Sa Pereira E, J.A. Galantini, M. Duval. 2017. Use of a three-compartment model to evaluate the dynamics of cover crop residues. Archives of Agronomy and Soil Science 1-7. doi 10.1080/03650340.2017.1296137
ISSN: 0365-0340 (Print) 1476-3567 (Online)
Cover crop (CC) residues protect the soil from erosion and their permanence on the surface is largely influenced by their biochemical constituents. In this study, the dynamics of CC residue decomposition by applying mathematical models was described. The kinetics of decomposition of residues was obtained from a laboratory incubation experiment. Three CC shoot residues were applied on the soil surface and incubated for 362 days (with eight sampling times). Oats and vetch residues decomposed the most than clover, where k values were 3.6 × 10−3, 3.7 × 10−3 and 5.3 × 10−3 day−1, respectively. The three-compartment model (nonstructural carbohydrates, cellulose–hemicellulose and lignin) to simulate residue decomposition presented a close fit between simulated and measured data. The decomposition rate constant (k) of CC can be used to estimate how long residues will remain in the field and how they could affect soil organic carbon.
Keywords: Residue decomposition; oats; vetch; clover
Martínez J.M., J.A. Galantini. 2017. A rapid chemical method for estimating potentially mineralizable and particulate organic nitrogen in Mollisols. Communications in Soil Science and Plant Analysis 48(1) 113-123. doi: 10.1080/00103624.2016.1254230
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.
Keywords: Chemical digestion; labile organic fractions; no-tillage
Behrends K.F., M.A. Soria, M.G. Castiglioni, M. Duval, J. Galantini, H. Morrás. Morpho-structural evaluation of various soils subjected to different use intensity under no-tillage. Soil & Tillage Research 169: 124-137. doi:10.1016/j.still.2017.01.013
According to many evidences, in Argentina, no-tillage (NT) coupled with soybean monoculture leads to adverse soil structure features. While some farmers have simplified the production system through soybean monoculture others have intensified the land-use by increasing the number and diversity in the crop sequence. The effects of this intensification, in terms of soil structural quality, are contradictory, possibly caused by the increase of machinery traffic. In order to assess soil structural quality and the performance of selected morpho-structural variables with different levels of intensification, we analyzed plots under NT with high and low crop sequence intensification (Good −GAP- and Poor −PAP-, agricultural practices respectively) and reference plots in four soils (two Argiudolls, an Haplustoll and an Hapludert) of the Argentinian Pampean region. The morpho-structural variables assessed were Visual Evaluation of Soil Structure at field scale (VESS), visible porosity (Vp), roundness (Rd), eccentricity (Ecc) and 3-D aggregate features (faces, corners and edges). Plots with higher frequency of cereals in the sequence (GAP) presented on average higher VESS scores, higher Vp values and less rounded aggregates with more faces and corners, suggesting that crop sequence intensification induces favorable structural features. VESS, Vp, number of faces and corners were strongly correlated with aggregate stability tests mainly with the fast and fast10s test (r: −0.56, −0.74; 0.48, 0.52; 0.46, 0.49 and 0.42, 0.50, respectively) and with the more labile organic carbon fractions −POCc and POCf- (r: −0.49, −0.5; 0.5, ns; 0.38, 0.48 and 0.31, 0.43, respectively). These observations suggest that the variables examined, concerning aggregates and pores were sensitive to changes in crop sequence and are useful soil quality indicators. However, the occurrence of platy structures also under GAP shows the need to adjust the VESS method to the NT system. Besides, the effect of agricultural intensification on soil morphology was modulated by soil type. In consequence, this last factor has also to be considered for the definition of a quality indicator to track the effect of crop sequences intensification under no-till management.
Keywords: Aggregate morphology; Image analyses; VESS
Martínez J.M., J.A. Galantini., M Duval. 2017. Tillage effects on labile pools of soil organic nitrogen in a semi-humid climate of Argentina: A long-term field study. Soil & Tillage Research 169:71-80. DOI 10.1016/j.still.2017.02.001
Tillage systems strongly affect nitrogen (N) mineralization. However, there is still only limited information on the relationship between N in labile soil organic matter (SOM) fractions and crop N uptake under different tillage systems in areas with poor water availability. This study discusses the long-term effect of two tillage systems on i) the N-content in labile organic matter fractions and their relationship with the N mineralization potential at three depths (0–5; 0–10 and 0–20 cm), ii) the factors that affect the N mineralization potential, and iii) the relationship between potentially mineralizable N (N0) and crop N uptake in a semi-humid climate. In a long-term experiment, a Typic Argiudoll was sampled under two contrasting tillage systems: no-tillage (NT) and conventional tillage (CT). The soil sampling was performed over four years of the crop sequence (2003, 2009, 2010 and 2011) when the plots were sown with winter wheat (Triticum aestivum L.). They were analyzed for N0 in the form of anaerobic N, soil organic nitrogen (SON), physically separated SOM fractions and crop N uptake. Higher values of SON and labile soil N fractions were observed under NT at all three depths. Significant differences in N0 were found between the tillage systems, with greater values under NT. Significant (P < 0.05) and positive correlations between N0 and fine particulate organic carbon (fPOM-C) (r ≥ 0.66) were found in CT and in NT at the three depths, whereas highly significant (P < 0.001) and negative relationships between N0 and fine particulate organic N (fPOM-N) (r ≥ −0.83) were found under both tillage systems at 0–5 and 0–10 cm. The most pronounced difference in these relationships between tillage systems was observed at the 0–5 cm soil depth. Significant correlations of N0 with residue input from previous crops and the fallow period were observed under both tillage systems and for all three depths. Regarding the relationships between N0 and wheat N uptake, no significant correlations were found for any tillage system or depth. Soil organic N fractions were shown to be strongly influenced by the residue input from the previous crop and by variable weather conditions during the fallow period. The higher content of SON fractions under NT was associated with a higher N mineralization potential, however, it did not result in increased N availability and N uptake by wheat, because of climatic conditions during the crop growing season.
Keywords: Potentially mineralizable N; Soil labile fractions; Tillage systems
Vanzolini J.I., J.A. Galantini, J.M. Martínez, L. Suñer. 2017. Changes in soil pH and phosphorus availability during decomposition of cover crop residues. Archives of Agronomy and Soil Science 63 () http://dx.doi.org/10.1080/03650340.2017.1308493
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.