Changes in some enzyme activities and browning rate of apricots during storage

Samples of two apricot cultivars grown in central Hungary were picked at canning maturity and stored for ten days at 5°C and 85% relative humidity in normal atmosphere. The initial rate of enzymatic browning (BA), polyphenol oxidase (PPO) and peroxidase (POD) activities as well as o-dihydroxy phenol (ODP) concentration of the fruit flesh were assayed at picking and after five and ten days of storage. During storage, BA decreased and POD activity increased. PPO activity and ODP concentration varied irregularly: the trends of the variations differed with cultivar but were similar for the two characteristics.(Cegled Research Station of the Research Institute of Fruits and Ornamental Plants, Budapest, Hungary), Cegled     

丰水梨多酚氧化酶基因的克隆与原核表达

通过PCR方法克隆丰水梨PPO基因全长,并将其登录Genebank,登录号JQ861265。基因全长1782 bp,无内含子,编码的PPO属于亲水性蛋白质,无跨膜结构,含有593个氨基酸,分子量约为65.8 k Da,理论等电点为8.4。N端含有一段由47个氨基酸组成的转运肽。去除转运肽的成熟PPO分子量为60.8 k Da,理论等电点为6.69。PPO中含有两个铜离子结合区,主要位于PPO二级结构中的α-螺旋区域中。原核诱导目的蛋白在诱导3~6 h后积累量较大。诱导蛋白(PPO前体和成熟PPO)均能氧化儿茶素形成茶黄素。     

In vitro fermentation patterns and methane production as influenced by cultivar and season of harvest of Lolium perenne L.

In some European countries, the majority of annual enteric methane (CH₄) emissions by ruminants occur at pasture – a direct result of the predominance of grazing within ruminant production systems. However, there are only limited data available as to the effect of perennial ryegrass cultivar and season of harvest on CH₄ production. Using the in vitro gas production technique, the effect of perennial ryegrass cultivar on fermentation characteristics and CH₄ production was determined (Experiment 1) and the persistence of these traits throughout the growing season for two cultivars, identified from Experiment 1 as having either a high or low methanogenic potential, was examined (Experiment 2). In Experiment 1, organic matter (OM) digestibility and cumulative total gas production profiles were unaffected by cultivar but, with regard to the kinetics of CH₄ production, the asymptote value (A), cumulative CH₄ yield at 72 h, and the fractional rate (μ) of CH₄ production at both time of 0·5A(T)(μCH₄T) and at 48 h (μCH₄48h) were significantly (P < 0·05) different. The amount of digested OM, as a proportion of cumulative CH₄ production (DigOM/CH₄) at 24 and 72 h after commencement of inoculation, revealed that the amount of substrate required to produce 1 ml of CH₄ also differed significantly between cultivars (P < 0·01). In Experiment 2, regrowth number significantly modified the majority of measured samples (P < 0·01); cultivar effects were limited to the lag phase of the cumulative CH₄ production curve and DigOM/CH₄ at 8 h only (P < 0·05). These results suggest that differences exist between cultivars in how OM is partitioned following microbial fermentation and that these differences demonstrate persistency throughout the growing season. In the course of time it may be possible to exploit these differences through cultivar selection and plant breeding programmes, and thereby reduce enteric CH₄ emissions within pastoral production systems.     

Forage yield and chemical composition of canola (Brassica napus L.) as affected by sowing methods

The sowing method of spring‐type canola (Brassica napus L. var. oleifera) for forage has a major influence on its productivity and agronomic management. A field experiment was conducted in Matamoros, Coahuila, Mexico, during two growing seasons (2008–2009 and 2009–2010) to determine dry matter (DM), crude protein (CP) and net energy for lactation (NE_L) yields, as well as canola forage chemical composition as a function of six sowing methods. The treatments assessed were broadcast sowing and five different row spacings: 0·19, 0·38, 0·57, 0·76 and 0·95 m (double row, 0·20 m apart). In the first year, with a mean growing season temperature of 17·2°C, sowing methods did not affect DM yield, but CP and NE_L content and yield were higher in 0·19‐m row spacing. The mean temperature in the second year (13·5°C) was slightly lower than the long‐term mean (14·8°C) in the region, resulting in the highest DM (8840 kg ha^?1), CP (2486 kg ha^?1) and NE_L yields (51 103 MJ ha^?1) with 0·19‐m row spacing. In row‐sowing methods with over 0·19‐m row spacing, DM, CP and NE_L yields decreased by 19·3–39·7, 20·4–42·1 and 21·2–42·7% respectively. Results indicate that sowing methods significantly affected canola forage productivity.     

Causes of differences in growth pattern,yield and quality of potatoes (Solanum tuberosum L.) in short rotations on sandy soil as affected by crop rotation,cultivar and application of granular nematicides

Summary A crop rotation experiment was carried out on a light sandy soil in 1979–1986 to study the effects of the frequency of potato cropping on yield, quality and on the occurrence of soil-borne pathogens other than potato cyst nematodes. Tuber yield decreased markedly with increasing cropping frequency, but also depended on what crops were grown in rotation with potato. Growth during the early part of the season, as well as the length of the growing period, were reduced in short rotations. The fungiVerticillium dahliae andRhizoctonia solani, and root-knot nematodes (Meloidogyne spp.) were the most important yield reducing pathogens. The effects of rotation depended on the cultivar used. The percentage of mis-shapen tubers increased with increasing cropping frequency and after application of granular nematicides, but the incidence of common scab (Streptomyces scabies) was not affected.     

Yield and nutritive value of timothy as affected by temperature,photoperiod and time of harvest

Scenarios of global climate change forecast an increase in air temperature of 3°C over the next 100 years in eastern Canada. Growth and nutritive value of cool‐season grasses are known to be affected by air temperature. It is also believed that grasses grown at high latitude have a greater nutritive value. The objectives of this study were to assess the effect of four combinations of day/night temperature and photoperiod (15 h–17/5°C; 15 h–22/10°C; 15 h–28/15°C; and 17 h‐17/5°C) on dry‐matter (DM) yield, in vitro true DM digestibility (IVTD), in vitro digestibility of neutral‐detergent fibre (NDF), and concentrations of NDF, acid‐detergent fibre (ADF), lignin, minerals and non‐structural carbohydrates (NSC) in timothy grown under controlled conditions. Furthermore, herbage was harvested in the morning and in the afternoon to assess the impact of the time of harvest. The dietary cation–anion difference [DCAD = (K⁺ + Na⁺) ? (Cl^? + 0·6 S^2?)] and the grass tetany index [GT index = K⁺/(Ca²⁺ + Mg²⁺)] were also calculated. Higher temperature regimes significantly decreased IVTD and digestibility of NDF but had a limited effect on concentrations of NDF, ADF and lignin. DM yield of herbage was less and the concentration of NSC was greater in timothy grown under a temperature regime of 28/15°C than the 17/5°C and 22/10°C regimes; this effect is mainly explained by a response to temperature stress. Values of DCAD and the GT index of herbage were also lower under the 28/15°C than the 17/5°C and 22/10°C regimes as a result of a decreased plant K concentration. Under the 17/5°C regime, an increase in 2 h of photoperiod resulted in increased DM yield, decreased concentrations of K, Ca, Mg, Cl and N, and an increased starch concentration; IVTD or digestibility of NDF were not affected, although lignin concentration was reduced. Harvesting timothy in the afternoon rather than in the morning resulted in higher NSC, mainly sucrose, concentrations, and decreased ADF and NDF concentrations. The forecasted increase in air temperature in eastern Canada over the next 100 years will result in lower yields and nutritive value of timothy.     

Contents and digestibility of carbohydrates of mung beans (Vigna radiata L.) as affected by domestic processing and cooking

Effects of common processing and cooking methods on sugar and starch contents and starch digestibility (in vitro) of mung bean (Vigna radiata L.) were investigated. Soaking reduced the level of total soluble sugars, reducing sugars, non-reducing sugars and starch and improved starch digestibility, significantly. Cooking (both ordinary and pressure cooking) increased the concentrations of the sugars and digestibility of starch of soaked as well a unsoaked seeds. Starch contents, however, were decreased. Germination decreased starch thereby raising the level of the soluble sugars. Starch digetibility was increased appreciably.     

Dry matter and nitrogen accumulation,partitioning, and retranslocation in safflower (Carthamus tinctorius L.) as affected by nitrogen fertilization

Safflower (Carthamus tinctorius L.) is a deep-rooted crop which can tolerate water stress and can be grown in rotation with other crop species. Nitrogen is one of the most important nutrients for the growth and development of safflower; however, the effect of N level on dry matter, accumulation, partitioning, and retranslocation has not been extensively studied. A 2-year field study was therefore conducted with the objective to determine the effect of N fertilization on crop phenology, dry matter, N accumulation, partitioning and retranslocation of safflower grown under rain-fed conditions. Three rates of N were used (0, 100, and 200 kg N ha⁻¹) and two hybrids (CW9048 and CW9050) of safflower were selected. The experiment was conducted during the 2003–2004 (2004) and 2004–2005 (2005) growing seasons on a calcareous sandy loam (Entisols, Orthents, Typic Xerorthent) at the experimental farm of the Aristotle University of Thessaloniki, in Northern Greece. During 2004 spring was quite mild with significant rainfall whereas during 2005 spring was hotter with lower rainfall. Our study found that N fertilization increased biomass at anthesis by an average of 24% and at maturity by an average of 25% compared with the control. Total above ground biomass increased after anthesis in both years, in both hybrids and for all fertilizer treatments. N fertilization increased the dry matter partitioning in leaves + stems and heads at anthesis and also in leaves + stems, seeds, and head vegetative components at maturity. Dry matter translocation was not affected by N fertilization but lower values were found during the second year. N content was affected by the fertilization treatments and increased in those plants treated with fertilizer compared with the controls. In addition, N fertilization increased N retranslocation from the vegetative parts of the plant to the seed, but it did not affect N gain. During the second year, which was drier, there were significant N losses but also greater N translocation efficiency and higher contribution of pre-anthesis N to seed. Seed yield was correlated with the dry matter and N translocation indices, and was higher for the fertilized plants, compared with the control. The present study indicates that N fertilization promoted the growth of safflower and increased the dry matter yield, N accumulation, translocation and seed yield under rain-fed conditions.     

Intercropped wheat (Triticum aestivum L.) and bean (Vicia faba L.) as a whole-crop forage: effect of harvest time on forage yield and quality

Abstract Sole crops and intercrops of wheat (Triticum aestivum L.) and bean (Vicia faba L.), at three harvest dates, representing successive growth stages, were evaluated for biomass production of whole‐crop forage and quality characteristics of crude protein (CP), neutral‐detergent fibre (NDF), acid‐detergent fibre (ADF), water‐soluble carbohydrate (WSC) concentrations and ash content. These tests were carried out for two field experiments, respectively, drilled during the spring of 1997 and autumn of 1997 on Imperial College Farm, Wye, UK. Results indicated that optimum forage yield and quality were obtained from the second to third harvest dates for the spring‐drilled experiment and the second harvest for the autumn‐drilled experiment. Wheat and bean intercrops were higher in total forage dry matter (DM) yield than either wheat or bean grown as sole crops. Field bean intercropped with wheat led to increased forage quality (CP and NDF concentrations) compared with sole wheat, and higher WSC concentrations compared with sole bean. Intercrops also enhanced weed suppression compared with sole bean. It is suggested that winter wheat–bean intercrops may have considerable potential as a moderate‐yielding, relatively high‐quality, low‐input and environmentally benign forage crop with considerable potential with regard to yield and quality and warrant further study.     

Weed control and sweet maize (Zea mays L.) yield as affected by pyroxasulfone dose

Pyroxasulfone is a new herbicide being considered for registration in sweet maize in Canada; however, there is still little information on the doses required to provide 90% control of annual grass and broadleaved weeds found in southwestern Ontario. The objective of this study was to determine pyroxasulfone doses that would provide at least 90% control of several economically important weeds, without impacting final sweet maize yield by more than 5% in comparison to a weed-free control. Six field trials were conducted over a two-year period (2007 and 2008) at three Ontario locations to evaluate the effectiveness of pyroxasulfone at doses ranging from 31.25 to 1000 g a.i. ha⁻¹. The doses required to reduce weed biomass by at least 90% (I₉₀) varied by weed species. Doses of 93, 499, and 111 g a.i. ha⁻¹ were required to reduce the biomass by 90% of redroot pigweed, common lambsquarters and green foxtail, respectively. There was greater than 95% control of velvetleaf, large crabgrass and barnyardgrass with 31.25 g a.i. ha⁻¹, the lowest dose tested. Sweet maize yield could not be consistently maintained within 5% of the weed-free control. There are several factors that may have contributed to the reduced yield, including soil texture effects, competition as a result of poor common lambsquarters control, and hybrid sensitivity. These results show that biologically effective weed control with pyroxasulfone may be achieved at lower than proposed doses for several weed species; it remains unclear if this is economically sustainable due to the potential impacts on yield.     

Water yam (Dioscorea alata L.) development as affected by photoperiod and temperature: Experiment and modeling

Water yam (Dioscorea alata L.) is one of the most popular tuber crops in the tropics. Although it is well known that photoperiod greatly affects yam development, little information is available on the effect of temperature on different developmental phases, and there has been no attempt to model the effect of both environmental factors. The aim of this study was to assess the combined effect of photoperiod and temperature on the development of two early maturing varieties of yam with similar growth pattern. For this we used a model proposed for potatoes grown under tropical conditions. Experimental information was obtained from 15 field experiments carried out in Guadeloupe (French West Indies) covering a wide range of planting dates. Two yam phases were analyzed: from emergence (EM) to tuber initiation (TI), and from TI to harvest (HA). The EM–HA period varied from 3 to 6 months, with the longer cycles corresponding to early planting dates (e.g. April). On average, EM–TI represented one-third of the EM–HA period, and was mainly affected by photoperiod and to a lesser extent by temperature. Both factors also affected the duration of TI–HA but their effects were less noticeable. The observed mean temperature during TI–HA was near the estimated optimum and its effect was less than that of photoperiod. The variation of the phase duration was higher for EM–TI (CV 45%) than for TI–HA (8%), which was satisfactorily explained by the model. For EM–TI there was a positive interaction between both environmental factors which, together with the greater influence of climatic conditions, resulted in much variability in its duration. For TI–HA, a small influence of environmental factors, coupled with a compensatory effect between environmental factors, resulted in a relatively smaller variation in the duration of this phase. The model estimated satisfactorily the dates and the duration of each phase. The root mean square error (RMSE) was 7.4 d which corresponded to 13% and 7% of the observed mean duration of EM–TI and TI–HA, respectively. Our results showed that small changes in photoperiod and temperature, which are very usual in the tropics, have a big effect on the tested yam varieties. We also showed that the model applied in this study can be a useful tool to predict yam development for management purposes as well as for the modeling of yam growth.     

Herbage yield,essential oil content and composition of three oregano (Origanum vulgare L.) populations as affected by soil moisture regimes and nitrogen supply

To compare the response of oregano (Origanum vulgare L.) populations to soil moisture regimes and nitrogen fertilization, a greenhouse experiment with three populations of oregano cultivated in Germany (O. vulgare var. creticum, O. vulgare ssp. hirtum, O. vulgare var. samothrake) was conducted during 2006–2007 at the research station Rauischholzhausen of Justus Liebig University in Germany. A completely randomized experimental design with three soil moisture regimes (optimal, consistent water deficiency and water deficiency from the beginning of flowering) and two nitrogen fertilization levels with six replications was realized. Dry matter production of population O. vulgare var. samothrake was stable for two experiment years, whereas those of the populations O. vulgare var. creticum and O. vulgare ssp. hirtum were higher in 2007 than in 2006. Among tested populations O. vulgare var. samothrake showed the highest essential oil content in both experiment years. Consistent water deficiency caused reduction of dry matter, but not essential oil content. Water deficiency in flowering stage reduced also dry matter production, but increased essential oil content, resulting in the highest essential oil yield in 2006 and a comparable essential oil yield as control in 2007. Higher nitrogen levels caused an increase in dry matter production of oregano for both experiment years and a decrease in essential oil content in 2007, which can be explained in terms of dilution effect. Totally, 42 compounds were identified in essential oils of three populations by means of GC–MS. Carvacrol was the dominant compound (70.0–77.4%) for all essential oil samples, followed by γ-terpinene (8.1–9.5%) and p-cymene (4.5–5.3%). The composition of essential oil of oregano populations was independent of cultivation conditions. In conclusion, the population of O. vulgare var. samothrake showed a stable dry matter yield with higher essential oil content than the populations of O. vulgare var. creticum and O. vulgare ssp. hirtum. Water deficiency after beginning of blooming (folded flowers) can induce an increase in essential oil content and thus result in higher quality of oregano herbage and higher water use efficiency of oregano plants.     

In vitro total and methane gas production as influenced by rate of nitrogen application, season of harvest and perennial ryegrass cultivar

The effects of rate of inorganic nitrogen (N) fertilization (0, 80 or 160 kg N ha^?1 per regrowth), season of harvest (regrowths 1, 2 and 3) and perennial ryegrass (Lolium perenne L.) cultivar [classified as having either a normal or elevated water soluble carbohydrate (WSC) concentration genotype] on in vitro gas production and digestibility were assessed. Increased N fertilizer application significantly decreased total gas production (TGP), methane (CH₄) production and organic matter digestibility (OMD). The results suggest that the decreases in TGP and CH₄ production were associated with a restriction in organic matter (OM) fermentation and an altered crude protein (CP) to structural carbohydrate ratio rather than a modification in the stoichiometry of fermentation. Season of harvest only significantly (P < 0·05) altered in vitro OMD and CH₄ production at 8 h, despite altering the chemical composition of the herbage. Cultivar effects on all measured in vitro parameters were not significant presumably because the elevated WSC concentration trait was not expressed strongly in the study.     

Effect of harvest time on yield and pre-harvest quality of semi-leafless grain peas (Pisum sativum L.) as whole-crop forage

The aim of the work was to study changes in the yield and nutritional characteristics of whole crop semi-leafless field pea over two growing seasons in the Po plain, Italy. Samples of two cultivars (Baccara and Sidney) were collected from flowering to grain maturity. The developmental stage, yield, dry matter (DM) content, crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), starch, water soluble carbohydrates (WSC), gross energy (GE), organic matter digestibility (OMD) and the net energy for lactation (NE_L) were determined at each harvest. The forage characteristics were regressed on the growing degree days (GDD) with 4.4 °C as the base temperature. The DM yield increased with advancing maturity from 0.5 to 8.91 Mg ha⁻¹, while the CP decreased from 261 to 159 g kg⁻¹ DM. During the whole growth cycle the GE, OMD, NE_L and milk forage units (milk FU) were almost steady. No differences were observed between the cultivars for any of the measured parameters. At grain maturity, the crop produced over 4.0 Mg ha⁻¹ DM of grain. The CP, starch and WSC of the grain did not show any differences between the cultivars or years. The data showed that the nutritive quality of the forage of the semi-leafless grain pea harvested as a whole crop for ensiling purposes did not diminish with maturity and could help improve the self-sufficiency of dairy farms, in terms of home-grown protein forages.     

Weed emergence as affected by maize (Zea mays L.)-cover crop rotations in contrasting arable soils of Zimbabwe under conservation agriculture

Weed control in smallholder farming systems of sub-Saharan Africa is labour intensive or costly. Many researchers have therefore advocated for the use of cover crops in weed management as an affordable alternative for smallholders. Cover crops may be grown in rotations to suppress weeds and reduce the reliance on herbicides. The use of cover crops creates microenvironments that are either conducive or inhibitive to the emergence of certain weed species. A study, initiated in 2008 in contrasting soils at four different locations of Zimbabwe, investigated the effect of maize (Zea mays L.)-cover crop rotations on the emergence of weeds that showed dominance in those soils. Weed assessments were however, carried out from 2011 to 2014. The weed species Galinsoga parviflora Cav., Commelina benghalensis L., and Richardia scabra L. showed dominance in all four locations with weed densities as high as 500 plants m⁻² being recorded for R. scabra L. in a sandy soil. Maize-cover crop rotations resulted in higher densities of Bidens pilosa compared with maize monocropping (control treatment) due to its high nitrogen (N) requirement to produce more seeds. On the other hand, the integration of cover crops such as pigeon pea [Cajanus cajan (L.) Millsp.] that had poor shading qualities, due to large gaps or spaces and slower initial growth, had limited effects on competitive weeds such as Cyperus esculentus L. which tend to dominate exhausted soils. The density of C. esculentus was 38% greater in maize–pigeon pea rotations compared with the control treatment. Variability between seasons and sites affected emergence of all weeds in the present study, which masked long-term trends. The results suggest that there is need to identify the germination and emergence requirements of specific weeds and select cover crops best suitable for their control. The study provides useful information for farmers and advisors on the best cover crops for control of certain problematic weeds in different soil types of Zimbabwe.     

Changes in phytochemical, antimicrobial and free radical scavenging activities of the Peruvian pepper tree (Schinus molle L.) as influenced by fruit maturation

The effect of stage of maturity on total lipids, fatty acids, yields and essential oil composition and their antimicrobial and free radical scavenging activities of the Schinus molle fruits was investigated. The content of total lipids varied from 2.87 to 5.35% (w/w, dw) and were rich in unsaturated fatty acids particularly linoleic acid. As maturation progress, the essential oil yield dropped from 5.18% to 1.15%. Monoterpene hydrocarbons with α-phellandrene (35.15-40.38%), limonene + β-phellandrene (21.47-36.62%), β-myrcene (7.61-24.96%) and α-pinene (1.92-2.58%) were found to be the main components. At the same time, the essential oils were evaluated for their antimicrobial and free radical scavenging activities. They were found to be active against Bacillus subtilis, Bacillus cereus, Salmonella typhymurium and Escherichia coli but they do not inhibit the growth of Candida albicans. Conversely, they showed very weak activity against the DPPH radical. In both assay, the oil derived from the intermediate stage was reported as more efficient.     

Structure,chemical composition and enzymatic activities of pearlings and bran obtained from pearled wheat (Triticum aestivum L.) by roller milling

While abrasive pearling (also referred to as debranning) of wheat kernels prior to milling increases the quality of the resultant flour for producing bread, the potential applications of the co-products of pearling is largely unknown. We studied the impact of different degrees of pearling (0, 3, 6, 9 and 12% by weight) on the composition of pearlings and bran obtained when subsequently roller milling pearled wheat kernels. Pearling does not remove the kernel outer tissues homogeneously as abrasion affects especially the accessible parts of the kernels. Nevertheless, the first 3% removed consisted of mainly pericarp. With 6% or more removed, a significant amount of starchy endosperm ended up in the pearlings. The starting bran material and bran obtained by subsequent roller milling of pearled wheat kernels had similar compositions but the latter had a lower average particle size. Moreover, removal of the outermost kernel layers substantially decreased the enzyme activity levels in the bran.     

Morphology,tannin concentration and forage value of 15 Swiss accessions of sainfoin (Onobrychis viciifolia Scop.) as influenced by harvest time and cultivation site

Fifteen accessions of sainfoin (Onobrychis viciifolia Scop.) were characterized for morphological and phenological traits at Reckenholz in the Swiss lowlands (Experiment 1). The effects of accession, harvest time and site on dry‐matter yield, condensed tannin (CT) concentration and forage value (Experiment 2) were determined at three sites in Switzerland varying in altitude from 440 to 559 m. Three to four harvests were taken in the first year after establishment (second year of stand) with harvests 1 and 2 chemically analysed. From the characterization in Experiment 1, a clear grouping of single flowering (Communis) and multiple flowering (Bifera) accessions emerged. Additionally, within the Communis accessions, distinct groupings were identified (historical landraces and newly collected ecotypes) based on morphological characteristics. Experiment 2 showed that Communis and Bifera accessions had a similar chemical composition in the first harvest. In the second harvest, Communis accessions were higher in crude protein and CT and lower in neutral and acid detergent fibre concentrations than Bifera accessions. Total dry‐matter yields were higher for Bifera accessions. Among the Communis accessions, ecotypes had consistently higher CT concentrations than landraces. In vitro organic matter digestibility did not significantly differ among accessions. There were clear effects of harvest time and site for most variables, with clear harvest time × sainfoin group interaction but no site × sainfoin group interactions. The results clearly demonstrate that historical landraces and newly collected ecotypes expand the range of available genetic variation for sainfoin breeding.     

The nitrogen response of potato (Solanum tuberosum L.) in the field: nitrogen uptake and yield, harvest index and nitrogen concentration

Summary The response of potato to different rates of nitrogen supply ranging from 0–40 g m⁻² N was studied in five field experiments near Wageningen. NL (52⁰ North). In total two late potato cultivars and two sites were used during successive seasons. The results are summarized in a set of regression equations separately for total crop and tubers. The relation between nitrogen taken up (g m⁻²) in the total crop and total dry matter production (g m⁻²) could be described with the exponential equation: 1942–1900 * 0.93^X (r²=0.953, n=62). Nitrogen concentrations in the dry matter increased linearly with nitrogen uptake. Harvest indices for dry matter and nitrogen tended to decline with increase in N uptake. Cultivars differed only in the effect on N on tuber dry matter concentration. The relation between nitrogen uptake and nitrogen supply could be fitted with quadratic regression models. but coefficients were influenced by site and season.