Abstract
The conversion of conventional tillage system (CTS) into no-tillage system (NTS) for onion crops with use of soil cover crops increases carbon and nitrogen contents in the soil aggregates. The objective of this work was to evaluate the effects of combinations of different plant species and soil management systems using rotation with soil cover crops for onion crops on the light organic matter (LOM), carbon (C), and nitrogen (N) contents in the organic matter granulometric fractions in soil macroaggregates and bulk soil. A nine-year experiment (2007-2016) was conducted using the treatments (T): maize-onion in NTS (T1); soil cover crops (winter)-onion in NTS(T2); maize-winter grasses-onion in NTS (T3); velvet bean-onion in NTS (T4); millet-soil cover crops (winter)-onion in NTS (T5); velvet bean-rye-onion in NTS (T6); maize-onion in CTS (T7); intercropped soil cover crops (summer)-onion in NTS (T8). C and N contents in the LOM, particulate organic C and N (POC and PON), and mineral- associated C and N (MOC and MON) were evaluated in soil macroaggregates (8.0 to 2.0 mm) and bulk soil (<2.0 mm) from the 0–5 cm, 5–10 cm, and 10–20 cm layers. High diversity and combinations of plant species in T2-T6, and T8 resulted in higher POC and MON contents in aggregates, and higher MOC and PON contents in bulk soil, when compared to T1 and T7. T2 was a better option to increase LOM and POC contents in aggregates (0-5 cm). The evaluation of POC (0–5 cm), PON, and MON (0-10 cm) contents in soil aggregates showed more significant differences between the treatments than the contents found in bulk soil. The onion crops under NTS combined with use of rotations with soil cover crops were more efficient to improve the evaluated soil attributes than those under CTS.
Highlights
Onion (Allium cepa) is a vegetable grown worldwide in approximately 9.2 million of hectares; China, India, and the USA are the main producers (FAO, 2020)
The frequent soil turning caused by the conventional tillage system (CTS) in the treatment T7 resulted in lower particulate organic C and N (POC and particulate organic nitrogen (PON)) contents in soil macroaggregates and bulk soil (0–5 cm layer) when compared to treatments under no tillage system (NTS)
The use of CTS (T7) resulted in lower light organic matter (LOM), LOM-C, and LOM-N contents in the soil surface layer when compared to the other treatments
Summary
Onion (Allium cepa) is a vegetable grown worldwide in approximately 9.2 million of hectares; China, India, and the USA are the main producers (FAO, 2020). Brazil is the tenth largest onion producer, with an estimated production of 1.61 million Mg in 2017, which decreased to 1.55 million Mg in 2018. Santa Catarina (SC) is the largest onion producing state in Brazil, with approximately 470,000 and 529,210 Mg in 2018 and 2019, respectively; this production is concentrated in the Upper ItajaíRiver Valley, with emphasis in the municipality of Ituporanga, which leads the onion production (Menezes Junior et al, 2013; SEAP, 2017; IBGE, 2020). Producers in SC traditionally use conventional tillage system (CTS) to prepare soils for onion crops, with frequent soil turning and use of highly-soluble soil fertilizers. Onion crops in CTS have degraded physical-chemical attributes of the soil, requiring alternatives to this system, such as no-tillage system (NTS) (Loss et al, 2015; Santos et al, 2018a,b; Loss et al, 2017a; Comin et al, 2018; Ferreira et al, 2018)
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