Fertility Assessment of Soils on Three Geological Materials For Production of Selected Horticultural Crops in Nsukka Area of South East Nigeria

Abstract

This study assessed the fertility of soils of three geological materials in Nsukka Area of Eastern Nigeria for horticultural crops (pepper, turmeric, ginger and tomato) production. The three geological materials are Upper Coal Measure (Agu-Ibagwa), False Bedded Sandstone (Nkpologwu) and Nkporo Shale (Opi-Agu). A total of three profile pits were dug and 14 core and auger samples were collected from the diagnostic horizons of the three pedons. Also, 36 auger samples (i.e. 18 top and subsoil) were collected from the locations. The samples collected were analyzed for their physical and chemical properties. The data obtained were subjected to descriptive statistics and two way ANOVA using genstat discovery software. The limitation method, parametric method and Multi-Criteria Decision Analysis (MCDA) were used to evaluate the suitability of soils for the production of horticultural crops. Morphologically, all the soils were very deep (> 150 cm) and well drained. The Agu-Ibagwa soils were dark reddish brown (2.5 YR 4/3) in Ap horizon, orange (2.5 YR 6/6) in Bt1, and bright brown (2.5 YR 5/8) in Bt2 and Bt3 horizons; the Opi-Agu soils were brown (7.5 YR 4/4), dark reddish brown (2.5 YR 5/4), bright reddish brown (5 YR 5/8) and red (10R 4/8) in Ap, A1, Bt and C horizons respectively whereas the Nkpologwu soils were very dark reddish brown (2.5 YR 2/3) in Ap horizon, over dark reddish brown (2.5 YR 3/6), red (10R 4/6), reddish brown (2.5 YR 4/8) and brown (10 YR 4/6). The structure varied from very fine weakly developed structure to fine medium massive granular in Nkpologwu soils; granular to sub-angular blocky structure in Opi-Agu soils and sub-angular blocky structure in Agu-Ibagwa soils. Generally, the horizon boundaries varied from clear smooth, gradual smooth, gradual wavy, diffuse smooth, abrupt smooth and gradually diffuse. Sand, silt and clay fractions range from 640 to 920 g kg–1, 50 to 270 g kg–1 and 30 to 170 g kg–1 respectively for the three locations. Soil texture varied from sand to sandy clay loam in all the soils. The bulk density ranged from 1.40 to 1.80 g cm–3, 1.40 to 1.70 g cm–3 and 1.70 to 1.80 g cm–3 at Agu-Ibagwa, Opi-Agu and Nkpologwu soils respectively. The macro, micro and total porosity ranged from 11.20 to 20.10%, 24.20 to 45.00% and 40.40 to 57.10% respectively with values varying irregularly down the depth in all the soils. The saturated hydraulic conductivity ranged from 1.70 to 13.90 cm h–1, 11.60 to 16.80 cm h–1 and 33.90 to 87.70 cm h–1 at Agu-Ibagwa, Opi-Agu and Nkpologwu soils respectively with highest values in the Ap horizons. Soil reaction ranged from very strongly acidic to neutral as their pH values in H2O ranged from 5.0 to 7.0 at Agu-Ibagwa, 6.0 to 7.30 at Opi-Agu, and 6.0 to 6.30 at Nkpologwu soils. The Soil Organic Matter (SOM), Total Nitrogen (TN), and Available Phosphorus (Av.P) were low with decreasing trend down the profiles. The exchangeable Na, K, H, Al and CEC, were generally low in all the soils. Also, exchangeable Ca and Mg, and BS ranged from moderate to high with the values of Ca decreasing down the profile and that of Mg and BS varying irregularly down the profile. The soils of the study area were classified as Typic Hapludalfs, Eutric Acrudox and Arenic Kanhapludults at the USDA classification and correlated to Loamic Lixisols and Arenic Acrisols at the WRB classification. Statistically, geological materials (location) significantly (p ≤ 0.05) influenced particle size distribution and some soil chemical properties (soil pH, OM, TN, exchangeable Ca and Mg, and TEA. Agu-Ibagwa significantly (p ≤ 0.05) recorded highest values of OM, TN, exchangeable cations and acidity; Opi-Agu significantly (p ≤ 0.05) recorded highest values of pH, Av. P and CEC whereas Nkpologwu significantly recorded the lower values. Soil depth significantly (p ≤ 0.05) influenced OM, exchangeable Na and Mg, and TEA with higher values occurring in the subsoil than the topsoil. Silt and sand contents, soil reaction, OM, TN, exchangeable cations, TEB and BS were not significantly (p ≥ 0.05) influenced by the interaction of geological materials (location) and soil depth. Using the aggregate suitability class, the three locations are highly suitable for the four test crops except Nkpologwu which was moderately suitable for ginger and tomato production. Using the Multiple-Criteria Decision Analysis (MCDA), the Agu-Ibagwa and Opi-Agu soils were highly and moderately suitable whereas Nkpologwu soils were moderately and marginally suitable for the four test crops.