If we want to compare the effects of both fertilizer consumption and irrigated area, we should do multiple regression. A linear multiple regression analysis leads to the following results.

y = 442.21 + 35.94 F + 13.26 I (for the entire period)

= 538.2 + 51.15 F - 1.71 I (1956-1970)

= 800.83 + 7.64 F + 3.7 I (1970-1989)

This shows that the effects are marginal. Again no firm conclusion can be drawn from this, since available data are not adequate enough to arrive at accurate analysis.

Similar regression analysis for production gives us the following relationship:

P = -98.26 + 2.207 A + 0.28 F - 0.09 I + 0.0219 R

where A - total area, R - rainfall

We can see from the above that we are getting marginal increases from irrigation and fertilizers. We need to improve our practice through the use of environmentally and ecologically sound methods so that long term yields also improve.