Deficit irrigation based on drought tolerance and root signalling in potatoes and tomatoes

Agriculture is a big consumer of fresh water in competition with other sectors of the society. Within the EU-project SAFIR new water-saving irrigation strategies were developed based on pot, semi-field and field experiments with potatoes (Solanum tuberosum L.), fresh tomatoes (Lycopersicon esculentum Mill.) and processing tomatoes as model plants. From the pot and semi-field experiments an ABA production model was developed for potatoes to optimize the ABA signalling; this was obtained by modelling the optimal level of soil drying for ABA production before re-irrigation in a crop growth model. The field irrigation guidelines were developed under temperate (Denmark), Mediterranean (Greece, Italy) and continental (Serbia, China) climatic conditions during summer. The field investigations on processing tomatoes were undertaken only in the Po valley (North Italy) on fine, textured soil. The investigations from several studies showed that gradual soil drying imposed by deficit irrigation (DI) or partial root zone drying irrigation (PRD) induced hydraulic and chemical signals from the root system resulting in partial stomatal closure, an increase in photosynthetic water use efficiency, and a slight reduction in top vegetative growth. Further PRD increased N-mineralization significantly beyond that from DI, causing a stay-green effect late in the growing season. In field potato and tomato experiments the water-saving irrigation strategies DI and PRD were able to save about 20-30% of the water used in fully irrigated plants. PRD increased marketable yield in potatoes significantly by 15% due to improved tuber size distribution. PRD increased antioxidant content significantly by approximately 10% in both potatoes and fresh tomatoes. Under a high temperature regime, full irrigation (FI) should be undertaken, as was clear from field observations in tomatoes. For tomatoes full irrigation should be undertaken for cooling effects when the night/day average temperature >26.5 °C or when air temperature >40 °C to avoid flower-dropping. The temperature threshold for potatoes is not clear. From three-year field drip irrigation experiments we found that under the establishment phase, both potatoes and tomatoes should be fully irrigated; however, during the later phases deficit irrigation might be applied as outlined below without causing significant yield reduction:

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Potatoes

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After the end of tuber initiation, DI or PRD is applied at 70% of FI. During the last 14 days of the growth period, DI or PRD is applied at 50% of FI.

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Fresh tomatoes

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From the moment the 1st truce is developed, DI is applied at 85-80% of FI for two weeks. In the middle period, DI or PRD is applied at 70% of FI. During the last 14 days of the growth period, DI or PRD is applied at 50% of FI.

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Processing tomatoes

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From transplanting to fruit setting at 4th-5th cluster, the PRD and DI threshold for re-irrigation is when the plant-available soil water content (ASWC) equals 0.7 (soil water potential, Ψ_soil = −90 kPa). During the late fruit development/ripening stage, 10% of red fruits, the threshold for re-irrigation for DI is when ASWC = 0.5 (Ψ_soil = −185 kPa) and for PRD when ASWC (dry side) = 0.4 (Ψ_{soil, dry side} = −270 kPa).

The findings during the SAFIR project might be used as a framework for implementing water-saving deficit irrigation under different local soil and climatic conditions.     

Prioritizing refuge sites for migratory geese to alleviate conflicts with agriculture

Expanding populations of geese feeding on farmland during winter and spring conflict with agricultural interests along their migratory flyway in north-western Europe. In Mid-Norway, farmers scare spring-staging pink-footed geese Anser brachyrhynchus off their land to protect crops, and this has had clear effects on goose distribution. To protect the geese, Norwegian authorities have implemented economic compensation to farmers to discourage scaring, but this has not been prioritised to accommodate the biological requirements and dispersal patterns of the geese, though such an approach is clearly needed. To address this need, we assessed the negative effects of scaring geese during 2004-2007, and built a species distribution model to identify sites suitable for goose foraging. We subsequently combined known foraging sites with sites identified by our model and prioritised these sites according to their connectivity, perimeter area ratio, years of historic use and proximity to roost. By combining historic data on foraging sites, a species distribution model, and a simple, accountable site selection process we demonstrate how the current compensation scheme can be made 10 times more efficient through strategic prioritisation. Our approach has direct implications for alleviating similar goose-agriculture conflicts throughout Europe.     

Organic Halogens in Landfill Leachates

Using a group parameter, totalorganic halogens (TOX), high TOX concentrationswere found in leachates and leachate contaminatedgroundwaters at two Danish mixed sanitary andhazardous waste sites. With commonly used screeningprocedures for organic contaminants, the individualhalogenated organic compounds behind the high TOXcould not be found. Conversely, part of the TOX couldbe attributed to halogenated humic substances that cannot be analysed with conventional organic contaminantanalyses. Even though TOX can still be considered anindicator of leachate contamination in the aquifers,attempts to identify the halogenated contaminantsbehind the TOX using screening methods such as GC-MSwill be unsuccessful in most cases.     

Development of potato late blight (Phytophthora infestans) in differently developed potato crops and the potential to graduate the fungicide dose according to crop biomass

Phytophthora infestans is a serious disease in potato production and control of the disease often requires 10 or more fungicide applications during the growing season. Control is typically carried out using a constant fungicide dose in the entire field although there may be large differences in crop development and biomass across the field. The objective of the study reported in this paper was to test whether the fungicide dose response curve controlling P. infestans was dependent on the crop development and biomass level. If such a biomass-dependent dose response was found it was further the purpose to evaluate the potential to optimize fungicide inputs in potato crops applying a site-specific crop density-dependent fungicide dose. The study was carried out investigating the fungicide dose response controlling P. infestans in potatoes at three biomass densities obtained growing the potato crop at three nitrogen levels. Furthermore, the field experiments included four levels of fungicide dose rate at each nitrogen rate, an untreated control, the recommended fungicide dose rate and two reduced dose rates and the experiments were replicated for three years. Nitrogen level and thus crop density had a limited although significant influence on attack of P. infestans whereas fungicide dose rate by far was the most influential variable. In contrast the interaction of nitrogen rate and fungicide dose rate that would indicate a biomass-dependent dose response was insignificant. If the variation in crop density and biomass level obtained in the study is representative for the variation found cultivating potatoes in heterogeneous fields there seem to be limited potential for fungicide optimization applying fungicides against P. infestans site-specific according to crop density or biomass.     

Characterization and inheritance of partial resistance to downy mildew, Peronospora parasitica, in breeding material of broccoli, Brassica oleracea convar. botrytis var. italica

Twenty doubled haploid broccoli lines from breeding material were evaluated for resistance to Peronospora parasitica at the seedling stage. All lines supported sporulation of the pathogen but to varying extents and intensities. Partial resistance of the more resistant lines,‘br8’and ‘br9′, reduced conidia production on cotyledons by 50-70% compared with the most susceptible lines. Inoculation of the two most resistant lines with 13 isolates of different geographical origins revealed that ‘br9′, showed a rather uniform level of resistance to all isolates while ‘br8’showed some isolate specificity Partial resistance was evaluated in six of the broccoli lines in a half diallel set of crosses. Disease assessment of seedlings showed that additive genetic effects explained 45.8% and 31.8% of the total variation of sporulation score and conidia production, respectively This suggests that recurrent selection for partial resistance to P. parasitica in early generation in breds or in populations of broccoli will be efficient to obtain cotyledon resistance.     

Alternate partial root-zone irrigation improves fertilizer-N use efficiency in tomatoes

The objective of this study was to investigate the comparative effects of alternative partial root-zone irrigation (PRI) and deficit irrigation (DI) on fertilizer-N use efficiency in tomato plants under mineral N and organic N fertilizations. The plants were grown in split-root pots in a climate-controlled glasshouse and were subjected to PRI and DI treatments during early fruiting stage. When analyzed across the N fertilizer treatments, PRI treatment led to significantly higher N yield, agronomic N use efficiency (ANUE), and apparent N recovery efficiency (ANRE) as compared with the DI treatment, indicating significantly higher fertilizer-N use efficiency and soil N availability as well as enhanced plant’s N acquisition ability in the PRI treatment. Analysis across the irrigation treatments showed that the mineral N fertilizer treatment (MinN) significantly increased N yield, ANUE and ANRE relative to the organic N fertilizer treatment (OrgN). Compared with DI, the rhizosphere and bulk soil mineral N content in the soil were significantly lowered in the PRI treatment, indicating the enhanced root N uptake efficiency. It is suggested that PRI-enhanced soil water dynamics may have increased soil nitrate mass/diffusive flow to the root surfaces and root N uptake efficiency in the wetting soil and stimulated soil N mineralization and plant N demand, contributing to the improved fertilizer-N use efficiency in the PRI relative to the DI treatment.     

A review of decision-making approaches to handle uncertainty and risk in adaptive forest management under climate change

• Context  

This review paper provides an overview of approaches to which we may resort for handling the complex decision problems involving uncertainty and risk that climate change implies for forest managers. Modelling approaches that could support adaptive management strategies seem to be called for, not only as climate change denotes increased economic uncertainty but also because new and more reliable information becomes available as time passes and climate changes.     

Quasi-non-linear fracture mechanics analysis of splitting failure in simply supported beams loaded perpendicular to grain by dowel joints

A quasi-non-linear fracture mechanics model based on beam on elastic foundation theory is applied for analysis of the splitting failure of dowel joints loaded perpendicular to grain. Simply supported beams symmetrically loaded by two dowels are considered, and the effects of edge distance, dowel spacing, and distance between dowels and supports are accounted for. The foundation modulus used in the beam on elastic foundation model is chosen so that the perpendicular-to-grain tensile strength and fracture energy properties of the wood are correctly represented. This ensures that a conventional stress analysis and failure criterion lead to the same solution as the compliance method of fracture mechanics. A semiempirical efficiency factor is proposed to account for the influence of the total beam depth, which does not enter the beam on elastic foundation model, but the effect of which is evident from tests. It is shown that the so-called Van der Put/Leijten model, which recently has been adopted in Eurocode 5, appears as a special case of the model presented. Tests on simply supported beams with a single dowel joint at midspan are compared with the theoretical predictions. Various edge distances, beam depths, and spans were tested.