Distribution of Primary Nutrients (NPK) to Crop Production in Profiles of Soils Derived from Coastal Plain Sand in Ikot Ekpo, Calabar, Cross River State, Nigeria

Abstract

This study was conducted to evaluate the distribution of primary nutrients (NPK) in profiles of the coastal plain soils of Ikot Ekpo, Calabar, as well as evaluate other soil properties critical to agricultural productivity, in a bid to generate data that will serve as a guide to effective land use and management of the soils for arable crop production. Three (3) Profile pits were dug on the crest, middle slope and valley bottom, and soil samples were collected from their pedogenetic horizons for analysis. Analytical results showed the three profiles of coastal plain soils studied had predominantly sandy particle sizes (ranged from 770 - 910 gkg-1 sand across the three profiles) and mostly loamy sand in texture; especially at the topsoil level. The soils were also acidic (pH 4.7 to 5.1) and low in organic matter (1.0 mg kg-1 to 16.0 mg kg-1) as expected. Generally, the soils were found to be low in total nitrogen content (0.1 to 1.3 mg kg-1) and exchangeable potassium (0.08 to 0.10 cmolc kg-1); however, they were high in available phosphorus (17.20 to 29.75 mg kg-1). NPK distribution charts showed that N and P decreased consecutively with increasing depth for the crest profile. The middle-slope and valley bottom profile showed no definite pattern of distribution. However, the concentration of NPK was highest at topsoil level across most profiles. N had the shallowest intra-profile distribution with significantly higher levels of topsoil concentration indicated by the high percentages of intra-profile CV (94%, 85% & 97% for CUF, MUF & VUF respectively). P showed a shallow intra-profile distribution across the three profiles but did not vary significantly from the intra-profile mean (12.5%, 12.0% & 2.6% for CUF, MUF & VUF respectively). On the other hand K was more evenly distributed within all three profiles ( CV  of 9.4%, 5.3% & 8.6% for CUF, MUF & VUF respective) compared to N and P. Inter-profile distribution of NPK showed that N and P had higher concentrations at crest level, with P showing consecutive decrease in concentration down the slope. This study therefore recommends adoption of different NPK fertilizer recommendations for different soil depths and topographic locations for optimal productivity.