dates of sowing i.e. D,-25" November D2-10" December, D;3-
25^ December and four nitrogen levels viz: NO-No nitrogen,
N,-50 percent, N,-100 per cent, N3-150 per cent of the
recommended dose(120 kg N per hectare), and five varieties
viz:V,-WH 542,V,-PBW 343,V;-UP 2338,V,-Raj 3765,
V;-Sonak. The experiment was laid out in a split plot design
with different dates of sowing, different nitrogen levels to main
plots and different varieties to subplots with three replications.
Recommended agronomic package of practices for irrigated
wheat were followed.
Multi-band spectral data was recorded with help of hand held
spectro-radiometer (Model-41) developed by Space Application
centre (SAC) Ahmedabad. The spectral reflectance was
recorded at one meter height above the crop canopy. Standard
readings (100% reflectance) were taken keeping the sensor over
Barium Sulphate plate. Percent reflectance values were
computed by dividing canopy reflectance with that of standard
one. These observations were taken on cloud free days between
1100-1200 hrs 30 days after sowing upto harvest at 15 days
intervals. Spectral indices were calculated at different stages by
using following formula:
Simple subtractions (SSb) =IR-R (Pearson et al., 1976).
Normalized difference (ND)
= (IR-R) / (IR+R) (Rouse et al., 1973)
Perpendicular vegetation index (PVI)
=v (Rsoil - Rveg) 2 + (IRsoil - IRveg)*
(Richardson and Weigand, 1977)
Greenness index (Gn)
= -0.29 (G) - 0.56 (R) + 0.60 (NIR) + 0.49 (MIR)
(Kauth and Thomas 1976)
The agronomic parameters, leaf area index(LAI) and total dry
biomass, were measured concurrently with spectral data at an
interval of 15 days starting from 30 days after sowing onwards
to physiological maturity. The grain weight was recorded from
the crop harvested from a net area of 1.4m*2.2m in each plot
and converted into g¢/ha. Photosynthetic pigments were
estimated according to the method of Hiscox and Isractstam
(1979) using dimethyl sulphoxide (DMSO). Calculation for Chl
a and b and in pmol/g dry weight were made according to
equation developed by Anderson and Board man (1964).
(12.3 X A 663 - 0.86 x A45)
Chla = x 5 ml = mg/g F.wt of leaf
1000x wt of sample
(19.3 X A45 -3.6x A663)
Chl b = x 5ml- mg/g F.wt of leaf
1000x wt of sample
Total chlorophyll = Chl a + Chl b
The wax content was estimated as per the procedure adopted by
Silva Fernandes et al. (1964).
RESULTS AND DISCUSSIONS
The experimental results of different aspects are given below:
Crop Parameters
Leaf area index (LAI)
IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002
The perusal of data indicates that LAI increased with the
advancement of crop age in respect of all treatments up to 90
days after sowing (DAS) and it decreased thereafter Tablel.
The LAI differed significantly with different date of sowing
and different doses of nitrogen. The maximum LAI was
observed at 90 days after sowing in all treatments. The LAI was
higher when the crop was sown on 25^ November and lower in
the 25" December sown crop. Bishnoi et al. (1996) reported
higher values of LAI for wheat in optimum date of sowing 25th
November as compared to the delayed one. The photosynthetic
potential manifested a huge improvement numerically with
enhancing level of nitrogen fertilizer. The application of
nitrogen (9 180 kg ha”! (N3) increased the LAI significantly
over lower nitrogen (N) rates at all the stages. The maximum
LAI was in N4 and minimum was in Nj treatment. Among the
varieties the LAI was highest in PBW343 followed by UP2338,
WH542 Raj 3765 and Sonak. In cultivars also LAI increased
with advancement of growth up to 90 DAS then decreased upto
maturity. Singh et al. (19952) also observed that leaf area and
leaf weight were highest in WH803 and lowest in WH108
among 4 wheat varieties at different stages of crop growth. The
LAI is very useful parameters in studying the radiation
interception for the quantification of accumulation of dry matter
and growth of the crop. Maximum value of LAI reached in
first date of sowing due to the fact that elongated vegetative
phase added more foliage to the crop growth as compared to
delayed sowing where the forced maturity due to high
temperature and vapour pressure deficit led to occurrence of
phenophases quickly and life cycle of the crop became shorter.
DRY MATTER PRODUCTION
The data on dry matter production (gm?) under various
treatments are presented in Table 2 and which reveal that it
increased with the advancement of crop age and maximum
increase was observed at 90 DAS and at harvest. Among the
sowing dates 25th November sown crop produced higher dry
matter as compared to the 10th and 25th December sown crop
at all the phenophases. This might be attributed to maximum
LAI. Further delay in sowing resulted in reduction in dry
matter accumulation. Irrespective of fertility levels, the dry
matter accumulation was statistically significant with increasing
nitrogen levels. The highest dry matter accumulation was
observed in N3 (180 kg ha!) and lowest in Ng (No nitrogen)
treatment. This was due to highest LAI recorded in wheat
fertilized with 180kg N ha" Singh et al. (1998) reported the
variation of dry matter accumulation was influenced by
different nitrogen doses. Among the varieties the dry matter
accumulation was statistically significant at all phenophases.
The highest dry matter accumulation at all the phenophases was
in PBW343 and followed by UP2338, WH542, Raj 3765 and
Sonak (Table2). Singh et al. (1995a) reported more dry matter
accumulation in variety WH803 than WH157, WH283 and
WH108. Dry matter of variety Raj3765 significantly higher
than var. Sonak. The dry matter at harvest was 1252.5, 1217.3,
1161.2, 1110.3 and 1086.6 gm/m2 in var. PBW343, UP2338,
Wh542, Raj3765 and Sonak, respectively.
YIELD
The grain yield showed a significant difference among sowing
dates. The maximum yield was recorded in D, followed by D;
and D3. The yield of D1 is significant higher than D2 The
decrease in yield with delay in sowing of wheat was attributed
