Darrell Cole
Research Plant Physiologist
Agricultural Research Service, USDA
Agronomy Department, NDSU
Fargo, North Dakota
Storage research during the past year included: 1) effects of irrigation and nitrogen; 2) effects of herbicides and a growth regulator; 3) effects of excess nitrogen and cultivars; 4) respiration rates of 6 commercial cultivars; 5) effect of mechanical damage on respiration.
Increase in leaf size of two cultivars were measured on leaves initiated at different periods of the growing season. Yield and sucrose content of two cultivars which were planted June 26, 1974 and irrigated up were measured. Effects of nitrogen and phosphorus on sucrose, extractable sucrose, and percent crown tissue were determined.
For storage experiments sugarbeet roots were harvested from all replications of three separate experiments in the fall of 1973. Roots were harvested manually and the petioles were hand trimmed at the base and the growing point removed. The roots from all replications were combined and separated into three classes (large, medium, and small) from each treatment. Samples of 10 beets were obtained by blending the three classes depending upon the number of beets in each class. Each sample of 10 beets was stored in a perforated plastic bag (15 x 29 in) at 40 F for 150 days. At harvest and 50-day intervals thereafter, samples from each treatment were removed and pulp was obtained by sawing with a "spreckle's" saw. Pulp samples were immediately frozen and stored at -5 F for later analysis.
Apparent sucrose was determined polarimeterically by the cold digestion method and invert sugars by 3, 5-dinitrosalyclic acid.
This experiment was conducted at the North Dakota Experiment Station at Fargo, ND. Biuret, being tested as a growth regulator, (L-102) and 3 herbicides were used in this experiment. Trichloracetic acid (TCA) was applied as a preemergence spray (May 15) at 8 lb/A. Phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) was applied as a post-emergence spray (June 20) at 1 lb/A and Eric (S-ethyl dipropylthiocarbanate) was incorporated before planting at 3 lb/A rate. The growth regulator was applied 45 days prior to harvest at 50 lb/A. All plots were hand weeded throughout the growing season. The field experimental design was a randomized complete block with 6 replications. Seed of American 2 Hybrid B' was planted on May 15, 1973. Soil test data showed a residual of 330 lb/A as NO3 to a depth of 60 cm. Six samples of 10 beets of each treatment were analyzed at each sampling period during storage.
Invert sugars of all treatments increased during the 150-day storage period. EPTC caused a significant increase in invert sugar after 150 days storage over the control, whereas invert sugar from roots grown with Phenmedipham were significantly lower than the control. Apparent sucrose was significantly higher in all treatments compared to the controls, average over the storage period (Table 1). Sugar beets grown with phenmedipham did not show a decrease in apparent sucrose, whereas the control beets showed a 14.2% decrease.
Seed of 'HH-10' were planted on April 24, 1973, at the Oakes Irrigation Experimental Site at Oakes, North Dakota. Phosphorus and potassium were plowed down at 150 lb/A of P2O5 and 75 lb/A of K2O, respectively. Nitrogen (N) was broadcast at 0 and 100 lb/A. Main plots were water levels replicated 3 times, with nitrogen level as the split-plot. The main plots were irrigated by a sprinkler system. Water level 1 was dryland conditions with no irrigation water added. Water levels 2 and 3 were irrigated when soil water tensions were 660 and 550 millibars at 12 in, respectively. Water level 3 was considered the optimum level. A total of 10.4 inches of rainfall was received during the growing season. Water levels 2 and 3 received an additional 9.3 and 12.5 inches of water, respectively. Seven samples of 10 beets of each treatment were analyzed at each sampling period during storage.
Sugarbeet roots grown under moisture stress conditions had a higher invert sugar content after storage than did roots grown under optimum moisture conditions (Table 2). Nitrogen did not significantly affect invert sugar content of roots grown under the different moisture levels when averaged over the storage period. However, under the optimum moisture level, sugarbeet roots grown with additional nitrogen showed a 31% increase in invert sugar content at the end of the storage period. Sugar beet roots grown under the two moisture stress levels only showed a 5% increase in invert sugars due to nitrogen. Apparent sucrose was significantly reduced by the addition of N (Table 2). Sugar beets grown under moisture stress conditions were significantly lower in apparent sucrose. All interactions between storage time, water level, and nitrogen were nonsignificant. Apparent sucrose did not show a significant decline in storage.
The experiment was conducted at Fargo, ND, and planted on May 8, 1973. The experimental design was a split-plot (6 replications) with nitrogen as main plots and cultivars as sub-plots. Nitrogen (N) was applied at 300 lb/A and the residual soil level was 150 lb/A. 'American 4 Hybrid A' and 'Bush Mono' were the cultivars tested. Six samples of 10 beets of each treatment were analyzed at each sampling period during storage.
High nitrogen did not significantly change invert sugar levels on two cultivars of sugar beets stored for 150 days (Table 3). The storage date by cultivar interaction was the only interaction which was significant for invert sugar. Invert sugar increased significantly in American 4 Hybrid A with time in storage, especially after 100 days. American 4 Hybrid A was significantly higher in invert sugar averaged over all storage dates.
High nitrogen caused a significant reduction in apparent sucrose averaged over cultivars (Table 3). American 4 Hybrid A and Bush-Mono showed a reduction 15.9 and 13.1% in apparent sucrose due to the addition of nitrogen. American 4 Hybrid A was significantly higher in apparent sucrose at harvest and after150 days of storage.
The results reported in these experiments indicate that several agronomic practices can affect changes in apparent sucrose and invert sugar levels during storage of the sugar beet roots. The practices become increasingly important when temperature increases within the storage piles, since the beets deteriorate faster at higher temperatures.
Increase in impurities causes a reduction in the amount of sucrose that can be extracted from the roots. Therefore, it becomes critical that all factors which can affect the storability of sugar beet roots be evaluated and managed to produce high quality roots for storage. These data show that nitrogen, cultivar, chemicals and moisture stress can significantly affect quality of the roots during storage.
Manually harvested roots of 6 sugarbeet cultivars (Bush-Mono, GOOD-2, Beta 93, Am 4A, Am 4T, Am 2B) were stored for 150 days after harvest at 40 F and 100% relative humidity. Respiration rates were measured during the last 75 days of the storage period using gas chromatographic techniques.
Respiration rates were significantly different among cultivars and the rates increased during the storage period. Rates averaged over cultivars were 1.3 and 2.4 ml CO2 kg-1 hr~1 at 75 and 145 days, respectively. Respiration rates of Mono-Hy D-2 were the lowest of all cultivars during the storage period (Fig. 1).
Roots of one cultivar (Am 2 Hybrid B) were selected from different harvesting operations of a commercial grower and stored at 40 F for 150 days to measure the effect of mechanical damage on respiration. Respiration rates of sugarbeet roots mechanically harvested and piled were 20% higher than rates of manually harvested roots (Fig. 2).
Leaves of two cultivars, 'Mon-Hy D-2' and 'HH-21', were selected when the petiole began to elongate, thereby allowing a label tag to be attached. Leaves selected were immature and had begun to unroll. Ninety leaves of each cultivar were tagged 5 times during the latter part of the growing season (Aug 13, 20, 27, Sept 3 and 24). Ten leaves of each cultivar were selected at random at periodic intervals (0, 1, 2, 3, 6, 7, 14, and 21 days) to determine leaf area and specific leaf weight. Leaf area was determined by photocopying the leaves and dividing the weight of the leaf images by the weight of a 1 cm2 area of the same paper. Specific leaf weight (ma cm2, SLW) was the ratio of leaf dry weight (80 C for 24 hr) and leaf area.
Leaf area increased rapidly during the first 14 days after the leaves were tagged (Fig. 3). Cultivar differences were detected at 21 days when the leaves were tagged on Aug 20 and Sept 24. Leaves initiated later in the growing season were smaller than leaves initiated earlier in the growing season. Leaves do not enlarge as rapidly during the time period when sucrose is increasing in the root. Specific leaf weight changes drastically during leaf expansion (Fig. 4). Specific leaf weight is high during the early stages of leaf development, decrease as the leaves expand, and increase as the leaves mature.
Seed of two cultivars were planted June 26, 1974 and irrigated up. Yield and sucrose content were determined on roots harvested Oct 25, 1974. There was no difference in yield between cultivars, however, sucrose was higher in Holly HH-21 (Table 4). Severe hail damage occurred on Aug 1 and probably reduced yields since over 9070 of the leaves were completely obliterated.
The effect of nitrogen and phosphorus on sucrose and percent crown tissue was determined on manually harvested beets. Roots were harvested and stored at 40 F for approximately 80 days. Root and crown tissue were separated at the lowest leaf scar on 20 consecutive beets in a row from each treatment. Nitrogen lowered apparent sucrose and extractable sugar and increased the amount of crown tissue (Table 5). The root tissue was lower in impurities and higher in apparent sucrose than crown tissue within treatments. Effects of phosphorus on apparent sucrose, extractable sucrose, and percent crown were not as clear cut as the nitrogen effects (Table 6). These data indicate that proper management of fertility can reduce the amount of crown tissue produced.
1974 Sugarbeet Research and Extension Reports. Volume 5, pages 145 - 154.
