An investigation into the effects of various levels of nitrogen conducted by a the agricultural department at a state university addressed the pounds per acre of nitrogen required to produce certain yield levels of corn on fields that had previously been planted with other crops. Suppose the data in the file titled Nitrogen indicate the amounts of nitrogen required to produce given quantities of corn planted.

a. Determine if there is interaction between the yield levels of corn and the crop that had been previously planted in the field. Use a significance level of 0.05.

b. Given your findings in part

a, determine any significant differences among the average pounds per acre of nitrogen required to produce yield levels of corn on fields that had been planted with corn as the previous crop.

c. Repeat part b for soybeans and grass sod, respectively.