Application of Sewage Sludge in a Rice (Oryza sativa L.)-Wheat (Triticum aestivum L.) System Influences the Growth, Yield, Quality and Heavy Metals Accumulation of Rice and Wheat in the Northern Gangetic Alluvial Plain

For a sustainable and profitable agriculture production system, balanced and integrated use of nutrients is a key strategy. In addition, partial replacement of chemical fertilizers with organics ones reduces both environmental concerns and economic costs and provides greater soil health benefits. With this hypothesis, an experiment was conducted to assess the yield and economic benefits of a rice-wheat cropping system (RWCS) as influenced by the joint application of sewage sludge (SSL) and fertilizer. The treatments comprised: without fertilizer or SSL; 100% recommended dose of fertilizers (RDF); 100% RDF + 20 Mg ha(−1) SSL; 100% RDF + 30 Mg ha(−1) SSL; 50% RDF + 20 Mg ha(−1) SSL; 60% RDF + 20 Mg ha(−1) SSL; 70% RDF + 20 Mg ha(−1) SSL; 50% RDF + 30 Mg ha(−1) SSL; 60% RDF + 30 Mg ha(−1) SSL and 70% RDF + 30 Mg ha(−1) SSL. The experiment was laid out in a randomized block design with three replications. The result of our study indicate that the highest percent increase in mean plant height i.e., ~14.85 and ~13.90, and grain yield i.e., ~8.10 and ~18.90 for rice and wheat, respectively, were recorded under 100% RDF + 30 Mg SSL ha(−1) treatment compared to 100% RDF, while 70% RDF + 20 Mg ha(−1) SSL produced a statistically equivalent grain yield of 100% RDF in RWCS. The application of 20 and 30 Mg SSL ha(−1) along with recommended or reduced fertilizer dose, significantly increased the heavy metal content in plant and soil systems above that of 100% RDF, but this enhancement was found within permissible limits. Moreover, the reduced use of SSL i.e., 20 Mg SSL ha(−1), resulted in lower heavy metal content in grain and soil than did the 30 Mg ha(−1) SSL treatment, but significantly higher than in the absolute control or 100% RDF treatment. In summary, the use of 20 Mg ha(−1) SSL along with 70% RDF provided a safer, profitable and sustainable option in a rice-wheat cropping system in the middle Ganegatic alluvial plain.