Soil organic matter conservation, paramount in tropical agriculture, is affected by the composition of
cultivated plant species and the input of dry matter and nitrogen into the system. However, SOM
development in tropical soils managed under no-till in the long term is not well understood. The
objective of this study was to evaluate SOM concentration and quality as a result of crop rotations under
NT in two soils in Botucatu, Brazil, over a 10-year experimental period (2003–2012). Crop rotations
including grasses and a legume grown in the fall/winter and spring were conducted for seven years in a
clay Rhodic Hapludox. In a clay Typic Rhodudalf, crop rotations were compared with a fallow/chiseled
treatment for 10 years. The cash crop was soybean grown every year in the summer. In both experiments,
SOM lability was affected mainly by the spring crops. The absence of spring cover crops in chiseled
treatments resulted in less total organic carbon in the 0.0–0.10 m soil depth. Soil concentration of TOC and
its fractions were higher under crop rotations with higher nitrogen input, especially where sunn hemp
was grown in spring. The strongest effects occurred in the Typic Rhodudalf, probably as a result of its
higher clay content and the longer period under crop rotation. Under NT, the increase in labile and stable
SOM is limited by the lack of cover crops in the spring or N availability. However, SOM humification
degree is decreased with higher C input. These results highlight the importance of the use of cover crops
and nitrogen inputs in soil conservation strategies and the sustainability of agricultural systems in the
tropics.
Soil organic matter conservation, paramount in tropical agriculture, is affected by the composition ofcultivated plant species and the input of dry matter and nitrogen into the system. However, SOMdevelopment in tropical soils managed under no-till in the long term is not well understood. Theobjective of this study was to evaluate SOM concentration and quality as a result of crop rotations underNT in two soils in Botucatu, Brazil, over a 10-year experimental period (2003–2012). Crop rotationsincluding grasses and a legume grown in the fall/winter and spring were conducted for seven years in aclay Rhodic Hapludox. In a clay Typic Rhodudalf, crop rotations were compared with a fallow/chiseledtreatment for 10 years. The cash crop was soybean grown every year in the summer. In both experiments,SOM lability was affected mainly by the spring crops. The absence of spring cover crops in chiseledtreatments resulted in less total organic carbon in the 0.0–0.10 m soil depth. Soil concentration of TOC andits fractions were higher under crop rotations with higher nitrogen input, especially where sunn hempwas grown in spring. The strongest effects occurred in the Typic Rhodudalf, probably as a result of itshigher clay content and the longer period under crop rotation. Under NT, the increase in labile and stableSOM is limited by the lack of cover crops in the spring or N availability. However, SOM humificationdegree is decreased with higher C input. These results highlight the importance of the use of cover cropsand nitrogen inputs in soil conservation strategies and the sustainability of agricultural systems in thetropics.
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