Iron deficiency symptoms in grapevine as affected by the iron oxide and carbonate contents of model substrates

Accurate assessment of the specific influence of calcium carbonate and iron (Fe) oxides in soil on Fe deficiency symptoms in plants has so far been made difficult by the covariance between their contents in many soils populations. In order to overcome this problem, we designed a completely randomized block experiment in which grapevine (cv. 161-49C) was pot-grown in substrates consisting of Fe oxide-coated sand (FOCS), calcium carbonate sand (CCS) and quartz sand for 100 days (five FOCS proportions, five CCS proportions, four replicates); in this way, covariance between the FOCS and CCS proportions was suppressed. An analysis of variance revealed the absence of interactions between FOCS and CCS in relation for any of the growth-related parameters studied (leaf size, increase in shoot length, internode length, and aerial biomass) and leaf chlorophyll concentration as measured via SPAD. Some growth-related parameters were found to be negatively correlated with the proportion of CCS, and leaf size to be positively correlated with the proportion of FOCS. Also, SPAD was more markedly influenced by the proportion of FOCS (positive correlation) than it was by CCS (negative correlation). Overall, these results indicate that the relative severity of the main symptoms of Fe deficiency, growth depression and leaf chlorosis, may differ from one case to another in response to the relative contents in carbonate and Fe oxides of soil. Also, they suggest the need to develop and calibrate soil tests capable of predicting the various Fe deficiency symptoms.