Predicting crop growth and aphid incidence in Brassica under semi-arid environment

Abstract

A field experiment was conducted in the sandy loam soils to predict crop growth parameters and aphid incidence in
Bassica using spectral reflectance and meteorological data. Three Brassica oilseed species, viz 'BO 54'(Brassica napus
L.), 'Pusa Bold' Indian mustard (Brassica juncea L.) and 'T 9' toria (Brassica campestris L.) were sown on three dates
at 14-day intervals starting from third week of October to create different photo-thermal environments during crop
growth period. The intercepted photosynthetically active radiation and 4 spectral indices, viz (Infra red / red ratio, normalized
difference, greenness index and brlghtness index) were derived to correlate plant growth parameters with these indices.
The intercepted photosynthetically active radiation was found to be. well correlated with biomass with the
correlation coefficient varying from 0.71 to 0.92 in different cultivars and sowing dates. It was found from correlation
study among different spectral and plant growth. paratmeters that there was strong relationship (at 5%  level of significance)
between infra red / red ratio, normalized difference and leaf area indexfor all  the 3 Brassica cultivars. On the other hand,
the brightness and greenness indices were more closely correlated (at 50% level of significance )with above ground biomass
as compared to infrared/red ratio and normalized difference. Model regression equations were also derived to forecast
aphid incidence in Brassica with most significant Weather variables. The aphid populations were found to be correlated
with maximum temperature, minimum temperature £tnd afternoon relative humidity with the correlation coefficients
varying from 0,67 to 0.90 for different cultlvars and sowing dates.