Epsilon Archive for Student Projects

Abstract

Seven representative soil sites at the Nigerian Institute for Oil Palm and Research (NIFOR) were studied to evaluate the present fertility status of the soils for sustainable production of palm oil and
in particular investigate the soil boron status. Profiles were sited at Edo State (Ed1, Ed2 and Ed3) and Akwa Ibom State (Akwa1, Akwa2, Akwa3 and Akwa4). Three of the sites were from Edo and four sites were from Akwa Ibom State. A total of 56 soil sample were analyzed, 24 soil samples from 24 layers in Edo State and 32 soil samples from 32 layers in Akwa Ibom State, with the same analytical treatments. Total annual precipitation amounts to about 1600-2000mm in Edo State, but 2000-4000, at Akwa Ibom State.
pH was measured at a 1:1 soil-water ratio using a pH meter, particle size analysis by the hydrometer method, organic carbon by wet-oxidation using the Walkey Black method, nitrogen by the macro Kjeldahl method, available phosphorus by the Bray II method, exchangeable base cations by the neutral ammonium acetate method, exchangeable acidity by normal potassium chloride, available boron by the azomethine-H colorimetric method and electrical conductivity by the electrode conductivity meter.
The soil texture was in general sandy with about 83 - 91% sand content at the Akwa Ibom State and 75 - 97% at the Edo State. The high sandy content implied low to moderate water retention capacity in most of the soils in the two regions. Soil colour values were dominantly dark grayish brown (2.5 Y 3/2) to black (2.5 Y 2/0). The soils were classified as plinthic arenosols in the Edo State and ferralic arenosols in the Akwa Ibom State. Most soil chemical parameters indicated a poor nutrient status.
All soils were acid with a low pH (4.2 – 6.3), and exchangeable acidity was predominately low with about 0.2 – 0.5 meq/100g soil at Edo State and predominately moderate to high 0.6 – 1.2 meq/100g soil at the Akwa Ibom State. The exchangeable Al was low with about 0.0 – 0.5 meq/ 100g soil at Akwa Ibom State. In general, there were no detectable levels of available Al at Edo State soils. The soil organic matter (measured as total organic carbon) was low with about 0.7 – 1.1% in the top 15cm soil layer at Edo State and 0.8 – 2.0% at Akwa Ibom State. Low organic matter content and high sand content resulted in low exchangeable cation capacities in both states. Thus, the silt and clay were somewhat higher at Akwa Ibom State than
at Edo State. In general there was a low electrical conductivity with about 8.3 – 33.9 μS/cm at Edo State and 6.0 - 240μS/cm at the Akwa Ibom State.
A low total N with about 0.0 - 0.1% in the top 15cm soil layer at Edo State and 0.1 – 0.2% at Akwa Ibom State, low exchangeable Ca with about 0.5 – 2.2meq/100g soil at Edo State and 1.6 – 3.2 meq/100g at Akwa Ibom State thus the content of exchangeable Ca in Akwa Ibom State were more than that of Edo State. Low exchangeable Mg with about 0.1 – 0.6meq/100g soil at Edo State and 0.2 – 2.1 meq/100g soil at Akwa Ibom State, comparatively the contents of exchangeable Mg in Akwa State were more than that of Edo State. The exchangeable Na were low to high with about 0.1 – 0.4meq/100g soil at Edo State and 0.4 – 0.9meq/100g soil at Akwa State. In general the exchangeable sodium percentages were comparatively considered low with about 11.1 – 17.5% at Edo State and 7.1 – 35.8% at Akwa Ibom State.
Exchangeable K was comparatively low with about 0.0 – 0.1meq/100g soil at Edo State and 0.1 – 0.4meq/100g soil at Akwa Ibom State. In general exchangeable base cations were low with about 0.9 – 3.3meq/100g soil at Edo State and 1.9 – 5.6meq/100g soil at Akwa Ibom State. The base saturation was generally high with about 63 – 95% at Edo State and 69 – 98% at Akwa Ibom State. In general the Ca/K ratios were high with about 5.3 – 36.7 in Edo State and 7.1 – 56.4 at Akwa Ibom State. The Mg/K ratios were generally high with about 2.0 – 10.4 at Edo State and 1.1 – 34.7 at Akwa Ibom State. C/N ratios were low to high 6.0 – 19.0 at Edo State and 7.0 – 39.0 at Akwa Ibom State.
Available B was generally low with about 0.0 – 11.2mg/kg at Edo State and 0.0 – 5.3mg/kg at Akwa Ibom State. Available P was low with about 3.0 – 21.4mg/kg at Edo State and predominately high 5.6 – 83.5mg/kg at Akwa Ibom State. Generally, available P contents at Akwa Ibom State were higher than that of Edo State.
The low silt and clay contents, low pH, and low organic carbon, low concentration of exchangeable base cations levels were the major constraints of the soils for sustainable oil palm production. Thus the soils were placed in the S3 category regarded as marginally suitable for oil palm production.
Based on the fertility standards (FAO, 1976), the NIFOR soils were generally rated low in fertility despite the high levels of available P, Ca/K, Mg/K and base saturation.
Management measures to be adopted should include application of required levels of organic and inorganic fertilizers, since fertility standards were not met.