Effect of organic and inorganic fertigation on yields, δ15N values, and δ13C values of tomato (Lycopersicon esculentum Mill. cv. Saturn)

We examined the effects of fertilizer application, especially the effects of fertigation and types of fertilizer (inorganic and organic) on yields and delta(15)N and delta(13)C values of tomato (Lycopersicon esculentum Mill. cv. Saturn). Fertigation is a method in which an appropriate diluted liquid fertilizer is applied to the plants each time they are drip-irrigated. We developed a method of organic fertigation using corn steep liquor (CSL) as the liquid fertilizer, because it is an industrial byproduct of cornstarch manufacture and can be used very effectively. We compared fruit yield, mineral content, delta(15)N value, and delta(13)C value of tomatoes grown under three different fertilizer treatments, basal dressing: basal dressing with granular chemical fertilizer; inorganic fertigation: fertigation with liquid chemical fertilizer; and organic fertigation: fertigaion with CSL. Mineral contents of tomatoes grown with basal dressing were generally lower than those grown under either fertigation treatment. These results indicated that yields and mineral contents were influenced more by the method of fertilizer application than by whether the fertilizers were inorganic or organic. There were, however, significant differences in the delta(15)N values of tomato fruits grown under different types of fertilizer applications, especially between inorganic and organic fertilizers. The delta(15)N value of the chemical fertilizer used for basal dressing was 0.81 +/- 0.45parts per thousand, that of the chemical fertilizer for fertigation was 0.00 +/- 0.04parts per thousand, and that of CSL was 8.50 +/- 0.71parts per thousand. The delta(15)N values of the soils reflected the delta(15)N values of the fertilizers. Moreover, the delta(15)N values of the fruits corresponded to the delta(15)N values of the applied fertilizers. The delta(15)N values were 3.18 +/- 1.34parts per thousand in the fruits grown with a basal dressing of chemical fertilizer, 0.30 +/- 0.61parts per thousand in those grown under inorganic fertigation, and 7.09 +/- 0.68parts per thousand in those grown under organic fertigation. On the other hand, although the delta(13)C values in the soil also reflected the delta(13)C values of the applied fertilizers, there was no significant difference in the delta(13)C values of fruits among the different treatments. In conclusion, because the delta(15)N values of fertilizers correlated well with those of the fruits, it may be possible to use delta(15)N values as an indicator of organic products.