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This study evaluated physical properties of selected soil series and their implications on the soil compaction and erosion in Abeokuta, southwestern Nigeria. Daily rainfall data (1999–2007) were collected to estimate the rainfall erosivity. Seven soil series (Iwo, Iseyin, Ekiti, Jago, Okemesi, Apomu, and Egbeda) were sampled from 0–15, 15–30, and 30–50 cm depths for particle size distribution, organic carbon, pH, upper plastic limit, and compactibility (Proctor test). Microtopographical changes along and across toposequences of two farmers’ fields cleared mechanically and manually, respectively, were monitored using the erosion pin method. Mean annual erosivity (EI30) was high (7646 MJ mm ha−1hr−1). Particle size, organic carbon, and pH were similar (p ≥ 0.05), while upper plastic moisture was ≤ 2% among different soil series. Soil-moisture density curves indicated a maximum bulk density of 1.77–1.99 g cm−3for a moisture range of 7.6–14%; while the soils were prone to compaction at low moisture content. Microtopographic changes were found between –2 and 0 cm and –8 and –2 cm on mechanically and manually cleared farmland, respectively. Spatial dependence showed that the soil erosion could be predicted within 5–8 m distance. To avoid erosion and compaction, soil water content should be less than 7.6% before the introduction of mechanical tillage. [ABSTRACT FROM AUTHOR]

Trees play a significant role in improving soils for crop production through root activities. This study was carried out on four farmers’ fields in Mokwa, central Nigeria in May 1999 to quantify root distributions of 2-year-old Gliricidia sepium (G. sepium) and Acacia leptocarpa (A. leptocarpa). Root samples were taken up to 300-cm soil depth. Root length, surface area, and volume densities were evaluated by using Delta-T Scan device. Mass density was also evaluated. Root length densities of G. sepium ranged from 0.56–11 mm mL−1 while those of A. leptocarpa ranged from 0.13–5.93 mm mL−1, declining with soil depth. Potential contribution of roots to soil total porosity was less than 3%. Soil bulk density ranged from 1.28–1.51 g cm−3 under G. sepium and from 1.29–1.61 g cm−3 under A. leptocarpa. Although G. sepium had relatively more roots deeper in the soil than A. leptocarpa, both trees demonstrated deep rooting, suggesting that the trees would improve soil productivity if sufficient fallow length were allowed. [ABSTRACT FROM AUTHOR]

• Single plough passage plus ridging is sufficient to increase cassava root yield in tropical soil. • Application of fertilizer generally improved cassava root yield in southwestern Nigeria. • Weed control in cassava by herbicide under zero plough system cannot be recommended. Cassava is growing in importance in Nigeria as a food and industrial crop. Current yields are low due to poor soil fertility and because farmers do not use improved germplasm, clean planting material, or improved crop management in Nigeria. To provide feasible agronomic recommendations targeting increased root yield, the effects of tillage intensity, fertilizer application, plant density and weed control were tested in 230 farmers' fields in southwestern Nigeria over two years. In 2016, tillage treatments were zero, single and double passage with a disc plough, followed by ridging (soil shaping) versus leaving the soil flat. Fertilizer application at 75:20:90 kg ha−1 NPK was tested against a control and two plant densities (10,000 versus 12,500 ha−1) were compared. In 2017, plant density at 10,000 ha−1 and double plough were excluded, while pre- and post-emergence herbicide application versus farmer's choice of weed control (i.e. manual weeding using hand hoe) was introduced. Cassava was harvested at 12 months after planting, and yields were recorded as fresh root mass. In 2016, double plough (15.9 Mg ha−1) had a minor advantage over single plough (14.3 Mg ha−1), while zero plough produced 12.9 Mg ha−1 (P < 0.001). Ridging increased yield significantly (P < 0.01) by 2.3 Mg ha−1 after single and zero plough, but not after double plough. Across tillage treatments, planting at 12,500 plants ha−1 and fertilizer application increased yields by 1.5 and 4.2 Mg ha−1, respectively. In 2017, ridging resulted in a yield increase of 1.7 Mg ha−1 after single plough and 5.6 Mg ha−1 after zero plough. Fertilizer application increased root yield by 2.9 Mg ha-1 across tillage treatments. The use of herbicides negatively affected cassava yields in zero plough fields, compared with manual weeding. After ploughing, yield in herbicide based and manual weed control were not different. Cassava root yield response to tillage intensity strongly varied across fields, with low-yielding fields commonly responding less frequently to tillage. We conclude that unresponsive fields require measures other than increased tillage intensity to increase cassava root yields and that cost-intensive tillage operations must be targeted to responsive fields together with fertilizer application and improved weed control. [ABSTRACT FROM AUTHOR]