José Dorado

13C NMR assessment of decomposition patterns during composting of forest and shrub biomass

A laboratory experiment was designed to investigate the degradation patterns of leaves from 12 forest and shrub species typical of Mediterranean ecosystems by solid-state 13 C NMR. The spectral data have been compared with those for the major organic fractions, and elementary composition in three transformation stages (zero time, intermediated and advanced (168 d)). The plant material in general showed a selective depletion of lipid and water-soluble products and a concentration in acidinsoluble residue (Klason lignin fraction), but the increasing percentage of total alkyl carbons (not observed in pine leaves) suggests that recalcitrant aliphatic material accumulates in the course of the 168 d incubation, when the total weight losses were up to 660 g kg ˇ1 . This contrasts with the fact that the concentration of extractable alkyl C (i.e. the lipid fraction) decreased in all cases. The results for the diAerent plants suggested some general transformation trends simultaneous to specific biodegradation patterns. The non-ameliorant, soil acidifying species (i.e. those a priori considered to favor the accumulation of humus with low biological activity) have high initial concentrations of extractives, alkyl structures and comparatively lower percentages of O-alkyl structures. The decay process in these species is not associated to the increase of the alkyl-to-O-alkyl ratio, which is shown by the ameliorant species. Superimposed on these major trends, the biomass of the diAerent plants underwent divergent paths in the course of composting, leading to, for example, (i) accumulation of recalcitrant, nonhydrolyzable alkyl and aromatic structures (Retama, Genista); (ii) enrichment of resistant O-alkyl structures such are stable fractions of carbohydrate and tannins (Pinus, Calluna); and (iii) accumulation of aliphatic extractives with the lowest stabilization of protein in resistant forms (Arctostaphylos, Ilex). In particular, in the acidifying species, the spectral patterns suggest that the apparent stability of the aromatic domain is compatible with selective preservation of tannins together with aliphatic structures. Such specific tendencies are also illustrated by the diAerence spectra (0 vs 168 d) which suggest that early humification processes are highly heterogeneous and distinct rather than the selective degradation of lipid and water-soluble fractions and carbohydrates, and they may include stabilization of tannins and aliphatic (cutin- and protein-like) macromolecules. 7 2000 Elsevier Science Ltd. All rights reserved.

Transformation of wheat straw in the course of solid-state fermentation by four ligninolytic basidiomycetes

Biological upgrading of wheat straw by the white-rot fungi Phanerochaete chrysosporium , Pleurotus eryngii, Phlebia radiata, and Ceriporiopsis subvermisporawas monitored during 60-day solid-state fermentation. Analysis of straw included determination of weight loss and lignin content, color analysis, and infrared spectroscopy, whereas the studies on the water-soluble fractions were carried out by infrared spectroscopy, elementary analyses and quantification of the total phenols and reducing sugars. The most selective degradation of lignin was produced by P. eryngii and especially by C. subvermispora, the former species releasing the greatest amount of colored water-soluble products, whereas an increase in straw brightness was caused by C. subvermispora.In general, the composition of the water-soluble fraction correlated with the extent of straw transformation. The initial fermentation stage (0 ‐15 days) was characterized by the accumulation of water-soluble products from lignin degradation and fungal metabolism, the concentration of which tended to stabilize in the second stage (16 ‐ 60 days). The degree of delignification at the second stage tended to coincide with the decrease of the water-soluble nitrogen.

Pyrolysis of carbohydrate-derived macromolecules: its potential in monitoring the carbohydrate signature of geopolymers

Abstract Two series of black-coloured macromolecular products were prepared by: (a) acid-catalyzed dehydration of a glucose solution and (b) heating crystalline cellulose. These substances were analyzed by standard chemical and spectroscopic techniques, which revealed a more or less marked carbohydrate signature. The analytical pyrolysis showed striking differences between the two series of substances. The carbohydrate origin of the charred celluloses (even after 48 wt.% loss) was evident from the major peaks of anhydrosugars, while the alkylbenzenes and alkylphenols were found in comparatively low amounts. In contrast, the glucose browning substances showed pyrolysis patterns where aromatic molecules coexist with lower amounts of furan compounds. The results are interpreted in terms of the possible diagenetic pathways of sedimentary carbohydrate, and of the potential of pyrolysis to reveal the carbohydrate origin of geomacromolecules.

Accuracy and Feasibility of Optoelectronic Sensors for Weed Mapping in Wide Row Crops

The main objectives of this study were to assess the accuracy of a ground-based weed mapping system that included optoelectronic sensors for weed detection, and to determine the sampling resolution required for accurate weed maps in maize crops. The optoelectronic sensors were located in the inter-row area of maize to distinguish weeds against soil background. The system was evaluated in three maize fields in the early spring. System verification was performed with highly reliable data from digital images obtained in a regular 12 m × 12 m grid throughout the three fields. The comparison in all these sample points showed a good relationship (83% agreement on average) between the data of weed presence/absence obtained from the optoelectronic mapping system and the values derived from image processing software (“ground truth”). Regarding the optimization of sampling resolution, the comparison between the detailed maps (all crop rows with sensors separated 0.75 m) with maps obtained with various simulated distances between sensors (from 1.5 m to 6.0 m) indicated that a 4.5 m distance (equivalent to one in six crop rows) would be acceptable to construct accurate weed maps. This spatial resolution makes the system cheap and robust enough to generate maps of inter-row weeds.

Discriminating Crop, Weeds and Soil Surface with a Terrestrial LIDAR Sensor

In this study, the evaluation of the accuracy and performance of a light detection and ranging (LIDAR) sensor for vegetation using distance and reflection measurements aiming to detect and discriminate maize plants and weeds from soil surface was done. The study continues a previous work carried out in a maize field in Spain with a LIDAR sensor using exclusively one index, the height profile. The current system uses a combination of the two mentioned indexes. The experiment was carried out in a maize field at growth stage 12–14, at 16 different locations selected to represent the widest possible density of three weeds: Echinochloa crus-galli (L.) P.Beauv., Lamium purpureum L., Galium aparine L.and Veronica persica Poir.. A terrestrial LIDAR sensor was mounted on a tripod pointing to the inter-row area, with its horizontal axis and the field of view pointing vertically downwards to the ground, scanning a vertical plane with the potential presence of vegetation. Immediately after the LIDAR data acquisition (distances and reflection measurements), actual heights of plants were estimated using an appropriate methodology. For that purpose, digital images were taken of each sampled area. Data showed a high correlation between LIDAR measured height and actual plant heights (R2 = 0.75). Binary logistic regression between weed presence/absence and the sensor readings (LIDAR height and reflection values) was used to validate the accuracy of the sensor. This permitted the discrimination of vegetation from the ground with an accuracy of up to 95%. In addition, a Canonical Discrimination Analysis (CDA) was able to discriminate mostly between soil and vegetation and, to a far lesser extent, between crop and weeds. The studied methodology arises as a good system for weed detection, which in combination with other principles, such as vision-based technologies, could improve the efficiency and accuracy of herbicide spraying.

An Approach to the Use of Depth Cameras for Weed Volume Estimation.

The use of depth cameras in precision agriculture is increasing day by day. This type of sensor has been used for the plant structure characterization of several crops. However, the discrimination of small plants, such as weeds, is still a challenge within agricultural fields. Improvements in the new Microsoft Kinect v2 sensor can capture the details of plants. The use of a dual methodology using height selection and RGB (Red, Green, Blue) segmentation can separate crops, weeds, and soil. This paper explores the possibilities of this sensor by using Kinect Fusion algorithms to reconstruct 3D point clouds of weed-infested maize crops under real field conditions. The processed models showed good consistency among the 3D depth images and soil measurements obtained from the actual structural parameters. Maize plants were identified in the samples by height selection of the connected faces and showed a correlation of 0.77 with maize biomass. The lower height of the weeds made RGB recognition necessary to separate them from the soil microrelief of the samples, achieving a good correlation of 0.83 with weed biomass. In addition, weed density showed good correlation with volumetric measurements. The canonical discriminant analysis showed promising results for classification into monocots and dictos. These results suggest that estimating volume using the Kinect methodology can be a highly accurate method for crop status determination and weed detection. It offers several possibilities for the automation of agricultural processes by the construction of a new system integrating these sensors and the development of algorithms to properly process the information provided by them.

A Novel Approach for Weed Type Classification Based on Shape Descriptors and a Fuzzy Decision-Making Method

An important objective in weed management is the discrimination between grasses (monocots) and broad-leaved weeds (dicots), because these two weed groups can be appropriately controlled by specific herbicides. In fact, efficiency is higher if selective treatment is performed for each type of infestation instead of using a broadcast herbicide on the whole surface. This work proposes a strategy where weeds are characterised by a set of shape descriptors (the seven Hu moments and six geometric shape descriptors). Weeds appear in outdoor field images which display real situations obtained from a RGB camera. Thus, images present a mixture of both weed species under varying conditions of lighting. In the presented approach, four decision-making methods were adapted to use the best shape descriptors as attributes and a choice was taken. This proposal establishes a novel methodology with a high success rate in weed species discrimination.

Spatial Distribution Patterns of Johnsongrass (Sorghum halepense) in Corn Fields in Spain

This study describes the distribution patterns of Johnsongrass populations present in 38 commercial corn fields located in three major corn growing regions of Spain. A total of 232 ha were visually assessed from the cabin of a combine during harvesting using a three-category ranking (high density, low density, no presence) and recording the georeferenced data in a tablet personal computer. On average, 10.3 and 3.9% of the surveyed area were infested with high and low density of Johnsongrass, respectively. Most of the infested area was concentrated in a few large patches with irregular shape. Small patches (less than 1,000 m2) represented only 27% of the infested area. Management factors could explain much of the spatial distribution of this weed in the studied fields. Tillage direction was the main factor explaining patch shape: the length width−1 ratio of the patches was greater than two in the tillage direction. In sprinkler irrigated fields, higher levels of infestation were generally observed close to the sprinkler lines. Areas close to the edges of the field had a higher risk of infestation than the areas in the middle of the fields: a negative relationship between distance from the edge and weed abundance was established. Because a few patches, located in some predictable parts of the field, such as field edges, represent most of the seriously infested area, site-specific treatments of these areas could reduce herbicide inputs, until more reliable, spatially precise and practical detection, mapping, and spraying systems are developed. Nomenclature: Johnsongrass, Sorghum halepense (L.) Pers. SORHA; corn, Zea mays L.

Pyrolytic descriptors responsive to changes in humic acid characteristics after long-term sustainable management of dryland farming systems in Central Spain

Structural changes in humic acids from a semiarid soil of an experimental farm in Central Spain have been studied by Curie-point pyrolysis. Soil has received periodic inputs of farmyard manure or crop wastes for the last 16 years, and mineral nitrogen fertilisation in 50% of the plots. Analytical pyrolysis suggested substantial differences in terms of the effect of soil management on the accumulation mechanisms of the humic acid fraction. When compared with control plots, humic acids from plots amended with crop wastes displayed well-defined methoxyphenol assemblages, indicating that the diagenetic transformation of lignin could be a dominant mechanism of organic matter stabilisation. The greatest yields of methoxyphenols after organic inputs were obtained in plots receiving nitrogen fertilisation, what agrees with the expected higher performance of the lignin biodegradation in nitrogen-limited media. Increased yields of lignin-derived methoxyphenols were also observed in plots treated with manure, which released in addition a conspicuous series of alkyl compounds suggesting recalcitrant wax-derived lipids incorporated to the humic acids. Highest yields of pyrolytic fatty acids were observed in humic acids from manure-amended plots without nitrogen fertilisation. Alkylbenzene proportions were also pyrolytic descriptors responsive to mineral nitrogen inputs, showing very significant differences (P<0.01) in both control and amended plots. Results suggested that continued organic inputs can not be considered to increase soil organic matter quality, since microbial reworking of lignins became the dominant mechanism of accumulation of humic acid-type substances, even when nitrogen inputs were applied.

Compounds released by sequential chemolysis from cuticular remains of the Cretaceous Gymnosperm Squamastrobus tigrensis (Patagonia, the Argentine)

Abstract The chemical composition of morphologically well-preserved cuticular remains of the Cretaceous Gymnosperm Squamastrobus tigrensis found in the Bajo Tigre locality (Patagonia) was analysed by a progressive chemical degradation sequence involving: (i) lipid extraction after ultrasonic treatments; (ii) further BF 3 -MeOH transesterification; and (iii) repeated mild NaBO 2 -H 2 O 2 degradation of the final residue. The compound assemblages released after the successive treatments were considered to reflect lipid speciation patterns in the different levels of the cuticular structure. In particular, after all the treatments, the dominance of a homologous series of α , ω -alkanedioic acids with maxima at C 9 and C 10 indicates a polymethylene network based on macromolecules; the units of this network contain in-chain unsaturations or substitutions in positions similar to those in precursor unsaturated C 16 and C 18 acids. The low yields of ω -hydroxyacids typical of cutins and suberins of extant plants are interpreted as an intense microbial alteration and/or diagenetic transformation of the fossil cuticle. In conjunction with data from infrared spectroscopy and analytical pyrolysis, this suggests that the Squamastrobus remains consist of a macromolecular alkyl mixture in which the original C backbone has been defunctionalized, reoxidized, and subjected to additional condensation by the probable contribution of newly-formed, non-hydrolyzable bridges. It appears that this cellulose-lacking material includes a small moiety of altered lignin, and has been subjected to extensive oxidation, but not to further thermal alteration leading to decarboxylation. A possible result of this diagenetic alteration is that a portion of the resin constituents were transformed into lower molecular weight alkylbenzenes and alkylnaphthalenes, whereas another portion condensed into a very stable, non-hydrolyzable residue. The chemical stability of this residue is not due to aromatization, but to secondary condensation of altered aliphatic biomacromolecules.