Rice intensification has been very successful in Indonesia and was even appreciated by FAO in 1985. However, despite the success, paddy soils are frequently polluted with Pb and Cd which are mostly derived from phosphate (P) fertilizers. Considering that the soils have been used for the long-term cultivation, Pb and Cd contents both in the soil and rice have exceeded the tolerance level in food as defined by WHO namely 2 and 0.24 mg kg-1, respectively. The highest Pb and Cd were found in soils cultivated for 80 years in Musi Rawas, Indonesia with values of 20.56 mg kg-1 and 0.72 mg kg-1 for soil and 3.11 mg kg-1 and 0.29 mg kg-1 for rice, while the lowest was found at 20 years with values of 17.82 mg kg-1 and 0.26 mg kg-1. Furthermore, the highest rice Pb and Cd were obtained at 80 years of cultivation with values of 3.11 and 0.29 mg kg-1, respectively, while the lowest was found at 20 years with values of 2.35 mg kg-1 Pb and 0.15 mg kg-1 Cd. Therefore, these metals need to be managed immediately. One of the methods to detoxify heavy metals is by application of organic material. Through a chelating process, heavy metals are immobilized and not absorbed by rice. Based on the results, rice straw biochar and compost at a rate of 10 tons ha-1 separately reduced Pb and Cd in soil from 13.60 to 3.00 mg kg-1 and 13.60 to 5.98 mg kg-1 for Pb and 0.62 down to 0.29 mg kg-1 and 0.64 down to 0.42 mg kg-1 for Cd, respectively.

Long-term cultivation of paddy soils has resulted in Pb and Cd accumulation that exceeds the WHO tolerance levels of 2 mg kg−1 and 0.24 mg kg−1 in food. In Musi Rawas, South Sumatra, Indonesia, the paddy soils with the greatest levels of Pb and Cd were those that had been intensively farmed for 80 years, reaching the concentrations of 20.56 mg kg−1 Pb and 0.72 mg kg−1 Cd for soil, and 3.11 mg kg−1 Pb and 0.29 mg kg−1 Cd for rice. The lowest concentrations were obtained with 20 years of cultivation at 17.82 mg kg−1 and 0.26 mg kg−1, for Pb and Cd in soils, respectively. The Pb content in the paddy fields in Pati, Central Java, ranged from 0.23 to 2.55 mg kg−1, while the Pb content in the lowland watershed of Solo Hilir ranged from 0.20 to 2.94 mg kg−1. The highest concentration of Pb and Cd in rice was found at 80 years old in paddy soils with the value of 3.11 mg kg−1 and 0.29 mg kg−1, respectively. The lowest concentrations were found at 20 years old of soils with a value of 2.35 mg kg−1 Pb and 0.15 mg kg−1 Cd, respectively.