Nutrient content of plants

A favourable effect of humic substances on the nutrient uptake and contents of plants has been reported for the major inorganic elements added to soil such as nitrogen, phosphorus, potassium and sulphur (Table 3). In addition, the uptake and contents of nutrients such as calcium, magnesium, sodium, and copper are also enhanced by humic substances (Table 4). 

Most of the reports on the effects of HA on the nutrient contents of plants are purely descriptive and little attempt was made in the earlier work to elucidate the mechanisms of the action of the humic material. The final concentration of a nutrient in a plant can depend on a number of factors such as the concentration in the nutrient solution, its interactions with other nutrients and/or humic substances, the pH of the nutrient medium in addition to the effects of the humic substances on the ion uptake mechanism and finally translocation within the plant. Several of these factors are well illustrated in a recent paper by Guminski e al. These workers showed for example that Mg is taken up to a greater extent at pH 5.0 than at pH 7.0 and that, in general, humate stimulated Mg uptake at both pH values. Guminski e a also demonstrated that the metabolic inhibitor 2,4-dinitrophenol had an adverse effect on any stimulation of ion uptake produced by HA. Such a result demonstrates that humates can influence nutrient concentration in plants directly through metabolic processes. 

The active uptake can be investigated by interfering with metabolism  

4- 1 metals. HA will thus complex Zn more readily than Na.  

Werff has shown for Holcus lanatus that HA, FA and EDTA inhibit the 

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A beneficial effect of humic substances on the nutrient uptake and contents of plants has been reported for the major inorganic elements, such as nitrogen, phosphorus, potassium (Mylonas and McCants, 1980), and sulfur (Guminski, 1968). In addition, the uptake and contents of nutrients such as calcium, magnesium (Mylonas and McCants, 1980), sodium (Vaughan and McDonald, 1976) and copper (Rauthan and Schnitzer, 1981) are also enhanced by humic substances. Most of these reports on the effects of HS on the nutrient contents of plants are purely descriptive, and little attempt has been made to elucidate the mechanisms of the action of the humic material. The authors proposed both an indirect and a direct effect of HS on plant nutrition. In the former case HS may, for example, chelate a cation, thus changing... 

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