Fig. 4

Effects of straw-returning and inorganic K fertilizer on nitrate and free amino acid contents in the functional leaf at the peak flowering (PFS), boll-setting (BSS) and boll-opening (BOS) stages of Siza 3 in 2012 and 2013. The data are means of three replications ± standard error. For each growth stage, bars bearing different letters are significantly different at P = 0.05