data a;
set soil;
proc glm order=data;
class soil_type trt_combinations;
model IRoR=soil_type trt_combinations;
means trt_combinations/tukey;
run;
proc glm order=data;
class Nitrogen Base_Rate_Percentage soil_type;
model IRoR=soil_type Nitrogen|Base_Rate_Percentage;
means Nitrogen|Base_Rate_Percentage/tukey;
run;