Enrichment of some B-vitamins in plants with application of organic fertilizers

Abstract

A review of the literature showed that plants grown with organic fertilizers often contain higher concentrations of vitamins B1 (thiamin) and B12 (cyanocobalamin) as compared with plants grown with inorganic fertilizers. Since plant roots were recently shown to be able to absorb B1 and B12, it was thus suspected that organic fertilizers (such as manure of diverse sources or sewage sludges which often contain relatively high concentrations of several vitamins) introduce additional vitamins into the soil which in turn leads to increased vitamins in the plants. This possibility was studied by measuring the B12 content in the seeds of soybean and barley and in the leaves of spinach plants grown in soils amended with pure B12 or cow dung (which is naturally rich in B12). The addition of pure B12 or cow dung did not alter the B12 content in the soybean seeds but significantly increased that in the barley kernels and in the spinach leaves. For example, the addition of cow dung at the rate of 10 g kg−1 increased the B12 content in barley kernels by more than threefold (from 2.6 to 9.1 ng g−1 DW) and in spinach leaves by close to twofold (from 6.9 to 17.8 ng g−1 DW). Long-term addition of organic fertilizers to the soil also significantly increased the soil content of this vitamin. Since plants cannot synthesize B12 and thus plant foods are normally fully devoid of (or have very low concentrations of) this vitamin, the finding that plants grown with organic fertilizers may contain relatively higher concentrations of this vitamin may have nutritional consequences in that the consumption of these plants by humans would inadvertently increase their intake of this vitamin. This may be of special benefit to people living by choice or by necessity on strict vegetarian diets who are known to be in danger of B12 deficiency.