A simple method was developed to estimate the fraction radiation intercepted by small eastern white cedar plants (Thuja occidentalis 'Brabant'). The method, which describes the crop canopy as rows of cuboids, was compared with methods used for estimating radiation interception by crops with homogeneous canopies and crops grown in rows. The extinction coefficient k was determined at different plant arrangements and an average k-value of 0.48 ± 0.03 (R' = 0.89) was used in the calculations. Effects of changing plant characteristics and inter-and intra-row plant distances were explored. The fraction radiation intercepted that was estimated with the method for rows of cuboids was up to 20% and for row crops up to 8% lower than estimated with the method for homogeneous canopies at low plant densities and a LAI of I. The fraction radiation intercepted by small plants of Thuja occidentalis 'Brabant' was best estimated by the simple method described in this paper.
UntIl recently, arable productIOn systems m the Netherlands were solely based on theIr productIOn functIOn, whIle ecologIcal and sOCIetal functIOns were not or hardly taken mto account. However, the Netherlands IS a small and densely populated country that reqUIres a well-planned management ofthe landscape If more functIOns are to be fulfrlled. In an attempt to utlhze the avaIlable space m a more effiCIent way, we desrgned Dutch arable productIOn systems wIth a productIOn, an ecologIcal and a sOCIetal functIOn, and tested systems dlffenng m level of bIOdIversIty m long-term field expenments. In thIs artIcle speCIal attentIOn IS paId to systems' sOCIetal functIOn, whICh IS attamed when productIve and blOdlverse systems make the landscape more attractIve than conventIOnal ones. To explam dIfferences m appreCIatIOn of arable productIOn systems as elements ofthe Dutch landscape a study was carned out conslstmg of mtervlews combmed wIth an appraIsal of contrastmg conventIOnal and blOdlverse systems and of field margms on the basIs of colour photographs taken when the crops and the wIld plants flowered. The pIctures mcluded fields wIth rye, barley, cereal-pea and cereal-pea-wlld flower mIXtUres. In addItIOn, pICtures of other arable productIOn systems m the Netherlands were used as a contrastmg reference; these mcluded forage maIZe, tulIP fields and blOdlverse field margms. The photographed systems were evaluated by a group of 30 mtervlewees, usmg the quahtatlve dIalogue method. Each of the respondents was offered the posslblhty to express hIs feelmgs and to explam underlymg thoughts when rankmg and classlfymg the photographed systems. Most respondents appreCIated the presence of wIld flowers, but the farmers amongst them were hesItant as they feared YIeld loss. Barley was preferred to rye. Pea m mIXtUres was not Irked much but was appreCIated more m mIXtUres wIth rye than wIth barley. Also the reference systems provoked mIXed feelmgs. Respondents engaged wIth nature or agrICulture appreCIated bIOdIversIty m fields more than respondents not engaged wIth these sectors.
Winter carrot for the fresh market is an important cash crop for many organic arable farms in the Netherlands. In recent years carrot roots from cold stores have been affected by superficial dark brown to black spots. To gain insight into the pathogens causing the blemish and the effect of agronomic practices on their occurrence, surveys were carried out among crops harvested in 2001 and 2002. In addition carrots harvested in 2003 were screened for root spotting pathogens. Rhexocercosporidium carotae (syn. Acrothecium carotae and Pseudocercosporidium carotae) was the dominant pathogen in blackish spots on carrots harvested in 2001. On carrots harvested in 2002 and 2003 Alternaria radicina was detected more frequently. Multiple regression analysis indicated that a higher occurrence of the blemish may be linked with harvest conditions and presence of umbelliferous plants. The effect of the temperature on conidial germination, mycelial growth and pathogenicity of R. carotae was studied. The estimated optimum and maximum temperature for growth of R. carotae was 19 and 29°C, respectively. Inoculation experiments demonstrated that wounds are good invasion routes. Infection occurred at 3, 10 and 20°C, but not at 30°C. Penetration into wounds was greatest at 20°C.
Current open field vegetable production systems in the Netherlands do not meet market and societal demands. These demands could not be fulfilled by adapting current production systems. Other kinds of production systems are needed and therefore two types of systems are designed by 1) a technological and 2) an agroecological vision. The technological vision aims at excluding and predicting external influences with the focus on control. Variants of this vision are production systems with fertigation and mulching with foil and hydroponic systems. Fertigation combined with mulching improves nutrient and water use efficiency and reduces leaching. Hydroponic systems exclude soil effects as well. The agro-ecological vision aims at creating buffers to make systems resilient against negative external influences with the focus on prevention. The general hypothesis is that diversity improves resilience and sustainability. Examples of various forms of diversity are discussed. The difference in paradigm between both visions is a mostly fundamental difference. The question is whether technological and agro-ecological farming systems can fulfill societal demands and in what timeframe systems will be ready for application in practice. Both visions need to be developed further to have a diverse set of production systems ready.
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