Effects of application of different wastewater sludge on loamy texture soil and plant growth

Abstract

The objective of this study was to determine the effects of four different wastewater sludges on loamy-texture soil chemical properties as well as plant dry weight and heavy metal uptake. Incubation experiment was performed in which sludges were applied at rates of 0, 40, 80, 120 and 160 t ha(-1), and the effects on soil properties were measured over a period of 150 days. The same doses of sludge were applied in a greenhouse experiment to determine the effects on plant (Brassica napus L.) growth and heavy metal contents.

The results showed that sludge treatment had significant effects (p <0.05 and p<0.01) on soil properties and plant dry matter and that the effects varied according to the application dosage and sludge properties. In the greenhouse experiment, plant dry weight, plant nutrient content and heavy metal content increased with increasing sludge application. However, high doses of sludge had negative effects on plant growth. The most unfavorable effects on plant growth were observed with the Si (BUSI(t) sludge. For example, the sludges were ranked by dry matter as S3>S4>S2>S1 sample.

According to the results of the incubation experiment, soil pH decreased and electrical conductivity (EC) value increased with increasing levels of sludge application. NH4-N, NO3-N, available P and DTPA extractable heavy metals also increased with the application rate of wastewater sludge. NO3-N content increased and NH4-N content decreased with days of incubation period.