Site description and data collection
The study site was Mymensingh, Bangladesh. Solar radiation and other climatic data were collected from Bangladesh Meteorological Department. Yield data was taken from the Annual Report of Bangladesh Institute of Nuclear Agriculture (BINA, 2003 and 2004).
Dry matter calculation
Dry matter production for a particular crop season was calculated as (Adapted from Ghuman and Singh, 1993):
DM = AE x Ep x Cd ................................................ (1)
Where, DM = dry-matter production, Mg/m2-day
AE = available solar energy, MJ/m2-day
Ep = photosynthetic efficiency
Cd = energy needed (MJ) to produce 1 gm dry-matter
For field crop, photosynthetic efficiency (Ep) was taken as 6.6 %, and energy needed to produce 1 gm dry-matter of field crop was taken as 4226 cal (0.01768 MJ) (Mitsui et al., 1977).
The increased production percentage (Pp) was calculated as:
Pp = 100(Production gap between potential and present drymatter )/ (Present drymatter production)
Calculation of atmospheric (extraterrestrial) radiation
The extraterrestrial radiation was calculated following the procedure of Smith et al. (1992).
Calculation of day-length or photo period
The photo-period for different locations were calculated from solar equations. The declination <span style="mso-bidi-font-size:11.0pt; line-height:115%;font-family:Symbol;mso-ascii-font-family:" times="" new="" roman";="" mso-hansi-font-family:"times="" roman";mso-bidi-font-family:"times="" mso-char-type:symbol;mso-symbol-font-family:symbol"="">d, defined by Hunt (1982), as the angle of the sun north or south of the equatorial plane, can be found from the approximate equation of Cooper (1969).
Crop season
Two crops were reported in cropping pattern for Mymensingh, Boro (Jan. – May.) and T. aman (July -Nov.) [BINA, 2004]. The effective growth period (for capturing solar energy) for Boro was taken as 121days of growth period (out of 155 days) and for T. aman it was taken as 108 days (out of 135 days of growth period).