A field experiment was conducted over two years to evaluate the effects of biochar (B) and poultry manure (PM) on soil properties, leaf nutrient concentrations and root yield of radish. The experiment consisted of 3 × 3 factorial combinations of B (0, 25 and 50 t ha⁻¹) and PM (0, 2.5 and 5.0 t ha⁻¹). Applications of B and PM on their own, and in combination, improved soil physical and chemical properties, leaf nutrient concentrations and yield components of radish. In the second year (2016), application of B on its own increased soil pH and concentrations of organic matter, N, P, K, Ca and Mg, as well as leaf nutrient concentrations and yield, but in the first year (2015) it only increased soil pH and organic matter. In both years, application of B influenced root length of the radish significantly. There was a significant interaction effect of biochar and poultry manure, which 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 resulted in the highest radish yield, with increases in root weight by 193%, 252% and 252% compared with B alone at 50 t ha⁻¹, at 25 t ha⁻¹ and no application of B or PM, respectively. Therefore, for a short season crop like radish the expected benefit of applying B on its own without PM may not be achieved within the first year.

Nutrients use efficiency of plants could be affected by the antagonistic or synergistic effects of two or more elements in the soil leading to decreased or increased yield. Field experiments were conducted in 2017 and 2018 cropping seasons at the Landmark University Teaching and Research farm, Omu-Aran, Nigeria, to determine the interaction between zinc (Zn) and phosphate (P) fertilizers on growth, yield, nutrient elements and some heavy metals composition of groundnut grown on an Alfisol. Treatments consisted of four levels of phosphorus (0, 40, 80 and 120 kg P ha^-1) and three levels of zinc (0, 4 and 8 kg Zn ha^-1). The experiment was laid out in a Randomized Complete Block Design (RCBD), replicated four times. The following parameters were taken: plant height, plant spread, total biomass, number of pods/plot, weight of pods/plot, number of seeds/plot, weight of seeds/plot. Laboratory analysis of some chemical constituents of groundnut seed was carried out to determine the nutrient and heavy metals composition. Results indicated that application of 8 kg Zn ha^-1 and 120 kg P ha^-1 had a synergistic effect on the growth parameters and antagonistic effect on the yield, yield parameters, some nutrient elements and beneficial heavy metals. Application of 8 kg Zn and 80 kg P ha^-1 is therefore recommended on an Alfisol without necessarily increasing the concentration of non-beneficial heavy metals in groundnut seed.

Field experiments were conducted during 2016 and 2017 cropping seasons in the derived agro-ecological zone of Nigeria to study the combined and sole effect of zinc and boron fertilizers on the growth, seed yield, and quality of groundnut (Arachis hypogaea L). The experiment was laid out in randomized complete block design (RCBD), replicated four times. Three levels of zinc (0, 4, and 8 kg·ha⁻¹) and four levels of boron (0, 300, 600, and 900 ml·ha⁻¹) were combined and evaluated. Groundnut seeds were analyzed at the end of the experiments to determine nutrient elements and some heavy metal contents. Data collected were subjected to Statistical Analysis of Variance using SAS 2000. Treatment means were compared using the Duncan multiple range test at 0.05 level of probability. The effect of zinc was not significant on the vegetative parameters, while application 8 kg Zn·ha⁻¹ significantly increased number of seeds, weight of seeds, seed yield per hectare, and seed quality though the values were similar to the application of 4 kg Zn·ha⁻¹ only on the seed yield and its parameters. Application of 600 and 900 ml B·ha⁻¹ gave higher and statistically similar values for vegetative parameters, yield, and yield parameters, while 600 ml B·ha⁻¹ significantly improved the seed quality. It can therefore be recommended that for optimum yield and seed quality, application of 8 kg Zn·ha⁻¹ combined 600 ml B·ha⁻¹ is sufficient in the study area without increasing the heavy metal concentration of groundnut seed.