Alteration of physical properties of substrates and accumulation of nutrients in strawberry hydroponic systems (Fragaria x ananassa Duch.)

The main thesis of this research is that when hydroponic substrates are submitted to continuous irrigation with a nutrient solution (NS), they show different rates of changes in their physical and chemical properties, and in their nutrient availability. Three substrates common in Mexico (tezontle volcanic rock, perlite, and coconut fiber) were used to test the hydroponic production of strawberries (Fragaria × ananassa Duch) cultivar 'Festival', without NS recirculation. A tower system was established with 16 plants per square meter, 2.5 L of substrate per plant, and 110 mL of NS plant^-1 day^-1. A Steiner solution with 20% lixiviates was applied; the concentration of N, P, K, Ca, and Mg (mg L^-1) was determined, as well as particles size, through sieve analysis, and foliar nutrient extraction curves; physical and chemical properties were compared at the beginning and the end of the crop cycle. Tezontle and perlite showed no significant differences in bulk density (Bd) and total porosity (TP), while aeration capacity (AC) increased in the coconut fiber and tezontle. Only tezontle increased the easily available water (EAW) but all increased the hardly available water (HAW): 9.98, 12.32, and 3.59% in coconut fiber, perlite, and tezontle, respectively. The chemical analysis of lixiviates showed higher content of K, Ca, and Mg and lower content of P in all substrates. After one cycle use, the results indicate that the physical alterations of substrates were small in general; however they showed different trends or intensity of alteration. Their interaction with the NS promoted changes in the nutrients contents for each substrate; the low amount of HAW and high amount of EAW in tezontle may be an indicator of a high concentration of Ca and Mg in lixiviates, while the coconut fiber showed greater interaction with the NS, which suggest high nutrient immobilization, especially Ca and Mg.