Scientific Publications

Galantini, J.A.; M. Duval; J.M. Martinez; V. Mora; R. Baigorri & J.M. García-Mina. 2016. Quality and quantity of organic fractions as affected by soil depth in an argiudoll under till and no-till systems. International Journal of Plant & Soil Science 10 (5) - doi:10.9734/IJPSS/2016/25205

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Extended abstract 

Soil organic matter (SOM) is made up of compounds with diverse biochemical properties and varying degrees of association to the mineral matrix. These organic compounds are a continuum of materials whose cycling rate ranges from weeks to millennia. This continuum can be conceptually divided into discrete kinetic pools. A large number of SOM fractionation and characterization techniques have been developed to gain an insight into the stabilization and destabilization mechanisms that underlie SOM dynamics in the short and long term (Galantini & Suñer, 2008).

Most studies used to apply only one type of extraction procedure, i.e. either chemical or physical separation. Nevertheless, the effects of cropping practices can be better understood if both methods are combined.

Our hypothesis is that under different tillage systems soil moisture and carbon input change both the quantity and quality of labile soil organic fractions at different depth levels.

The objective of this study was to evaluate the effect of 25 years of tillage (conventional tillage and no-tillage) on the quantity and quality of physically and chemically separated soil organic carbon fractions, and to determine the main physico-chemical changes of humic substances at different soil depths.

Methodology:

The field experiment was carried out at Tornquist (38º 07’ 06” S - 62º 02’ 17” O), Argentina, and soil sampling was performed during wheat seeding (June 2011) at 0-5, 5-10, 10-15 and 15-20 cm depth.

Total soil organic carbon (SOC) content and the following fractions were determined: coarse particulate (POC_c, 105-2000 µm), fine particulate (POC_f, 53-105 µm) and mineral-associated (MOC, 0-53 µm) organic carbon; humic (HA) and fulvic (FA) acids; and total (CH_t) and soluble (CH_s) carbohydrates. The main physico-chemical properties of HA and FA were analyzed using both FT-IR and fluorescence spectroscopies.

Results and conclusions:

After 25 years under two tillage systems, total SOC at the 0-20 cm depth was 9% higher in no-tilled than in tilled soil. The POCf (53 to 105 µm) was the SOM fraction that turned out to be the most sensitive to tillage effects, as others studies (Duval et al., 2013; Galantini et al., 2014; Duval et al., 2016).

The no-tillage system presented a different pattern which can be related to distribution of crop residues and conditions for humification along the soil depth.

Residue cover (NT) and soil tillage mixing (CT) produced contrasting conditions for organic matter transformation and humification. The surface NT soil (0-5 cm) had highest C input with better conditions for its transformation than deeper layer. Under CT, however, the tilled layer (0-10 to 0-15 cm) presented similar residue input and condition for its transformation, which was slow down probably by its driest condition.

The POC_c:POC_f:MOC ratio at 0-20 cm was similar for NT (3:14:82) and CT (5:10:84); however, differences were found across soil depths.

Soil tillage system produced different trends in the molecular functionality of HA fraction (Galantini & Rosell, 1997; Rosell et al., 2000). The conventional tillage system showed higher molecular humification, starting by CH-degradation, at more superficial soil depths. The no-tillage system, however, presented changes which are more difficult to interpret in the context of a simple humification process where microbial activity, oxygen availability, and/or labile carbon content are governed by soil depth. In fact, some results indicated that, apart from processes linked to SOM aerobic degradation, other relevant factors might be involved, mainly residue cover effect on SOM dynamics and humification across depths.

Distribution of crop residues and soil moisture modified concentration of soil organic fractions as well as the characteristics of humic and, particularly, fulvic acids.

Texture influence on soil phosphorus content and distribution in semiarid Pampean grasslands

Suñer L., J.A. Galantini. 2015. Texture influence on soil phosphorus content and distribution in semiarid Pampean grasslands. InternationalJournal of Plant & Soil Science (ISSN: 2320-7035) Vol.: 7, Issue.: 2 109-120, no.IJPSS.2015.136, PDF

Extended Abstract

Soil texture affects the soil environment and the mineralization of soil organic matter (SOM) in several ways. It has been reported that a rich clay content in the topsoil results in high levels of soil organic matter; at the same time, it enhances nitrogen, phosphorus and sulphur availability (Galantini et al., 2004; Duval et al., 2016). Soil P (phosphorus) equilibrium and availability can be modified by soil texture as a consequence of changes in physicochemical properties, in phosphate adsorption-desorption-diffusion processes, and in SOM mineralization-immobilization processes.

Physical fractionation methods based on SOM particle size have been developed to separate organic fractions with different characteristics and dynamics (Andriulo et al., 1990; Galantini et al., 1997). It is therefore now possible to distinguish between SOM associated with the fine and with the coarse fractions, which have different structures and roles. The fine soil fraction (clay, silt) corresponds to a more humidified or mineral-associated organic matter (MOM), and the coarse fraction (different sizes of sand) to less transformed, labile, light or particulate organic matter (POM). Considering that both fractions are crucial to soil fertility, it is important to determine the organic (Po) and inorganic (Pi) phosphorus contents in each size fraction and to relate them to soil texture. Differences in P content are expected to be found in both particle size fractions: the fine fraction is likely to contain the more stable Po (Po-MOM) and the more available Pi (Pi-clay and silt sizes); the coarse fraction, instead, is assumed to contain the more labile Po (Po-POM) and Pi (Pi-sand size) with low availability in the short term.

The hypothesis is that soil texture affects the equilibrium of the different P-forms in soils of the semiarid Pampas region, mainly through stabilization in the resistant organic forms of fine-textured soils and accumulation in the labile organic forms of sandy soils. The aim of the study is to determine the content and distribution of the main P-forms in texturally different soils and to relate them to the available P-index.

Soil samples (0-0.15 m) were collected from 27 sites with different textures in a 25-year-old pasture located in the Experimental Station of Bordenave, Argentina (63°01’20”W; 37°51’55”S). Soil particle size fractions were obtained through wet sieving by separating the fine (0-100 µm) and coarse (100-2000 µm) fractions. Soil organic matter was determined in both fractions, and thus mineral-associated (MOM) and particulate organic matter (POM) were obtained, respectively. Extractable (Pe), organic (Po), inorganic (Pi) and total extractable (Pt) phosphorus were determined. Occluded P (Pocl) was calculated as the difference of [Pt - (Po+Pi)] applied to the whole soil and the particle fractions.

In these soils, texture determines P content and the equilibrium of its different forms. Available P-forms (estimated by Pe) were related to the inorganic form present in the fine fraction of the soil. Phosphorus content in its different forms was closely associated with soil fractions. The level of Po was higher in the coarse fraction of the soils containing more fine fractions. All the studied P-forms were higher in fine-textured soils than in coarse ones. However, P-forms in particle size fractions showed different tendencies. In coarse-textured soils, Po in MOM was lower than in fine-textured ones, whereas P-content was higher in MOM and lower in POM compared with fine-textured soils (Rosell et al., 2000).

Based on these results as well as previous ones, we propose a conceptual model to identify P changes in soils of different textures (Galantini et al.2005, 2007; Rosell et al., 2000; Suñer & Galantini, 2012; Suñer et al., 1998, 2002, 2013, 2014; Zalba & Galantini, 2007).

Soil organic fractions and their P-content within the sand fraction are inside the labile pool, whereas those within the silt and clay fractions are inside the intermediate and passive pools. Inorganic minerals of the coarse fraction can be considered a passive pool of P, while P in the fine fraction represents an active pool. According to this finding, a conceptual model can be proposed where P could be linked to SOM fractionation schemes. The principal flows in this model are a) weathering and physico-chemical processes, which reduce the size of coarse minerals until mineral particles reach a size below 50 µm and are then included in the fine fraction; b) humification, by which organic inputs are transformed into more complex molecules with a lower size; c) mineralization of SOM fractions, which produce nutrient release and make P available for plants; d) physico-chemical equilibrium, e) P-uptake by plants; f) recycled P, by which crop residue returned to the soil can improve Po by a POM increase.

Andriulo A., J.A. Galantini, C. Pecorari, E. Torioni. 1990. Materia orgánica del suelo en la región pampeana. I. Un método de fraccionamiento por tamizado. Agrochimica (Italia) XXXIV (5-6) 475-489.

Duval M.E., J.A. Galantini, J.M. Martinez, F.M. López, L. Wall. 2016. Sensitivity of different soil quality indicators to assess sustainable land management: Influence of site features and seasonality. Soil & Tillage Research 159: 9-22.

Galantini J.A., R.A. Rosell. 1997. Organic fractions, N, P, and S changes in a semiarid Haplustoll of Argentine under different crop sequences. Soil & Tillage Research 42: 221-228. ISSN: 0167-1987  ELSEVIER

Galantini J.A., L. Suñer, H. Krüger. 2005. Dinámica de las formas de P en un Haplustol de la región semiárida pampeana durante 13 años de trigo continuo. Revista Investigaciones Agropecuarias (RIA – INTA) 34 (2): 13-31.

Galantini J.A., L. Suñer, J.O. Iglesias. 2007. Sistemas de labranza en el sudoeste bonaerense: efectos de largo plazo sobre las formas de fósforo en el suelo. Revista Investigaciones Agropecuarias (RIA – INTA) 36 (1): 63-81.

Galantini J.A., N. Senesi, G. Brunetti, R. Rosell. 2004. Influence of texture on the nitrogen and sulphur status and organic matter quality and distribution in semiarid Pampean grassland soils. Geoderma 123: 143-152  PDF

Rosell R.A., J.A. Galantini, L.G. Suñer. 2000. Long-term crop rotation effects on organic carbon, nitrogen and phosphorus in Haplustoll soil fractions. Arid Soil Research and Rehabilitation 14 (4) 309-316.

Suñer L., J.A. Galantini, G. Minoldo. 2014. Soil phosphorus dynamics of wheat-based cropping systems in the semi-arid region of Argentina. Applied and Environmental Soil Science Volume 2014 (2014), 6 págs. Article ID 532807, http://www.hindawi.com/journals/aess/2014/532807/  PDF

Suñer L., J.A. Galantini. 2013. Dinámica de las formas del P en suelos de la región sudoeste pampeana: Estudio de la incubación con fertilizante fosfatado. Ciencia del Suelo 31: 33-44.

Suñer L.G., J.A. Galantini, R.A. Rosell, M.D. Chamadoira. 2002. Cambios en el contenido de las formas de fósforo en suelos de la región semiárida pampeana cultivados con trigo (Triticum aestivum). Rev. Fac. Agron., La Plata 104(2): 105-111.

Suñer L.G., J.A. Galantini, R.A. Rosell. 1998. Comparación de métodos para la determinación de fósforo orgánico de suelos de la Región Semiárida Pampeana Argentina. Información Tecnológica (Chile) 9 (6) 51-54.

Suñer L.G., J.A. Galantini. 2012. Fertilización fosforada en suelos cultivados con trigo de la región pampeana. Ciencia del Suelo 30(1) 57-66.

Zalba P., J.A. Galantini. 2007. Improved soil tests methods for available phosphorus in acid, neutral and alkaline soils. Communications in Soil Science and Plant Analysis 38: 1579-1587.