Question

The table shown is the detail for consumptive requirments for a certain crop having crop factor 0.75, using Blaney-criddle formula, determine the field irrigation requirement if water application efficiency is 0.7.

Month	Avg.monthly temperature (${}^0$C)	Month% of Sunshine hours	Useful rainfall (cm)
Nov.	19	7.19	-
Dec.	16	7.15	1.2
Jan.	12.5	7.30	0.8
Feb.	13	7.03	-

• A. 42.6 cm
• B. 45.5 cm
• C. 51.4 cm
• D. 57.8 cm

Answer 1

The correct option is A 42.6 cm

Month	t${}^0$C	p	$R_e$	$f=\frac{p}{40}(1.8t+32)$
Nov.	19	7.19	-	11.90
Dec.	16	7.15	1.2	10.87
Jan.	12.5	7.30	0.8	99.5
Feb.	13	7.03	-	9.74

$\sum =42.46$
$C_u=0.75\times 42.46=31.84cm$
$R_e=1.2+0.8=2cm$
$NIR=C_u-R_e=29.84cm$
$FIR=\frac{NIR}{{\eta }_a}=\frac{29.84}{0.7}=42.63cm$