Effects of nitrogen and phosphorus on growth, development, yield, and oil content of safflower (Carthamus tinctorius L.)

Abstract

Safflower is a multipurpose crop grown for the orange-red dye that is obtained from its petals, medicinal properties, feed value and especially for its high quality oil (Dajue and Mondel. 1996; Dwivedi, 2005; Sirel and Aytac, 2016). A field experiment was carried out to evaluate the effects of nitrogen (N) and phosphorus (P) on the growth, development, seed yield and oil content of safflower. The experimental design was a split-plot design in randomized complete blocks with three replications. The treatments were 0. 25. 50. 75. and 100 kg N/ha (main-plots) and P at 0, 25, 50, and 75 kg P/ha (sub-plots). Nitrogen and P fertilizer application interacted significantly (P < 0.05) to increase safflower capitula number/plant, seed protein and oil contents, and leaf N and P contents. While N application independently significantly (P < 0.0001) increased safflower plant height, 100-seed weight and seed yield. Phosphorus fertilizer application significantly (P < 0.0001) increased safflower seed yield. Based on vegetative growth, yield, yield components and oil content of safflower, it was concluded that under sandy loam soils of Botswana, the optimal N and P fertilizer application rate to optimize safflower seed yield and oil content was 75 kg N/ha and 50 kg P/ha. Application of N and P beyond 75 and 50 kg/ha, respectively, resulted in decrease in safflower yield, yield components and oil content. The author recommended that for wider application of these fertilizer rates in Botswana, N and P trials be undertaken in various parts of the country under different soil types, irrigation regimes and rain-fed agriculture to confirm the current findings.