Emergence and growth dynamics of spring sunflower (Helianthus annuus L.) in relation to sowing dates, densities and nitrogen rates

Emergence and growth dynamics of sunflower were studied at Punjab Agricultural University, Ludhiana during spring seasons of 2014 and 2015. The experiment consisted of three sowing dates (D1-January 20, D2-February 10 and D3-March 2), two intra row spacing (S1–30 cm and S2-24 cm) and four nitrogen (N) doses (N0-0, N45-45, N60-60 and N75-75 kg ha−1). Results revealed reduction in number of days taken for initiation and completion of emergence vis-a-vis emergence percentage with concomitant increase in emergence rate and vigour index due to delayed sowing. Late sown crop (D3) exhibited higher absolute growth rate (AGR), crop growth rate (CGR) and specific leaf weight (SLW) during initial phases of crop growth but early sown crop (D1) surpassed the late sown crop 50 days onward up to maturity. Early sown crop maintained higher relative growth rate (RGR) throughout the crop growth. Wider sown crop showed higher AGR, whereas CGR was higher under closer sowing. Application of N improved the AGR, CGR and RGR but SLW was improved during later growth stages (50 days onwards) only. Net assimilation rate (N AR) decreased progressively due to each delay of sowing during later growth stages. Application of N improved the NAR up to 75 DAS but between 75 DAS and maturity, application of N lowered NAR as compared to control. Correlation studies indicated significant positive correlation of seed yield with AGR, CGR and RGR between 50 and 75 DAS, emphasizing the importance of higher growth rate during grand growth period for best yield accrual in sunflower.