Influence of soil nitrogen and potassium levels on the growth and composition of lucerne grown to first flower in four temperature regimes

One‐year‐old plants of lucerne were grown through two first‐flower harvests in growth chambers set at 35/29, 28/22, 21/16 and 16/10 °C day/night temperatures with and without N and K fertilisation. Time to first flower decreased from 50 to 17 days as temperatures increased. Averaged over all fertility levels, shoot heights; shoot numbers; and yields of leaflets, stems, herbage, roots and total plant decreased as temperatures increased. Neither N nor K materially affected these growth measurements, with a few exceptions. Averaged over all fertility levels, concentrations of P, K, Fe, B, Cu and Zn in the herbage, and all N fractions in the leaflets, stems and herbage, decreased as temperatures decreased; Ba, Sr and total non‐structural carbohydrates (TNC) increased; Ca changed very little; while Mg, Na, Al and Mn were variable. Neither N nor K affected the percentages of most minerals. However, N and K increased herbage Mg and K percentages, respectively. N increased all N fraction percentages, but K had little effect on them. K did not affect TNC percentages, but N decreased them in the herbage at 35/29 and 28/22 °C and in the roots at 35/29 °C.