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The conversion of Pampa Biome soils into no-till system for grain production requires acidity correction, at least to fully neutralize exchangeable aluminum (Al). The aim of the study is to evaluate changes in solid phase acidity and Al speciation in soil solution that was conducted to prepare the soil for the implementation of a no-tillage system in a natural pasture area in Southern Brazil. We collected soil samples from the 0–5, 5–10, 10–15 and 15–20 cm layers in soils subjected, or not, to acidity correction to pH 6.0, as well as in soils with, and without, limestone incorporation through plowing and harrowing. Changes in the solid and solution phase attributes, such as soil acidity, were limited to 5 and 10 cm, respectively, 44 months after surface and incorporated liming. Regardless of liming addition to, or lack of thereof in the soil, Al found in the soil solution was mainly associated with organic carbon. This was the main way to decrease plant toxicity under these conditions, which can be supported by plant behavior, especially that of soybean. Liming induced the soil solution Al to exchange its ligand from organic carbon to hydroxyl. [ABSTRACT FROM AUTHOR]

• Surface liming reduced soil acidity down to −60 cm one year after its application. • Liming increased soybean grain yield by 9%, but it had no effect on cereal crops. • The lime reactivity had no effect on crop grain yield. • Gypsum did not increase crop grain yield in this moderate acidic Oxisol. • Combined application of gypsum and lime did not benefit crop yields. The low solubility of lime (CaCO 3) and the absence of soil disturbance in fields under no-tillage (NT) may diminish the effectiveness of surface liming to reduce exchangeable Al3+ (toxic to plants) and increase the base saturation in deep soil layers. However, the effects of subsurface soil acidity can be attenuated by applying agricultural gypsum (CaSO 4 ⋅2H 2 O), which is more soluble than lime, and thus, can leached bases (exchangeable Ca2+, Mg2+ and K+) and S-SO 4 2− to deeper soil layers as well as decrease Al3+ toxicity to plants. Therefore, gypsum can be applied individually or in combination with lime. Herein, we conducted a field experiment aiming to evaluate short- (1 year) and long-term (11 years) effects of surface liming and gypsum application on the chemical properties of the 0.00–0.10, 0.10–0.20, 0.20–0.40 and 0.40–0.60 m soil layers and also on crop yield of 22 crop seasons (i.e., 10 soybean, 3 maize, 4 white oat, 3 wheat and 2 barley crops). The study was performed in a clayey Typic Hapludox of moderate acidity managed under NT for more than 25 years in Guarapuava, Paraná State, southern Brazil. Three soil surface-applied lime strategies were tested in order to raise base saturation to 70%, namely: (a) 4.62 Mg ha–1 rate of lime of low effective calcium carbonate equivalent (ECCE = 75%); (b) 3.47 Mg ha–1 rate of lime with a high ECCE value (101%); and (c) the same rate of high-ECCE lime split in three applications (i.e., 1/3 at the start of experiment; 1/3 after 1 year and 1/3 after 2 years). A control treatment without liming was also conducted. The liming strategies were combined with four rates of agricultural gypsum (i.e., 0, 3, 6 and 9 Mg ha–1) applied at the start of the experiment. Our findings did not reveal synergistic effect of lime and gypsum on soil chemical properties nor on crop yield. Gypsum resulted in very slight gains in grain yield (4% on average) and limited to just 25% of cereal (corn and winter cereals) crop seasons. On the other hand, liming increased soybean yields by 14% in 40% of crop seasons. Gypsum was more efficient than lime in raising exchangeable Ca2+ levels up to −0.60 m in the short term; however, lime promoted greater reduction of soil acidity and had a more marked residual effect on exchangeable Ca2+ contents than gypsum. The liming strategies did no promote substantial differences in crop yield, but low-ECCE lime sustained better soil chemical condition to plant growth for a longer period. Surface liming efficiently reduced subsurface acidity in a moderately acidic Oxisol managed under NT even in the short-term, promoting increments on soybean crop yields. In this case, the application of gypsum rates did not bring additional benefits to soil or plant yield. [ABSTRACT FROM AUTHOR]

Abstract: The stabilisation of soil organic matter (SOM) is the result of the simultaneous action of three mechanisms: chemical stabilisation, biochemical stabilisation and physical protection. The objectives of this study were (i) to evaluate carbon-protection mechanisms in different SOM pools in soil aggregates and (ii) to identify the association of Ca2+ with total organic carbon (TOC) under the influence of surface liming in a medium-textured Oxisol in a long-term experiment under no-till system (NTS) in southern Brazil (25° 10′ S, 50° 05′ W). The treatments consisted of application of zero or 6tons ha−1 of dolomitic lime on the soil surface in 1993 and a reapplication of zero or 3tons ha−1 of dolomitic lime in 2000 to plots with or without previous lime application. Soil samples collected at depths of 0–2.5, 2.5–5, 5–10 and 10–20cm were separated into seven aggregate classes. In each of these classes, TOC, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) were analysed. The 8–19mm sized aggregates from the 0–2.5cm layer were assessed by energy-dispersive X-ray spectroscopy (EDS) for the elemental analysis of carbon (C) and calcium (Ca). The liming caused an accumulation of TOC in the aggregates, mainly at a depth of 0–2.5cm. The aggregates from soils treated with lime had a higher mean weight diameter (MWD) that resulted in the accumulation of TOC, especially in the 8–19mm aggregate class, that was linear and closely related with C input (R2 =0.99). The proportion of large aggregates in the treatments with lime was closely correlated with the TOC content of the whole sample. The largest dose of lime (9tons ha−1) resulted in higher TOC, POC and MAOC values, mainly in the 8–19mm aggregate class. The elemental analyses for C and Ca revealed similar spectra between them for the surface-liming treatments in the clay fraction found in the centres of the 8–19mm aggregates. The surface application of lime to NT fields provided greater stability and protection of the intra-aggregate C, presumably due to Ca2+ acting as a cationic bridge between OC and the kaolinite in the clay fraction. [Copyright &y& Elsevier]

Abstract: Crop residues that are left on the soil surface to serve as mulch can diminish the soybean response to surface application of lime under no-till management by ameliorating soil chemical and physical attributes and the plant nutrition. A field experiment was performed in the period from 2000 through 2003 in Parana State, Brazil, on a clayey-sandy Rhodic Hapludox. Soil chemical attributes and soybean [Glycine max (L.) Merrill] nutrition, grain yield, and quality were evaluated after surface application of lime and covering with crop residues of black oat (Avena strigosa Schreb) and corn (Zea mays L.) under a no-till system. Dolomitic lime was surface applied at the rates of 0, 2.5, 5.0, and 7.5 t ha-1 on the main plots, and three treatments with vegetable covering were applied on the subplots: (i) without covering, (ii) with covering of corn straw, and (iii) with covering of corn straw and black oat residue (oat-corn-oat). After 30 months, surface-applied lime increased soil pH and the exchangeable calcium (Ca2+) and magnesium (Mg2+) levels down to a 10-cm depth, independent of the vegetable covering treatments. The black oat and corn residues on the soil surface increased the soil exchangeable K+ level at the 5- to 10-cm depth. Liming increased leaf potassium (K) content and phosphorus (P) content in the soybean grain and reduced leaf zinc (Zn) content and manganese (Mn) content in the soybean leaf and grain. There was no effect of liming on soybean grain, oil, or protein yields, independent of the vegetable residues kept on the soil surface. The treatment with black oat covering and corn straw increased leaf N content, P content in the leaf and grain, and the contents of K, Mg, copper (Cu), and Zn in the soybean grain. It also increased soybean grain and protein yields. The corn straw left at the surface after harvesting was very important to the performance of the no-till soybean. [ABSTRACT FROM AUTHOR]