The influence of nitrogen and phosphorus fertilisation on seed yield and oil content of safflower in southern Botswana

Safflower (Carthamus tinctorius L.) is a versatile crop used as edible oil, vegetable, 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 determine the influence of nitrogen (N) and phosphorus (P) on the seed yield and oil content of safflower. The experiment was a split-plot laid 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. Nitrogen was supplied as calcium ammonium nitrate (28% N) and phosphorus as single super phosphate (8.3 % P as P2O5). The results revealed that nitrogen and phosphorus interactions at 40 kg N/ha + 25 kg P/ha and 40 kg N/ha + 50 kg P/ha significantly (P < 0.0001) increased the seed number per capitulum and seed yield of safflower, respectively. There was no significant interaction of N and P on seed oil content, but application of N and P independently significantly (P < 0.05) increased safflower seed oil content, with maximum oil content of 46.4 and 46.1% obtained through application of 120 and 25 kg/ha of N and P, respectively. Key words: Botswana, Carthamus tinctorius L, nitrogen, phosphorus, soil fertility