 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com 186 DOI: 10.1002/jpln.200800309 J. Plant Nutr. Soil Sci. 2011, 174, 186–194 Use of reactive phosphate rocks as fertilizer on acid upland soils in Indonesia: accumulation of cadmium and zinc in soils and shoots of maize plants § Sri Rochayati 1,2 , Gijs Du Laing 1 *, Jörg Rinklebe 3 , Ralph Meissner 4 , and Marc Verloo 1 1 Department of Applied Analytical and Physical Chemistry, Laboratory of Analytical Chemistry and Applied Ecochemistry, Ghent University, Coupure Links 653, 9000 Ghent, Belgium 2 Indonesian Soil Research Institute, Jalan Ir. H. Juanda 98, Bogor 16123, Indonesia 3 University of Wuppertal, Department D, Pauluskirchstraße 7, 42285 Wuppertal, Germany 4 UFZ-Helmholtz Centre for Environmental Research, Department of Soil Physics, Lysimeter Research Station Falkenberg, Dorfstraße 55, 39615 Falkenberg, Germany Abstract A pot experiment was conducted to study the contribution of reactive phosphate rocks (RPRs) on the accumulation of Cd and Zn in 10 acid upland soils in Indonesia and shoots of Zea mays plants grown on these soils. Two types of RPR were used at a rate of 0.5 g (kg soil) –1 : RPRL containing 4 mg Cd kg –1 and 224 mg Zn kg –1 , and RPRH containing 69 mg Cd kg –1 and 745 mg Zn kg –1 . Zea mays was harvested at 6 weeks after planting. The application of RPRH signifi- cantly increased the concentrations of Cd in the shoots. The application of this RPR also in- creased the amount of Cd which could be extracted by 0.5 M NH 4 -acetate + 0.02 M EDTA pH 4.65 from the soils. More than 90% of the added Cd remained in the soil. As Zn is an essential element and the studied acid upland soils are Zn-deficient, increased plant growth upon RPR application might be partly attributed to Zn present in the phosphate rock. However, more experi- ments are needed to confirm this hypothesis. The Cd and Zn concentrations and CEC of the soils were important soil factors influencing the concentrations of Cd and Zn in the shoots of maize plants grown on these soils. Key words: Cd / Zn / bioavailability / mobility / maize plant / phosphorus Accepted June 6, 2010 1 Introduction Phosphorous (P) is one of the most limiting nutrients for crop production in acid tropical soils. Crops grown on these soils require high inputs of fertilizers, and consequently the finan- cial cost to obtain an optimum productivity is high. Because of the high cost of water-soluble P fertilizers, such as triple superphosphate, single superphosphate, and di-ammonium phosphate, there is an interest in identifying low-cost alterna- tive P fertilizers. Direct application of reactive phosphate rock (RPR) is one possible less expensive source of P. The use of RPR as a fer- tilizer already received some attention in the past. It has been shown to be suitable for direct application to acidic soils (Kha- sawneh and Doll, 1978; Hammond et al., 1986; Chien and Menon, 1995; Chien et al., 1995). Reviews of phosphate rock use in annual cropping systems in Indonesia indicated that direct application of RPR at initial rates of 80–360 kg P 2 O 5 ha –1 (35–157 kg P ha –1 ) not only increased yield of maize, upland rice, soybean, and groundnut on acidic soils but also resulted in similar or even higher yields than triple superpho- sphate (Partohardjono and Adiningsih, 1991). Since RPR slowly releases P to the soil (Allen et al., 1995), the direct application of RPR containing moderately soluble P com- pounds supplies P continuously and could maintain a P pool in the soil over a long period (Rajan et al., 1996). Nassir (2003) reported that the application of RPR at a rate of 300 kg P 2 O 5 ha –1 (131 kg P ha –1 ) was able to maintain resi- dual effectiveness over five cropping seasons on upland acidic soils in Indonesia. Nevertheless, RPRs contain heavy metals and other impuri- ties that may be harmful at certain concentrations upon their dissolution in the soil (FAO, 2004). Concentrations of Cd and Zn are highly variable in phosphate rocks. The Cd content varies from <1 to 100 mg Cd (kg PR) –1 (Sauerbeck, 1992; Syers and Cisse, 2002), whereas the Zn content varies be- tween < 2 and 2412 mg (kg PR) –1 (Sauerbeck, 1992). Cad- mium is one of the heavy metals, which may be highly toxic, even at very low concentrations (Jensen and Bro-Rasmus- sen, 1992). On the other hand, Zn is considered as an essen- * Correspondence: Dr. Du Laing; e-mail: Gijs.DuLaing@UGent.be § This publication is based on Rochayati, S. (2008): Reactive phos- phate rock application on acid upland soils in Indonesia: Effects on the availability of cadmium and zinc. PhD thesis, Ghent University, Belgium.