Impact of Fertilization and Planting Density of Irvingia Wombolu on the Physical and Chemical Properties of Soil

  • S.A Amosu
  • S.O.S Akinyemi
  • I.A Olabode
  • G.S. Akinwumi
Keywords: bush mango, Nigeria, plant population, soil nutrients, soil acidity


In a young Irvingia wombolu orchard established at the National Horticultural Research Institute (NIHORT), where yearly fertilization was done, the impact of this inorganic fertilization on the physical and chemical properties of an alfisol was investigated between 2006 and 2008. Pre-cropping soil sampling was done at 0-30cm soil depth with a soil auger using judgement composite sampling, while post-cropping soil sampling was done at 1.5m at each stand and bulked as a composite sample per treatment combination. The soil parameters analysed for were pH, total nitrogen (N), available phosphorus (P), exchangeable bases (sodium – Na, calcium – Ca, magnesium – Mg and potassium – K), base saturation, organic matter, micronutrients (zinc – Zn, copper – Cu and iron – Fe), particle size distribution, soil texture and bulk density. The treatments consisted of five fertilizer levels of NPK 20:10:10 (0, 75, 150, 225, and 300 kg/ha) while there were three plant densities (204, 238 and 286 plants/ha). The results after 2 years of fertilizer application showed that there was a slight change in soil physical properties and a significant increase in soil acidity with increasing fertilizer rates at a density of 286 plants/ha. The sand particles increased from 75.8% to 83.8% in 238 plants/ha under 150 kg/ha fertilization, and there was also a significant increase in available P from 1.55 mg/kg to 28.75 mg/kg, and in exchangeable K from 0.17 cmol/kg to 0.50 cmol/kg in 268 plants/ha and 238 plants/ha under 225 kg/ha and 150 kg/ha of fertilizer application, respectively. There was an increase in acidity with increased fertilization from 6.6 to 4.5 in 286 plants/ha, while at 204 plants/ha, there was a decrease in acidity with an increase in fertilization. Soil organic matter increased after cropping from 1.08 g/kg to as high as 3.59 g/kg after fertilization in all the plant populations showing no distinct trend. There was also a significant increase in Zn, Cu and Fe from 2.32 mg/kg to 86.65 mg/kg, 1.53 mg/kg to 2.22 mg/kg and 34.05 mg/kg to 137.25 mg/kg in 286 plants/ha, 238 plants/ha and 238 plants/ha under 75 kg/ha, 300 kg/ha and 150 kg/ha fertilizer application, respectively. Overall, this trial showed that application of inorganic fertilizer increased the acidity of the soil and the concentration of micronutrients. The application of inorganic fertilizer should be done with caution as its high dose led to increase in soil acidity resulting in restricted availability of some macronutrients especially K and Na.