Sewage sludge used as organic manure in Moroccan sunflower culture: Effects on certain soil properties, growth and yield components

The wastewater treatment and sludge production sectors in Morocco are recent. Considered as waste, no management strategy for sewage sludge (SS) has been implemented. Thus, its disposal definitely represents a major environmental problem since sludge is either incinerated, used as landfill or simply deposited near wastewater treatment plants. The objective of this study was to determine the effects of dehydrated SS on certain soil properties (pH, electrical conductivity (EC), Mineral nitrogen, available phosphate P₂O₅, and soluble potassium K₂O), and also on growth and yield components of the sunflower (Helianthus annuus L.). An experiment was conducted using six treatment rates (0; 0 + NPK; 15; 30; 60 and 120 t ha^-1). The results showed that soil pH was significantly affected by SS, becoming less alkaline compared to the control, while electrical conductivity increased significantly when the applied doses were above 30 t ha^-1. Also, a significant enrichment in mineral N and available phosphorus was detected in amended soil. However, no differences were found between pots having received the mineral fertilization and the SS at 15 t ha^-1. Stem height growth of the sunflower seedlings receiving SS increased significantly compared to the two controls. For both the aerial and root parts, significant increases in dry biomass accumulation were observed compared to the unamended plants. Net CO₂ assimilation (A_n) increased, while stomatal conductance (g_sw) and transpiration rates (T_r) decreased with increasing SS rates. SS application at 15 t ha^-1 presented similar values of the yield components compared to plants fertilized chemically. However, grain yield (in quintals ha^-1) was noted to be 2.4, 5 and 8 times higher in treatments receiving SS respectively at the rate of 30, 60 and 120 t ha^-1.