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

The salinity-nitrate (NO 3 - ) leaching paradox is an increasingly important issue in soil-grown intensive vegetable production systems in drier regions. Traditional management of either salinity or NO 3 - leaching promotes the other. This is an issue in the greenhouse vegetable production system of Almeria where legislation requires reduced NO 3 - 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 NO 3 - . 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 (EC ss ) 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 [NO 3 - ] of the NS was reduced to 50 %. This was restored to 100 % when monitoring of crop N status, using petiole sap [NO 3 - ], 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 EC ss was reached (LF-NS), and (iv) the control where no LF was applied (CT). With LF-W&RN unlike other strategies, EC ss was always within or very close to the threshold EC ss , 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-NO 3 - leaching paradox in intensive vegetable production. • The salinity-NO 3 - leaching paradox is a problem in intensive vegetable production in drier regions. • Strategy was developed to deal with paradox by monitoring soil solution EC (ECss) and crop N status as petiole sap [NO 3 - ]. • This strategy maintained acceptable ECss, and reduced amounts of N applied, and N loss compared to other strategies. • Successful use of this monitoring-based strategy is “proof of concept” for managing the salinity-NO 3 - leaching paradox.