EFFECT OF DIFFERENT ORGANIC FERTILIZATION STRATEGIES ON VEGETATIVE GROWTH AND SOIL PROPERTIES OF NON BEARING CITRUS TREES (cv Clemenules)

In order to evaluate the effect of different organic fertilization strategies, as nitrogen source, on vegetative growth of young citrus plants as well as on chemical and microbiological soil properties, a two-year xperlment was performed on eighteen months old citrus plants (cv Clemenules) grafted on Poncirus trifoliata. The trees were transplanted in 35 L pots filled with a sandy-loam soil and drip irrigation. The following treatments were compared: Control (unfertilized):, Mineral fertilizer (MF); Vermicompost (VC), Vermicompost + blood meal (VC + BM); Citrus compost (CC). Each treatment was applied to 6 plants (replicates). At the end of each vegetative season the following parameters were measured: rootstock section area, plant height, leaf and shoot number per plant, leaf fresh and dry matter. Three plants per treatment were harvested and leaf total area, branches and roots (divided in fine and coarse) fresh and dry matter were recorded. In addition, soil samples of each pot were collected and soil chemical and microbiological properties were measured. Plant growth was positively affected by VC + BM fertilization strategy in comparison to the other treatments. Such effect was observed despite the total amount of N supplied to VC + BM, was about 40% lower than the N applied to plants by mineral source MF The supply of blood meal contributed to avoid the temporary soil N-deficiency occurred when organic fertilizer is incorporated into the soil. VC and CC strategies induced limited effects on plant growth likely due to the lower soil N-availability than the plant requirements. Moreover, only VC + SB promoted soil total N and microbial soil respiration. Generally, the macronutrient concentration in the leaves was adequate in relation to P, K, Ca and Mg, except for N, giving evidence of the high request for N at the beginning of growing and development stage of Clemenules tangerines.