Sewage Sludge Impacts on Yields, Nutrients and Heavy Metals Contents in Pearl Millet–Wheat System Grown Under Saline Environment

TLDR: In this paper, a field trial was conducted for two consecutive years (2017-2019) with three irrigation levels [canal water (0.35 dS m−1), I1, 8 dSm−1, I2, I3, and I4] to assess domestic sewage sludge (SS) under saline conditions to boost crop productivity has become crucial.

Abstract: Salinity prompts heavy metals accumulation and adversely affects nutrient contents in soil and plants, thereby reducing crop yields. The assessment of domestic sewage sludge (SS) under saline conditions to boost crop productivity has become crucial. A field trial was conducted for two consecutive years (2017–2019) with three irrigation levels [canal water (0.35 dS m−1), I1; 8 dS m−1, I2; and 10 dS m−1 saline water, I3]; and five fertilization levels [control, F1; SS (5 t ha−1), F2; SS (5 t ha−1) + 50% RDF, F3; SS (5 t ha−1) + 75% RDF, F4; and RDF, F5]. The results revealed that treatment I3 (10 dS m−1) reduced the grain yield of pearl millet and wheat by an average of 31.2 and 32.6%, respectively, compared to I1 (0.35 dS m−1). However, among fertilizer treatments, F5 obtained significant highest grain and straw yields statistically at par with F4 treatment. Also, in the context of nutrients content in crops, a similar trend has been reported. In the addition, with the usage of saline irrigation (EC 8 and 10 dS m−1) and SS (5 t ha−1), the availability of heavy metals in crops and soil had increased (p = 0.05). The soluble ions in soil increased with increasing salinity levels of irrigation water. The extractability series of heavy metals were: Pb > Co > Ni > Cr > Cd. The addition of SS, however, recorded a higher concentration of DTPA-extractable metals in soil over control. The heavy metals content did not exceed toxicity levels in soil and plants. Hence, the incorporation of SS (5 t ha−1) resulted in saving 25% mineral fertilizers and, also combined use of SS with mineral fertilizers proved to be economically beneficial for crop production.