a mixing system for dissolving water soluble additive into irrigation water employs a venturi system for introduction of water soluble additive into a water stream for injection into a dispersion tank employing low speed contradirectional impellers . dispersion of the additive through the venturi and gentle yet vigorous agitation in the dispersion tank by contradirectional impellers mixes the additive without shearing of long chain polymers thereby assuring maximum efficacy for the additive solution .