Little is known about the effect of nitrogen (N) application via biochar on the removal of trace elements by crops, and the effects with chemical fertilizers are inconsistent. We determined, from a previous study, the influence of increased N addition via biochars produced from switchgrass (SGB) and poultry litter (PLB) on cadmium (Cd) removal by ryegrass. The biochar rates of 0, 0.5, 1, 2, and 4% w/w were applied to a Cd-contaminated soil before seeding in a potting experiment with a complete randomized block design (CRBD). Ryegrass yield and N and Cd removed by harvest were strongly related (p < 0.05). The ryegrass yields increased up to 1% of PLB, and Cd removal was also the highest at 1% of PLB. The biomass of ryegrass roots increased with Cd accumulation (p < 0.05). Overall, the Cd transfer factor (TF) from ryegrass roots to shoots increased when up to 206 ± 38 kg N ha⁻¹ was removed in ryegrass shoots (p < 0.0001). The application of PLB up to 1% might be a viable option since it is a practical rate for handling operations requiring less volume of material than SGB. Additionally, the Cd concentration in the aboveground forage remained acceptable for grazing cattle. Future studies are encouraged to evaluate different sources of N fertilizers affecting Cd uptake on cash crops.

中文翻译：

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生物炭源氮对污染土壤中黑麦草去除镉的影响

关于通过生物炭施用氮（N）对农作物去除微量元素的影响知​​之甚少，而化肥的作用却不一致。从先前的研究中，我们确定了柳枝（（SGB）和家禽垫料（PLB）产生的生物炭增加的氮添加量对黑麦草去除镉（Cd）的影响。在采用完全随机区组设计（CRBD）的盆栽实验中播种之前，将0、0.5、1、2和4％w / w的生物炭比率应用于受Cd污染的土壤。黑麦草的产量与收获时去除的氮和镉有很强的相关性（p<0.05）。黑麦草的产量增加了PLB的1％，而Cd的去除率也最高达到PLB的1％。黑麦草根系的生物量随镉的积累而增加（p <0.05）。总体而言，当黑麦草芽中去除高达206±38 kg N ha ^-1时，从黑麦草根部到芽的​​Cd转移因子（TF）增加（p <0.0001）。最多使用1％的PLB是可行的选择，因为对于处理需要比SGB更少的材料的操作，这是一个实用的比率。此外，地上草料中的镉浓度对于放牧牛仍然可以接受。鼓励未来的研究来评估影响经济作物中镉吸收的不同氮肥来源。