Intercomparison of Crop Establishment Methods and the Efficacy of ZnO Nanoparticles on Crop Growth and Plant Stand in Rice under the Rice–Wheat System in the Eastern Indo-Gangetic Plains

This two-year field study (2023 and 2024) carried during kharif season at BHU, Varanasi investigated the comparative effects of conservation agriculture-based versus conventional agriculture practices and zinc management strategies (ZnO nanoparticles versus conventional ZnSO4) on plant stand establishment and crop growth in rice under the rice-wheat system. The experiment was conducted in a split-plot design with three crop establishment (CE) methods: CE1: PTR–CTW; CE2: RT DSR –SSW + RR; CE3: ZT DSR+WR - ZTW+RR were tested in the main plots. Seven zinc management treatments were used: Z0: RDF + no zinc application; Z1: RDF + soil application of zinc as basal (Zn @5 kg ha-1) through ZnSO₄. H₂O; Z2: RDF + three foliar sprays of ZnSO₄. H₂O @ 0.3%; Z3: RDF + seed priming with ZnO NPs @ 200 mg L⁻¹; Z4: RDF + seed priming with ZnO NPs @ 400 mg L⁻¹; Z5: RDF + 3 foliar sprays of ZnO NPs @ 100 mg L⁻¹; and Z6: RDF + 3 foliar sprays of ZnO NPs @ 200 mg L⁻¹ were evaluated in the sub-plots. The results showed that CE3 significantly improved the initial plant stand compared to CE2 and CE1. Plant height, crop growth rate (CGR), relative growth rate (RGR), and net assimilation rate (NAR) were highest under CE1 in the first year but were comparable to those under CE3 in the second year. Zinc management practices involving the foliar spray of ZnO nanoparticles (NPs) at 200 mg L⁻¹ (Z6) and 100 mg L⁻¹ (Z5) consistently improved growth parameters, followed by the foliar spray of ZnSO₄ (Z2) and seed priming with ZnO NPs (Z3 and Z4). The effects of Zn management on crop growth were more pronounced during the early and mid-growth stages but diminished with crop maturity. Thus, conservation agriculture-based crop establishment (CE3) and efficient Zn management using ZnO NPs are potential alternatives for improving stand establishment and crop growth in rice under the rice-wheat system in the Eastern Indo-Gangetic Plain region.