Good question Shantharaja, it depends on the crop , annual or perennial in nature. in perennials , we implement foliar spray as long as leaves are in sink stage , moment current cycle leaves enter into source, leaves will no longer be in a position to acquire the foliarly applied nutrients , so the best course would be to allow two-third or three -fourth of full growth , and then take the index leaves from either fruiting or non-fruiting terminals , depending upon the standardized time of sampling . In annual crops , probably this lag to follow is not possible .
After spray, at least ten to 15 days as to enhanced chlorophyll due to foliar spray can be detected in annuals
Depend on what are foliar spray. If they have lost nitrogen, it can be quickly change of chlorophyll content. And usually, it take about at least 2 weeks.
Depends on cultivar, weather and input used. Initiation of reaction can be within 24 hours, but full results within 10-15 days.
I think you better set up your own time series of analyses rather than listening to figures coming through the internet!
Follow the leaf emergence, the newly emerged leaf after full expansion is the best indicator
The rate at which foliar sprays affect chlorophyll concentration is dependent on a number of factors: the nutrient in question, temperature, leaf water potential, leaf cuticle, translocation efficiency, stage of growth of the plant to name a few factors. Responses to iron foliar fertilisers are usually 2-3 days whereas responses for some macronutrients are often weeks. Foliar application of calcium is unlikely to have any effect on chlorophyll per se but only indirectly.
Penetration of the liquid compound into inner tissue will mostly affected by stomatal density, stomata size, transpiration rate, and environmental conditions. If your plant has a high density and conductance of stomata and have optimum conditions for gasses exchange so it will not take too long. 1 or 2 week after treatment, the effect should be seen.
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