Total Carbon and Nitrogen and Granulometric Fractions of Soil Organic Matter Under No-Till System and Conventional Tillage with Onion Cultivation

Objective: The objective of this work was to evaluate the total carbon (C) and nitrogen (N) contents and the granulometric fractions of soil organic matter (SOM) under different management systems with single and intercropped winter cover crops in the cultivation of onion in Ituporanga, SC.   Theoretical framework: Onion cultivation typically occurs in a conventional tillage system (CTC), which favors the loss of C and N from the soil due to soil mobilization. The vegetable no-tillage system (VNTS) uses sustainable practices with continuous soil cover and restricted soil tillage, promoting improvement of edaphic attributes.   Methodology: The experiment was implemented in 2009 and the collection of soil samples took place in 2019 in the layers of 0-5, 5-10 and 10-30 cm in the treatments under VNTS, being black oat (AV); rye (CE); oilseed radish (NB); rye + radish (CE+NB); black oat + oilseed radish (AV+NB) and spontaneous vegetation (VE). In addition to these treatments, two adjacent areas were used, one under CTS and the other in a secondary forest area (MATA). The content of total organic C (TOC), total N (NT), light organic matter in water (LOM), particulate organic carbon (POC), particulate nitrogen (PN), C associated with minerals (COam) and N associated with to minerals (NAM).   Results and conclusions: VNTS increased TOC and NT contents with the use of grass and cruciferous intercropping to the detriment of single crops and CTS. The LOM content was higher in VNTS with the use of single grasses and stood out in relation to VNTS with consortium. There were no differences for PN between MATA, CE and CE+NB, demonstrating that VNTS is efficient in raising these levels in substitution of CTS. The CE+NB consortium increased the levels of COam and NAM in the surface layer of the soil after replacing CTS with VNTS.   Research implications: In VNTS, the use of intercropping between cover crops is an efficient management in adding C and N to the soil, as the simultaneous cultivation of different species of cover crops produces straw with an intermediate C/N ratio, the roots exploit different soil extracts and nutrient cycling is more efficient.   Originality/Value: The results of this study are from a long-term experiment (10 years), which demonstrates the effectiveness of VNTS in recovering and increasing C and N levels in soil previously cultivated for a long period in the CTS, in addition to to match the forest area.