Thermal indices in relation to crop phenology and seed yield of pigeon pea (Cajanus cajan L. Millsp.) grown in the north bank plains zone of Assam

Abstract

Two varieties of pigeon pea viz., BC (local) and ICPL 88039 were grown on the sandy loam soils of AICRPDA research farm of B. N. College of Agriculture, AAU in two consecutive kharif seasons of 2012-13 to 2013-14. Both the cultivars were sown on three different dates at ten days interval starting from 3^rd June to 23^rd June. GDD accumulation for attaining different phenological events viz., emergence, initiation of 1^st flower bud and flower appearance, 50 per cent flowering, 1^st pod formation, 1^st seed formation and physiological maturity were worked out. The cumulative GDD accumulations up to physiological maturity were relatively higher in BC (local) which varied from 3395.6 to 3593.5 °C day, whereas, in ICPL 88039, it varied from 2945.0 to 3296.7 °C day in different sowings and seasons. A decreasing trend in accumulated GDD for attaining any Phenological event was observed with successive delay in sowings in both the cultivars in the two seasons. In both the crop seasons, Pheno-Thermal Index (PTI) varied from 16.67 to 18.18 °C day growth day^-1, in BC (local) and 18.31 to 19.11 °C day growthday^-1 in ICPL 88039 during the vegetative growth period under all the sowing dates while, in the reproductive growth stage, it was comparatively lower and ranged from 7.96 to 8.23 °C day growthday^-1 in BC (local) and 10.28 to 11.87 °C day growthday^-1 in ICPL 88039. Seed yield heat use efficiency (HUE) in BC (local) varied from 0.207 to 0.296 kg ha^-1 °Cday^-1, whereas, in ICPL 88039 it varied from 0.201 to 0.312 kg ha^-1°Cday^-1 under different sowing dates in both crop seasons. Seed yield heat use efficiency was relatively higher in 2013-14 followed by 2012-13 in both the cultivars which indicated the significant differences in using the heat, available to the plants.