Hanne L. Kristensen

Uptake of15N labeled nitrate by root systems of sweet corn, carrot and white cabbage from 0.2–2.5 meters depth

Leaching of NO3− from vegetable cropping systems can be very high compared to arable systems. This is a problem for vegetable growers in general as it decreases groundwater quality, and for organic growers in particular as the organic production is often limited by N. In a field experiment, we investigated the N uptake and root growth of three vegetables using minirhizotrons reaching 2.4 m with the purpose to study the relationship between vegetable root distribution and uptake of NO3− from deep soil layers. NO3− uptake was studied over a 6 d period at the end of September by injection of 15 NO3− at four depths in the ranges: 0.2–0.8, 0.6–1.8, and 1–2.5 m under late sweet corn (Zea mays L. convar. Saccharata Koern.), carrot (Daucus carota L.), and autumn white cabbage (Brassica oleracea L. convar. capitata (L.) Alef. var. alba DC), respectively. The root depths of the three crops were 0.6, 1.3, and more than 2.4 m, respectively. Uptake of15N was close to zero from placements below root depth, and linear relationships were found between root density and15N uptake from different depths. N inflow rates (uptake per unit root length) were in the same range for all species and depths. This indicates that the very different N use efficiencies often found for vegetable crops depend on species specific differences in root development over time and space, more than on differences in N uptake ability of the single root. Thus deep rooting is important for deep N uptake. Knowledge about deep root growth enables design of crop rotations with improved N use efficiency based on re-cycling of deep soil NO3− by vegetables.

Quality of carrots as affected by pre- and postharvest factors and processing

The aim of this review is to provide an update on factors contributing to quality of carrots, with special focus on the role of pre- and postharvest factors and processing. The genetic factor shows the highest impact on quality variables in carrots, causing a 7-11-fold difference between varieties in content of terpenes, β-carotene, magnesium, iron and phenolics as well as a 1-4-fold difference in falcarindiol, bitter taste and sweet taste. Climate-related factors may cause a difference of up to 20-fold for terpenes, 82% for total sugars and 30-40% for β-carotene, sweet taste and bitter taste. Organic farming in comparison with conventional farming has shown 70% higher levels for magnesium and 10% for iron. Low nitrogen fertilisation level may cause up to 100% increase in terpene content, minor increase in dry matter (+4 to +6%) and magnesium (+8%) and reduction in β-carotene content (-8 to -11%). Retail storage at room temperature causes the highest reduction in β-carotene (-70%) and ascorbic acid (-70%). Heat processing by boiling reduces shear force (-300 to -1000%) and crispiness (-67%) as well as content of phenolics (-150%), terpenes (-85%) and total carotenes (-20%) and increases the risk of furan accumulation. Sensory and chemical quality parameters of carrots are determined mainly by genetic and climate-related factors and to a minor extent by cultivation method. Retail temperature and storage atmosphere as well as heating procedure in processing have the highest impact in quality reduction.

Increase of vitamin D 2 by UV-B exposure during the growth phase of white button mushroom ( Agaricus bisporus )

Background Mushrooms are the only non-animal food source of vitamin D. Wild mushrooms have naturally high vitamin D2 content, and cultivated mushrooms produce vitamin D2 from ergosterol when exposed to supplementary UV-B during the post-harvest phase. Objectives This study investigated the effects of providing supplementary UV-B during the growth phase on vitamin D2 formation and the interactions with growth of mushrooms, as compared to supplementary UV-B during the post-harvest phase or exposure to sunlight for both cultivated and wild mushrooms. Methods Experiments were carried out with exposure to supplementary UV-B just prior to harvest in the range of 0–2,400 mJ cm−2. Mushrooms grew for 2 days with or without repeated UV-B exposure each day. Vitamin D2 and growth rate were determined. In addition, some mushrooms were post-harvest treated by exposure at 200 mJ cm−2 supplementary UV-B or natural sunlight, prior to vitamin D2 determination. Results The content of vitamin D2 was 0.2–164 µg 100 g−1 fresh weight, and there was a linear relationship between UV-dose up to 1,000 mJ cm−2 and vitamin D2 content. The fast growth rate of the mushrooms diluted the vitamin D2 from 24 to 3 µg 100 g−1 within 2 days of exposure at 200 mJ cm−2. Following repeated UV-B exposure, vitamin D2 increased to 33 µg vitamin D2 100 g−1. Growth was unaffected by UV-B. Post-harvest exposure to supplementary UV-B resulted in a higher vitamin D2 content of 32 µg 100 g−1 compared to the 24 µg 100 g−1 obtained from exposure to UV-B during the growth phase. In contrast, wild and cultivated mushrooms with and without exposure to sunlight had vitamin D2 content in the range of 0.2–1.5 µg vitamin D2 100 g−1. Conclusions This study showed that mushrooms with a well-defined content of vitamin D2 can be obtained by exposure to supplementary UV-B just prior to harvest.

Root pruning reduces root competition and increases crop growth in a living mulch cropping system

Abstract In two field experiments, growth of white cabbage in pure stands was compared with that of cabbage grown in living mulch systems to reduce pest attacks. The roots of the living mulch were pruned early in the season, with the aim of reducing competition and increasing growth of the white cabbage. Root pruning was shown to increase the above-ground biomass of white cabbage, with two prunings giving higher cabbage yields than one, but there were clear differences between the living mulch species tested (red clover, birdsfoot trefoil, salad burnet, winter rye). Below-ground growth and competition were examined by measuring root distribution in minirhizotrons and uptake of 15N placed at different soil depths. These studies showed that the ability of mulch species to compete for resources at depth was restricted by pruning, and that this was crucial for the development of the white cabbage crop.

Effect of differential N and S competition in inter- and sole cropping of Brassica species and lettuce on glucosinolate concentration.

Field and greenhouse pot experiments were conducted to evaluate the potential to use intercropping as an alternative method to increase glucosinolates in Brassicas by manipulating nitrogen (N) and sulfur (S) balance by intercropping with lettuce (Lactuca sativa L. var. capitata). In both experiments, four combinations of N and S fertilization were used. In the field experiment no effect of intercropping on the total glucosinolate concentration was found as the growing lettuce was strongly inhibited by the presence of broccoli (Brassica oleracea L. var. italic). In contrast to this, in the pot experiment both total and individual glucosinolate concentrations in red leaf mustard (Brassica juncea L.) increased by intercropping. Fertilization treatments influenced glucosinolate concentrations in both experiments, and an interaction between N and S fertilization was noticed.

Root development of beetroot, sweet corn and celeriac, and soil N content after incorporation of green manure

Summary Root development in beetroot (Beta vulgaris L. ssp. vulgaris var. conditiva Alef.), sweet corn (Zea mays L. convar. Saccharata Koern.) and celeriac (Apium graveolens L. var. rapaceum Gaud.) was followed during two growing seasons with the aim of describing the root systems and nitrogen (N) utilisation of the three vegetables. The crops were grown after incorporation of green manure either in the preceding Autumn or Spring. Beetroot reached a final root depth of 1.55 – 1.8 m. For sweet corn, the final root depths were 0.6 and 0.9 m and, for celeriac, 0.45 and 0.6 m, in the two years, respectively. The simple measure of average root depth reflected the depth to which soil mineral N was depleted over the season by each of the three vegetables. Autumn incorporation of green manure resulted in higher mineral N contents in the soil layers below 0.5 m compared to a Spring incorporation. For beetroot, this resulted in 0.5 m-deeper root depths and higher root intensity below 0.5 m at harvest. This study shows large differences in root intensity between years, and in root depths between species. This knowledge can be used to improve N-use efficiency in vegetable production.

Multi-method comparison of carrot quality from a conventional and three organic cropping systems with increasing levels of nutrient recycling

BACKGROUND There is a need to advance the study of the effects of organic and conventional systems on product quality. In particular, little is known about the importance of different farming practices concerning nutrient cycling and the use of external inputs within organic farming for the quality characteristics of the products. In this study the quality characteristics of carrot grown under different farming practices (conventional and three organic cropping systems) over a two-year period were analysed with the aim of discriminating between organic and conventional and investigating the effect of different organic farming practices concerning nutrient recycling and use of external nutrient input. RESULTS All quality characteristics measured did not give a clear differentiation between the carrots from the different growing systems, even when multivariate statistical evaluation (principal component analysis) was applied, because of the significance of the differences between the field replicates within each management system and of the seasonality. Only some tendencies were emphasised over the two years that could be related to the fertilisation practices and the external inputs used. CONCLUSION The results indicated that it was not possible to discriminate over the years between carrots from conventional and different organic cropping systems even though controlled conditions and a multi-method approach of analysis were adopted.

Eating Quality of Carrots (Daucus carota L.) Grown in One Conventional and Three Organic Cropping Systems over Three Years

The eating quality of carrots (Daucus carota L.) was investigated to evaluate the impact of cropping systems (one conventional and three organic systems) and growing years (2007, 2008, and 2009) on root size, chemical composition, and sensory quality. The content of dry matter, sugars, polyacetylenes, and terpenes as well as the sensory quality and root size were related to the climate during the three growing years. A higher global radiation and a higher temperature sum in 2009 as compared to 2007 and 2008 resulted in larger roots, higher contents of dry matter, sucrose, total sugars, and total polyacetylenes, and lower contents of terpenes, fructose, and glucose. No differences were found between conventional and organic carrots with regard to the investigated parameters. This result shows that organically grown carrots have the same eating quality as conventionally grown carrots, while being produced in a more sustainable way.

Nitrogen split dose fertilization, plant age and frost effects on phytochemical content and sensory properties of curly kale (Brassica oleracea L. var. sabellica).

We investigated how concentrations of sensory relevant compounds: glucosinolates (GLSs), flavonoid glycosides, hydroxycinnamic acid derivatives and sugars in kale responded to split dose and reduced nitrogen (N) fertilization, plant age and controlled frost exposure. In addition, frost effects on sensory properties combined with N supply were assessed. Seventeen week old kale plants showed decreased aliphatic GLSs at split dose N fertilization; whereas reduced N increased aliphatic and total GLSs. Ontogenetic effects were demonstrated for all compounds: sugars, aliphatic and total GLSs increased throughout plant development, whereas kaempferol and total flavonoid glycosides showed higher concentrations in 13 week old plants. Controlled frost exposure altered sugar composition slightly, but not GLSs or flavonoid glycosides. Reduced N supply resulted in less bitterness, astringency and pungent aroma, whereas frost exposure mainly influenced aroma and texture. N treatment explained most of the sensory variation. Producers should not rely on frost only to obtain altered sensory properties.

Can living mulches in intercropping systems reduce the potential nitrate leaching? Studies of organic cauliflower (Brassica oleracea L. var. botrytis) and leek (Allium porrum L.) production across European conditions

The effect of introduction strategy for living mulches (LMs) to reduce the potential nitrate leaching was investigated when grown with vegetables with high nitrogen (N) demand and low use efficiency in four European countries: Italy, Slovenia, Germany and Denmark over 2 yr. The plant N uptake and soil nitrate N content at harvest, in the autumn, and in the following spring were measured below open-pollinated and hybrid cultivars of cauliflower and leek crops. The cultivars performed differently over the 2 yr. In Italy and Slovenia, when LM of burr medic or white clover was broad sown (addition design ADD) at the same time as crop transplanting, the N uptake of crops was hampered without increasing the total aboveground N accumulation. Delaying LM sowing by 2.5–4 weeks maintained the N uptake of crops. In Germany, delaying white clover sowing for a month in cauliflower reduced soil nitrate at the start of leaching by 17–33 kg N ha−1 in the ADD design and 25 kg N ha−1 in the substitution design (SUB), where rows of cash crops were replaced by rows of LM. An overwintering LM of grass–clover incorporated in strips and root pruned decreased soil nitrate at the start of the leaching period by 35 kg N ha−1 in cauliflower, and in leek, an LM of dyers woad decreased the soil nitrate by 55 kg N ha−1 at harvest and 30 kg N ha−1 at the start of leaching. The effect of delayed LM sowing depended on the LM species and system design. Overall, the SUB and ADD designs showed potential to reduce nitrate leaching, whereas the ADD design had stronger competition against either cash crop or LM. The key to reduce soil nitrate N without jeopardizing crop yields may be to identify suitable growing periods, sometimes combined with root pruning, for each LM species and system design. The LM introduction strategy can be used to control competition and reduce the potential leaching, but the performance depends on the intensity of the interspecific competition and the local conditions.