Agronomic Performance of Root Chicory, Jerusalem Artichoke, and Sugarbeet in Stress and Nonstress Environments.
Although fructans have some specific food and nonfood applications, root chicory and Jerusalem artichoke have to compete with established high yielding crops for the same markets. For example, high-fructose syrups are also made from corn starch and beet sugar. Furthermore, through rapid progress in genetic engineering, the traditional classification, according to the primary storage carbohydrate, into sucrose-, fructan-, and starch-crops, is becoming increasingly inappropriate. A recent example is the creation of a fructan beet through inserting into sugarbeet a single gene from Jerusalem artichoke that encodes an enzyme which converts sucrose to fructan (Sevenier et al., 1998). From an agroecological point of view, it is desirable to have for each kind of agricultural raw products one or few alternative crops, instead of a single multiple-use major crop. However, under present conditions in agriculture, root chicory and Jerusalem artichoke will only become true alternative sugar crops if the raw materials are produced at prices competitive to those of established high yielding crops.
Several studies have compared Jerusalem artichoke and root chicory side-by-side (Haber et al., 1941; Sah et al., 1987; Thome and Kuhbauch, 1987; Meijer et al., 1993) as well as Jerusalem artichoke and sugarbeet (Zubr, 1989). To the best of my knowledge, no studies have been performed so far in which root chicory and Jerusalem artichoke have been tested together with sugarbeet in the same experiment. In a previous study, Sah et al. (1987) compared productivity of beets, root chicory, and Jerusalem artichoke at different levels of N fertilization. However, since these authors were primarily interested in fuel energy, they used fodder beet instead of sugarbeet. The present study was conducted to assess the effect of water and weed stress at different levels of N supply on important agronomic traits of root chicory, Jerusalem artichoke, and sugarbeet in a three season trial at a site typical of the North-German plain.
MATERIALS AND METHODS
Field experiments were conducted in 1995, 1996, and 1997 on a sandy loam soil (Haplic Luvisol) at the Federal Agricultural Research Center (FAL), Braunschweig, Germany (52 [degrees] 17'75" N, 10 [degrees] 26'16" E; altitude 80 m). In each year, soil samples were taken to a depth of 0.9 m between late April and early May, just before N-fertilization, to determine the available residual mineral N in the soil. An average of 58, 66, and 59 kg N [ha.sup.-1] in 1995, 1996, and 1997, respectively, was measured. A substantial amount of N was made available through mineralization as indicated by the high biomass N yield of the plots which had not received any fertilizer N. In the fall of each year prior to spring planting, 140 kg [K.sub.2]O [ha.sup.-1], 70 kg [P.sub.2][O.sub.5] [ha.sup.-1], and 21 kg MgO [ha.sup.-1] were applied to the experimental fields. In 1995 and 1996, the experimental fields had oats followed by a phacelia (Phacelia tanacetifolia Benth.) catch crop grown on them in the year before, while in 1997 annual ryegrass (Lolium multiflorum Lam.) was the previous crop. Data on monthly mean air temperature and rainfall were obtained from the Agrometeorological Research Station of the German Weather Service located on the research site.
Experimental Design and Treatments
In 1995 and 1996, the experiment was laid out in a randomized complete block design with a split-split plot arrangement and four replications. Main plots consisted of two levels of water supply: with and without supplemental irrigation. Overhead nozzle boom irrigation was performed whenever crops showed symptoms of water shortage. The same amount of water was supplied to all crops at the same time. Subplots were crops, with each crop being represented by one cultivar: Reka (SB), Fredonia Nova (RC), and Topstar (JA). Subsubplot treatments were a factorial combination of three N fertilizer rates and two weed levels. Nitrogen was supplied in a single pre-emergence application of granular calcium ammonium nitrate at rates of 0, 60, and 120 kg N [ha.sup.-1], denoted as ON, 60N, and 120N, respectively. Two weed treatments were applied to each crop: complete weed control by regular hand hoeing and no weed control. The weed flora was scored in three 0.25-[m.sup.2] random sections per plot during the second half of June when sugarbeet and root chicory were in the 6-to-8 true-leaf stage and Jerusalem artichoke had formed 6 to 10 pairs of leaves.
To detect possible genetic differences within crops, the experimental design was modified in 1997 by including a second set of cultivars and omitting the experimental factor weed control. Otherwise, the 1997 experiment had the same treatment arrangement, plot size, and data collection as in the previous 2 yr. The second set of cultivars consisted of Olivia (SB), Bergues (RC), and Gigant (JA). Both sugarbeet and root chicory cultivars were commercially grown in Europe at the time of the study. The two Jerusalem artichoke cultivars are releases from a breeding program conducted by the author in the 1980s (Schittenhelm, 1987). Sowing dates for sugarbeet and root chicory were 25 April in 1995 and 23 April both in 1996 and 1997. Planting dates for Jerusalem artichoke were 12 April 1995, 17 April 1996, and 9 April 1997. Root chicory was sown with an Accord-Fahse pneumatic seed drill (Duren, Germany) and sugarbeet was sown with a Becker mechanical single seed drill (Gieselwerder, Germany). Pelleted seeds were used throughout the study for sugarbeet but only in 1997 for chicory. In 1995 and 1996, naked chicory seeds were treated with the fungicide thiram (tetramethylthiuram disulfide) at a rate of 0.66 g a.i. [kg.sup.-1] of seeds. Sugarbeet and root chicory were sown at an excess of seeds and thinned at the seedling stage to the desired densities of 80 000 and 160 000 plants [ha.sup.-1], respectively. The final average plant densities in 1995, 1996, and 1997 were 83 000, 87 000, and 82 000 plants [ha.sup.-1] for sugarbeet and 164000, 162 000, and 134 000 plants [ha.sup.-1] for root chicory. Jerusalem artichoke tubers were hand-planted at a density of 40 000 plants [ha.sup.-1] and plots were ridged immediately after planting. The sub-subplots of each crop were 5 m long and consisted of five rows spaced 0.50 m apart for sugar-beet, six rows spaced 0.44 m apart for root chicory, and four rows spaced 0.75 m apart for Jerusalem artichoke. To ensure optimal growth conditions, foliar diseases and insects were controlled with fungicides and insecticides according to the rates recommended by the manufacturers. All plots were hand-harvested within about 1 wk beginning on 9 October, 14 October, and 13 October in 1995, 1996, and 1997, respectively. In each crop, only the central rows, excluding the terminal plants from each end of the rows, were used in determining the yields. The net sub-subplot sizes were 7.1, 8.2, and 5.5 [m.sup.2] for sugarbeet, root chicory, and Jerusalem artichoke, respectively.
Chemical Analysis, Data Acquisition, and Analyses
Total fresh weights of separately hand-harvested storage organs and aboveground biomass from each plot were determined in the field. Samples of [approximately equals] 10 kg [plot.sup.-1] each from sugarbeet and chicory roots, and [approximately equals] 5 kg [plot.sup.-1] of Jerusalem artichoke tubers were weighed before and after washing. Dirt tare was determined on the basis of these measurements and then used in calculating corrected total storage organ yields. Averaged across years, dirt tare was 8.3, 5.3, and 3.2% for sugarbeet, root chicory, and Jerusalem artichoke, respectively. The washed roots and tubers were mashed in a cutter and two samples, each 10 g, were immediately stored at -20 [degrees] C for sugar analyses. Additionally, [approximately equals] 250-g samples were taken from the mash and together with two [approximately equals] 500-g samples of aboveground biomass were dried at 105 [degrees] C for 2 d to determine the percentage dry matter. Dried samples of both fractions were ground to pass a 1-mm screen in determining their mineral compositions. The sucrose content of sugarbeet roots was measured by means of a polarimeter (Carl Zeiss, Model OLD 4, Oberkochen, Germany). The amount of fructose and glucose present in chicory roots and Jerusalem artichoke tubers before hydrolysis was measured enzymatically by means of test kits (Boehringer Mannheim, Germany). In determining the total fructose content, fructans were hydrolyzed at 60 [degrees] C for 30 min by 12.5 U m[L.sup.-1] of the inulinase Novozyme SP 230 (Novo Industries, Copenhagen, Denmark) as described by Klaushofer and Wolfslehner (1983). The fructose and glucose released on hydrolysis were determined by HPLC using a Bio-Rad Aminex HPX-87C column (Bio-Rad Laboratories GmbH, Mtinchen, Germany) run at 75 [degrees] C with degassed HPLC-grade water at a flow rate of 0.6 mL [min.sup.-1]. Carbohydrates were detected by a Shodex RI-71 refractive index detector (Showa Denko K.K., Tokyo, Japan). Total Kjeldahl N of storage organs and aboveground biomass was determined with a Tecator Kjeltec 1035 analyzer (Tecator, Hoganas, Sweden). A nitric, perchloric, and sulfuric acid digestion was used to determine the P, K, Na, Ca, and Mg contents of roots and tubers. Phosphorus content was measured by colorimetry with a spectrophotometer (Carl Zeiss, Model PM2DL, Oberkochen, Germany). Potassium, Na, Ca, and Mg were determined with an atomic absorption spectrophotometer (PerkinElmer, Model 430, Norwalk, CT).
Dirt corrected yields of storage organs and aboveground biomass were adjusted to dry weights per hectare. Harvest index (H1) was calculated as storage organ dry weight divided by total biomass dry weight multiplied by 100. Sugar yield per hectare was calculated by multiplying dirt corrected storage organ fresh matter yield by the sucrose (SB) and total fructose (RC and JA) content, respectively. Since the total fructose and glucose after enzymatic hydrolysis includes a certain amount of fructose and glucose which is not bound in the fructans, the mean degree of polymerization (DP) of the fructans was estimated according to Klaushofer et al. (1987) as follows:
Mean fructan DP = [([F.sub.t] - [F.sub.f])[([G.sub.t] - [G.sub.f]).sup.-1]] + 1,
where [F.sub.1] and [G.sub.1] represent the content of total fructose and glucose, whereas [F.sub.f] and [G.sub.f] represent the content of free fructose and glucose. N uptake is the N yield per hectare of the total biomass at harvest. N utilization efficiency was calculated as sugar yield (kg [ha.sup.-1]) divided by total plant N (kg [ha.sup.-1]). N harvest index was determined as the ratio of root or tuber N yield [ha.sup.-1] to total plant N yield [ha.sup.-1] and expressed as a percentage.
All measured and derived data were subjected to analysis of variance (ANOVA) carried out with the PLABSTAT computer program (Utz, 1991). Year and treatment effects were considered fixed. The 1995 and 1996 experiments, embodying the weed treatments, were analyzed combined over years as a split-split plot experimental design (Carmer et al., 1989). Because a second set of crop cultivars was added in the 1997 experiment to the debit of the weed control treatment, in determining the crop's response to water stress and N fertilization, each year was analyzed individually using a reduced model. The two cultivar sets of the 1997 experiment were also analyzed separately to accurately show and discuss the performance of the individual crop cultivars. When F-ratios were significant (P [is less than] 0.05), least significant difference values (LSD, P [is less than] 0.05) were calculated and used to compare means of statistically significant sources of variance. The LSDs for interaction effects were calculated with standard errors and approximate t-values as outlined by Steel and Torrie (1980, Chapter 16). Significance of aboveground and storage organ dry weight losses through water and weed stress at the various N levels of each crop were determined by t-tests.
RESULTS AND DISCUSSION
Weed Infestation and Response to Weed Stress
Averaged across crops and levels of water and N supply, a total of 82 and 322 weeds [m.sup.-2] were recorded in the weedy plots in 1995 and 1996, respectively. The three most predominant weeds were field pansy (Viola arvensis Murr.), annual bluegrass (Poa annua L.), and common groundsel (Senecio vulgaris L.) in 1995, and low cudweed (Gnaphilium uliginosum L.), annual bluegrass, and smallflower galinsoga (Galinsoga parviflora Cay.) in 1996.
In the combined analyses across the 1995 and 1996 seasons, weed level x year interactions as well as three-way interactions including weed level x year mostly were significant for the traits studied. Such interactions were expected because of the extremely different weed pressure in the 2 yr of the study. Consequently, the data were analyzed separately for each year. The individual year analyses showed that weed infestation significantly (P [is less than] 0.001) reduced aboveground dry weights, storage organ dry weights, sugar yields, and N uptake by 30, 31, 31, and 35% in 1995 and by 54, 56, 57, and 56% in 1996. The other traits under study were not or only slightly affected by weed infestation. ANOVA for the above mentioned four traits also exhibited significant weed level x crop interactions (P [is less than] 0.001) whereas the incidence of weed level x crop x water supply interactions were few and relatively minor or not significant. This indicated that crops responded differently to weed infestation while the response patterns were similar at the two levels of water supply.
For the above reasons and to simplify data presentation, the effect of weed stress is presented and discussed below for the aboveground and storage organ dry weights in the irrigated plots (Fig. 1). For all crops in each year, percentage losses through weed interference were similar for both aboveground and storage organ dry weights. Because of more severe weed pressure, dry weight losses were substantially higher in 1996 than 1995. Among the crops investigated, Jerusalem artichoke yields were least affected by weed infestation. Significant tuber yield reductions only occurred at ON in 1996. The exceptionally high weed competitiveness of Jerusalem artichoke is attributable to the rapid growth and enormous final plant size, eliminating most of the weeds by shade. Consequently, weed control in Jerusalem artichoke may be only necessary early in the growing season in highly infested fields.
[Figure 1 ILLUSTRATION OMITTED]
Although weed competition significantly reduced storage organ dry weights of both root crops in each year at all N levels, yield losses were less striking in root chicory than in sugarbeet (32 vs. 57% in 1995; 62 vs. 82% in 1996). Thus, the expectation that root chicory because of its smaller and more upright leaves might be less competitive with weeds than sugarbeet was not confirmed. The competitive advantage of root chicory probably was attributable to the more narrow row spacing and higher planting density as compared with sugarbeet. Nevertheless, it was interesting to notice that the weed competitiveness of sugarbeet was improved through higher N rates, whereas that of root chicory was decreased. This contrasting pattern most likely was attributable to the inability of root chicory to respond to higher N fertilization with a correspondingly greater aboveground biomass (see Table 2). While not greatly affecting leaf mass of root chicory, increasing N rates increased growth of weeds, thus altering the competitive balance between crop and weeds. In contrast to root chicory, the aboveground biomass of sugarbeet markedly increased through addition of N fertilizer. Consequently, sugarbeet at the highest N level was nearly as competitive with weeds as root chicory.
[TABULAR DATA 2 NOT REPRODUCIBLE IN ASCII]
Climate and Response to Water Stress
The individual growing seasons differed substantially for mean monthly air temperature and total rainfall (Table 1). In 1995, a lengthy drought period from mid-July to late August (14 mm of rainfall during 5 wk) coupled with very hot weather caused severe water deficit in the nonirrigated plots. Seasonal rainfall and temperature in 1996 were similar to the 30-yr average. Although little rainfall occurred from early to late June in 1996, abundant and evenly distributed rainfall during the months July and August ensured adequate soil moisture in the rapid growth phase of storage organs. In 1997, a 3-wk dry period from early to late August without any rainfall occurred during the hottest period of that year. During the crop growing season the well-watered plots received four irrigations of 100 mm in 1995, and each six irrigations of 170 and 175 mm in 1996 and 1997, respectively. In 1995 and 1997, total and about half amount of irrigation, respectively, was given during the extended drought periods referred to above.
Table 1. Monthly mean air temperatures, rainfall, and irrigation during the 1995, 1996, and 1997 growing season at Braunschweig, Germany Mean air temperature Month 1995 1996 1997 30-yr mean [degrees] C April 8.9 9.4 6.9 7.9 May 12.7 11.6 12.9 12.7 June 14.8 15.4 16.4 15.8 July 20.4 16.2 17.9 17.1 August 19.1 18.2 21.1 17.0 September 13.5 11.3 14.1 13.9 October 12.5 9.9 8.3 9.8 Mean or Total 14.6 13.1 13.9 13.5 Rainfall (irrigation) Month 1995 1996 1997 30-yr mean mm April 44 32 43 48 May 47 70 77 58 June 56 28 (30) 60 74 July 52 (50) 64 (65) 71 58 August 47 (50) 47 (45) 25 (115) 66 September 85 53 (30) 14 (60) 47 October 22 101 42 40 Mean or Total 353 (100) 395 (170) 332 (175) 391
The individual year ANOVAs for the weed-free plots showed that water supply had statistically significant effects mostly on the traits studied. The most remarkable effect of water deficiency was a decrease in aboveground dry weight, storage organ dry weight, sugar yield, and N uptake as well as a decrease in Na content of roots and tubers. N level x crop interactions were generally significant (P [is less than] 0.05), whereas the N level x crop x water supply interactions were often not significant. Thus, the response patterns of crops to N rates were similar for both levels of water supply.
Averaged over crops and N levels, yield losses due to water deficiency in the weed-free plots in 1995, 1996, and 1997 were 20, 13, and 10%, respectively, for aboveground dry weights, and 39, 8, and 14%, respectively, for storage organ dry weights (Fig. 2). The aboveground biomass of root chicory generally was more sensitive to water deficiency than that of the other crops. In 1995, the year with the most severe water stress, significant but similar dry weight losses for storage organs occurred in the nonirrigated plots for all crops. As expected, the reduction of storage organ dry weights in that year were lowest in the plots that received no fertilizer N. In this case, yield depression could have been attributed more to N deficiency than water shortage. In the 1996 and 1997 growing seasons, storage organ yields of Jerusalem artichoke were more affected by drought than those of sugarbeet and root chicory. This contrasting response pattern was probably attributable to differences in the crops root architecture. Under moderate water stress, as was prevailing in 1996 and 1997, root chicory and sugarbeet with their long taproots probably were more capable in efficiently exploiting water from the lower soil layers than the comparatively shallow rooting Jerusalem artichoke. Nevertheless, under severe water stress in 1995, even the long tap roots were not able to reach down to the ground water; thus, storage organ yields of all crops were reduced to about the same extent. The two cultivars per crop studied in 1997 exhibited almost identical storage organ dry weight losses. This indicates that interspecific rather than intra-specific effects were important for the response to water stress.
[Figure 2 ILLUSTRATION OMITTED]
Response to N Fertilization without Water and Weed Stress
Dry Matter Yield and Partitioning, Sugar Yield, Sugar Content, and Mean Fructan DP
Although 60N and 120N storage organ dry weights were not always statistically significant, Jerusalem artichoke and sugarbeet tended to have their maximum yields at the highest N rate, whereas root chicory peak yields were already attained at 60N (Table 2). Storage organ dry weights averaged over years at their respective optimal N levels were 14.8, 15.0, and 11.5 Mg [ha.sup.-1] for sugarbeet, root chicory, and Jerusalem artichoke, respectively. The greatest aboveground dry matter yields, except for root chicory in 1995, were attained at the highest N level. The crops differed markedly in their response to N fertilization. Averaged across years, the aboveground dry weights at 120N exceeded those at ON by 72% for sugarbeet and by 43% for Jerusalem artichoke, but only by 7% for root chicory. Except in 1995, root chicory and Jerusalem artichoke had similar but much lower harvest indices than sugarbeet. The ranking of crops for sugar yield was similar to those for the storage organ dry weights. Averaged across years, SB, RC, and JA at their respective optimal N levels gave sugar yields of 11.5, 11.2, and 8.1 Mg [ha.sup.-1], respectively. In root chicory, the highest sugar yields were attained at 60N, whereas in sugarbeet and Jerusalem artichoke it occurred mostly at 120N. Root chicory had the highest storage organ sugar content, followed by sugarbeet, and finally Jerusalem artichoke. The different N regimes inconsistently affected the fructan chain length. Averaged across years, the mean fructan DP for root chicory was markedly higher than for Jerusalem artichoke (11.7 vs. 8.0).
The finding of this study, that root chicory required relative small amounts of fertilizer N for attaining maximum root yield, confirmed the results of Sah et al. (1987) and also agreed with the 40 kg [ha.sup.-1] or less N recommended for commercial root chicory production in Belgium (Baert, 1993). The relatively high root yields of chicory, as compared with sugarbeet, are quite remarkable, since little breeding work is being devoted to this crop. However, both public and private root chicory breeding programs in Europe ensure limited but steady crop improvement. Nevertheless, since hand-harvesting was performed in this study, root chicory yields represent potential rather than harvestable yields. Owing to the small and brittle chicory root, comparatively high yield losses occur during mechanical harvest. Furthermore, root chicory yields may also have been overestimated since hand instead of chemical weeding was practiced in this study. Chemical weed control options for chicory are limited and inadequate in most countries because of lack of authorized and nondamaging herbicides. In contrast to the situation for root chicory, appropriate herbicides are available for sugarbeet and chemical weed control in Jerusalem artichoke is not generally necessary. Since resistance to glyphosate and sulfonylurea herbicides has been found in chicory (Sellin et al., 1992; Vermeulen et al., 1992; Lavigne et al., 1994), herbicide-resistant root chicory cultivars may offer a new herbicide option in the near future.
The high total biomass yield of root chicory concurrent with its relative low HI may offer possibility for further yield improvement. Averaged across years, total biomass dry weight of root chicory exceeded that of sugarbeet by 37% at ON, 17% at 60N, and 3% at 120N. Assuming that His of root chicory in each of the 3 yr were identical to those of sugarbeet, potential dry weight root yields for chicory are estimated to exceed those of sugarbeet by 10% at ON, 8% at 60N, and 5% at 120N. Besides an improved partitioning of photosynthate, higher chicory root yields may also be attainable by exploiting the great within-population genetic variability through development of hybrid cultivars (Desprez et al., 1994) and by extending the growing season via earlier sowing (Baert, 1993; Westerdijk, 1997), provided that cultivars with enhanced bolting resistance are also developed.
The relatively poor yields of Jerusalem artichoke, as compared with sugarbeet and root chicory, agreed with previous reports from California (Sah et al., 1987), Germany (Thome and Kuhbauch, 1987), Denmark (Zubr, 1989), and the Netherlands (Meijer et al., 1993). In contrast to these studies, Haber et al. (1941) reported similar yields of Jerusalem artichoke and root chicory grown in Iowa. However, crop yields in their study were attained from unreplicated field trials and, most likely, root chicory yields were underestimated through the appearance of a considerable number of bolters. Meijer et al. (1993) attributed the comparatively low tuber yields of Jerusalem artichoke to the (i) large portion of assimilates which is fixed in the structural stem matter at tuber harvest, (ii) formation and maintenance of the storage tissue needed for the temporary storage of fructan in the stem, and (iii) metabolic costs of relocation of fructans from the stem to the tubers. The extra energy costs for relocation alone have been estimated to correspond to 4 to 8% of the stored carbohydrates (Meijer and Mathijssen, 1991). No doubt, the physiological specialty of temporary stem storage in Jerusalem artichoke is a limitation for fructan production. However, another explanation for the large yield gap to sugarbeet and root chicory is due to the fact that Jerusalem artichoke crop improvement programs in the past had very limited dimensions and were only performed at irregular intervals. Private plant breeders are not much interested in Jerusalem artichoke because of inadequate markets and the ease of vegetative propagation of this healthy plant which does not regularly force farmers to buy certified seeds.
Nitrogen Uptake, Utilization, and Partitioning
Since excess N fertilizer in the soil is undesirable for economic and ecological reasons, an important criterion in determining the relative excellence of crops is the efficiency with which fertilizer N is taken up from the soil and later utilized in producing sugars in the storage organs. As expected, concurrent with increased N rates was higher N uptake in all crops (Table 3). At low N fertilization, root chicory was more efficient in N absorption than either of the other crops. At each N level, with the same amount of nitrogen used, root chicory produced the highest sugar yields in 1995, while sugarbeet was most efficient in N utilization in 1996 and 1997. Jerusalem artichoke was by far least effective in utilizing the accumulated N for sugar production. The crops differed significantly in the fraction of total N that was translocated to the storage organs. Averaged across years and N levels, Jerusalem artichoke had a higher N harvest index (80%) than sugarbeet (51%) and root chicory (58%). The results of this study contradict that of Sah et al. (1987), who found higher N uptake potential for Jerusalem artichoke than for root chicory, but agrees with their observation of greater N utilization efficiency of root chicory and higher N harvest index of Jerusalem artichoke.
[TABULAR DATA 3 NOT REPRODUCIBLE IN ASCII]
Mineral Composition of Storage Organs
The crops differed greatly in the mineral composition of their storage organs (Table 4). From a comparison of the two cultivar sets in 1997, it was evident that differences in mineral accumulation among cultivars at a certain N rate were small compared to the conspicuous differences among crops. Nitrogen application affected the concentration of nitrogen, sodium, and phosphorous, but had little effect on potassium, calcium, and magnesium. While Jerusalem artichoke tubers contained the greatest amount of N, K and P, chicory roots had highest contents of Na and Ca, and sugarbeet roots were highest in Mg. It is interesting to note that sugarbeet exhibited the lowest content of N and K and the second lowest content of Na. Since the amount of potentially extractable sugar from sugarbeet is reduced through [Alpha]-amino-N, K, and Na, the relative low quantity of these elements may reflect successful selection against these elements by sugarbeet breeders. In contrast to sugarbeet, where quality criteria are precisely defined, so far no published information is available from the inulin-processing industry as to the relative importance of individual constituents for the technological quality of chicory roots and Jerusalem artichoke tubers. The quality requirements, of course, differ from those of sugarbeet since no crystallization is needed in fructose syrup production. Demineralization of the raw juice in all three European root chicory processing factories is achieved via ion exchangers (de Leenheer, 1994). In the preparation of high-fructose syrup from Jerusalem artichoke, anion and cation-exchange resins have been applied on a laboratory scale (Fleming and Groot Wassink, 1979, and references cited therein). Therefore, a low mineral content appears desirable to reduce the frequent and costly regeneration of ion exchangers. According to Dutilleul et al. (1990), the saturation of ion exchange columns is primarily caused by potassium and [Alpha]-amino-N, and to a lower extent by Na and Ca. But according to L. de Leenheer (1998, personal communication), proteins and especially organic acids like malic acid, which occur at high amounts in root chicory, are more crucial than ionic compounds.
[TABULAR DATA 4 NOT REPRODUCIBLE IN ASCII]
SUMMARY AND CONCLUSIONS
The question of which crop is most suitable to deliver a possibly expanding fructan or fructose market largely depends on the crop's yield potential and the costs for means of production necessary in realizing this yield. Evidence was found that storage organ yields of root chicory and sugarbeet were less affected by mild water deficit stress than those of Jerusalem artichoke, suggesting that the root crops were capable of avoiding drought by developing deep rooting systems. It would be desirable in future comparative studies with these crops to include measurements of root distribution and root water uptake capacity and efficiency. Root chicory was comparatively more competitive with weeds than sugarbeet, although storage organ yields of both crops were significantly reduced by weed infestation. In contrast, the Jerusalem artichoke yield was only affected under conditions of high weed and N stress. In the absence of water and weed stress, root chicory and Jerusalem artichoke produced average maximum sugar yields of 97 and 70% relative to those of sugarbeet, respectively. In contrast to sugarbeet and Jerusalem artichoke, which generally attained maximum sugar yields at the highest level of N fertilization, root chicory attained peak sugar yields at a medium N rate. A limitation on this study was that crop comparisons were based on gross instead of recoverable sucrose and fructose yields. However, an unbiased comparison of these crops would require knowledge of the factors accounting for the impurity of root chicory and Jerusalem artichoke raw juice. In conclusion, this study showed that root chicory has the potential to become a fully competitive alternative sugar crop in Germany. Since root chicory had a larger total biomass yield and smaller harvest index than sugarbeet, it should be possible to further increase chicory root yield by selecting genotypes that allocate a greater portion of the dry matter to the roots. The weed control by Jerusalem artichoke itself is a commercial advantage over sugarbeet and root chicory which generally require a herbicide. However, the costs saved on herbicides do not compensate for the markedly lower sugar yield of Jerusalem artichoke.
The assistance of Sabine Peickert, Martina Kreibich, and Martina Schabanoski in the field work, and that of Christel Methner and Bernd Arnemann in the chemical analysis is gratefully acknowledged. Also, I wish to thank Dr. Lothar Frese and Dr. James A. Okeno for valuable comments on the manuscript. Thanks are due to the breeding companies Strube Saatzucht KG, Kleinwanzlebener Saatzucht AG, SAREA GmbH, and Florimond Desprez for their gift of seeds of sugarbeet and root chicory.
Abbreviations: DP, degree of polymerization; HI, harvest index; HPLC, high pressure liquid chromatography; JA, Jerusalem artichoke; RC, root chicory; SB, sugarbeet.
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Institute of Crop Science, Federal Agricultural Research Center (FAL), Bundesallee 50, 38116 Braunschweig, Germany. Received 4 Dec. 1998. (*)Corresponding author (firstname.lastname@example.org).
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