No abstract

Dwindling carbon (C) and nitrogen (N) levels in paddy soils decreases rice production and threaten human food security globally. The efficient maintenance of C and N fluxes in soil-rice systems is a crucial prerequisite for agricultural and environmental sustainability. Herein, we examined the C and N fluxes from 63 rainfed rice paddy fields under conventional farming (CF) and organic farming (OF) systems in Thailand. The C and N fluxes were measured based on a detailed analysis of relevant influxes (fertilizer, manure, and biomass addition) and effluxes (biomass harvest and greenhouse gas emission). The results demonstrated that the harvested grain and straw contributed to the most abundant C and N effluxes for both farming systems. The CH4 effluxes were moderate, whereas the N2O effluxes were meager relative to their total effluxes. Stubble incorporation and animal manure addition to soil were the most extensive C influxes. However, the primary N influxes were stubble incorporation and animal manure addition for the OF system, and chemical-N fertilizers for the CF system. Net C depletions were observed in both the CF and OF systems. However, net N was depleted and accumulated in the CF and OF systems, respectively. Straw incorporation to soils could restore the net C accumulations for the CF and OF systems and elevate the net N accumulation for both systems. This study highlighted that complete straw removal has exacerbated the C and N stock in soil-rice systems, inducing insecurity for the environment and the agricultural systems. Effective straw management is a simple approach for sustaining paddy rice production.

Soil phosphorus (P) plays an essential role in rubber tree plantations that are rapidly and extensively being established in Southeast Asia. However, available information is quite limited on soil P fractions and arbuscular mycorrhizal fungi (AMF) in the tropical region. Herein, we investigated P fractions and AMF community under natural forest and rubber plantations at different ages of 5 years, 11 years, and 22 years in tropical coarse-textured soils from Thailand. The studied loamy sand soils were acidic (pH=5.0-5.7) with low available P concentrations (1.73-6.48 mg/kg). Data on the P fractions data revealed that the labile P (water-extractable Pi and NaHCO3-extractable Pi) and moderately labile P (NaOH0.1-extractable Po and HCl-extractable Pi) pools in rubber-growing soils were higher than those in the natural forest soil. Elevated values of these properties were substantial with increasing stand ages. The rubber monocropping systems declined in the density and diversity of AMF spores compared to the natural forest site. Glomus badium, Rhizophagus fasciculatus, Acaulospora Laevis, and Ambispora appendiculata were the most dominant and tolerant AMF species across the rubber stands (>50% of the total species). The P fractions and AMF were correlated with soil labile-P forms. Soil labile and moderately P fractions were the important factors affecting the difference in AMF community. This study highlighted that long-term rubber plantations in tropical ecosystems promoted labile P fraction but demoted AMF density and diversity.