Long-term Impact of No Tillage in Two Intensified Crop Rotations on Different Soil Organic Matter Fractions in Argentine Rolling Pampa

Abstract

It is expected that the agricultural intensification occurred in recent decades in the Argentine Rolling Pampa significantly alters the SOM reserves. Therefore, it is necessary to identify soil organic carbon (C) and nitrogen (N) fractions to understand the functionality and stabilization of these reserves. Our objectives were to study the NT effect in two crop rotations, corn-double cropped wheat/soybean (MWS) and double cropped wheat/soybean (WS) on: 1) SOM and its particle size and biological fractions contents, 2) C and N stubble biomass and 3) some soil properties in order to explain the SOM differences found. The larger biomass residue remaining on the soil surface under NT promoted higher aggregate stability and lower soil temperature and pH. At 0-5 cm soil depth, NT exhibited higher C and N contents, for both uncomplexed and intimately associated to the mineral components fractions. However, the results indicated variations in the SOM protection according to the rotation: in MWS the high aggregate stability showed better physical protection, while in WS the greater cation exchange capacity and the lower value of N released by anaerobic incubation would indicate the presence of transformed SOM. At 5-20 cm soil depth, only in WS, C microbial biomass was higher with a low metabolic rate, indicating again the presence of highly decomposed SOM. The results obtained in WS under NT would indicate the possibility of achieving slower recycled of the SOM.

Effect of Continuous Agriculture of Grassland Soils of the Argentine Rolling Pampa on Soil Organic Carbon and Nitrogen

“…One possible explanation is that the sites with less than twenty years of tillage (1970-1990s), as opposed to the oldest sites, have been, in general, cropped in soybean monoculture or soybean double cropped with wheat with many tillage operations per year, including mechanical weed control, and sometimes carried out under conditions, which favored mineralization. Besides, we have previously suggested that soybean accelerates SOM decomposition [77]. The comparison of the SOC stocks between soybean monoculture (site A) and crop rotations (T period) 33 years after the introduction of agriculture showed a smaller SOC stock with soybean monoculture than with crop rotation (Figure 7(a)).…”

Projection of Soil Organic Carbon Reserves in the Argentine Rolling Pampa Under Different Agronomic Scenarios. Relationship of these Reserves with Some Soil Properties

“…The type and quantity of the crop residue input to the soil are among possible stabilization factors [67]. In support of this idea, we have previously found higher SSI in M than in S under NT [68] and the same tendency for MWS compared with WS [31]. The latter would indicate different mechanisms of stabilization between rotations with or without maize: a very important physical protection of macroaggregates around organic matter of recent incorporation and around POM [69,70].…”

“…However, under CP, POC was higher when crop sequences included maize due to the nature and morphology of its residue, which offers a contact surface with the soil of about half of wheat stubble [63] and thus leads to a low rate of mineralization [64]. In contrast, in WS, besides the high contact of the wheat residue with the soil, the fall of soybean leaves of second sowing (rich in N) accelerates the decomposition of wheat straw, leading to the incorporation of very processed fractions and relatively slower SOM turnover times into the soil, not measured as POC [31].…”

“…Efforts are being made to relate such kinetically defined pools to the biophysical or chemical features of the measurable organic fraction and to associate nutrient with carbon dynamics [21,30]. The organic matter fractions related to the active and slow pools influence nutrient supply, determine soil aggregation and reflect management practices [21,28,31]. More recalcitrant SOM fractions that are equated with the slow, passive or resistant pools are more relevant for long-term C sequestration, sorption, cation exchange capacity, and soil waterholding capacity [21].…”

A Review on Impact of Tillage and Nutrient Management on Maize Production in Indian Scenario

“…Due to the availability of herbicides, insecticides and fungicides and also more mechanization, the farmers prefer new tillage options compared to conventional tillage that is required mainly for seedbed preparation and weed control (Mohanty et al, 2006). The research findings have confirmed that minimum tillage increases aggregate stability Rusu (2005), zero tillage also promotes high aggregate stability, decreases soil temperature and maintains high carbon and nitrogen (Irizar et al, 2013). Zero tillage also reduces weed population in wheat (Sen et al, 2002).…”