Effect of in situ incorporation of three types of green manure on soil quality, grain yield and 2-acetyl-1-pyrrolline content in tropical region

Fragrant rice is widely consumed worldwide due to its pleasant aroma and better cooking qualities. Incorporation of green manure plays a good substitutable role in reducing chemical fertilizer applications while enhancing soil fertility. Field experiments were conducted to evaluate the effects of in situ incorporation of different green manures on soil physio-chemical properties, nitrogen (N) uptake, grain yield and the 2-acetyl-1-pyrroline (2-AP) of subsequently grown fragrant rice across two seasons. Treatments included fragrant rice grown with fallow (T0 as control), with incorporation of rice biomass in field (T1), with incorporation of Sesbania biomass in field (T2), and with incorporation of Stylosanthes biomass in field (T3). Results showed that yields of T1, T2 and T3 were increased by on average of 13.1%, 29.1% and 23.9%, respectively, across two seasons compared with T0. And 2-AP contents in rice grains under T1, T2 and T3 were increased by 44.6–56.5%, 97.2–138.1% and 75.2–174.6%, respectively. Further analysis indicated that in situ incorporation of leguminous green manure significantly decreased soil bulk density, while increased the soil total organic carbon, and N availability. Thus, the plant N uptake and the partial factor productivity for N fertilizer (PFP_N) were markedly increased by incorporation of leguminous green manure. Results suggested in situ incorporation of leguminous green manure was beneficial to sustain the production of fragrant rice in tropical regions. The mechanisms underlying the improvement of 2-AP content of fragrant rice with incorporation of the leguminous green manure will be addressed in the future.