Comprehensive evaluation of sewage sludge and sewage sludge char soil amendment impact on the industrial hemp growth performance and heavy metal accumulation

Industrial hemp (Cannabis sativa L.) has emerged as a potential multipiurpose crop: fibre crop, energy crop, and phytoextractor of pollutants from the soil. However, the multipurpise grwoth of hemp was restricted as its cultivation in EU was legalized only in the past two decades. Most scientific researches of sewage sludge (SS) describe it at relatively low application levels for cultivation of different crops. Such lack of information requires a wide range of practices for fertilizing hemp with high level of sewage sludge or sewage sludge char (SSCh) doses. At this moment there are no guidelines for sewage sludge char fertilization of energetic plants, depending on soil type. The aim of the study was to analyze and compare SS and SSCh soil application effect on industrial hemp (Cannabis sativa L.) growth performance, and heavy metals accumulation to determine optimum SS or SSCh application rates for the growth of hemp. The experimental design consisted of four treatments: 1-25; 2-50; 3-100; 4-200 of sewage sludge and sewage sludge char Mg ha(-1), and control soil (clay loam). It was determined that hemp ability to accumulate heavy metals depending on fertilisation intensity of sewage sludge and sewage sludge char decreased in all parts. Heavy metal distribution of hemp was selective; therefore their contents were decreasing in the following order: roots > stems > leaves. The study has confirmed the nutritional value of SS and SSCh. The potential of using the sewage sludge and its char as a source of organic matter for improvement of clay loam soil and a reasonable production of bioenergy crop like hemp without the use of inorganic fertilizers was shown.