Effectiveness of Trichoderma harzianum in soil and yield conservation of tomato crops under saline irrigation

Protected horticultural crops in the Mediterranean region are typically under deficit irrigation and intensive cultivation practices and must cope with poor irrigation and soil quality due to salinization. The effects of variable irrigation water quality and use of the beneficial fungus Trichoderma harzianum on the evolution of soil salinization and yield during a single cropping season are examined at a small-scale Solanum lycopersicum L. cv Elpida greenhouse experiment. The experiment simulates typical coastal Mediterranean greenhouse cultivation conditions of the RECARE Project soil salinization Case Study in Greece (Timpaki basin in Crete). Local NaCl-free but highly calcareous planting soil as well as local cultivation practices were used to replicate prevailing conditions at the Case Study. Tomato plants were drip irrigated with NaCl solutions of low (L) (ECw = 1.1 dS m−1) and high (H) (ECw = 3.5 dS m−1) concentration to emulate a typical “good quality” and “marginal quality” irrigation water, respectively. T. harzianum (T) was selectively applied resulting in a total of 2 treatments colonized with the fungus (LT, HT) and two not (N) colonized (LN, HN). For high salinity irrigation treatments HN and HT, sodium adsorption ratio (SAR) values settled at 22.2 and 13.4, respectively, showing that T. harzianum reduced the effect salinity significantly. Monitoring of soil nutrients showed a significant decrease of P-Olsen in non-T. harzianum treatments versus no change in P-Olsen in T. harzianum treatments. Final total and marketable tomato yield for treatment HN were reduced compared to LN by 28% and 42%, respectively, with in T. harzianum treatments having no significant effect. Fruit quality characteristics were overall less sensitive to higher irrigation salinity than to timing of harvest. We conclude that, under high salinity irrigation, an early harvest and termination of the cultivation has no significant impact on tomato yield while obviating pressure on soil resources and conserving agricultural input.