Gce Model Questions Vol1 2024 Agricultural Science Question 30

A farmer practices a 4‑year crop rotation: Year 1 - maize, Year 2 - soybean, Year 3 - maize, Year 4 - fallow. The soil initially contains \(80\) kg N ha\(^{-1}\). Maize requires \(120\) kg N ha\(^{-1}\) and yields \(6\) t ha\(^{-1}\) per \(100\) kg N applied (linear). Soybean fixes \(50\) kg N ha\(^{-1}\) and consumes \(20\) kg N ha\(^{-1}\); its yield is \(2.5\) t ha\(^{-1}\) per \(30\) kg N added (including fixation). No fertilizer is applied.\n(a) In which years will the maize crop experience a nitrogen deficiency (available N < 100 kg ha\(^{-1}\))?\n(b) Assuming yields are proportional to the nitrogen actually available to each crop, calculate the total grain yield (maize + soybean) over the 4‑year cycle in tonnes per hectare.