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Soil with heavy metals contamination, mainly lead (Pb), cadmium (Cd), and chromium (Cr) is a progressively worldwide alarming environmental problem. Recently, biochar has been used as a soil amendment to remediate contaminated soils, but little work has been done to compare with other organic amendments like compost. We investigated biochar and compost's comparative effect on Pb, Cd, and Cr immobilization in soil, photosynthesis, and growth of maize plants. Ten kg soil was placed in pots and were spiked with Pb, Cd, and Cr at concentrations 20, 10, 20 mg kg−1. The biochar and compost treatments included 0, 0.5, 1, 2, and 4% were separately applied to the soil. The crop from pots was harvested after 60 days. The results show that the highest reduction of AB-DTPA extractable Pb, Cd, and Cr in soil was 79%, 61% and 78% with 4% biochar, followed by 61%, 43% and 60% with 4% compost compared to the control, respectively. Similarly, the highest reduction in shoot Pb, Cd, and Cr concentration was 71%, 63% and 78%with 4% biochar, followed by 50%, 50% and 71% with 4% compost than the control, respectively. The maximum increase in shoot and dry root weight, total chlorophyll contents, and gas exchange characteristics were recorded with 4% biochar, followed by 4% compost than the control. The maximum increase in soil organic matter and total nitrogen (N) was recorded at 4% biochar application while available phosphorus and potassium in the soil at 4% compost application. It is concluded that both biochar and compost decreased heavy metals availability in the soil, reducing toxicity in the plant. However, biochar was most effective in reducing heavy metals content in soil and plant compared to compost. In the future, more low-cost, eco-friendly soil remediation methods should be developed for better soil health and plant productivity. [ABSTRACT FROM AUTHOR]

In this study, we explored the role of biochar (BC) and/or urease inhibitor (UI) in mitigating ammonia (NH3) and nitrous oxide (N2O) discharge from urea fertilized wheat cultivated fields in Pakistan (34.01°N, 71.71°E). The experiment included five treatments [control, urea (150 kg N ha−1), BC (10 Mg ha−1), urea + BC and urea + BC + UI (1 L ton−1)], which were all repeated four times and were carried out in a randomized complete block design. Urea supplementation along with BC and BC + UI reduced soil NH3 emissions by 27% and 69%, respectively, compared to sole urea application. Nitrous oxide emissions from urea fertilized plots were also reduced by 24% and 53% applying BC and BC + UI, respectively, compared to urea alone. Application of BC with urea improved the grain yield, shoot biomass, and total N uptake of wheat by 13%, 24%, and 12%, respectively, compared to urea alone. Moreover, UI further promoted biomass and grain yield, and N assimilation in wheat by 38%, 22% and 27%, respectively, over sole urea application. In conclusion, application of BC and/or UI can mitigate NH3 and N2O emissions from urea fertilized soil, improve N use efficiency (NUE) and overall crop productivity. [ABSTRACT FROM AUTHOR]

An important source of the destructive greenhouse gas, nitrous oxide (N2O) comes from the use of ammonium based nitrogen (N) fertilizers that release N2O in the incomplete conversion (nitrification) of NH4+ to NO3ˉ1. Biochar has been shown to decrease nitrification rates and N2O emission. However, there is little information from semi-arid environments such as in Pakistan where conditions favor N2O emissions. Therefore, the object was to conduct field experiment to determine the impact of biochar rates in the presence or absence of urea amended soils on yield-scaled N2O emissions, and wheat yield and N use efficiency (NUE). The experiment on wheat (Triticum aestivum L.), had a randomized complete block design with four replications and the treatments: control, sole urea (150 kg N ha−1), 5 Mg biochar ha−1 (B5), 10 Mg biochar ha−1 (B10), urea + B5 or urea + B10. In urea amended soils with B5 or B10 treatments, biochar reduced total N2O emissions by 27 and 35%, respectively, over the sole urea treatment. Urea + B5 or + B10 treatments had 34 and 46% lower levels, respectively, of yield scaled N2O over the sole urea treatment. The B5 and B10 treatments had 24–38%, 9–13%, 12–27% and 35–43%, respectively greater wheat above-ground biomass, grain yield, total N uptake, and NUE, over sole urea. The biochar treatments increased the retention of NH4+ which likely was an important mechanism for reducing N2O by limiting nitrification. These results indicate that amending soils with biochar has potential to mitigate N2O emissions in a semi-arid and at the same time increase wheat productivity. [ABSTRACT FROM AUTHOR]