The effects of gibberellic acid and nutrient sprays on growth and yield of brussels sprout

Abstract

SUMMARY Young plants of brussels sprout, cv. Cambridge Special, growing in pots in a glasshouse, were sprayed on ten occasions with gibberellic acid (GA) at 0, 25, 100 and 400 p.p.m. and ammonium nitrate (NH4NO3) at 0, 0·0125, 0·025 and 0·05 M concentrations in all combinations. In 24 days both GA and NH4NO3 increased leaf area, leaf number, dry weights of leaf, stem and root, and fresh weights of leaf and stem. GA increased stem height and decreased fresh weight/unit leaf area (leaf thickness), whereas NH4NO3 did not affect stem height and increased leaf thickness. Of the GA treatments, 100 p.p.m. gave the largest plants as judged by fresh weight of the whole plant and leaf area, and of the N treatments 0·05 M NH4NO3 increased growth most. The best treatment combination was 0·05 M NH4NO3 with 100 p.p.m. GA, which gave the greatest fresh and dry weights of the whole plant, leaf area and leaf dry weight as well as increasing leaf thickness. Significant interactions were found between GA and N for dry weight of leaf, fresh and dry weight of root, and leaf thickness but not for leaf area or stem growth (fresh weight, dry weight, height). The combination of levels of GA and N that can be expected to increase leaf area, leaf dry weight and leaf thickness simultaneously, may lie within narrow limits for a particular crop. In a second experiment plants were sprayed with all combinations of GA (0 and 100 p.p.m.) seven times under glass in pots and ten times in the field, and three levels of KH2PO4 on twelve occasions in the field. Sprouts (axillary buds) were harvested in October and February. At the first harvest GA did not affect fresh weight or number, but increased both the total number of sprouts picked (with GA = 80·7; without GA = 69·8 per plant) and the total fresh weight of saleable sprouts (with GA = 2·59; without GA = 2·33 lb/plant). KH2PO4 also increased the weight and number of sprouts at the final harvest and the number of small sprouts at the first. There were interactions between GA and KH2PO4 (P= < 0·001) for both tota weight and number of saleable sprouts.