Effect of phosphorus in fertilizer on available cadmium and zinc uptake by sugarcane

Abstract

To enhance sugarcane yield, phosphorus is generally applied to soil in the form of NPK fertilizer. However, phosphorus (P) fertilizer is known as a source of Cd and some other metals. Besides, phosphorus to be uptake to plant may affect the uptake of other ions including Cd and Zn. Therefore, this study aimed to investigate phosphorus in fertilizer on available Cd and Zn in soil and hence in sugarcane. The study was conducted both in field and in pot experiment. In field experiment, soil and sugarcane samples were collected from three areas difference in the range of Cd concentration in soil (< 3, 3-20 and >20 mg Cd/kg) in Mae Sot district, Tak province, Thailand. These areas was applied with 16-16-8 NPK fertilizer at the rate of 50 kg fertilizer/rai in the first month after cultivation and a repeat application of fertilizers was conducted at the same rate in the fifth month. Pot experiment was set up in order to investigate the effect of P in the fertilizer on available Cd and Zn in soil and its uptake to sugarcane under the control conditions at various rates of fertilizer application. The soil used for pot experiment was taken from Cd contaminated areas in Mae Sot district with the range of < 3 mg Cd/ kg. In each experimental pot sugarcane was planted by a piece of mature cane stem as normally practice. The 16-16-8 NPK fertilizer was applied to every experimental pot at rate 0 (control), 50, 100 and 200 kg fertilizer/rai in the first month and the fifth month. Soil and sugarcane samples were collected at the end of the second and sixth months after cultivation, respectively for both field and pot experiment. As expected, the result from field experiment showed that available Cd and Zn in soil were significantly higher (P < 0.05) in the area contaminated Cd at the rate of >20 mg Cd/kg as compared to the other two areas (<3 and 3-20 mg Cd/kg). Consequently, the accumulation of Cd and Zn in sugarcane cultivated in the area of Cd contaminated >20 mg Cd/kg areas was higher than the other two areas. This is because the higher total Cd and Zn concentrations in soil tend to provide higher available Cd and Zn in soil and hence in sugarcane. For pot experiment, the fertilizer application rate showed insignificant affects on the total accumulation of Cd and Zn in soil. In contrast, the different fertilizer application rates affect on available Cd and Zn concentrations in soil and in sugarcane. The results showed that the higher the rate of the fertilizer application, the lower the available Cd and Zn concentration in soil and the lower Cd and Zn concentration in sugarcane. This may be explained by the higher P through increasing fertilizer application rate competed with Cd and hence reduced its uptake to the plant. The results also indicated that concentrations of Cd and Zn were highest in root and lowest in juice for both field and pot experiment.