Enumeration of carbon and nitrogen contents of water-stable aggregates in layers of topsoils from cultivated and adjacent bush-fallow loamy soils

Soil organic carbon (SOC) and total soil nitrogen (TSN) dynamics have both pedological and agronomic basis. Knowledge of their retention within aggregate hierarchies of varying soil textures as influenced by land use change is limited. The capacity of loam (L), clay loam (CL), sandy loam (SL) and sandy clay loam (SCL) soils to retain SOC and TSN in water-stable aggregate (WSA) at 10-cm intervals of 0-30 cm topsoil depths under cultivated and bushfallow/ uncultivated systems was investigated. The soils showed high dispersion ratio and great variations in aggregate silt and clay indices (CL > L > SCL > SL) under both land uses. Across soil depths, the uncultivated CL, SL and SCL soils had moderate to high > 2.00 mm WSA whose reduction due to cultivation impact was more pronounced in SL than in CL soil. Across soil depths and land uses, SOC content seemed higher in the macro- (> 0.50 mm) than in the micro- (< 0.50 mm) aggregates of all the soils while the reverse marked aggregate TSN content in almost all the soils. Cultivation mostly reduced macro-aggregate-associated SOC and TSN in L > CL > SL and in L > SL > CL > SCL soils, respectively. However, cultivation showed no reduction influence on micro-aggregate-associated SOC of all the soils. Cultivation-related reduction in micro-aggregate-associated TSN was more pronounced in the generally more ‘clayey’ CL and SCL than the L and SL soils. So, the potential of bush-fallowing to enhance micro-aggregateassociated TSN storage and stabilization against adverse influence of cultivation depends on soil texture.

Effects of continous cropping and NPK fertilizer on growth and yield of cowpea (Vigna unguiculata (L) Walp) grown on soils from different management systems

Studies were conducted to investigate the effect of continuous cropping and NPK fertilizer on the growth and yield of cowpea (Vigna unguiculata (L) Walp) grown on soils from different management systems. The investigations were carried out in two parts. The first dealt with the effect of continuous cropping while the other focused on the effect of NPK fertilizer on cowpea. Representative soil samples were obtained at 0-15 cm depth from land which had been continuously cropped, under forest tree fallow, and secondary bush fallow. These were bulked, processed, and analyzed. Six (6) kg of each type of soil were weighed into 25 x 22 cm polybag of 500 gauge. The continuous cropping experiment involved three cropping cycles of 35days each of cowpea on the same soils from 3 cropping systems. In the second experiment, a 2 x 3 factorial involving 2 levels of fertilizers (0, 40 kg NPK/ha) and 3 sources of soil were carried out to test their effects on cowpea. The growth parameters measured were plant height, number of leaves/plant and number of branches/plant. Number of nodules/plant, number of pods/plant, dry matter and grain yield were also estimated. Successive cropping of soils significantly reduced cowpea growth. Cowpea plants grown on soils from continuously cropped land had the least growth performance. Number of nodules/plant increased with successive cropping. Higher dry matter yield was obtained from the continuously cropped land. A significant (r = +0.55) positive correlation was found between soil P and dry matter yield of cowpea. NPK fertilization had only significant effect on plant height at 10 WAP but not on other growth parameters measured. The highest grain yield was obtained from unfertilized secondary bush fallow soil. Sources of soil (soil management system) had significant effect on some of the agronomic characters of cowpea.

Evaluation Of Selected Soil Structural Properties of Different Land Uses In Oforola, Imo State, Nigeria

This study centered on evaluating selected soil structural properties of different land uses in Oforola, Imo State, Nigeria. Soil samples were collected from six different land-use types, namely, secondary forest, bush fallow, bare plot, cassa- va cultivated plot, oil palm plantation, and grassland vegetation. Soil auger was used to collect soil samples from each of the land use types at two (2) depths (0 – 15 cm and 15 – 30cm). The samples from each land use at different depths were composited, mixed thoroughly and sub-sample, and analyzed in the laboratory for selected physical and chemical parameters. The data were analyzed statisti- cally using GENSTAT software Ver. 8.2 in Completely Randomized Design (CRD). The soils of the study area were principally sandy, with sand accounting for more than 65% of the inorganic mineral fragment in the soil at 0 – 15 cm depth and 15 – 30 cm depth. Land use effect on the dispersion ratio (DR) was significant (P ≤ 0.05) at the 0 -15 cm and 15 – 30 cm depth. However, oil palm plantation recorded significantly (P ≤ 0.05) higher dispersion ratio at the 0 – 15 cm depth. Bulk density was highest (1.57 g/cm3) in grassland vegetation and lowest in secondary forest and bush fallow (1.25 g/cm3). The bulk density val- ues for bare plot, cassava cultivated plot and oil palm plantation were 1.51 g/ cm3, 1.35 g/cm3, and 1.29 g/cm3, respectively. The total porosity of the soil was significantly higher in secondary forest (51.84%). Total porosity values for bush fallow, Cassava cultivated plot, oil palm plantation, bare plot, and grassland veg- etation were 51.83%, 48.38%, 50.97%, 42.36%, and 40.08%, respectively. The proportion of water stable aggregates were significantly (P ≤ 0.05) influenced by the various land-use types. On the average, secondary forest and bush fallow had higher water-stable aggregates of various sizes compared to the cassava cultivat- ed plot that had moderate water-stable aggregates. The least water-stable aggre- gates of various sizes were recorded in grassland vegetation and oil palm planta- tion. The mean weight diameters were significantly (P ≤ 0.05) influenced by var- ious land-use types. Low mean weight diameter was observed for oil palm plan- tation, grassland vegetation and cassava cultivated plots. Based on the findings of the study, secondary forest and bush fallow land-use types possessed the most stable structural properties and also showed optimal impact compared to other land uses in Oforola soils, Imo State, Nigeria

Changes in the Structure of a Nigerian Soil under Different Land Management Practices

Quantification of soil physical quality (SPQ) and pore size distribution (PSD) can assist understanding of how changes in land management practices influence dynamics of soil structure, and this understanding could greatly improve the predictability of soil physical behavior and crop yield. The objectives of this study were to measure the SPQ index under two different land management practices (the continuous arable cropping system and natural bush fallow system), and contrast the effects of these practices on the structure of PSD using soil water retention data. Soil water retention curves obtained from a pressure chamber were fitted to van Genuchten’s equation, setting m (= 1-1/n). Although values for soil bulk density were high, soils under the continuous arable cropping system had good SPQ, and maintained the capacity to support root development. However, soils under the natural bush fallow system had a worse structure than the continuous arable system, with restrictions in available water capacity. These two management systems had different PSDs. Results showed the inferiority of the natural bush fallow system with no traffic restriction (which is the common practice) in relation to the continuous arable cropping system in regard to physical quality and structure.