Models in Irrigation andWater Management - Practices of Irrigation and On-farm Water Management - page 416

(continued)

Year Yield rate (t/ha) Degree-day Rainfall (cm)

1988 1.0736 1,305 73.5

1989 0.9963 1,354 47.6

1990 1.2589 1,175 68.6

1991 1.2876 1,355 47.4

1992 1.2484 1,364 25.6

1993 1.2101 1,350 61.7

1994 1.4541 1,314 39.5

1995 1.4134 1,367 44.1

1996 1.4197 1,325 43.3

1997 1.3648 1,289 46.7

Now, we have to formulate regression based yield prediction model based on
weather variables.

10.5.5.1 Formulation

Step 1

Yield rate data are arranged corresponding to relative year. For this purpose, the
starting year of the data series is taken as year 1 (one).

Year Relative year Yield rate (t/ha)

1980 1 0.8970

1981 2 0.9725

1982 3 0.8069

1983 4 0.9285

1984 5 0.8512

1985 6 0.8797

1986 7 1.0856

1987 8 1.0334

1988 9 1.0736

1989 10 0.9963

1990 11 1.2589

1991 12 1.2876

1992 13 1.2484

1993 14 1.2101

1994 15 1.4541

1995 16 1.4134

1996 17 1.4197

1997 18 1.3648

Step 2

Plot the yield data against the relative year value, yield being the dependent variable.
The slope of the regression line represents the “trend.” From the below figure,
the trend (slope) is 0.0369 t/ha/yr.