Evaluation of the Co-application of Sewage Sludge and Chemical Fertilizer on Forage Growth and Yield of Barley

In Tunisia, as around the world, the increasing production of sewage sludge (SS) is surging and the problem of its disposal becomes therefore a major environmental problem. Safe agricultural recycling of SS is considered an environment-friendly way of its disposal, since it could serve as a source of soil organic matter and other major nutrients (especially N). A study was carried out in rhizotrons to assess root and shoot growth and biomass production of barley crops (Hordeum vulgare L.) as influenced by the conjoint application of SS and conventional nitrogen fertilizer (MF). The treatments comprised: without MF or SS (T1), 100% N from MF (T2), 100% N from SS (T3), and three combinations of MF and SS as follows: 30% N from MF + 70% N from SS (T4), 50% N from MF + 50% N from SS (T5), and 70% N from MF + 30% N from SS (T6). The results indicated that all treatments led to an increase in root elongation and shoot growth of barley compared with control (T1). Plant height increased with SS application. Among the sources of N, the combinations containing more than 50% of N derived from SS (T3, T4, and T5) resulted in highest growth and yield (roots and shoots) of barley. T6 (30% N from SS + 70% N from MF) gave nearly equal yield than T2 (100% N from MF). Results indicated that application of SS would reduce the excessive use of chemical fertilizers (by at least 30%), and its environmental risks associated with nutrient losses without compromising yield and economic advantages. Nevertheless, to ensure its safe agricultural valorization, SS should be free from pathogenic organisms and contain acceptable levels of inorganic and organic pollutants.