Changes in Soil Fertility and Plant Uptake of Nutrients and Heavy Metals in Response to Sewage Sludge Application to Calcareous Soils

Abstract

Pot experiment was conducted to evaluate the response of lettuce to application of Sewage Sludge (SS) to calcareous soils. The following treattnents were investigated zero SS application (control), 20, 40, 80 and 160 t SS ha-'. Additional treatment (80 kg P,O, ha-') as diammonium phosphate (OAP) was included to represent the recommendation rate. Lettuce was grown for 8 weeks then the plant dry and fresh weights were recorded. Grounded plant tissue and soil were analyzed for chemical and physical parameters. Results showed that application of SS increased the fresh and dry weights over fertilizer and control treattnents. High rates (80 and 160 t ha-') of SS gave similarly the highest plant dry and fresh weights while the DAP fertilizer treattnent and the two lowest SS rates (20 and 40 ha-') resulted in similar plant growth. Macronutrients, microelements and heavy metals were increased with SS application over the control and the DAP fertilizer treatments. SS addition decreased soil pH and increased electrical conductivity, organic matter and soil P. Addition of SS increased DTPA-extractable micronutrients and heavy metals over the DAP fertilizer and the control treatments. Addition of 40 SS t ha-' was equivalent to the recommended fertilizer rate in increasing lettuce growth. Higher rates of SS resulted in farther increase in lettuce growth but resulted in higher plant heavy metal content. Therefore, addition of 40 t ha-' to calcareous soil is recommended to achieve acceptable level of plant growth with minimal adverse effect on plant and soil qualities. Key