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  • 1
    Language: English
    In: Scientia Horticulturae, June 7, 2013, Vol.156, p.113(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scienta.2013.04.003 Byline: Martin Sandmann, Jan Graefe, Carmen Feller Abstract: acents Leaf area index is measured using direct and indirect methods with several setups. acents Direct methods are destructive, expensive, laborious and time-consuming. acents Less laborious indirect methods yielded precise values in kohlrabi and lettuce. acents Digital photography is a good alternative to destructive methods in these crops. Author Affiliation: Leibniz-Institute of Vegetable and Ornamental Crops Gro[sz]beeren and Erfurt, Theodor-Echtermeyer-Weg 1, 14979 Gro[sz]beeren, Germany Article History: Received 27 January 2012; Revised 18 February 2013; Accepted 2 April 2013
    Keywords: Digital Photography -- Methods
    ISSN: 0304-4238
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Journal of phytopathology, 2011, Vol.159(1), pp.35-44
    Description: The impact of continuous cropping of lettuce on the disease dynamics of bottom rot and genotypic diversity of the causal pathogen Rhizoctonia solani AG 1-IB was studied over 3 years with two crops per year within a field naturally infested with R. solani the pathogen. This field had not had lettuce cultivated in it for 7 years. The disease incidence (DI) and disease severity (DS) were assessed at each harvest and mapped. Surprisingly, a high DI was already observed in the first crop of year one of this field study. In addition, the pathogen was also found to be evenly distributed. Severely infected plants occurred mainly in patches, and the position varied between crops. A significant increase in DS was already observed in the second year, and both temperature conditions and continuous cropping influenced the DS on average over time. Rhizoctonia isolates were randomly collected from the first crop in 1999 and the sixth crop in 2001. The genotypic diversity within the subgroup of R. solani AG 1-IB was analysed by BOX-PCR genomic fingerprinting and the aggressiveness of isolates by bioassay. The fingerprints revealed a high level of genotypic diversity within the AG 1-IB field population. However, continuous cropping was found not to have an impact on genotypic diversity and aggressiveness. ; Includes references ; p. 35-44.
    Keywords: Cropping Systems;
    ISSN: 0931-1785
    E-ISSN: 14390434
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  • 3
    Language: English
    In: Nutrient Cycling in Agroecosystems, 2011, Vol.91(3), pp.327-337
    Description: The nitrogen (N) use efficiency of field vegetable production systems needs to be increased in order to, reduce the detrimental effects of N losses on other ecosystems, save on production costs, and meet the limits set by the German government concerning N balance surpluses. Winter catch crops (CCs) have been shown to be a useful tool for reducing N losses in many agricultural production systems. This study was designed to test the effects of different CCs: rye ( Secale cereale L.), fodder radish ( Raphanus sativus L. var. oleiformis Pers.), bunch onion ( Allium cepa L.), and sudangrass ( Sorghum sudanense Stapf), planted at different sowing dates (early, late), on the N balance of 2-year vegetable crop rotation systems. The crop rotations started with a cauliflower ( Brassica oleracea L. var. botrytis L.) crop, which was fertilized with N in a conventional manner. The experiments took place at three different sites in Germany. Results revealed that the average N balance surplus, when taking into consideration, fertilization, soil mineral N, and aboveground plant biomass N, was 217 kg N ha −1 in the control treatments without a CC. This high value was mainly a consequence of large quantities of crop N and soil mineral N remaining after the harvest of the cauliflower. In spite of these high N surpluses, the application of CC only reduced the N balance surplus, on average across all sites and experiments, by 13 kg N ha −1 , when compared to the control treatments. The type of CC and the sowing date had only minor effects on the N balance. The findings of this study suggest that for many sites the application of CCs does not solve the problem of high N balance surpluses in intensive field vegetable production systems.
    Keywords: Catch crop ; Crop rotation ; Vegetable production ; Nitrogen losses ; Leaching ; Nitrogen balance
    ISSN: 1385-1314
    E-ISSN: 1573-0867
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  • 4
    Language: English
    In: Agricultural Sciences, 2012-07-01, 3卷4期 (Vol.3, Issue 4), pp.455-461
    Description: Objectives of our study were to quantify the effects of apical dominance and bud cluster activity on asparagus yield patterns and to collect data for process-oriented modeling of the asparagus crop. Plants were grown in 40 L containers. After four years the soil above the asparagus crowns was removed and the containers were placed in a growth chamber at 20°C for three months. During this time, spear length was measured daily except at weekends, and spears were cut when longer than 25 cm. Each spear was assigned to a bud cluster, defined as a dense group of buds clearly distinct from other bud groups on the crown. Although temperature was constant, several properties measured in this study changed during the experiment. The number of active bud clusters first increased then decreased, the lag time between spears growing at the same cluster increased, and the relative growth rate of spears decreased. The constant increase of harvested spears per plant stopped abruptly when the plants ran out of viable buds. At the crop level, i.e. the average for all plants, which is normally monitored in field trials, the transition from linear yield increase to zero increase was less abrupt since plants stopped growing spears on different dates. In our study asparagus yield, i.e. the number of harvested spears, was not limited by low carbohydrate in storage roots, but by a lack of viable buds. This was concluded from the abrupt halt in spear production observed in all plants despite the fact that some plants still had considerable carbohydrate content.
    Keywords: Asparagus Officinalis ; Model ; Yield ; Physiology ; "Backlim" ; "Gijnlim"
    ISSN: 2156-8553
    E-ISSN: 21568561
    Source: 中文電子期刊服務 - Chinese Electronic Periodical Services (CEPS) (Airiti Library)〈img src="http://exlibris-pub.s3.amazonaws.com/airiti_logo.gif" style="vertical-align:middle;margin-left:7px"〉
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  • 5
    In: Agricultural Sciences, 2012, Vol.03(04), pp.455-461
    ISSN: 2156-8553
    E-ISSN: 2156-8561
    Source: CrossRef
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  • 6
    Language: English
    In: Scientia Horticulturae, 07 June 2013, Vol.156, pp.113-120
    Description: The dimensionless leaf area index (LAI) is a fundamental crop characteristic. Since the direct measurement of LAI or leaf area is labour intensive and destructive, fast and reliable indirect methods have been devised to estimate LAI of different crops. The objective of this work was to test indirect methods for the non-destructive estimation of LAI in kohlrabi ( L.) and lettuce ( L.). Focusing on the gap fraction methodology, digital photographs and simultaneous radiation interception measurements were taken using a Li-Cor plant canopy analyser (LAI-2200) on 12 sampling dates from planting to harvest, with concurrent destructive estimations of the leaf area. Several geometric protocols of the LAI-2200 and inversion algorithms of the accompanying software were evaluated. Very good indirect-direct LAI relationships were obtained for kohlrabi ( 〉 0.97, = 12) and lettuce ( 〉 0.99, = 9) for the most suitable protocols and algorithms.
    Keywords: Brassica Oleracea Var. Gongylodes L ; Lactuca Sativa Var. Capitata L ; Leaf Area Index ; Plant Canopy Analyser ; Gap Fraction ; Agriculture
    ISSN: 0304-4238
    E-ISSN: 1879-1018
    Source: ScienceDirect Journals (Elsevier)
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  • 7
    Language: English
    In: European Journal of Agronomy, 2010, Vol.32(3), pp.195-204
    Description: To obtain a better understanding of the factors affecting asparagus spear growth and yield, a process-oriented and stochastic model for asparagus ( L.) grown under soil ridges was developed and tested. This model describes a population of asparagus plants with a binomial distributed bud cluster number per plant. Each bud cluster starts to grow after exposure to an exponential distributed temperature sum. The length growth response of spears, which is mainly dependent on soil temperature and spear length, is affected by the soluble carbohydrate ( ) concentration in the storage root system and the temperature gradient between the spear tip and the rhizome. The spear growth rate is assumed to be normally distributed, while a stochastic dependency to the required temperature sum for bud break is assumed. For each bud cluster, a broadly varied apical dominance relation between successive spears is described by an exponential distributed temperature sum for spear length growth induction. After removal of the dominating spear, the required temperature sum decreases exponentially. The time progression of spear diameter is a function of spear generation number within a bud cluster and the mean temperature during spear growth induction and can be used to derive the spear fresh weight. The change of soluble concentrations in the storage root system is derived from maintenance and growth respiration requirements. Some of the model parameters are derived from independent measurements of spear growth. Regarding the tremendous variability of daily yields, the model performed well in the prediction of daily spear number, diameter and yield over the whole harvest season across two production sites with various soil temperatures induced by different types of ridge covering. The effects of soluble concentration and soil temperature gradient on spear growth rate are regarded as preliminary and should be tested in further experiments. Due to the apical dominance relation between spears, asparagus is subject to endogenous rhythmic growth, which invalidates simple statistical yield forecast approaches. In its current state, our yield forecast model is well suited to test the impact of various plant traits on asparagus yield, and thus to guide early selection in crop improvement projects. Finally, the current model could be used to derive easier to handle yet physiological sound yield models to be useful for field-scale applications.
    Keywords: Asparagus ; Model ; Yield ; Physiology ; Agriculture
    ISSN: 1161-0301
    E-ISSN: 1873-7331
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  • 8
    Language: English
    In: Biology and Fertility of Soils, 2010, Vol.46(2), pp.159-167
    Description: One of the challenges in organic farming systems is to match nitrogen (N) mineralization from organic fertilizers and crop demand for N. The mineralization rate of organic N is mainly determined by the chemical composition of the organic matter being decomposed and the activity of the soil microflora. It has been shown that long-term organic fertilization can affect soil microbial biomass (MB), the microbial community structure, and the activity of enzymes involved in the decomposition of organic matter, but whether this has an impact on short-term N mineralization from recently applied organic substances is not yet clear. Here, we sampled soils from a long-term field experiment, which had either not been fertilized, or fertilized with 30 or 60 t ha −1 year −1 of farmyard manure (FYM) since 1989. These soil samples were used in a 10-week pot experiment with or without addition of FYM before starting (recent fertilization). At the start and end of this experiment, soil MB, microbial basal respiration, total plant N, and mineral soil N content were measured, and a simplified N balance was calculated. Although the different treatments used in the long-term experiment induced significant differences in soil MB, as well as total soil C and N contents, the total N mineralization from FYM was not significantly affected by soil fertilization history. The amount of N released from FYM and not immobilized by soil microflora was about twice as high in the soil that had been fertilized with 60 t ha −1 year −1 of FYM as compared with the non-fertilized soil ( p  〈 0.05).
    Keywords: Decomposition ; Microbial biomass ; Organic fertilization ; Soil adaptation
    ISSN: 0178-2762
    E-ISSN: 1432-0789
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  • 9
    In: HortScience, 02/2007, Vol.42(1), pp.57-60
    Description: The objective of our study was to determine how accurately refractometry can quantify soluble carbohydrates in the storage roots of asparagus (Asparagus officinalis L.). Fructose, glucose, sucrose, and fructans as well as refraction were measured in 51 root samples that were taken from commercial fields. There was substantial variation in refraction both within roots of the same plant (cv, 6%) and within plants in the same field (cv, 20%). Samples of asparagus root sap contained fructose, glucose, sucrose, and fructans in varying fractions and, in addition, significant amounts of other solubles, which contributed considerably to refraction. Therefore, refraction readings are no direct measure of fructose, glucose, sucrose, and fructans in asparagus root sap. However, the concentration of these carbohydrates can be well estimated by a regression function, which uses refraction readings as input (r = 0.89). ; Includes references ; p. 57-60.
    Keywords: Asparagus Spears ; Roots ; Measuring Devices ; Sucrose ; Fructans ; Measurement ; Sap ; Perennials ; Optical Properties ; Chemical Constituents Of Plants ; Glucose ; Fructose ; Carbohydrate Content ; Asparagus Officinalis ; Regression Analysis ; Root Sap ; Refractometry;
    ISSN: 0018-5345
    E-ISSN: 2327-9834
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  • 10
    In: HortScience, 08/2005, Vol.40(5), pp.1320-1323
    Description: The nitrogen requirement of broccoli (Brassica oleracea var. italica) ranges from 300 to 465 kg.ha(-1). Recommendations for N fertilization are accordingly high. High fertilizer rates applied at planting result in a high soil mineral N content that remains high for weeks because the N requirement of the crop is low at early growth stages. Therefore, the risk of leaching is high for several weeks until the available N is finally taken up by the crop. Our study had two objectives: 1) to quantify yield responses to preplant fertilization, and 2) to test our hypothesis that the preplant fertilization rate could be reduced without yield losses by increasing the N content in the transplants and improving crop establishment. Field experiments were carried out on transplants with four levels of N content in dry matter (0.018 to 0.038 g.g(-1) dry weight), which were tested in all combinations with four fertilization timings. All treatments received the same amount of N fertilizer (270 and 272 kg.ha(-1) in 2001 and 2002, respectively), but with different rates of supply at the time of planting (0 to 90 kg.ha(-1) N fertilizer plus 30 and 28 kg.ha(-1) soil mineral N in 2001 and 2002, respectively). Total and marketable yields increased significantly with an increasing N supply at time of planting. In our experiments, in which topdressing was applied 25 days after planting, an N supply at planting of 80 to 118 kg.ha(-1) was required to obtain maximum marketable yields. The N content in transplants had little effect on growth and yield, and there were no significant interactions between the N content in the transplant and fertilizer timing. ; Includes references ; p. 1320-1323.
    Keywords: Fertilizer Rates ; Propagation Materials ; Crop Yield ; Planting ; Nitrogen Fertilizers ; Field Experimentation ; Fertilizer Application ; Top Dressings ; Nitrogen Content ; Cole Crops ; Plant Growth ; Broccoli ; Application Timing ; Brassica Oleracea Var. Italica ; Plant Nutrition;
    ISSN: 0018-5345
    E-ISSN: 2327-9834
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