|Full Text: |
1 Introduction Natural rubber (Hevea brasiliensis) is an important plantation crop that is grown in over 10.3 million hectares globally (International Rubber Study Group, 2012). Along with its ecological importance, rubber is mainly grown in the humid tropical areas of Nigeria where the soil is highly weathered, characterized by rapid organic matter decomposition (Awodun et al., 2007) Strongly acid with low exchangeable base cations and available phosphorous (P) as well as high iron (Fe) and manganese (Mn) concentration (Waizah et al., 2011; Oku et al., 2012; Suchartgul et al., 2012). Soil is a reservoir of plant nutrients and greatly varies with their distribution in time and space due to changes in chemical and physical characteristics (Awe et al., 2007). The productivity depends on the equilibrium between organic input supply and decomposition. Plant growth and development depend largely on the combination and concentration of mineral nutrients available in the soil and this is greatly influenced by root adaptations. For plants to maintain nutrient homeostasis, nutrient uptake and respond to changes in the soil and within the plant must be regulated (Kumar et al., 2017). Essential nutrients for plant growth could either be from organic or inorganic source or their combination. The inorganic sources involved the use of fertilizers. However, organic amendments decompose very rapidly under hot and warm humid tropical conditions and require repeatedly application at short intervals to sustain soil productivity (Jenkinson & Ayanaba, 1977; Dharmakeerthi et al., 2012).To improve and obtain sustainable Hevea bud stick and latex yield, proper management of essential nutrients is required. Soil and plant nutrient content analysis have often been used for nutrient diagnosis based on the hypothesis that there is relationships between plant growth rates (yield) and its nutrient content (Marschner, 1997). Soil nutrient management with inorganic fertilizer or integrated nutrient application in rubber supporting soils in terms of improved vigour and establishment, latex yield, dry rubber content of latex and soil nutrient conservation have been reported (Okore et al., 2007; Esekhade et al., 2013; Abraham et al., 2015; Alle et al., 2015; Okore et al., 2016). Previously conducted studies revealed significant effects of organic manure on the growth and nutrient cycling of Hevea (Tolentino, 2010; Waizah et al., 2011; Dharmakeerthi et al., 2012; Damrongrak et al., 2015). Various researchers have utilized various available numerical analysis methods like multivariate technique; Cluster Analysis (CA), Discriminant Analysis (DA) , Principal component analysis (PCA) for characterizing distinct agronomic characteristics and soil relationships in various crops such as rubber (Alika, 1991; Gouvêa et al., 2010; Omokhafe & Alika,2000), rice (Nassir, 2002; Adebisi et al., 2013), melon (Idehen et al., 2007), wheat (Habibpour et al., 2012), African yam bean (Nwofia et al., 2014) and in soil properties characterization (Nageswara & Jose, 2002; Campbell, 2004; Couto et al., 2006; Iwara et al., 2011; Edokpayi et al., 2015). Principal Component Analysis is a method that reduces data, exhibits the association between two or more parameters of a crop dividing the total variance of the original parameters into limited number of uncorrelated new variables. The reduction leads to linear transformation of the original variables into a new set of noncorrelated variables, known as Principal Components (PCs) (Wiley, 1981). The analysis also helps to identify the genetic distance between crop genotypes (Aremu et al., 2007). PCs are orthogonal and independent of each other revealing different properties of the original data as may be interpreted independently. According to Mohammadi & Prasanna (2003), total variation of the original data could be partitioned into components that are cumulative in nature. The purpose of this study is to investigate the effect of fertilizer and bud wood age on bud take of Hevea brasiliensis as well as assess their effects on the soil and leaf nutrient contents of the crop. 2 Materials and Methods The field experiment was conducted between 2014 and 2015 Hevea brasiliensis bud wood garden cut back and budding seasons at the Rubber Research Institute of Nigeria Substation Akwete, Abia State (lat. 4° 50' and 4° 65´N and Long.70 00' and 70 19' E). The climate is humid tropics with an average precipitation of 2,163 mm. The temperature is generally high ranging from 33-34oC as the maximum and 28 - 29oC as the minimum. It has two distinct seasons (rainy season- March / April to October and dry season- November to March). The soils of Akwete are mainly coastal plain acid sands of Niger Delta Basin derived from unconsolidated sedimentary deposits of Miocene Pleistocene periods (ILACO- NEDECO, 1966; Kamalu et al., 2014). The treatments comprised a 5 X 3 factorial combinations arranged in a randomized complete block design with three replications. The first factor consisted of five bud wood garden of different ages (2, 5, 10, 15 and 20 years) while the second factor consisted of three doses of NPK 20:10:10 fertilizer (NPK) (0, 100 and 150 kg/ha). The fertilizer was applied in late October 2014 after cutting back the bud woods, while budding was carried out in 2015. The budded stumps were transplanted to the field at 0.5m x 0.5m spacing. All the standard agronomic practices for bud wood garden establishment and management were adopted.