Humification and N mineralization of crop residues in semi-arid Argentina

Crop residues in the soil play a fundamental role in organic matter dynamics and have effects on numerous beneficial soil properties. The humification of residues depends on soil nutrient status and physical and meteorological conditions. The prediction of the humification rate and of the size and decomposition of fresh and humified soil organic matter has been attempted with equations and models which require several constants. To simplify the procedure. Janssen developed an equation which utilizes only one constant, permits calculation of the young (fresh) and old (humified) soil organic matter pools and predicts the production of available or mineralized nitrogen. The validity of Janssen's equation was tested in three production systems (a crop rotation and two tillage procedures) in a sandy-loam textured, thermic, entic Haplustoll soil in the Pampean semi-arid region of Argentina. The model produced results compatible with actual field data, but information on soil available water was essential for fitting and interpreting the organic matter dynamics.

Humification; residue; mineralization; semi-arid region; wheat; agricultural systems

Galantini J.A., R.A. Rosell, A.E. Andriulo, A.M. Miglierina, J.O. Iglesias. 1992. Humification and N mineralization of crop residues in semi-arid Argentina. The Science of the Total Environment (Holanda), 117/118: 263-270.

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Soil stabilisation by water repellency under no-till management for soils with contrasting mineralogy and carbon quality

No-till soil management is common around the globe, but the impacts on soil structural quality varies depending on cropping practice and inherent soil properties. This study explored water repellency as a driver of soil stabilization, as affected by soil mineralogy, granulometry and organic carbon quality in three Mollisols and one Vertisol under no-till management and with different levels of cropping intensity. The studied soils were located along a west-east textural gradient in the northern part of the Pampean region of Argentina. Cropping intensity treatments evaluated in each one of the soils were: Poor Agricultural Practices (PAP) close to a monoculture, Good Agricultural Practices (GAP) involving a diverse crop rotation and more targeted inputs, and the soil in the surrounding natural environment (NE) as a reference. NE had the greatest aggregate stability (MWD) of all cropping intensities, with GAP being more stable than PAP for Mollisols and PAP being greater than GAP for the Vertisol. This trend matched the Repellency Index (Rindex), with greater Rindex associated with greater MWD, including the difference between the Mollisols and Vertisol. However, the persistence of water repellency, measured by the Water Drop Penetration Time (WDPT) test followed the trend NE > GAP > PAP regardless of soil type. The increases in Rindex and MWD were related to higher intensification as measured by the Crop Sequence Index, and decreased with greater soybean occurrence in the sequence. Both WDPT and Rindex were closely related to aggregate stability, particularly for Mollisols. These results highlight the importance of considering the inherent soil characteristics texture and mineralogy to understand aggregate stabilization mediated by water repellency. Good correlations between soil water repellency, organic carbon fractions and aggregate stability were found. Under no-till, crop rotations can be altered to increase soil stability by inducing greater water repellency in the soils. The findings suggest that water repellency is a major property influencing soil structure stabilization, thus providing a useful quality indicator

Behrends Kraemer F., P. Hallett, H.J.M. Morrás, L. Garibaldi, D. J. Cosentino, M. Duval, J.A. Galantini. 2019. Soil stabilisation by water repellency under no-till management for soils with contrasting mineralogy and carbon quality. Geoderma 355: 113902. Doi 10.1016/j.geoderma.2019.113902

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Organic fractions: Stratification under soil tillage

Quality and Quantity of Organic Fractions as Affected by Soil Depth in an Argiudoll under Till and No-till Systems

Aims: The aim of this study was to evaluate the long-term effect of tillage systems on the quantity and quality of organic carbon fractions at different soil layers.

Study Design: The experimental design was a split plot with three blocks. The long-term effects (25 years) of conventional- (CT) and no-tillage (NT) systems on a Tipic Argiudoll was sampled at 0-5, 5-10, 10-15 and 15-20 cm soil depth.

Place and Duration of Study: The field experiment was carried out at Tornquist (38° 07’ 06” S - 62°02’ 17” O) and soil sampling was performed during wheat seeding (June 2011).

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

Results: After 25 years, total SOC at the 0-20 cm depth was 9% higher in no-tilled than in tilled soils. The POCf was the SOM fraction that turned out to be the most sensitive to tillage effects. The POCc:POCf: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. Tilled soils showed higher aromaticity, starting by CH-degradation, in more superficial soil layers.

Conclusion: 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.

Tillage system; soil organic carbon; chemical and physical fractionation.

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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Soil organic fractions: Soil quality

Soil organic fractions content and quality under wheat production systems in the semiarid Pampas

Soil organic matter (SOM) is the key factor in the production systems, and the knowledge of their fractions dynamic and equilibrium is important to reach high productivity and agriculture sustainability. The effect on organic fractions distribution and quality of the following production systems were studied: continuous wheat (TT), wheat–natural grass each year (TP) and wheat – legume (TL). Labile fractions, physically separated (particulate SOM, MOP) and chemically separated (fulvic acid, AF), showed high sensibility to crop sequence. Continuous wheat affected labile and recalcitrant organic fractions contents. The tillage increase caused SOM decrease, changes in labile to recalcitrant fraction ratios, nutrient losses (N and S) and modified humic acid (AH) structure. The AH from cultivated soils showed higher aromatic groups content and lower aliphatic and N compounds groups than AH from reference soil.

Organic fractions, Production systems, Semiarid region

Galantini J.A. 2001. Contenido y calidad de las fracciones orgánicas del suelo bajo rotaciones con trigo en la región semiárida pampeana. Revista de Investigaciones Agropecuarias (RIA-INTA) 30 (1) 125-146.

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Soil organic fractions: Carbon, Nitrogen, Phosphourus and Sulphur

Organic fractions, N, P, and S changes in a semiarid Haplustoll of Argentine under different crop sequences

Crop sequences play an important role in changing soil properties. The knowledge of the chemical composition, turnover, dynamics, and biological effects of different fractions of soil organic carbon (SOC), nitrogen (N), phosphorus (P) and sulfur (S) components will result in a better understanding of soil productivity. The objective of this research was to compare the effects of crop rotation on SOC, N, P, and S evolution in two granulometric fractions of an Entic Haplustoll. Rotations of mixed pasture (5.5 years)-annual crops (4.5 years) (Pa-C), and wheat (Triticum aestivum L.)-sunflower (Heliantus annus L.) (W-S), and a reference (Ref), which was located between them, were studied. Fine (<100 µm, FF) and coarse (100-2000 µm, CF) soil granulometric fractions were separated by wet sieving. In each fraction total N and S, and several SOC and P forms were determined. Similar contents (5.23 to 6.07 Mg ha-1) of humic acid (HA) carbon were found in the three situations. The Pa-C rotation maintained the SOC level at 17.33 Mg ha-1 in the Fine Fraction during a 10-year period. On the contrary, SOC was sharply lower (11.16 Mg ha-1) in the same fraction in the W-S treatment. Losses of SOC, N, P and S were highest in the Coarse Fraction thus showing the dynamics of this soil fraction and its important role in plant nutrient turnover and availability to growing crops.

Soil organic carbon, N, P, S, Semiarid, Entic Haplustoll

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

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