Rice yield and nutrient dynamics in a fertilizer-free and agrochemical-free paddy field with inter-tillage weeding

Abstract

Excessive fertilizer and agrochemical applications cause many environmental problems. Some studies in Japan have indicated that high yields can be obtained without fertilizers and agrochemicals and with frequent inter-tillage weeding. After conversion from conventional cultivation, we evaluated the plant conditions and soil nutrients of this cultivation system for five years (2018–2022) under three different inter-tillage frequencies: no inter-tillage (0-T), twice inter-tillage (2-T), and five times inter-tillage (5-T). Control plots (CI) were established in 2022, where fertilizers and chemicals were applied as a conventional method, to compare the yield. In the inter-tillage fields, the yield significantly decreased in the second year but increased in the fourth year, ultimately reaching 81 % of the fertilized control field yield in the final year. Higher frequency inter-tillage weeding improved rice growth by suppressing weeds within one season. Soil ammonium concentration and nitrogen in plants decreased in the second and third years and began to recover, contributing to increased yield. Without fertilizer application, the soil carbon content increased while the soil total nitrogen content decreased, and nitrogen mineralization is expected to be promoted with long-term inter-tillage practices. Different mechanical tillage before transplanting and inter-tillage weeding during the cultivation season did not affect soil organic carbon content. Phosphorus, potassium, and silica deficiency did not occur during the five years without fertilizer input. These results provide a fundamental understanding of fertilizer- and agrochemical-free rice cultivation and contribute to the development of new sustainable cultivation systems to reduce fertilizer and agrochemical applications.