Assessment of different strategies to balance high Mg levels in the irrigation water when preparing nutrient solution for soilless strawberry crops.

摘要

In some cases, the levels of dissolved Mg in the irrigation water may exceed recommended Mg concentrations for hydroponic nutrient solutions (NS) to be used in strawberry (Fragaria x ananassa Duch.) crops. In this paper, three different strategies of managing a too high Mg concentration (2.1 mM) in irrigation water when preparing NS for hydroponically-grown strawberry crops, so as to minimize crop damage by excess Mg, were compared, using also a NS with a standard Mg level (1.4 mM) as control. In particular, the excessive Mg level was: (i) either electrochemically balanced by equally increasing the sulphates, while not altering the levels of the other macrocations (Strategy I), (ii) or accompanied by commensurate increases in the K, Ca and SO₄-S levels, thereby maintaining the same K:Ca:Mgratio as in the control treatment (Strategy II), (iii) or compensated for by proportional decreases in the K and Ca levels, so as to maintain the same total salt concentration as in the control treatment (Strategy III). The electrical conductivity (EC) in the control NS was 1.8 dS m-1 but increased to 1.9 and 2.6 dS m-1 by strategies I and II, respectively. When Strategy II was applied, the fresh shoot and fruit weights decreased to 78and 84%, respectively, of those measured in the control treatment, despite the application of an optimalK:Ca:Mg ratio. These results indicate that, forstrawberry performance, the EC of the supplied NS is more important than the K:Mg or Ca:Mg ratios. The reduction of plant growth and fruit yield by Strategy II was associated with an increase of EC to 3.4 dS m-1 in the drainage solution and significant reductions from -0.57 to -0.85 MPa in leaf water potential and from -1.1 to -1.4 MPa in leaf osmotic potential, while leaf turgor pressure and relative water content were similar in all treatments. Gas exchange parameters and chlorophyll levels were not affected by the increased Mg level, regardless of the strategy used to compensate for the excess Mg in the irrigation water.