serious problem. In this cropping system, complete nutrient solutions (NS) are applied in every irrigation (every 1–4 days), most N is applied as NO3-. A management strategy, called Leaching Fraction of Water and Reduced N (LF-W&RN) developed to deal with this paradox was examined in two greenhouse-grown sweet pepper crops. After the EC of the soil solution (ECss) had increased to a specified maximum threshold value, a leaching fraction (LF) of water was applied immediately prior to each irrigation with NS. Concurrently, the [NO3-] of the NS was reduced to 50 %. This was restored to 100 % when monitoring of crop N status, using petiole sap [NO3-], indicated imminent N deficiency. This management strategy was compared with: (i) application of a LF of water before every irrigation with NS throughout the crop (CLF-W), (ii) application of a LF of NS with all NS irrigations after the threshold ECss was reached (LF-NS), and (iv) the control where no LF was applied (CT). With LF-W&RN unlike other strategies, ECss was always within or very close to the threshold ECss, and appreciably less N was applied. Additionally, appreciably less N was leached and accumulated in soil as mineral N. Yield and fruit quality were very similar for the four strategies in the two crops. The results with the LF-W&RN strategy incorporating on-going monitoring of soil salinity and crop N status can be regarded as “proof of concept” of an effective general approach for dealing with the salinity-NO3- leaching paradox in intensive vegetable production.