Amelioration of salt stress by irrigation management in pepper plants grown in coconut coir dust

A long-term greenhouse experiment was conducted to study the effects of irrigation frequency and salinity on pepper fruit yield and quality in crops growing in coconut coir. Two salinity levels (4 mM NaCl, 2.6 dS m-1 and 24 mM NaCl, 4.6 dS m-1) were combined with four irrigation treatments (one irrigation event every two days (0.5), one irrigation event per day (1), four irrigation events per day (4), and eight irrigation events per day (8)) in a 2 x 4 factorial combination. The effect on fruit quality was evaluated at the early and late harvest seasons, corresponding with two different periods of fruit production (May and July). We found that above-ground total biomass and marketable fruit yield decreased in the salinized treatments. When salinized (24 mM NaCl) nutrient solution (NS) was applied, increasing the number of irrigation events to eight per day resulted in a decrease in the incidence of blossom-end rot and a corresponding increase in the marketable fruit yield. When control (4 mM NaCl) NS was applied, one irrigation event per day yielded as much marketable fruit as was produced with the highest irrigation frequency, and therefore increased water use efficiency, expressed as marketable fruit weight per L of NS applied. When NS containing 24 mM NaCl was used, there was an increase of Cl- but not Na+ in the leaf tissue, with this increase reaching its maximum in the treatment involving eight irrigation events per day. Salinity decreased the Ca2+ concentration of the fruit only in the early harvest season of production. However, increasing irrigation frequency consistently resulted in higher Ca2+ concentration in the fruit. The effects of salinity on the morphological and organoleptic properties of the fruit were more pronounced in the late harvest season.