The sustainability of a no-tillage mechanized transplanting rice system: an evaluation based on energy inputs, yield, and soil fertility

Tillage mechanized transplanting (TMT) is a widely used cultivating system for irrigated rice. However, methane gas emissions from it have raised environmental concerns. No-tillage (NT) mechanized transplanting (NTMT) offers a solution, as NT can reduce gas emissions relative to tillage, but its sustainability remains to be determined. We assessed the sustainability of NTMT by evaluating its energy inputs, yield, and soil fertility. Experiments were conducted in 2022 and 2023 at Yamagata University, Japan, in three paddy fields, with NTMT and TMT applied in half of each field. Energy inputs, rice growth, rice yield, and soil fertility indicators were measured. NTMT reduced the energy used for tilling, puddling, transplanting, and harvesting by 2971 MJ ha−1 but required an extra 78 MJ ha−1 for weeding, resulting in a net reduction of 2893 MJ ha−1, or 16.0 % of the total energy input into TMT. With effective management of weeds and weedy rice, NTMT can maintain comparable rice grain yields: 5309 kg ha−1 in NTMT versus 5924 kg ha−1 in TMT. Soil fertility measured as total C and N, available N and P, and exchangeable K was comparable or higher under NTMT. NTMT can be more sustainable than TMT if weeds and weedy rice are well-controlled. Applying NTMT to whole-crop silage rice is recommended because weedy rice can be used as feed.