Influence of Eggshell Nanopowder on Calcium Uptake in Tomato

Tomato (Lycopersicon esculentum) is a popular and nutritious vegetable high in vitamin C, minerals and lycopene.  However, the fruits are susceptible to ‘blossom-end rot, a physiological disorder caused by low calcium in the fruit.  Calcium (Ca) is transported to the vegetative parts of the plant via the transpiration stream, while fruits are supplied via phloem transport.  However, Ca is low in phloem sap and the transpiration rates are low in fruits. This study investigated the potential of eggshell nanopowder (ESNP) to supply Ca to fresh market tomatoes. Tackling this issue, we explored finer nanoscale Ca source which has size dependent and unexpected properties capable of facilitating Ca transport in the plant, unlike the micron size lime. Hence, ESNP was prepared by subjecting chicken eggshells to mechanical attrition and ultrasonic irradiation. This was characterized with TEM and XRD which revealed ESNP as calcite crystals with sizes >100 nm. The addition of 125-300 mg of ESNP to soil samples used for cultivating tomato plants showed significant increments in the plant heights (~7-16 %)  and leaf areas (~16-22 % ) relative to the control plants. Fruit yield increased by 16% and 21 % due to micro and nano eggshell sourced lime respectively. No significant difference existed in fresh foliage weight for regular lime and nano eggshell sourced lime but that due to micron eggshell lead to about 8 % reduction. Stem diameters remained constant over the entire duration of growth. The incidence of blossom-end rot was 1.5 fold more in the nano eggshell cases than in the micron counterparts and the weight of fresh fruits was also 27% lower than those for micron regular lime and eggshell. This is likely due to the total absorption of calcium in the nano eggshell sourced lime by other plant tissues before fruits begin to develop. These preliminary findings however, suggest that ESNP is a vital and cheap source for effective supplementation of plant Ca and could be envisioned to lead to increase in the tomato fruit yield and concentration.