CASTOR BEAN FRUIT HUSKS AS SUBSTRATE FOR PALM SEEDLINGS

Castor bean fruit husk is a residue that accumulates in high amounts in the castor bean oil industry. This research evaluated the use of composted castor bean fruit husks (CM) ground to different sizes (5 and 10 mm), either pure or in mixture with coconut fiber (FC) and with the commercial substrate (SC) PLANTMAX^®, as substrate for seedlings of the fishtail palms, Caryota mitis and C. urens. Two experiments were carried out. Experiment 1, with Caryota mitis, consisted of four treatments: S1- CM 10 mm and SC (1:1; v/v); S2 – CM 10 mm and FC (1:1; v/v); S3 – CM 5 mm and SC (1:1; v/v); S4 – CM 5 mm and FC (1:1; v/v); in four randomized blocks, with two pots per plot with one seedling each. The second experiment, with Caryota urens, consisted of three treatments: S1 – CM 10 mm; S2 – CM 10 mm and SC (1:1; v/v); S3 – CM 10 mm and FC (1:1; v/v), in three randomized blocks, each plot with two plastic pots (1 L) containing one plant each. Fertilization was carried at three months after planting using 0.5 g per pot of (8-28-16). The number of leaves (NL), stem height (SH) and diameter (SD), the petiole (PL) and leaf (LL) lengths, the leaf width (LW), leaf (LDW), petiole (PDW), stems (SDW) and root (RDW) dry matter weights, and leaf SPAD index were evaluated. Composition of CM was also determined. There was no difference among treatments on C. mitis LN, LL, LW, SD, LDW, PDW, SDW and RDW; substrates S1, S2 and S3 could be used indifferently considering most characteristics. There was no difference among treatments on C. urens NL, LW, SD, PL, LDW and RDW and, considering most characteristics, S2 was the best substrate. Castor bean fruit husk can be used as substrate for growing fishtail palm seedlings.