A factorial field experiment was conducted on sunflower (Helianthus annuus L.) grown on a sand soil (98% sand) supplied the different combinations of 4 N rates of 0, 105, 140 and 175 kg N ha"-"1 i.e. N_0, N_1, N_2, and N_3 respectively - as (NH_4)_2SO_4 and 4 bio fertilization inoculation (B) of none, Azotobacter chroococcum, Azospirillum brasilense and Bacillus megaterium. i.e. B_0,B_1,B_2, and B_3 respectively. Labeled ammonium sulphate with 2% "1"5N atom excess was used for "1"5N assessment. All plots were supplied with 21 Mg compost +24 kg P +80 kg K ha"-'1. Non-treated plants gave 0.534 Mg seeds ha"-"1 while the treated ones - especially those of N or N + bio fertilizers - gave increases of up to 403% (N_2B). Main effect response patterns were: N: N_3>N_2>N_1, for B: B_1≥B_3≥B_2. Seed oil content in the N_0B_0 treatment was 222 gkg"-"1 increased reaching as high as 445 gkg"-"1by N_2B_3; with N main effect of N_2>N_3>N_1and B main effect of B_2>B_3>B_1. Seed oil yield was 113 kg ha"-"1 by N_0B_0 increased to as high as 1105 kg ha"-"1 by N_2B_1 with main effects of N_2>N_3>N_1and B_3≥B_2>B_1.Uptake of N (in total plant parts of roots + stems + leaves + discs + seeds) increased by N application; averages for non-N were 18.1 kg ha"-"118.5,14.7,17.4 by N_0B_0, N_0B_1, N_0B_2, and N_0B_3 respectively; increased considerably by up to 667% (N_3B_3) upon N application. Plants recovered a portion of fertilizer N of 19.6 to 40.9% by N_1B_1and N_2B_1 respectively as determined by "1"5N technique, but 27.7 to 59.6% respectively as calculated by subtraction of non-N from N treatments. The subtraction estimation considerably exceeded the "1"5N determined ones by + 39.5% to as high as + 194.6% indicating a non-real estimation of recovered fertilizer-N in crops. Thus, in studies using non-tracer techniques, estimation of uptake of fertilizer N could be erroneous. The reason in the current study could most certainly be a greater volume of root system expansion of N-treated plants, causing more uptake of non-fertilizer-N than in the no-N-treated ones. |
