Analysis Using SAS 

The analysis of the data is performed using PROC RSREG of SAS. The SAS commands are given in the sequel.

Data Input:

For performing analysis, input the data in the following format. 

{Here the two factors are termed as N and S. It may however, be noted that one can retain the same name or can code in any other fashion}.

Prepare a SAS data file using

data rsd;

input N S yield;

cards;

0          0          4121.212

0          20        4678.03

0          40        4742.424

0          60        4727.273

50        0          6083.333

50        20        6041.667

50        40        6223.485

50        60        6715.909

100      0          6761.364

100      20        6916.667

100      40        6852.273

100      60        6810.606

150      0          6174.242

150      20        7022.727

150      40        7003.788

150      60        6943.182

;

/* To fit a second order response surface design and to obtain the co-ordinates of the stationary point and also to find the nature of the stationary point use the following statements.*/

proc rsreg;
model yield=N S/nocode;      /*NOCODE performs the canonical and ridge analysis with the parameter estimates 
                                                derived from fitting the response to the original values of the factors variables, rather than  their 

                                                coded values.*/  

run;

NOTE: If the experiment is conducted using a RCB design for more than one replication perform ANOVA and test the significance of replication effects. If replication effects are founded to be non-significant use the average yield for fitting a response surface otherwise replication effects are to be defined as covariates. For defining covariates, please use the linearly independent contrasts. For optimization purpose, however, optimum is obtained at average level of covariate. It is better if soil status can be taken as covariate rather than replication.