A little bit often gives the best results.

On soil/pasture once or twice per year – Spring and Autumn

Through fertigation – a little bit each watering or every second watering whatever suits best. Small amounts often are better than larger infrequent lots.

On foliar – horticulture and vegetables an application is best about every 2-3 weeks.

Home gardeners – once per fortnight on vegetables. Roses every 2-3 weeks.

(This cannot be practical for commercial applications.)