Soil “biofilms”: “Bioclusters” would be a much better descriptor

Soil “biofilms”: “Bioclusters” would be a much better descriptor

Chemical diversity and molecular signature of soil humic fractions used as proxies of soil quality under contrasted tillage management

Increasing food production while avoiding the progressive degradation of agricultural soils has become one of the major challenges at a global level. In consequence, the development of sustainable tillage methodologies or cultivation strategies is an important subject of current research. In fact, it has been observed that the implementation of reduced tillage (RT) vs. traditional tillage (TT) in the long term not only improves soil physicochemical properties but also global soil quality in terms of soil health. In particular, the increase of the soil organic carbon (SOC) content under RT conditions is one of the most important factors, but there is little information about the chemical composition and humification level of this carbon, and thus about its persistence at long-term. This is of particular importance considering the policies of carbon sequestration and climate change mitigation, such as the “4 per 1000” initiative. In this study, molecular-level characterization of the humic acid (HA) and fulvic acid (FA) fractions isolated from a soil after 19 years under RT and TT practices was carried out. This study would provide objective descriptors of the impact of these two tillage practices in the chemical composition of the resulting SOC. With this purpose, the potential of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS) for assessing changes in the molecular assemblages released from the humic fractions (HA and FA) was examined. The results showed enhanced diversity and chemical richness (expressed as number of molecular formulas) in the composition of SOC under RT. Different tillage-specific compound classes were associated with both tillage practices. As a whole, the humic fraction showed a higher proportion of molecular formulas for lipid and hydroaromatic families in the case of RT compared to TT, while the same fraction under TT showed a greater richness of oxidized protein-derived formulas than RT. In the case of FAs, a similar pattern was observed for hydroaromatic and protein-derived formulas, but the proportion of molecular formulas assigned to unsaturated lipids was higher in TT than in RT. In addition, increased number of formulas for aromatic and condensed aromatic compounds was observed in FAs under TT respect to RT.

Soil and grapevine leaf quality in organic vineyards of different ages in DO Rioja-Alavesa, northern Spain

The soil from three organically cultivated plots in Rioja Alavesa vineyards, specifically in Lanciego (Álava, Spain), and the foliage of their vines were analyzed. The aim of this study was to determine differences in soil and grapevine quality between different aged vineyards. The first 20 centimeters of the soil were sampled and leaves were collected during the growing season. The results show that the quality of the soil in the three plots was optimal and did not differ from reported values of soils from traditionally cultivated plots. The only element found at a lower concentration in the three plots and the leaves was iron. Organic cultivation of vineyards is a viable mode of cultivation and could help reduce greenhouse gas emissions and contamination by pesticides and fertilizers.

Soil parameters and bioclimatic characteristics affecting essential oil composition of leaves of Pistacia lentiscus L. from València (Spain)

The variability of the soils found in an area together with the diversity of the bioclimatic parameters will affect the chemical profile of plant species, in our case <em>Pistacia lentiscus</em> L. The aim of this work is to analyse the bioclimatic characteristics and soil parameters affecting the essential oil (EO) composition of the leaves of the <em>Pistacia lentiscus</em> L. growing in València (Spain). The EO compositions of dried leaves of <em>Pistacia lentiscus</em> L. from five sampling sites with noticeable differences in soil and climate features were analysed by GC(MS) and GD(FID). The main bioclimatic and soil parameters were also determined in order to relate them to oil composition. a-pinene (2.8-39.2%), myrcene (0.6-59.3%), b-phellandrene (0.0-42.8%), germacrene-D (3.9-20.4%) and terpinen-4-ol (0.2-19.0%) were found to be the major compounds showing a high variability. The five sampling sites presented well-defined bioclimatic and edaphic characteristics that could be related to specific EO profiles. The results suggested that the EO composition of <em>P. lentiscus</em> L. depends more on the edaphic factors interacting with bioclimate conditions than on the geographical origin itself. Some general trends could be established based on the results: the Calcaric Arenosol (Saler) with a high evapotranspiration index was associated with a high sesquiterpenic fraction, (germacrene-D and b-caryophyllene, mainly). The Luvisol (Borrell and L’Ull), with high amounts of a + b-pinene, were found to be related to sub-humid bioclimatic conditions and clayey and fertile soils (high CEC and OM levels). This last requirement was also observed to be related to the myrcene content, but with drier climatic conditions and calcareous soils (Haplic Calcisol) with high level of carbonates and active lime (Lliria). The rest of hydrocarbon monoterpene and oxygenated monoterpene (terpinen-4-ol, mainly) fractions could be related to a dry climate and non-calcareous and low fertility soils (Eutric Regosol, Segart). Given the most suitable composition related to specific and useful biological activities, new research of controlled environmental factors (soil features and bioclimatic conditions) should be conducted in order to define the best conditions to manage industrial crops of <em>P. lentiscus </em>L<em>.</em>

Investigating the effect of farmyard manure on clay soil compactibility

One of the important factors that can control and decrease soil compaction is incorporation farmyard manure to the soil. It increases soil elasticity and soil tolerance to the imported load. To evaluate the farmyard manure effect on the soil compaction, it was incorporated in the clay soil at different rates of 0, 45, 60, and 90 Mg ha^-1. Tests were conducted at different tire passes of 1, 6, 11 and 16 on the same track at three soil moisture contents of 8%, 11% and 14% (dry base); soil bulk density was measured at depths of 10, 20, and 30 cm. To evaluate soil compaction, cylindrical cores were employed to measure the soil bulk density. To assess soil behavior during the soil compaction process, three displacement transducers were placed in the soil in three coordinate directions of x, y and z. The soil volumetric change was measured using the transducers and soil sinkage was also measured. A single-wheel tester was used in a soil bin with a Barez 8.25-16 (8) P.R HLF agricultural tractor tire operated at a forward velocity of 0.8 m s^-1 under a vertical load of 4 kN and an inflation pressure of 300 kPa. Incorporating the farmyard manure noticeably decreased the final vertical and longitudinal displacement below the tire track, while the lateral displacement increased. Bulk density decrements of 14.7%, 9.7% and 6.3% were occurred via farmyard manure application rates of 90, 60 and 45 Mg ha^-1, respectively. Maximum soil sinkage occurred at 14% moisture, 16 passes of tire and with no manure condition.

Traditional knowledge on soil management and conservation in the inter-Andean region, northern Ecuador

Local farmers' knowledge of edaphic fertility indicators is a decisive factor for decision making and sustainable soil management. Thus, the purpose of this study was to determine soil fertility indicators according to the criteria of small farmers and contrast it with scientific knowledge. A field study was developed in northern Ecuador, where 95 semi-structured surveys were applied to farm owners in the Andean and Subtropical zones. Each questionnaire grouped several questions with topics such as plant indicators of soil fertility, physical indicators of soil fertility, forms of soil degradation and conservation strategies, as well as the acquisition of knowledge over time according to farmers' perception. Farmers consider that crops are indicators of soil fertility, while the presence of “weeds” indicate poor soils. Additionally, characteristics like color, texture, stoniness, depth, the presence of macrofauna and crop yield indicated soil fertility. Also, farmers are aware of the soil's contamination and of conservation strategies available to avoid this; however, since their main objective is to improve crop yield and not precisely soil conservation, they do not always apply these strategies. Some of these practices are transmitted from one generation to the next and are at risk of being lost, hence the importance of integrating farmers’ perception and scientific knowledge to generate guidelines for sustainable soil management.

Liquid digestate features as fertilizer: carbon fractions, phytotoxicity and microbiological analysis

The circular economy promotes the use of renewable fuels as an alternative to natural gas. Anaerobic digestion for waste management produces methane, carbon dioxide and a residue-the digestate- which must be recovered. This residue can be separated into two parts, namely the liquid and solid fractions, the former characterized by its large volume, presence of nutrients in mineral forms, and highly variable composition. Here we studied the fertilizing capacity of the liquid fractions obtained from the waste derived from artichoke canning (LF-Ar), orange juice manufacturing (LF-Or) and pig slurry (LF-Sl). To this end, we examined the physical-chemical parameters, carbon fractions, phytotoxicity and presence of pathogens in these fractions. The liquid fraction derived from fruit and vegetables had a low nutrient content compared to that of slurry ( ̴1.0 kg total-N m^-3<em>vs.</em> 5.6 kg total-N m^-3 respectively). The NH₄⁺-N content of the fractions ranged between 70-93% of total N. Given the permissible dose in non-vulnerable areas, LF-Sl, LF-Ar and LF-Or would provide 0.9-1.0 t of organic matter ha^-1 and 134, 128 and 98 kg of C ha^-1 from the total humic extract, respectively. The proportion of humic acids in the total humic extract was 59%, 51% and 34% respectively. The slurry digestate showed phytotoxicity probably due to high salinity, so it should be diluted based on the needs of the crop. On the basis of our findings, the characterized liquid fractions could be recovered in agricultural soils in line to circular economy principles.</p> <p><strong>&nbsp;</strong>

Medium-term influence of tetracyclines on total and specific microbial biomass in cultivated soils of Galicia (NW Spain)

This work examines the results of a soil incubation experiment in the laboratory, under controlled conditions of humidity and temperature. The purpose was to determine the medium-term influence of the presence of antibiotics on the total and specific microbial biomass, determined by means of the phospholipid fatty acids (PLFAs) analysis (total microbial biomass, and specific fungal, bacterial, actinobacterial, Gram-negative bacterial and Gram-positive bacterial biomass), as well as the relationship between some of these groups (fungal biomass/bacterial biomass, Gram-negative-bacterial /Gram-positive bacterial). The experiment was performed with four different cultivated soils with a similar pH but different organic matter (OM) content, to which eight doses of three antibiotics of the tetracycline group (tetracycline, oxytetracycline and chlorotetracycline) were added. Microbial biomass measurements (total and specific groups) were performed after 42 days of incubation. As expected, the total and specific microbial biomass values were different in the four soils studied. Both the total and the specific microbial biomass showed a similar response to the presence of antibiotics, although in several cases the data were inconsistent and difficult to interpret. In general, in all soils the addition of chlorotetracycline and tetracycline slightly modified or increased, to a greater or lesser extent, the values of both total and specific microbial biomass, particularly at higher doses. However, in certain cases, biomass values decreased due to the addition of the highest dose of oxytetracycline. With regard to fungal/bacterial and Gram^-bacteria/Gram⁺ bacterial biomass ratios, values slightly changed after the addition of the antibiotics.

Tuning of the proficiency testing methodology for soil fertility analysis. Preliminary results

This work includes the methodology for carrying out a proficiency testing program between Spanish laboratories that offer soil fertility analysis. Aliquots of each of the two large volume samples were prepared, taken from two surface horizons of soils with marked differences between them. Once the homogeneity of aliquots was tested, one sample of each soil was sent to each of the twenty-one participating laboratories, together with the instructions and a format for the submission of results. Throughout the process, special care was taken to ensure the confidentiality of the results of each individual participant. Once the responses were received, the results were analyzed, consensus values were assigned and each result was evaluated using the “z-score” indicator. The exercise was very well received by the participating laboratories, and has been very effective in characterizing the quality of the results issued. It has been shown that there are parameters with very homogeneous results (pH) compared to others with differences incompatible with the reliable agronomic use of analyses (granulometry, assimilable phosphorus, etc.). The urgent need to maintain this type of intercomparison exercise periodically, as an external quality control that increases the reliability of laboratories, is evident.

Influence of intensive horticultural cultivation on soil salinity in Campo de Cartagena (Murcia)

The electrical conductivity (EC) and ionic composition of the soil solution of a Haplic Calcisol in Campo de Cartagena (Murcia, Spain) were studied <em>in situ</em> for four years in an experimental open-air vegetable plot, together with the relationship between these parameters, the quality of the irrigation water and the management of the plot. The results show that there were very significant fluctuations in these variables during the study period and that these fluctuations depended on the management of the plot and in particular on the irrigation water used. Therefore, for an adequate management of these agro-ecosystems, it is necessary to establish a network of experimental plots <em>in situ</em>, where sensitive indicators of soil degradation are monitored, in our case the EC and the ionic composition of the soil solution. Such indicators are capable of detecting these degradation processes and their relationship with the inappropriate management of this resource.