Indicadores físicos e químicos na ciclagem biogeoquímica de solos com diferentes tempos de cultivo sucessivo com arroz irrigado

Abstract

Rice (Oryza sativa L.) is the base food for almost half-global population. China, India, Indonesia, Vietnam, Thailand, Brazil, USA and Pakistan are the largest rice producers in the world. In Brazil, rice is grown in all regions, being the southern region the largest rice producer with 81.4% of the national production. In the state of Roraima, rice production is carried out in irrigated floodplains and last yields showed an average productivity of 7.1 t ha-1, considered the highest productivity in the northern region. In this sense, the state of Roraima presents favorable climatic and soil conditions for rice production, making it important to evaluate soil quality, being of whether physical, chemical or biological nature submitted to a different cultivation system, in order to contribute to the decision-making process on the use of most rational and sustainable technology for land use. The objective of this study was to determine the changes in physical and chemical indicators in biogeochemical cycling in irrigated rice soils with different successive cultivation times. The experiment was carried out in commercial plantation areas of the Paraíso farm, located in Roraima, Bonfim Municipality, between 3 ° 19 '01.56' 'N and 60 ° 23' 43.65 '' W coordinates. Installed in “Gleissolo Háplico Distrófico Tb” (Typic Fluvaquent – Soil Taxonomy, USA). The experimental design used was a complete randomized block design with four replications. The evaluations were performed in areas with 2 years (A2: conventional planting), 4 years (A4: conventional planting), 9 years (A9: three years No-tillage system), 14 years (A14: three years No-tillage system), and 26 years (A26: one year of No-tillage system) of rice development; and 0-0.10 m; 0.10-0.20 m and 0.20-0.30 m soil layers. To compare the effects of cultivated soil management, a native forest area was used as a control. In relation to physical indicators, A9 and A14 areas presented more clay texture, greater stability of aggregates, implied by high indexes of geometric mean diameter (GDM) and weighted mean diameter (WMD) along the assessed profile. In relation to chemical indicators, same areas showed the highest total organic carbon (TOC) content and a positive relation with total Nitrogen, total Phosphorus (Pt), inorganic Phosphorus (Pi), Calcium (Ca2+), Base Sum (SB), Cation Exchange Capacity (CEC) and Zinc (Zn2+) in the 0-0.10 m layers; 0.10-0.20 m and 0.20-0.30 m, K + in the 0-0.10 m layers; 0.10-0.20 m and Organic phosphorus (Po) in the 0-0.10 m layer. Furthermore, regardless of the soil management system, the availability of P increases with cultivation years. On the other hand, the management of areas A9, A14 and A26 favored the production of grains, reaching the highest harvest rates. Adverse conditions were observed in areas A2, A4 and A26 in relation to the physical and chemical indicators evaluated. In this sense, it was shown that the conversion of native areas to areas of rice production under flooded conditions, changes the physical and chemical attributes of the soil. However, reduced preparation and maintenance of crop residues on the soil surface contributes to the storage of organic carbon, improving soil quality over time.