So, it says 3-4 kg per hectare which is 1000 square meters. If we want to say 3.5 kg (3500g) per 1000sq.meters we get 3.5 g per square meter. That's about 3/4 of a teaspoon per square meter.
I know I am mixing weights and volumes with the teaspoon measure but its a guess. You would have to weigh it to get accurate measure.