The present invention provides a concentrate for dilution with water in the preparation of an agricultural composition for application to crops, soil or animals. The concentrate is recommended for use with agricultural chemicals whose agricultural activity varies with the pH of the water. It comprises an active ingredient and a combination of pH indicators for colouring the water, the pH indicators being selected so as to indicate different colours of spray water at different pH levels. The proportions of active ingredient and pH indicators are selected so that when the concentrate is added to water, the pH indicators indicate visually upper and lower pH limits for optimum activity of the agricultural chemical.