Incidencia de las secuencias de cultivos, sistemas de labranza y fertilización sobre algunas propiedades físicas y su relación con el carbono

p.151-158

Sustentabilidad de los sistemas de siembra directa

p.285-304

Agricultural intensification and biodiversity partitioning in European landscapes comparing plants, carabids, and birds

Effects of agricultural intensification (AI) on biodiversity are often assessed on the plot scale, although processes determining diversity also operate on larger spatial scales. Here, we analyzed the diversity of vascular plants, carabid beetles, and birds in agricultural landscapes in cereal crop fields at the field (n = 1350), farm (n = 270), and European-region (n = 9) scale. We partitioned diversity into its additive components alpha, beta, and gamma, and assessed the relative contribution of beta diversity to total species richness at each spatial scale. AI was determined using pesticide and fertilizer inputs, as well as tillage operations and categorized into low, medium, and high levels. As AI was not significantly related to landscape complexity, we could disentangle potential AI effects on local vs. landscape community homogenization. AI negatively affected the species richness of plants and birds, but not carabid beetles, at all spatial scales. Hence, local AI was closely correlated to beta diversity on larger scales up to the farm and region level, and thereby was an indicator of farm-and region-wide biodiversity losses. At the scale of farms (12.83-20.52%) and regions (68.34-80.18%), beta diversity accounted for the major part of the total species richness for all three taxa, indicating great dissimilarity in environmental conditions on larger spatial scales. For plants, relative importance of alpha diversity decreased with AI, while relative importance of beta diversity on the farm scale increased with AI for carabids and birds. Hence, and in contrast to our expectations, AI does not necessarily homogenize local communities, presumably due to the heterogeneity of farming practices. In conclusion, a more detailed understanding of AI effects on diversity patterns of various taxa and at multiple spatial scales would contribute to more efficient agri-environmental schemes in agroecosystems.

Detection of soil compaction using seismic surface waves

Seismic geophysical methods have rarely been used in precision agriculture, predominantly due to the perception that they are slow and results require a complex evaluation. This paper explores the possibility of using a recently developed surface wave seismic geophysical approach, the multichannel analysis of surface waves (MASW) method, for assessment of agricultural compaction. This approach has the advantage of being non-intrusive, rapid and is able to produce 2D ground models with a relatively high density of spatial sampling points. The method, which was tested on a research site in Oakpark, Ireland, detected a significant difference in shear wave velocity between a heavily compacted headland and an uncompacted location. The results from this approach compared favourably with those obtained
from measurements of bulk density and penetrometer resistance and demonstrate that the MASW approach can distinguish between the extreme states of heavily compacted and uncompacted soil.

Response of farmland biodiversity to the introduction of bioenergy crops: effects of local factors and surrounding landscape context

The recent growth in bioenergy crop cultivation, stimulated by the need to implement measures to reduce net CO emissions, is driving major land-use changes with consequences for biodiversity and ecosystem service provision. Although the type of bioenergy crop and its associated management is likely to affect biodiversity at the local (field) scale, landscape context and its interaction with crop type may also influence biodiversity on farms. In this study, we assessed the impact of replacing conventional agricultural crops with two model bioenergy crops (either oilseed rape Brassica napus or Miscanthus × giganteus) on vascular plant, bumblebee, solitary bee, hoverfly and carabid beetle richness, diversity and abundance in 50 sites in Ireland. We assessed whether within-field biodiversity was also related to surrounding landscape structure. We found that local- and landscape-scale variables correlated with biodiversity in these agricultural landscapes. Overall, the differences between the bioenergy crops and the conventional crops on farmland biodiversity were mostly positive (e.g. higher vascular plant richness in Miscanthus planted on former conventional tillage, higher solitary bee abundance and richness in Miscanthus and oilseed rape compared with conventional crops) or neutral (e.g. no differences between crop types for hoverflies and bumblebees). We showed that these crop type effects were independent of (i.e. no interactions with) the surrounding landscape composition and configuration. However, surrounding landscape context did relate to biodiversity in these farms, negatively for carabid beetles and positively for hoverflies. Although we conclude that the bioenergy crops compared favourably with conventional crops in terms of biodiversity of the taxa studied at the field scale, the effects of large-scale planting in these landscapes could result in very different impacts. Maintaining ecosystem functioning and the delivery of ecosystem services will require a greater understanding of impacts at the landscape scale to ensure the sustainable development of climate change mitigation measures.

Soil microbes and community coalescence

Community coalescence is a recently introduced term describing the interaction of entire communities and their environments. We here explicitly place the concept of community coalescence in a soil microbial context, exploring intrinsic and extrinsic drivers of such coalescence events. Examples of intrinsic events include the action of earthworms and the dynamics of soil aggregates, while extrinsic events are exemplified by tillage, flooding, litter-fall, outplanting, and the addition of materials containing microbial communities. Aspects of global change may alter the frequency or severity of coalescence events. We highlight functional consequences of community coalescence in soil, and suggest ways to experimentally tackle this phenomenon. Soil ecology as a whole stands to benefit from conceptualizing soil biodiversity in terms of dynamic coalescent microbial assemblages.

Is agricultural policy promoting a new role for farmers?: a case study

European Agenda 2000 considers the integration of environment in CAP and the role farmers can play on natural resources management. Alternative tillage technologies to seed cereals play an important economic and environmental role on the development of a sustainable agriculture and its adoption may depend on the agricultural policy, particularly policies on income support. The results obtained clearly show that the use of alternative soil tillage technologies would be promoted by the change of supports from the first to the second pillar of CAP and we can conclude that, in general, this change will encourage a faster technological adoption. (c) 2006 Society for Policy Modeling. Published by Elsevier Inc. All rights reserved.

Assessing soil erosion due to land use change at the Alqueva reservoir surrounding area

Tese de doutoramento, Ciências do Mar, da Terra e do Ambiente, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015

Development and Integration of Biocontrol Products in Branched Broomrape (Phelipanche ramosa) management in Tomato

Parasitic weeds of the genera Striga, Orobanche, and Phelipanche pose a severe problem for agriculture because they are difficult to control and are highly destructive to several crops. The present work was carried out during the period October, 2009 to February, 2012 to evaluate the potential of arbuscular mycorrhizal fungi (AMF) to suppress P. ramosa on tomatoes and to investigate the effects of air-dried powder and aqueous extracts from Euphorbia hirta on germination and haustorium initiation in Phelipanche ramosa. The work was divided into three parts: a survey of the indigenous mycorrhizal flora in Sudan, second, laboratory and greenhouse experiments (conducted in Germany and Sudan) to construct a base for the third part, which was a field trial in Sudan. A survey was performed in 2009 in the White Nile state, Sudan to assess AMF spore densities and root colonization in nine fields planted with 13 different important agricultural crops. In addition, an attempt was made to study the relationship between soil physico-chemical properties and AMF spore density, colonization rate, species richness and other diversity indices. The mean percentage of AMF colonization was 34%, ranging from 19-50%. The spore densities (expressed as per 100 g dry soil) retrieved from the rhizosphere of different crops were relatively high, varying from 344 to 1222 with a mean of 798. There was no correlation between spore densities in soil and root colonization percentage. A total of 45 morphologically classifiable species representing ten genera of AMF were detected with no correlation between the number of species found in a soil sample and the spore density. The most abundant genus was Glomus (20 species). The AMF diversity expressed by the Shannon–Weaver index was highest in sorghum (H\= 2.27) and Jews mallow (H\= 2.13) and lowest in alfalfa (H\= 1.4). With respect to crop species, the genera Glomus and Entrophospora were encountered in almost all crops, except for Entrophospora in alfalfa. Kuklospora was found only in sugarcane and sorghum. The genus Ambispora was recovered only in mint and okra, while mint and onion were the only species on which no Acaulospora was found. The hierarchical cluster analysis based on the similarity among AMF communities with respect to crop species overall showed that species compositions were relatively similar with the highest dissimilarity of about 25% separating three of the mango samples and the four sorghum samples from all other samples. Laboratory experiments studied the influence of root and stem exudates of three tomato varieties infected by three different Glomus species on germination of P. ramosa. Root exudates were collected 21or 42 days after transplanting (DAT) and stem exudates 42 DAT and tested for their effects on germination of P. ramosa seeds in vitro. The tomato varieties studied did not have an effect on either mycorrhizal colonization or Phelipanche germination. Germination in response to exudates from 42 day old mycorrhizal plants was significantly reduced in comparison to non-mycorrhizal controls. Germination of P. ramosa in response to root exudates from 21 day old plants was consistently higher than for 42 day-old plants (F=121.6; P<.0001). Stem diffusates from non-mycorrhizal plants invariably elicited higher germination than diffusates from the corresponding mycorrhizal ones and differences were mostly statistically significant. A series of laboratory experiments was undertaken to investigate the effects of aqueous extracts from Euphorbia hirta on germination, radicle elongation, and haustorium initiation in P. ramosa. P. ramosa seeds conditioned in water and subsequently treated with diluted E. hirta extract (10-25% v/v) displayed considerable germination (47-62%). Increasing extract concentration to 50% or more reduced germination in response to the synthetic germination stimulants GR24 and Nijmegen-1 in a concentration dependent manner. P. ramosa germlings treated with diluted Euphorbia extract (10-75 % v/v) displayed haustorium initiation comparable to 2, 5-Dimethoxy-p-benzoquinon (DMBQ) at 20 µM. Euphorbia extract applied during conditioning reduced haustorium initiation in a concentration dependent manner. E. hirta extract or air-dried powder, applied to soil, induced considerable P. ramosa germination. Pot experiments were undertaken in a glasshouse at the University of Kassel, Germany, to investigate the effects of P. ramosa seed bank on tomato growth parameters. Different Phelipanche seed banks were established by mixing the parasite seeds (0 - 32 mg) with the potting medium in each pot. P. ramosa reduced all tomato growth parameters measured and the reduction progressively increased with seed bank. Root and total dry matter accumulation per tomato plant were most affected. P. ramosa emergence, number of tubercles, and tubercle dry weight increased with the seed bank and were, invariably, maximal with the highest seed bank. Another objective was to determine if different AM fungi differ in their effects on the colonization of tomatoes with P. ramosa and the performance of P. ramosa after colonization. Three AMF species viz. GIomus intraradices, Glomus mosseae and Glomus Sprint® were used in this study. For the infection, P. ramosa seeds (8 mg) were mixed with the top 5 cm soil in each pot. No mycorrhizal colonization was detected in un-inoculated control plants. P. ramosa infested, mycorrhiza inoculated tomato plants had significantly lower AMF colonization compared to plants not infested with P. ramosa. Inoculation with G. intraradices, G. mosseae and Glomus Sprint® reduced the number of emerged P. ramosa plants by 29.3, 45.3 and 62.7% and the number of tubercles by 22.2, 42 and 56.8%, respectively. Mycorrhizal root colonization was positively correlated with number of branches and total dry matter of tomatoes. Field experiments on tomato undertaken in 2010/12 were only partially successful because of insect infestations which resulted in the complete destruction of the second run of the experiment. The effects of the inoculation with AMF, the addition of 10 t ha-1 filter mud (FM), an organic residues from sugar processing and 36 or 72 kg N ha-1 on the infestation of tomatoes with P. ramosa were assessed. In un-inoculated control plants, AMF colonization ranged between 13.4 to 22.1% with no significant differences among FM and N treatments. Adding AMF or FM resulted in a significant increase of branching in the tomato plants with no additive effects. Dry weights were slightly increased through FM application when no N was applied and significantly at 36 kg N ha-1. There was no effect of FM on the time until the first Phelipanche emerged while AMF and N application interacted. Especially AMF inoculation resulted in a tendency to delayed P. ramosa emergence. The marketable yield was extremely low due to the strong fruit infestation with insects mainly whitefly Bemisia tabaci and tomato leaf miner (Tuta absoluta). Tomatoes inoculated with varied mycorrhiza species displayed different response to the insect infestation, as G. intraradices significantly reduced the infestation, while G. mosseae elicited higher insect infestation. The results of the present thesis indicate that there may be a potential of developing management strategies for P. ramosa targeting the pre-attachment stage namely germination and haustorial initiation using plant extracts. However, ways of practical use need to be developed. If such treatments can be combined with AMF inoculation also needs to be investigated. Overall, it will require a systematic approach to develop management tools that are easily applicable and affordable to Sudanese farmers. It is well-known that proper agronomical practices such as the design of an optimum crop rotation in cropping systems, reduced tillage, promotion of cover crops, the introduction of multi-microbial inoculants, and maintenance of proper phosphorus levels are advantageous if the mycorrhiza protection method is exploited against Phelipanche ramosa infestation. Without the knowledge about the biology of the parasitic weeds by the farmers and basic preventive measures such as hygiene and seed quality control no control strategy will be successful, however.

Untersuchungen zu Controlled Traffic Farming und satellitenbasierten Lenksystemen

Diese Arbeit behandelt Controlled Traffic Farming (CTF) Anbausysteme, bei denen für alle Arbeitsgänge satellitengesteuert immer dieselben Fahrspuren benutzt werden. Lässt sich mit CTF die Belastung des Bodens verringern und die Effizienz von Direktsaat-Anbausystemen steigern? Neben agronomischen und bodenphysikalischen Parametern wurden Auswirkungen von Lenksystemen und Umsetzungsmöglichkeiten von CTF in die Praxis untersucht. Die Analyse einer CTF-Umsetzung unter europäischen Bedingungen mit der Verwendung von Standardmaschinen zeigte, dass sich CTF-Anbausysteme mit den heute zur Verfügung stehenden Maschinen für Dauergrünland, Mähdruschfrüchte und Mais auf kleiner und grösser strukturierten Flächen relativ einfach mechanisieren lassen. Bei Zuckerrüben und Kartoffeln können Kompromisse notwendig sein. Generell erfordern CTF-Anbausysteme eine sorgfältige Planung und Umsetzung in die Praxis. Im dreijährigen Feldversuch (Winterweizen, Wintergerste, Kunstwiese mit Kleegrasmischung) auf einem Lehmboden wurde CTF-Direktsaat mit konventionell zufällig befahrenen Direktsaat- und Pflugverfahren verglichen. Unter CTF zeigte sich eine Differenzierung der nicht, gering und intensiv befahrenen Varianten. Auf dem vorliegenden kompakten Boden mit 1150 mm Jahresniederschlag waren die Unterschiede zwischen den nicht befahrenen Flächen und den mit niedrigem Kontaktflächendruck befahrenen Flächen eher gering. In den nicht befahrenen Flächen entwickelten Eindringwiderstand und Kohlendioxidgehalt der Bodenluft nach drei Jahren signifikant bessere Werte. Bodendichte und Porosität zeigten hingegen keinen eindeutig interpretierbaren Trend. Aufgrund teils suboptimaler Feldaufgänge liess sich keine generelle agronomische Tendenz ableiten. Die intensive Befahrung der Pflegefahrgassen zeigte allerdings klar negative bodenkundliche und planzenbauliche Auswirkungen. Es bietet sich daher an, vor allem für Pflegearbeiten permanent dieselben Fahrspuren zu nutzen. In der Untersuchung zu den Auswirkungen von Lenksystemen zeigten sich signifikante Vorteile von Lenksystemen in einer Verminderung der Fahrerbelastung und einer höheren Lenkgenauigkeit vor allem bei grossen Arbeitsbreiten ohne Spuranreisser. Die meisten anderen Messparameter waren mit Lenksystem leicht vorteilhafter als ohne, unterschieden sich aber nicht signifikant voneinander. Fahrer und naturräumliche Gegebenheiten wie die Schlagform hatten einen wesentlich grösseren Einfluss. Gesamthaft betrachtet erweitert CTF in Kombination mit weiteren Bodenschutzmass-nahmen die Möglichkeiten, Bodenverdichtungen zu vermeiden, den Bedarf an energieintensiver Bodenlocke-rung zu reduzieren und die Entwicklung einer stabileren Bodenstruktur mit höherer Tragfähigkeit zu fördern. Zusammen mit einer an Kultur und Anbausystem angepassten Saatbettbereitung und den in geraden Reihen einfacher durchführbaren mechanischen Pflegemassnahmen ergeben sich gute Voraussetzungen für die Gestaltung agronomisch leistungsfähiger und ökologisch nachhaltiger Anbausysteme.

Effects of grassland renovation on carbon concentrations and aggregate distribution in temperate grassland soils

The effects of continuous tillage on the distribution of soil organic matter (SOM) and aggregates have been well studied for arable soils. However, less is known about the effects of sporadic tillage on SOM and aggregate dynamics in grassland soils. The objectives of the present thesis were (I) to study the longer-term effects of sporadic tillage of grassland on organic carbon (Corg) stocks and the distribution of aggregates and SOM, (II) to investigate the combined effects of sporadic tillage and fertilization on carbon and nitrogen dynamics in grassland soils, and (III) to study the temporal dynamics of Corg stocks, aggregate distribution and microbial biomass in grassland soils. Soil samples were taken in three soil depths (0 – 10 cm; 10 – 25 cm; 25 – 40 cm) from a field trial with loamy sandy soils (Cambisols, Eutric Luvisols, Stagnosols, Anthrosols) north of Kiel, Germany. For Objective I we have sampled soil two and five years after one or two tillage operation(s). Treatments consisted of (i) permanent grassland, (ii) tillage of grassland followed by a re-establishment of grassland and (iii) tillage of grassland followed by a re-establishment of grassland with one season of winter wheat in between. The tillage in grassland led to a reduction in Corg stocks, large macroaggregates (>2000 µm) and SOM in the top 10 cm soil depth. These findings were still significant two years after tillage; however, five years after tillage no longer present. Regarding the soil profile (0 – 40 cm) no significant differences in the mentioned parameters between the tilled plots and the permanent grassland existed. A second tillage event and the insertion of one season of winter wheat did not lead to any further effects on Corg stocks as well as aggregate and SOM concentrations in comparison with a single tillage event in these grassland soils. Treatments adapted for Objective II included (i) long-term grassland and (ii) tillage of grassland followed by a re-establishment of grassland with one season of winter wheat in between. The plots were split and received either 240 kg N ha-1 year-1 in the form of cattle slurry or no cattle slurry application. The application of slurry within a period of four years had no effects on the Corg and total nitrogen stocks or the aggregate distribution, but led to a reduction of free and not physically protected SOM. However, the application of cattle slurry and the grassland renovation seems to change the plant species composition and therefore generalizations on the direct effects are not yet possible. For studying Objective III a further field trial was initiated in September 2010. Soil samples were taken six times within one year (from October 2010 to October 2011) (i) after the conversion from arable land into grassland, (ii) after the tillage of grassland followed by a re-establishment of grassland and (iii) in a permanent grassland. We found an increase in the microbial and fungal biomass after the conversion of arable land into grassland, but no effect on aggregate distribution and Corg stocks. A one-time tillage operation in grassland led to a reduction in large macroaggregates and Corg stocks in the top 10 cm soil depth with no effect on the sampled soil profile. However, we found large variations in the fungal biomass and aggregate distribution within one year in the permanent grassland, presumably caused by environmental factors. Overall, our results suggest that a single tillage operation in grassland soils markedly decreased the concentrations of Corg, larger aggregates and SOM. However, this does not result in long-lasting effects on the above mentioned parameters. The application of slurry cannot compensate the negative effects of a tillage event on aggregate concentrations or Corg stocks. However, while the Corg concentration is not subject to fluctuations within a year, there are large variations of the aggregate distribution even in a permanent grassland soil. Therefore conclusions of results from a single sampling time should be handled with care.

Soil, water and nutrient loss under conventional and organic vegetable production managed in small farms

Agricultural systems with conventional tillage and intensive use of agrochemicals, especially those on high slopes and with shallow soils, have the potential to release pollutants. This study aimed at evaluating the soil, water and nutrient lost via agricultural runoff in large plots (small catchments) under conventional and organic farming of vegetables as well as under forest (control) system in a Cambisol in the Campestre catchment. Samples of runoff were collected biweekly for one year through a Coshocton wheel. The soil and water losses from the conventional farming were 218 and 6 times higher, respectively, than forest. Under organic farming the soil and water losses were 12 and 4 times higher, respectively, than forest. However the soil losses (0.5 to 114 kg ha^(−1) year^(−1)) are considered low in agronomy but environmentally represent a potential source of surface water contamination by runoff associated pollutants. The concentrations and losses of all forms of phosphorus (P) were higher in the conventional system (9.5, 0.9 and 0.3 mg L^(−1) of total P for conventional, organic and forest systems, respectively), while the organic system had the highest concentrations and losses of soluble nitrogen (4.7, 38.6 and 0.4 mg L^(−1) of NO_3-N, respectively). The percentage of bioavailable P was proportionally higher in the organic system (91% of total P lost was as bioavailable P), indicating greater potential for pollution in the short term.

Assessment of soil particle redistribution on two contrasting cultivated hillslopes

The particle size distributions of surface soils from two cultivated silty fields (Moorfield and Railway South) in Herefordshire, UK, were assessed by sampling on 20-m grids across the fields. Moorfield (8 ha) had a uniform landscape sloping mainly in a North-South direction while Railway South (12 ha) had complex undulating landscape characteristics. Samples from 3 surficial layers were also taken at 3 landscape positions at Moorfield to investigate recent (within-season) soil particle redistribution. Size fractions were determined using chemical dispersion, wet sieving (to separate the sand fractions) and laser gramilometry (for the finer fractions). The distribution of various fractions and the relationships between elevation and the various fractions suggest preferential detachment and movement of coarse to very coarse silt fractions (16-63 mu m), which were found mostly at downslope or depositional areas. Upper slope samples had higher clay to fine silt (< 16 mu m) contents than bottom slope samples. The upslope-downslope patterns of size fractions, particularly on uniformly sloping areas, of the 2 fields were similar and their deposited sediments were dominated by coarse silt fractions. Samples from 3 landscape positions at Moorfield became coarser from the less eroded summit, through the eroding side-slope to the bottom-slope depositional area. Within each of these landscape positions the top 0-2.5 cm layers were more enriched in coarse silt fractions than the bottom layers. The spatial patterns of soil particle size distributions in the 2 fields may be a result of sediment detachment and deposition caused by water erosion and tillage operations. (c) 2005 Elsevier B.V. All rights reserved.

Cropping systems, carbon sequestration and erosion in Brazil, a review

Soils represent a large carbon pool, approximately 1500 Gt, which is equivalent to almost three times the quantity stored in terrestrial biomass and twice the amount stored in the atmosphere. Any modification of land use or land management can induce variations in soil carbon stocks, even in agricultural systems that are perceived to be in a steady state. Tillage practices often induce soil aerobic conditions that are favourable to microbial activity and may lead to a degradation of soil structure. As a result, mineralisation of soil organic matter increases in the long term. The adoption of no-tillage systems and the maintenance of a permanent vegetation cover using Direct seeding Mulch-based Cropping system or DMC, may increase carbon levels in the topsoil. In Brazil, no-tillage practices (mainly DMC), were introduced approximately 30 years ago in the south in the Parana state, primarily as a means of reducing erosion. Subsequently, research has begun to study the management of the crop waste products and their effects on soil fertility, either in terms of phosphorus management, as a means of controlling soil acidity, or determining how manures can be applied in a more localised manner. The spread of no-till in Brazil has involved a large amount of extension work. The area under no-tillage is still increasing in the centre and north of the country and currently occupies ca. 20 million hectares, covering a diversity of environmental conditions, cropping systems and management practices. Most studies of Brazilian soils give rates of carbon storage in the top 40 cm of the soil of 0.4 to 1.7 t C ha(-1) per year, with the highest rates in the Cerrado region. However, caution must be taken when analysing DMC systems in terms of carbon sequestration. Comparisons should include changes in trace gas fluxes and should not be limited to a consideration of carbon storage in the soil alone if the full implications for global warming are to be assessed.