Questions 1. Draw the TPP and MPP curves for the three sites in the table. 2. Rainfall and the amount of nitrogen naturally occurring in the soil will cause differences in the position of the TPP curve between sites. One will cause vertical differences in the curves and one will cause horizontal differences. Explain which one causes which effect (and why). . Apart from gures on yields, what else will a farmer need to know before deciding whether to use 600 kg/ha of nitrogen fertiliser