The influence of nitrogen and phosphorus nutrition on growth and yield components of safflower (Carthamus tinctorius l.

Abstract

Safflower (Carthamus tinctorius L.) is a versatile crop used for edible oil, vegetable, cut flower production, colouring foods, cosmetics, pharmaceuticals, livestock feed, biofuels, textile, and medicinal purposes. Soil fertility is one of the factors that limit crop production in Botswana. The objective of this study was to evaluate the influence of N and P fertilizer application on the growth, seed yield, and oil content of safflower. The experimental design was a split-plot laid down in randomized complete blocks with three replications. The treatments were N application at 0, 40, 80 and 120 kg/ha allocated to main-plots and P application at 0, 25, 50 and 50 kg/ha allocated to sub-plots. The results revealed that N and P significantly (P < 0.05) influenced vegetative growth, yield components, seed yield, and oil content of safflower. Application of 40 N + 50 P kg/ha to safflower plants produced maximum first branching height, leaf area, and chlorophyll content. Maximum safflower plant dry matter was obtained from plants applied with 120 N + 75 P kg/ha. While N and P independently significantly (P < 0.05) increased plant height (40 N, 50 P kg/ha), primary branch number (80 N, 50 P kg/ha) and stem diameter (40 N, 75 P kg/ha) compared to control plants. The interaction of N and P also significantly (P < 0.05) affected NUpE, NUtE, NUE, PUpE, PUtE, and PUE in both summer and winter. Application of 40 N + 50 P and 40 N + 25 P kg/ha, optimised NUpE, NUtE and NUE, and PUpE, PUtE and PUE, respectively. The interaction of N and P significantly (P < 0.05) influenced safflower yield components. Maximum capitula number/plant, capitula diameter, seed number/capitulum, and 1000-seed weight were produced by safflower plants applied with 40 N + 50 P and 40 N + 25 P kg/ha, respectively. Application of 40 N + 50 P and 80 N + 75 P kg/ha to safflower plants significantly (P < 0.0001) increased the seed yield to 1356 and 3528 kg/ha in summer and winter, respectively. There was no significant interaction of N and P on seed oil content in summer, but the application of N and P independently xii significantly (P < 0.05) increased safflower seed oil content with a maximum oil content of 46.4 and 46.1% obtained through the application of 120 and 25 kg/ha of N and P, respectively. In winter, N and P significantly (P < 0.0001) interacted at 0 kg N/ha + 25 kg P/ha to produce the maximum oil content of 71.8%. The results revealed that winter grown safflower produced seed with high oil content than summer grown safflower. From the results based on the performance of safflower as N and P influenced vegetative, yield components, seed yield, and seed oil content it was concluded that application of 40 N + 50 P kg/ha was recommended to maximize safflower production. However, it was also recommended that this study be repeated in Southern Botswana for confirmation of the current results. Also, fertilizer trials to be done in other parts of the country where farmers are currently growing safflower.