With a 'payload' of just 16 litres, I don't think it will replace an aircraft - and with existing battery technology I can't see an ability to scale up to a useful broadacre payload in the near future.
That said, I believe drones have a big future in agriculture. Certain chemicals can be applied at ultra low rates, but more interestingly, there is plenty of existing tech that allows very precise targeting. For example, instead of 'blanketing' a field with glyphosate (Roundup), ground rigs can now target individual weeds, reducing chemical use by up tp 90%. When this kind of tech is applied to drones, I think we'll see a revolution in aerial agriculture.