Fertilisers and eutrophicationAQA A-Level Biology: Mind map

Exam questions on Fertilisers and eutrophication

1. A farmer grows wheat on the same field every year. At harvest the grain is sold off the farm and the straw is baled and removed. Soil tests show that the concentrations of nitrate ions and phosphate ions in the field fall each year.
   Explain why nitrate and phosphate concentrations fall in this field but would not fall in an undisturbed woodland.2 marks
2. A freshwater lake lies next to arable fields. In spring the farmer spread fertiliser on the fields and there was heavy rain the following week. Over the next month, a green layer of algae spread across the lake surface. By midsummer, submerged plants had died and many fish were found dead.
   Explain why the fish died after the submerged plants and the surface algae died.2 marks
3. A farmer grows potatoes in a field that slopes down towards a stream. She is deciding how much nitrogen fertiliser to apply. In a trial she applied ammonium nitrate at four rates and recorded the mean yield of potatoes: no fertiliser gave 28 tonnes per hectare, 100 kg per hectare gave 41 tonnes per hectare, 200 kg per hectare gave 47 tonnes per hectare and 300 kg per hectare gave 48 tonnes per hectare. She can also spread manure from a neighbouring farm.
   Suggest why a heavy downpour is more likely to cause nitrate to leach into the stream if she has just applied ammonium nitrate than if she has just applied manure.3 marks