Investigation of Biochar Application and Different Levels of Irrigation on Physico-chemical Properties and Microbial Respiration of Cadmium Contaminated Soil in Tomato Cultivation

Soil pollution with heavy metals and moisture stress are the main threats to food security in the world. The aim of this study was to investigate the effect of biochar on physico-chemical properties and soil microbial respiration in reducing cadmium (Cd) stress in tomatoes, and to determine the optimal irrigation level for plant growth. A factorial-based experiment in a randomized complete block design using three levels of rice bran (0 (B0), 3 (B3), and 6 (B6) ton/ha) and seven irrigation levels (50 (L50), 60 (L60), 70 (L70), 80 (L80), 90 (L90), 100 (L100), and 110 (L110) percent of full irrigation (L100) based on soil moisture depletion, respectively  were performed on tomato cultivation in the research greenhouse, Faculty of Agriculture, Lorestan University, in 2019. The results showed that the best treatments in improving soil physical properties (bulk density, total porosity, mean weight diameter, water-stable aggregates, and stability index), soil nutrients (nitrogen, phosphorus, potassium, iron, manganese, zinc, and copper), and increasing soil microbial respiration, were L90B6, L100B6, and L110B6 treatments. The best tomato fruit yield with 1459.00, 1588.70, and 1610.30 g plant-1 was observed in L90B6, L100B6, and L110B6 treatments, respectively, which have not significantly different. In addition, Cd concentration in tomato fruit in these treatments was 0.02 mg/kg, which is lower than that of the global average (FAO/WHO), while in treatments B0 and B3, severe toxicity of tomato fruit and reduced yield were observed. Therefore, in the irrigation level of %90 percent of soil moisture depletion (L100) with the application of 6 ton/ha rice husk biochar (B6), minimum Cd stress and maximum yield for the plant were observed, and more water consumption was prevented.