A B S T R A C TStudies on the effect of biochar and poultry manure on soil properties and radish productivity is rare, hence, field experiments were conducted over two years, 2015 and 2016, to evaluate the effects of biochar (B) and poultry manure (PM) on soil properties, leaf nutrient concentrations and root yield of radish (Raphanus sativus L.). Each year, the experiment consisted of 3 × 3 factorial combinations of biochar (0, 25 and 50 t ha −1 ) and poultry manure (0, 2.5 and 5.0 t ha −1 ). Application of B and PM alone, and in combination, improved soil physical and chemical properties, leaf nutrient concentrations and yield components of radish. In 2016, the application of B alone increased the soil pH and concentrations of organic matter, N, P, K, Ca and Mg, as well as leaf nutrient concentrations and yield of radish, but in 2015 it only increased soil pH and organic matter and not leaf nutrient concentrations and yield. In both years, the application of B significantly influenced the root length of the radish. In both years, there was a significant interaction effect of biochar and poultry manure (B × PM) and this was attributed to the ability of the B to increase the efficiency of the utilization of the nutrients in the PM. The combination of 50 t ha −1 B and 5 t ha −1 PM (B 50 + PM 5 ) resulted in the highest radish yield. Averaged over the two years, (B 50 + PM 5 ) increased the root weight of radish by 192, 250 and 257% compared with biochar alone at 50 t ha −1 , biochar alone at 25 t ha −1 and no application of B or PM (control). Therefore, for a short season crop like radish the expected benefit of the biochar alone without the addition of poultry manure may not be achieved within the first year. + , and NO 3 − in animal manure (Steiner Notes: Values followed by the same letters, within column, are not significantly different at p < 0.05 according to Duncan's multiple range test. * =significant at 5% level of probability; ns = not significant at 5% level of probability; B = Biochar; PM = Poultry manure.

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A field experiment was conducted in the forest-savanna transition zone of Nigeria from May to July 2014 and September to November 2015 to determine the impacts of poultry manure (PM) and NPK fertilizer on soil physical properties, and growth and yield of carrot (Daucus carota L.). The five treatments included no manure or fertilizer (control); 10, 20, and 30 megagrams (Mg)·ha -1 of PM; and 300 kg·ha -1 of 15 N-15 P-15 K fertilizer. All levels of PM reduced soil bulk density and temperature, and improved total porosity and moisture content compared to the NPK fertilizer and the control. Plant height, number of leaves, root diameter, root length, and fresh root yield in the PM and NPK fertilizer treatments were improved compared to the control. Growth and yield parameters of carrot plants treated with 20 and 30 Mg·ha -1 PM were higher than the other treatments. The 10 Mg·ha -1 PM and NPK fertilizer treatments produced similar growth and yield responses. There was an interaction for year (Y) × fertilizer (F) on plant height, number of leaves, and fresh root yield. Relative to the control 10, 20, or 30 Mg·ha -1 PM and NPK fertilizer increased fresh root yield of carrot by 39.9%, 62.0%, 64.9%, and 37.3%, respectively. The 20 Mg·ha -1 PM treatment best improved soil properties and carrot productivity as indicated by the benefit-to-cost ratio.

Among agricultural soil amendment that can enhance crop productivity and soil sustainability is biochar. Hence, two-year field experiments were conducted on a sandy loam Alfisol at Owo, southwest Nigeria, to evaluate the effects of biochar produced from hardwood on soil physical and chemical characteristics, erosion potential, and cocoyam (Xanthosoma sagittifolium (L.) Schott) yield. The study was a 2 × 4 factorial experiment with two years (2017 and 2018) and four biochar levels (0 (control), 10, 20, and 30 t ha−1). The treatments were laid out in a randomized complete block design with three replications. Results indicated that biochar application significantly in both years improved yield of cocoyam and soil physical (bulk density, porosity, moisture content, mean weight diameter (MWD) of soil aggregates, dispersion ratio, and infiltration rate) and chemical (soil organic matter, pH, N, P, K, Ca, Mg, and CEC) properties and erosion resistance. Soil characteristics and cocoyam yield improved with level of biochar from 0–30 t ha−1. When 2018 is compared with 2017 in term of soil loss, in the amended plots, 2018 reduced soil loss by 7.4, 20, and 73.5%, respectively, for 10, 20, and 30 t ha−1biochar, whereas there was an increase of 2.7% soil loss in the control plot in 2018 compared with 2017. Therefore, application rate of 30 t ha−1 biochar is considered as suitable for severely degraded soil because this application rate efficiently improves cocoyam yield and soil properties and reduces soil loss.

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Field experiments were conducted at Owo, southwest Nigeria to select organic fertilizer treatments most suitable for sustaining high soil fertility and yam productivity on a nutrient-depleted tropical Alfisol. Eight organic fertilizer treatments were applied at 20 t ha 71 with a reference treatment inorganic fertilizer (NPK 15-15-15) at 400 kg ha 71 and natural soil fertility (control), laid out in a randomized complete block design with three replications. Results showed that organic fertilizers significantly increased (p ¼ 0.05) tuber weight and growth of yam, soil and leaf N, P, K, Ca and Mg, soil pH and organic C concentrations compared with the NSF (control). The oil palm bunch ash þ poultry manure treatment increased tuber weight, vine length, number of leaves and leaf area of yam by 66, 25, 21 and 52%, respectively, compared with inorganic fertilizer (NPK) and 37, 22, 19 and 44%, respectively, compared with poultry manure alone. Sole or mixed forms of organic fertilizers showed significant improvement in soil physical conditions compared with IF (NPK) and NSF (control). Synergistic use of oil palm bunch ash þ poultry manure at 10 t ha 71 each was most effective for sustainable management of soils and for improving agronomic productivity of yam.