RISPOSTA DEL COTONE ALLA COMPETIZIONE CON AMARANTO (Amaranthus retroflexus L.) IN PRESENZA DI SALINITÀ SODICA

Effects of increasing levels of sodicity (NaCl) on growth and yield of cotton (Stroman 75) in pure stand or in competition with redroot pigweed (Amaranthus retroflexus L.) were evaluated. Experiment was carried out in plastic pots according to a replacement design. ECe levels were: 0.5 (control), 8, 16 and 32 mS cm-1. Results stressed that starting from 30 days after transplanting, cotton growth was negatively affected by weed presence. When ECe of 16 mS cm-1 was applied, competition reduced plant height and leaf number by 35 and 50% respectively compared to control. When in competition and in presence of ECe of 8 and 16 mS cm-1 capsule number per plant was higher compared to the cotton in pure stand. Competition ability of cotton was lower when watered with control and in presence of ECe of 8 mS cm-1. Amaranthus competition significantly affected only Mg++ uptake while total N, Na+ and Cl- content were not influenced. NaCl increase uptake of all ions both for cotton and redroot pigweed. The weed accumulated high quantities of Na+ and Cl- : 58 and 11 times higher respectively compared to control. Stroman 75 can be considered a salt tolerant genotype but susceptible to Amaranthus competition already during the early growth stages and in absence of sodicity. Yet, weed presence reduces negative effects of NaCl at higher ECe on cotton productive characteristics. This effect can be ascribed to the capability of Amaranthus in absorbing high amounts of Na+.