The effect of intracanopy lighting on cucumber fruit yield—Model analysis

Intracanopy lighting is a recently developed supplementary lighting technique for high-wire grown vegetable production in greenhouses where a part of the lamps is mounted within instead of above the canopy. A potentially higher yield using intracanopy lighting compared with top-lighting, is based on three assumptions: (1) increased light-absorption by the crop; (2) a higher photosynthetic light use efficiency due to a more homogeneous vertical light distribution; (3) a preserved photosynthetic capacity of leaves deeper in the canopy. We used an explanatory crop model to quantify the relative importance of these assumptions for a cucumber crop during an experiment in winter in the Netherlands (Trouwborst et al., 2010). Photosynthesis and yield data of this intracanopy lighting experiment with light-emitting diodes (34% of supplemental PAR) in combination with top-lighting (66% of supplemental PAR) were used to parameterise our model. In that study intracanopy lighting did not result in an increased yield compared with 100% top-lighting due to extreme leaf curling and a lower dry matter partitioning to the fruits. Our model predicted an 8% increase in fruit yield for the intracanopy lighting treatment if there were to be no leaf curling and no lower dry matter partitioning. This increase can be largely explained by the change in light distribution and light absorption. The model further revealed unexpectedly large consequences of the lower dry matter partitioning to the fruits whereas the negative effect of leaf curling was small. The direct effect of a greater A_max at deeper canopy layers was slightly positive. The last however might have indirectly caused the greater partitioning to the leaves as the greater A_max was associated with a preserved leaf mass per area. Solutions for this problem are discussed. Our explanatory model allowed us to disentangle the interacting effects of intracanopy lighting on fruit yield. Overall, intracanopy lighting has been shown here to potentially increase the assimilation light use efficiency.     

The distribution of a threatened migratory bird species in a patchy landscape: a multi-scale analysis

Understanding the driving forces behind the distribution of threatened species is critical to set priorities for conservation measures and spatial planning. We examined the distribution of a globally threatened bird, the corncrake (Crex crex), in the lowland floodplains of the Rhine River, which provide an important breeding habitat for the species. We related corncrake distribution to landscape characteristics (area, shape, texture, diversity) at three spatial scales: distinct floodplain units (“floodplain scale”), circular zones around individual observations (“home range scale”), and individual patches (“patch scale”) using logistic regression. Potential intrinsic spatial patterns in the corncrake data were accounted for by including geographic coordinates and an autocovariate as predictors in the regression analysis. The autocovariate was the most important predictor of corncrake occurrence, probably reflecting the strong conspecific attraction that is characteristic of the species. Significant landscape predictors mainly pertained to area characteristics at the patch scale and the home range scale; the probability of corncrake occurrence increased with potential habitat area, patch area, and nature reserve area. The median potential habitat patch size associated with corncrake occurrence was 11.3 ha; 90% of the corncrake records were associated with patches at least 2.2 ha in size. These results indicate that the corncrake is an area-sensitive species, possibly governed by the males’ tendency to reside near other males while maintaining distinct territories. Our results imply that corncrake habitat conservation schemes should focus on the preservation of sufficient potential habitat area and that existing management measures, like delayed mowing, should be implemented in relatively large, preferably contiguous areas.     

Resistance toPhytophthora porri in leek and some of its wild relatives

Summary Winter leek and related plant material was evaluated for resistance to white tip disease (Phytophthora porri) in the Netherlands. Significant differences in partial resistance were found between winter leek accessions in field tests with zoospore and natural inoculation. These differences were consistent over three years, and indicate that resistance can be improved through mass selection in winter leek cultivars. Some accessions of wild or cultivated relatives of winter leek with higher levels of resistance were found in a glasshouse test with zoospore inoculation. These sources of resistance were also highly resistant in field experiments over a two year period.     

Salt River Project experience in conversion from agriculture to urban water use

Salt River Project (SRP) was established in 1903 to deliver water to farms on about 250,000 ac (100,000 ha) located in South-Central Arizona. While SRP continues to deliver water to the entire area, today only about 10% of that land is still in agriculture. The remainder has been urbanized. Urbanization of the vast majority of water service area has caused SRP to rethink and adjust every aspect of its business, from daily operation and maintenance to the overarching issues of liability and public involvement. Some of the issues being addressed and lessons learned are addressed in this paper.     

Comparison of sources of resistance to leaf aphids in lettuce (Lactuca sativa L.)

Summary Three lines of lettuce with resistance to Nasonovia ribisnigri, based on the dominant Nr-gene, and four lines selected for partial resistance to Myzus persicae were tested against three species of leaf aphid: N. ribisnigri, M. persicae and Macrosiphum euphorbiae. The effect of the Nr-gene was also studied in a segregating F2 population.In the material tested, resistance to N. ribisnigri was exclusively based on the Nr-gene, lines selected only for resistance to M. persicae showed no resistance to N. ribisnigri. The Nr-gene also induces partial resistance to M. persicae, but the level of this resistance is influenced by other genes, because the lines with Nr-gene differed significantly from each other for reproduction of M. persicae. The Nr-gene had no effect on the resistance of lettuce to M. euphorbiae.In lines with the Nr-gene, levels of resistance to M. persicae and to M. euphorbiae were correlated, suggesting that the resistance may be determined by the same genes. The Nr-line with highest resistance to M. persicae was comparable for this characteristic to the lines selected for resistance to M. persicae.The cultivars Taiwan and Ravel possess a resistance factor to M. euphorbiae that has no effect on M. persicae or N. ribisnigri. Lines selected for resistance to M. persicae also showed partial resistance to M. euphorbiae. Based on the present results no conclusions can be drawn whether this resistance is based on the same genes that provide resistance to M. persicae, or on a resistance factor comparable to that found in Taiwan and Ravel.     

Use of GIS and remote sensing for soil mapping and for locating new sites for permanent cropland — A case study in the “highlands” of northern Thailand

Until a few decades ago, the highlands of northern Thailand were predominantly under forest. Since then, a growing pressure on the land, partly from hill tribes living in the highlands, has led to rapid deforestation and land degradation. To counteract these problems, the Royal Thai Government started a “Highland Development Project” in 1990. Activities of this project include soil inventories and the use of soil and other data to locate new sites for cropland and settlements for hill tribes. In this paper, a case study is described in which the use of a Geographic Information System (GIS) and digital remote sensing methods is compared with the methods currently used in these activities. The GIS is used for the preparation of a terrain mapping unit (TMU) map which integrates data from existing maps and data interpreted from satellite images. The GIS is also used (i) to derive relevant information from the TMU/soil map (e.g. land suitability and estimated erosion rates) and (ii) to integrate this information with land cover/use and accessibility information. This integrated information is used to locate physically suitable, accessible and not yet used areas that could become potential new cropland sites for highland people after resettlement.

A comparison between the currently used methods and the GIS methods shows that apart from considerable time savings, also improvements in data quality are achieved, e.g. by the preparation of a slope map based on a digital terrain model and by up-dating of existing land use information with satellite imagery. The spatial and attribute data base in the GIS makes it possible to use the original, non-aggregated data and, in addition, facilitates the integration of the various data for the analysis of potential sites for resettlement according to various criteria and objectives.     

ULTRASONOGRAPHY OF THE EQUINE TARSUS

Ultrasonography was used to delineate the sonographic anatomy of the equine tarsus with emphasis on the flexor tendons and plantar ligament at the plantar surface of the tarsus, the medial collateral ligaments and the dorsomedial joint capsule of the tibiotarsal joint. The cross-sectional gross anatomy of these tendons and ligaments was evaluated in 6 cadaver limbs. Using a 5.5 MHz mechanical sector scanner, the examined tendons and ligaments were easily identified as hyperechoic structures in 10 limbs of normal live horses. The normal ultrasonographic appearance of the dorsomedial tibiotarsal joint capsule was studied in 8 cadaver limbs. The inner surface of the tibiotarsal joint capsule was covered with villi; short and pointed in the mid region, resembling a small nodular mass proximally and a straggly beard distally. In 4 lame horses diagnostic ultrasound aided the diagnosis of plantar swellings, medial collateral joint ligamentous injury and hypertrophic synovitis.     

Uncertainties in global-scale reconstructions of historical land use: an illustration using the HYDE data set

Land use and land-use change play an important role in global integrated assessments. However, there are still many uncertainties in the role of current and historical land use in the global carbon cycle as well as in other dimensions of global environmental change. Although databases of historical land use are frequently used in integrated assessments and climate studies, they are subject to considerable uncertainties that often are ignored. This paper examines a number of the most important uncertainties related to the process of reconstructing historical land use. We discuss the origins of different types of uncertainty and the sensitivity of land-use reconstructions to these uncertainties. The results indicate that uncertainties not only arise as result of the large temporal and spatial variation in historical population data, but also relate to assumptions on the relationship between population and land use used in the reconstructions. Improving empirical data to better specify and validate the assumptions about the relationship between population and land use, while accounting for the spatial and temporal variation, could reduce uncertainties in the reconstructions. Such empirical evidence could be derived from local case studies, such as those conducted in landscape ecology, environmental history, archeology and paleoecology.