Green manuring improves soil quality, grain yield, and grain anthocyanin content in colored rice cultivated in tropical regions

Green manuring is the process by which vegetative crops are incorporated into the soil, and it plays a good substitutable role in reducing chemical fertilizer applications while enhancing soil fertility. Field experiments were conducted at Lingao City of Hainan Province in 2020 and 2021, to evaluate the effects of in situ incorporation of different green manures (fallow (as control), rice, sesbania, and stylosanthes) on soil physical and chemical properties, nitrogen (N) uptake, grain yield, and the grain anthocyanin content in colored rice. Treatments included colored rice cultivated with previous fallow (T0), with previous rice straw manure (T1), with previous sesbania manure (T2), and with previous stylosanthes manure (T3). The seedlings of the colored rice variety Suixiangheinuo were transplanted 23 days after the incorporation of green manure. Our results indicated that both the grain yield and grain anthocyanin content of colored rice were significantly increased when green manure was incorporated into the soil compared to that of the control. Therein, grain yields of T1, T2, and T3 were increased by an average of 12.7%, 29.0%, and 24.5%, respectively, across 2 years in comparison with those of T0. And grain anthocyanin content in colored rice under T1, T2, and T3 was increased by 7.2%–7.5%, 13.9%–24.2%, and 9.8%–20.6%, respectively. In addition, in situ incorporation of leguminous green manure in the soil significantly increased soil fertility and partial factor productivity for N fertilizer. The above results suggested that colored rice crops should be followed in rotation with leguminous green manure, which was beneficial to increasing both grain yield and grain anthocyanin content of colored rice. This research elucidated that the incorporation of leguminous green manure sustained the production of colored rice in tropical regions, which was beneficial to reconcile the relationship between rice production and environmental protection.