EFFECTS OF FERTILIZERS ON SOIL PROPERTIES AND HEALTH, GROWTH AND DEVELOPMENT OF CACAO (Theobroma cacao L) SEEDLINGS IN SOUTHWESTERN NIGERIA

Abstract

Low soil fertility and debilitating effects of harmful soil borne microbes are major problems of cacao seedlings establishment (CSE) on the field; however, cacao (Theobroma cacao L) is characterized by high nutrient demand particularly N, P, K, Ca and Mg during establishment. In this study, the manurial potentials of some organic wastes and their effects on soil properties, health, growth and development of cacao in Ibadan and Owena soils of Southwestern Nigeria were investigated in 2011 and 2012. The experiments were 4 x 4 factorial fitted into Randomized Complete Block Design (RCBD) with 3 replicates. The 4 fertilizers were: Goat Dung (GD), Sunshine Organic and Organo-Mineral Fertilizers (OF and OMF) and NPK 15:15:15 and the rates of application were : 0, 200, 400 and 600 kg/ha. Four hundred and thirty two (432) plantain suckers were planted at 3 x 3 m spacing while 432 cacao seedlings (F3 Amazon) were also transplanted at 3 x 3 m respectively at each experimental site for 2011 experiment. For 2012 experiments, in both Ibadan and Owena, plantain suckers were established (at 3 x 3 m) in June, 2011. While cacao seedlings were transplanted into the plots one year later (June, 2012). Top soil samples were collected randomly from each experimental sites using soil auger. The samples were bulked and air dried before being subjected to routine laboratory analysis. Two grammes (2g) each of the organic fertilizers used were also analyzed for nutrient their composition. The fertilizers were applied to treatment plots one month after cacao seedlings were transplanted using ring method (July, 2011 and 2012 respectively). Data were collected on cacao growth parameters such as plant height, stem diameter, number of leaves, and leaf area and number of branches, monthly commencing at 3 MAT. Leaf samples (4th leaf) which were collected from 4 tagged cocoa seedlings at 12 months after transplanting were analyzed in the laboratory for chemical compositions. The experiments were monitored for 36 months (144 weeks after planting). Survival count was carried out 12 MAT. At 15 MAT, soil samples were collected from treatment plots and were processed and analyzed for physical (sand silt, clay, bulk density, moisture), chemical properties ( soil organic matter, soil pH, N, P, K, Mg, Ca, and Na), Biological properties (arbuscular myccorhizal, nematodes, moulds, yeast and bacteria) were also determined on the soil samples using standard procedures. Data collected were subjected to statistical analysis using Analysis of variance (ANOVA) and significant means separated by Tukey’s HSD (P < 0.05) test. Goat dung (GD), organo-mineral fertilizer (OMF) and organic fertilizers (OF) had pH of 8.17, 7.00 and 7.30 respectively. They contained in similar order 2.86, 0.63 and 3.64 g/kg OC, 4.80, 1.09 and 6.27 OM, 1.26, 0.06 and 2.16% N, 113.24, 138.06 and 7.08 cmol/kg P, 2.60, 2.00, and 13.10 cmol/kg Ca, 0.38, 0.18, and 2.30 cmol/kg Na respectively. Cacao seedlings grown under 600 kg/ha OF application had 100 and 95 percent survival count at Ibadan and Owena (2011 experiments). While 400 kg/ha OF gave 100 % survival count at Owena (2012 experiment). At Ibadan (2012 experiment), 600, 400, 200 kg/ha GD and 200 kg/ha OF gave 94 % survival count at 12 MAT. All fertilizer types and rates at Ibadan and Owena ( 2011 and 2012 experiments) significantly increased cacao seedlings height, number of leaves, stem diameter, number of branches and leaf area relative to the control plots at 3, 4, 5, 15, 16 and 17 MAT in Owena (2011 experiment). Application of 200 kg OMF, 600kg/ha GD and 400 kg/ha GD, 400 kg/ha OF significantly increased soil moisture contents in both Ibadan and Owena 2011 and 2012 experiments. Application of GD, OMF & OF significantly reduced soil bulk density compared with NPK 15: 15: 15 and the control. In addition, these treatments enhanced soil and leaf chemical properties at 15 MAT at both locations (2011 and 2012 experiments). Application of GD, OMF and OF increased albuscular mychorizal spores relative to NPK and the control. The population of other soil microbes (bacteria Yeast & Moulds) was also influenced by fertilizer types and rates at Ibadan and Owena (2011 and 2012 experiments). Application of 600 kg/ha NPK significantly reduced soil nematode population when compared with other fertilizer types, rates and the control plots in Ibadan (2011 and 2012 experiments), while 400 kg/ha OF and 200 kg/ha OMF significantly reduced nematode population relative to other fertilizer types, rates and the control plots in Owena (2011 and 2012 experiments). Goat dung applied at 600 kg/ha gave the highest number of flowers, cherelles and pods at 24 and 36 MAT in Owena (2011 experiment). While non of these yield parameters were obtained for 200 kg/ha OF and the control plots at both 24 and 36 MAT. Also, there were no yield parameters recorded for Ibadan (2011 and 2012 experiments) at 24 and 36 MAT, while non significant number of flowers were observed in Owena (2012 experiment) at 36 MAT.