Juan Manuel Martinez

Changes in soil pH and phosphorus availability during decomposition of cover crop residues

ABSTRACT The aim of this study was to determine the effect of winter cover crop (CC) residues on soil pH and phosphorus (P) availability. Three incubation assays were performed in pots using two CC: vetch (V) (Vicia villosa Roth.) and oats (Oa) (Avena sativa L.). Soil samples were taken from 10 sites at 0–20-cm depth. The rate of residues were 0 (D0), 10 (D1), 20 (D2), 30 (D3), and 40 (D4) g dry matter kg−1 soil and the soil sampling was after 10, 20, 30, 60, 90, and 120 days of incubation. Soil pH, extractable P (Pe), and soil organic matter (SOM) and its fractions were determined. The pH increase was correlated with the rate applied (D1 < D2 < D3 < D4). No differences were found for pH comparing V and Oa residues with low residue rates. Soil pH changes were dependent from initial pH and SOM fractions in different soils across the incubation period. The multiple regression models showed that the pH changes were dependent on initial pH level and SOM fractions with a high R2 (0.81). CC residues and its quantities produced different changes on pH – especially at the beginning of the incubation – which influenced the P availability.

A Rapid Chemical Method for Estimating Potentially Mineralizable and Particulate Organic Nitrogen in Mollisols

ABSTRACT The objective of this study was to obtain an indicator of labile nitrogen (N) through a cost- and time-saving procedure by evaluating the relationships among potentially mineralizable N (N0), particulate organic matter N (POM-N) and soil organic N extracted through partial soil digestion with different concentrations of sulfuric acid (H2SO4). Soil sampling (0–20 cm) was from nine fields under no-tillage. The N0 and POM-N were determined by long-term aerobic incubation and soil physical fractionation, respectively. A simple chemical method was developed by soil digestion at 100°C for 4 h with different concentrations of H2SO4 (0.1, 0.5, 1, 6, 12, and 24 mol L−1). All acid concentrations showed significant relationships with N0 as POM-N; however, the best prediction was resulted for 0.5 mol L−1 (R2 = 0.90–0.94, respectively), thus using this methodology as soil labile N indicator. This method would optimize N0 and POM-N estimation in short term and at a low cost.

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.