The Effect of Croton macrostachyus, Plectranthus barbatus Leaf Aqueous Extracts and Inorganic Fertilizers on Growth and Nutrients Concentration of Brassica oleracea L. in a Greenhouse at Nairobi

The study was undertaken in Sustainable Development Initiatives Centre greenhouse at United States international university -Africa. The greenhouse experiment was laid out in potted containers in a randomised complete Block design (RCBD), with 3 replications. A total of four treatments composed of decomposed leaves extracts of Plectranthus barbatus (PB) and Croton macrostachyus (CM), inorganic fertilizer (IF) and Untreated soils (US) as control were used. The level of mineral and nutritive elements in leaf extracts and kales were determined by ICPE, β-carotene was determined by HPLC while Phosphorus Nitrogen were determined by UV-VIS. Data was analyzed using (ANOVA) and significant treatment means separated using the Turkey’s Honestly Significant Difference Test. The highest mean levels macro nutrients in leaves (μg/g) K+; 228.31±1.76; Mg2+, 188.35 ± 1.24; PO43-, 16.21 ±3.36 and NO3-, 95.35 ± 2.36 for croton macrostachyus and K+: 412.71 ± 2.55. Mg2+: 369.72± 3.25, PO43-: 29.59 ± 2.04 and NO3-, 63.24± 1.47 for Plectranthus barbatus. Application of croton macrostachyus, and Plectranthus barbatus leaf water extracts resulted in increased mean shoot length, leaf length, and number of leaves of kales as compared to the control. The mean growth rate for kales (shoot length 8.69 ± 3.68-12.64cm, Mean leaf length 8.34 ± 4.17- 12.82 ± 5.53, Mean number of leaves 8.38 ± 2.94-12.53± 4.73 and Yield (t/ha) ranged from 2.44 -5.89. Kales grown using leaf extracts had higher nutritive values as compared to the control. The mean nutritive values in kales were Iron (Fe) 3.87 – 5.24 mg/100g; Magnesium (Mg) 250.96-323.67 mg/100g; Sodium (Na) 216.21-320.81mg/100g; Phosphorus (P) 261.82-294.31 mg/100g; zinc (Zn) 1.17 -1.36 mg/100g; and β-carotene 4.73±0.15 - 3.38± 0.09 mg/100g.There was significant difference in nutritive values between leaf extracts and control. The growth of kales using leaf extracts of Croton macrostachyus responded better and gave a yield that was comparably higher to those of inorganic fertilizer and control. This study suggests that Croton macrostachyus and Plectranthus barbatus leaves may be potential source of plant nutrients for crop production and higher nutritive values.