Seedling fertilizer in soil-less nursery establishment improves paddy performance and complements the early nitrogen requirements: A quantitative field analysis

Weak seedling vigor of machine-transplanted rice during the recovery stage often limits basal-tillering nitrogen (N) uptake and yield, particularly under the split urea application with the increasing N. In this experiment, the effect of tandem long-mat seedlings (TLMS) transplanted with seedling fertilizer (SF) on yield and N use efficiency (NUE) was studied. Three-season field experiments at two sites consisting of TSF (transplanting with 7.0 kg ha -1 SF) and T (transplanting without SF) based on five different dosages of basal-tillering N were conducted to comprehensively study the effect of SF in field. The results show that SF released rapidly after transplanting and significantly increased dry matter accumulation, N uptake and their rates during tillering stage. Consequently, TSF showed enhanced growth with early emerging tillers, significantly higher proportion of effective tillers and panicle numbers, and 7.8% higher yield than T. Consistently, basal tillering and total NUE (13.8%) of TSF was significantly higher than that of T. Notably, in some growing seasons, even with a 37.5 kg ha -1 reduction in basal-tillering N, TSF still achieved a comparable dry weight, N uptake and yield to that of T, supporting the quantitative significance of seedling fertilizer in TLMS. Further quantification through regression analysis of yield and dosage verified that 7.0 kg ha -1 N supplied via SF was equally effective as 24.1 kg/ha basal-tillering N, in terms of yield response. Overall, TLMS transplanting with SF is an effective strategy to enhance the early growth vigor, improve yield and NUE, and reduce basa-tillering N input in machine transplanted rice. This study successfully integrates the soilless nursery establishment with SF within mechanical rice-transplanting system and quantitatively demonstrating its contribution to post-transplantation performance of rice seedlings.