Matias Ezequiel Duval

Bacterial Indicator of Agricultural Management for Soil under No-Till Crop Production

The rise in the world demand for food poses a challenge to our ability to sustain soil fertility and sustainability. The increasing use of no-till agriculture, adopted in many areas of the world as an alternative to conventional farming, may contribute to reduce the erosion of soils and the increase in the soil carbon pool. However, the advantages of no-till agriculture are jeopardized when its use is linked to the expansion of crop monoculture. The aim of this study was to survey bacterial communities to find indicators of soil quality related to contrasting agriculture management in soils under no-till farming. Four sites in production agriculture, with different soil properties, situated across a west-east transect in the most productive region in the Argentinean pampas, were taken as the basis for replication. Working definitions of Good no-till Agricultural Practices (GAP) and Poor no-till Agricultural Practices (PAP) were adopted for two distinct scenarios in terms of crop rotation, fertilization, agrochemicals use and pest control. Non-cultivated soils nearby the agricultural sites were taken as additional control treatments. Tag-encoded pyrosequencing was used to deeply sample the 16S rRNA gene from bacteria residing in soils corresponding to the three treatments at the four locations. Although bacterial communities as a whole appeared to be structured chiefly by a marked biogeographic provincialism, the distribution of a few taxa was shaped as well by environmental conditions related to agricultural management practices. A statistically supported approach was used to define candidates for management-indicator organisms, subsequently validated using quantitative PCR. We suggest that the ratio between the normalized abundance of a selected group of bacteria within the GP1 group of the phylum Acidobacteria and the genus Rubellimicrobium of the Alphaproteobacteria may serve as a potential management-indicator to discriminate between sustainable vs. non-sustainable agricultural practices in the Pampa region.

Continuous Wheat in Semiarid Regions: Long-term Effects on Stock and Quality of Soil Organic Carbon

Abstract Continuous wheat (Triticum aestivum L.) cropping in semiarid regions results in variable dry matter production. As a consequence, the balance of soil organic carbon (SOC) may vary across time. The aim of this research was to assess the dynamics and long-term changes of physically and chemically extracted SOC fractions. Soil samples (0- to 5-, 5- to 10-, and 10- to 20-cm depths) from continuous wheat with (f) and without (nf) fertilizer (N + P) under conventional tillage ((CT) for 25 years) and no-tillage ((NT) for 6 years) were taken during the experiment. Mineral-associated ((MOC) 0–0.053 mm), fine particulate ((POCf) 0.053–0.100 mm), and coarse particulate ((POCc) 0.1–2.0 mm) SOC and humic substances were obtained. The SOC variability depended on water availability during fallow periods (SOC decomposition) or crop cycles (dry matter production). The mean wheat yields were 1.33 (nf) and 2.09 (f) Mg grain ha−1, with an estimated carbon input of 1.64 (nf) and 2.20 (f) Mg C ha−1 year−1. Losses from the initial level were higher in labile fractions, POCc (−75%) and POCf (−53%), than in MOC (−15%). Humic acids present slight differences in their structure and quantity as a result of long-term cropping. Conversion from CT to NT resulted in contrasting results. For an equivalent soil mass, fertilizer application increased SOC by 4.31 Mg ha−1 (under CT) and 7.29 Mg ha−1 (under NT). The SOC turned out to be higher under NT with fertilizer use and lower without application. No-tillage does not increase SOC content by itself; it must be combined with other agricultural practices such as fertilization and/or crop rotation.

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 05, 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 Original Research Article

Nitrogen mineralization indicators under semi-arid and semi-humid conditions: influence on wheat yield and nitrogen uptake

ABSTRACT The objectives were i) to assess indicators for potential nitrogen (N) mineralization and ii) to analyze their relationships for predicting winter wheat (Triticum aestivum L.) growth parameters (yield and N uptake, Nup) in Mollisols of the semi-arid and semi-humid region of the Argentine Pampas. Thirty-six farmer fields were sampled at 0–20 cm. Several N mineralization indicators, wheat grain yield and Nup at physiological maturity stage were assessed. A principal component (PC) analysis was performed using correlated factors to grain yield and Nup. The cluster analysis showed two main groups: high fertility and low fertility soils. In high fertility soils, combining PCs in multiple regression models enhanced the wheat yield and Nup prediction significantly with a high R2 (adj R2 = 0.71–0.83). The main factors that explained the wheat parameters were associated with water availability and N mineralization indicator, but they differ according to soil fertility. Abbreviations: N: nitrogen; SOM: soil organic matter; POM: particulate organic matter; SOC: soil organic carbon; SON: soil organic nitrogen; POM-C: particulate organic carbon; POM-N: particulate organic nitrogen; Nan: anaerobic nitrogen; Nhyd: hydrolyzable N; NO3-N: cold nitrate; N205: N determined by spectrometer at 205 nm; N260: N determined by spectrometer at 260 nm; Pe: extractable P; Nup: wheat N uptake; NO3-N: inorganic N in the form of nitrate; FR: fallow rainfalls (March-Seeding rainfall); FLR: flowering rainfalls (October-December rainfall); GFR: grain filling rainfall (November rainfall); CCR: crop growing season rainfall (June-December rainfall); PCA: principal component analysis; PC: principal component; MR: multiple regression

A rapid method for estimating labile carbon and nitrogen pools in Mollisols under no-tillage

ABSTRACT The objective of this study was to adapt the partial chemical digestion method for estimation of labile soil organic matter pools by evaluating the effect of different digestion times in Mollisols of the Argentine Pampas. The soils were sampled from nine agricultural fields under no-tillage at the 0–20 cm depth. A chemical method was performed through partial soil digestion with dilute sulphuric acid at 100°C on the basis of four digestion times: 1 (Nd1), 2 (Nd2), 4 (Nd4) and 6 (Nd6) hours. Soil organic carbon (C) and nitrogen (N) fractions were determined. The extracted organic N (Nd) ranged from 0.076 g kg−1 to 0.273 g kg−1, with a mean of 0.154 g kg−1. Statistically, the means for each digestion time indicated highly significant differences (P = 0.008). High correlations were found between Nd for different times and labile C and N fractions. However, the best fit prediction was observed between Nd2 and soil total carbohydrates (CHt), with a high coefficient of determination (R2 = 0.94). Partial chemical digestion for 2 h can be used as a rapid indicator to accurately predict CHt. Because of its speed and simplicity, this method may also be useful for rapid soil quality assessments.

Decomposition from legume and non-legume crop residues: Effects on soil organic carbon fractions under controlled conditions

Cover crop (CC) residues protect the soil from erosion and their permanence on the surface is largely influenced by their biochemical constituents. We performed a study under controlled conditions to investigate the dynamics of legume and non-legume CC residues decomposition and the transformations of the soil labile organic carbon fractions in the surface layer (0-15 cm). The experiment was carried out on a Typic Argiudoll (clay loam, 27.4 g kg-1 soil organic matter, 14 mg kg-1 extractable phosphorus and 6.5 pH) placed in undisturbed pots (1570 cm3) in a greenhouse under controlled conditions of temperature (25 ± 1 °C). We evaluated three CC species (oat, Avena sativa L.; vetch, Vicia sativa L.; Persian clover, Trifolium resupinatum L.) and a no-CC control (fallow). Shoot residues were applied on the soil surface at 5.4, 5.4 and 2.7 g dry matter (equivalent to 6, 6 and 3 Mg ha-1 for oat, vetch and clover, respectively) and incubated for 362-days (eight sampling times). The water content in the pots was maintained periodically by weight at 60% of soil water-holding capacity. The soil samples were analyzed for particulate organic carbon (POC), and total and soluble carbohydrates (CHt and CHs, respectively). Oat and vetch residues decomposed faster than clover, with the decomposition rate constant (k) values of 1.3, 1.4 and 1.9 year-1, respectively. At the end of the experiment, POC concentration was lower in vetch (1.83 g kg-1) and clover (1.96 g kg-1) than in oat (2.21 g kg-1) and fallow (3.00 g kg-1), indicating a loss of 45-64% from their initial values. Soil CHt was influenced by residue quality, where the periods of greatest residue decay (vetch 21-59 days and oat 93-130 days) corresponded to higher soil CHt. Hence, this organic carbon fraction is sensitive to residue decomposition and can be indicators of changes in soil organic matter over short periods of time.