Synergistic Effects of Nutrients

Various interactions between macro- and micronutrient elements are known, which, under particular circumstances, affect the solubility and uptake of these elements by crops. It has been known for many years that the application of silicate-containing fertilisers will increase the availability and uptake of soil phosphate. The added silicate is believed to displace the phosphate which is adsorbed on Fe and A1 hydroxides, thus increasing the available phosphate for soil solution. 

There is evidence that the efficiency of phosphate fertilisers is increased by the presence of NHJ from nitrogen fertilisers. The addition of manure may under some circumstances increase the available P. Its decomposition releases organic acids which are believed to complex some of the Fe and AF+ cations present. 

Conversely, an excess soil P may effect the uptake of some micronutrient elements. A high P content can induce a zinc deficiency in the plant, even if sufficient zinc is present in the soil. On the other hand, the uptake of manganese from alkaline manganese-deficient soils can be increased by the presence of phosphatic fertilisers. There is also some evidence that excessive and prolonged buildup of phosphatic fertilisers in the soil might lead to toxic effects due to the trace quantities of certain metals (e.g. Cd above) in the fertilisers [38,59-61]. 

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