Indian Journal of Agronomy

An experiment was conducted during spring seasons of 2014 and 2015 at Ludhiana, Punjab, to investigate the effect of intra-row spacing and nitrogen application to sunflower (Helianthus annuus L.) sown on different dates on growth, photosynthetic parameters, root density, yield forming traits and sink development. Treatments comprised combinations of 3 sowing dates (20 January, 10 February and 2 March), 2 intra-row spacings (24 cm and 30 cm) as main factor and 4 nitrogen doses (0, 45, 60 and 75 kg/ha) as sub-factor in split-plot design with 3 replications. The early sowing resulted in higher total dry-matter accumulation (DMA) (4.84 t/ha) and DM partitioning to seed (2.03 t/ha). The results indicate that higher DMA under earlier-sown crop could be associated with the higher chlorophyll content, chlorophyll fluorescence (Fv/Fm ratio), optimal dry-matter partitioning (%) to leaf with consequent reduction in DM partitioning to stem. Early-sown crop also recorded higher root mass density than late-sown crop at 0–15, 15–30 and 30–45 cm soil depth. Closer intra-row spacing resulted in higher DMA by all the plant parts except seed. Each graded N dose led to improved DMA, but the improvement in dry-matter partitioning to seed was significant up to 60 and 75 kg N/ha during 2014 and 2015, respectively, owing to higher chlorophyll content, Fv: Fm ratio, chlorophyll content index, root density and dry matter partioning to leaf under respective treatments.