Tissue tests

Tissue tests are widely used in horticulture practice and have in comparison with soil or substrate testing advantages as well disadvantages in comparison with soil testing. One of the main advantages of tissue tests is the certainty that analysed nutrients in plant tissues are really present in the tissue analysed, while analytical data of soil and substrate testing only estimate the availability of nutrients to plants. There is no guarantee that nutrients determined in the root environment as available quantities will be absorbed by plants. Numerous factors can hinder or stimulate the uptake by plants of nutrients determined with soil and substrate testing as being sufficiently available for that. The best known example of such a hindrance or stimulation is the root zone temperature. Low root zone temperature generally reduces shoot tissue concentrations, whereby Ca, P and Mg are mostly more affected than N and K. But shoot tissue concentrations also can be negatively affected by evidently too high root zone temperatures. The effects differ for crops and growing conditions (Daskalaki and Burrage, 1998; Ikeda and Osawa, 1984; Moustafa and Morgan, 1984). Huge effects on nutrient concentrations in plant tissues occur, when crops are grown at root temperature far below the optimum for crop development (Ali et al., 1994). Another example of a factor that can affect the uptake of some minerals is the use of root stocks. The effect of grafting apparently differs for crops and probably rootstocks. Baas (1998) found for rose a stimulation of the uptake of B by grafting, while Edelstein et al. (2005) reported for melons a reduced B uptake for grafted plants when compared with non grafted. The effects also differ for elements. Cabrera (2002) using the same rootstock “Natal Briar” with roses like Baas (1998) found besides a higher uptake of B also higher uptakes of Cl, Na and Mg, while P, K and Fe were significantly decreased by grafting.