Effect of Sowing Date on Canopy Development, Light Interception, Light Use Efficiency and Grain Yield in Brassica Campestris and Brassica Juncea

Two Brassica species, B. campestris cv. Pusa kalyani and B. juncea cv. Varuna, were sown on several dates in two seasons. The value of the extinction coefficient (K*) was higher during the vegetative than the reproductive stage and declined progressively with increasing green area index. Interception of solar radiation reached a maximum of 80% at a green area index of 3.5 to 4 in both species. Maximum percent interception of solar radiation was highest in the crops sown in early October and reduced progressively with later planting. A linear relationship between cumulative intercepted photosynthetically active radiation and dry matter showed that both species produced about 1.1 g of above ground dry matter for every megajoule of intercepted solar radiation during vegetative growth, but during the reproductive stage, LUE was considerably higher, being 2.6g MJ⁻¹m². However, values of LUE calculated separately for each planting date declined progressively with later planting from October to December. Seed yield was positively related to PAR intercepted during reproductive growth.