Effects of cover crops on the physical protection of organic matter and soil aggregation

Abstract

The objective of this study was to evaluate the effects of cover crops grown under no-tillage on the aggregation and physical protection of organic matter in soil macro and microaggregates. The experiment consisted of a randomized complete block design with three replications. The following cover crops were investigated in corn rotation systems: T1 = Braquiária ruziziensis (Urochloa ruziziensis), T2 = Canavalia brasiliensis Mart. ex Benth., T3 = Pigeon pea 'BRS Mandarin' [Cajanus cajan (L.) Millsp.], T4 = millet 'BR05' [Pennisetum glaucum (L.) R.Br.], T5 = turnip-forage (Raphanus sativus L.), T6 = velvet bean (Mucuna aterrima Merr.) and T7 = native Cerrado vegetation as a reference environment. Soil was sampled at a depth of 0-10 cm in September 2015 for the determination of organic matter fractions in macro and microaggregates. There was a reduction in aggregate size and its stability when native Cerrado areas were converted into agricultural systems. Nevertheless, some cover crops such as velvet bean, millet and turnip-forage favored restructuring the soil, forming stable aggregates similar to the native Cerrado. Among the cover crops, millet was highlighted as presenting elevated capacity to accumulate labile organic carbon in macroaggregates (2.32 g C kg-1) and microaggregates (2.34 g C kg-1). These values are, on average, 60% higher than those presented by turnip-forage. In general, the conversion of land use under Cerrado vegetation to agroecosystems reduced the total organic carbon content, mainly due to macroaggregate breakup, resulting in a lower physical protection of soil organic matter.