Evaluation of Growth and some Growth Analysis Components in Sugar beet Genotypes Grown under Low Nitrogen Fertilizer Levels in Khartoum State- Sudan

A field experiment was carried out during 2018/2019 at Demonstration Farm of University of Bahri at Al Kadro on latitude 15^◦ 45′N, longitude 32^◦ 39′E and altitude of 398 m above sea level, in Khartoum State, Sudan. In a semi-arid zone with maximum and mean temperature of 45^◦C and 30^◦C during summer, 25^◦C and 10^◦C during winter, respectively, the annual rainfall ranges from 0 mm to 100 mm, with relative humidity ranging from 16% to 50% ⁷. The soil is a mixture of sand ≥ 40%, silt ≤ 32% and clay ≤ 36^%8. The land was properly prepared and divided into four blocks running perpendicular to the gradient. Each block contained 4 plots randomized with six sugar beet genotypes, namely, Blaladi. Strube Sudan 01/14, Strube Sudan 02/14, Strube Sudan 04/14, Strube Sudan 05/14 and Strube Sudan 06/14, and each plot was divided into three subplots randomized with nitrogen fertilizer levels in form of urea viz., 0. 80 and 120 kg/ ha in two times; one at sowing and the other after 4 weeks from sowing date. The design used was split plot. The seeds were sown manually, three seeds per hill and then thinned to a plant in 3 to 4 weeks after sowing The spacing was 20 cm plant to plant and 70 cm between ridges. Weeding was done manually and insects were sprayed with Melthion. The experiment was irrigated immediately after sowing and then every 7- 10 days depending on the weather conditions. The collected data composed of growth attributes from 3 plants randomly taken per subplot at 5 terms of sampling namely; 4, 7, 10, 13 and 16 weeks after sowing (WAS). The growth parameters were: leaf number/plant, leaf area index, fresh and dry weight of leaves/ plant(g/p), length and diameter of root (cm), fresh and dry weight of foliage per plant (g), fresh and dry weight of root (g) and some growth analysis parameters: crop growth rate (CGR), root crop growth rate (RCGR), relative growth rate (RGR), root relative growth rate (RRGR) and net assimilation rate (NAR) were computed using the following formulae:

The method was suggested by ⁹. The CGR explains the dry matter accumulated per unit land area per unit time (g m^-2 day^-1)

Where, W1and W2 are whole plant dry weight at time t1– t2 respectively, ρ is the ground area on which W1 and W2 are recorded. CGR of a species are usually closely related to interception of solar radiation.

 Relative Growth Rate (RGR). The term was coined by ¹⁰ RGR expresses unit dry weight / unit dry weight / unit time (gg^-1day^-1). Where, W1and W2 are whole plant dry weight at t1 and t2 respectively t1 and t2 are time interval in days.

The term, NAR was used by ¹⁰. NAR is defined as rate of increase of dry weight per unit time per unit area of leaf surface (gcm^-2day^-1). Where, W1and W2 is dry weight of whole plant at time t1 and t2 respectively, L1 and L2 are leaf weights or leaf area at t1 and t2 respectively t1 –t2 are time interval in days.

Statistical analysis of experimental data was carried out by using the SPSS software package and the means were separated by Duncan’s multiple range test with at least P≤0.05.

The data analysis of this study is presented in the table 1, table 2, table 3, table 4, table 5, table 6): listed below:

Table 1, G0, G1, G2, G3, G4 & G5 designate for; Blaladi StrubeSudan 01/14, Strube Sudan 02/14, Strube Sudan 04/14, Strube Sudan 05/14 and Strube Sudan 06/14 genotypes. N0, N1, & N2 designate for 0, 80 & 120 Kg urea per ha., while Sy- designates for standard error., NS, * and ** designate for non significant, significant at 5%., and highly significant at 1%, respectively. Means followed with the same letter (s) within a column indicate non-significant effect at 5% level.

Considering table 6, 2-1, 3-2and 4-3 stand for time between 7-4 WAS, 10-7WAS and 13 -10 WAS, respectively. PCGR, RCGR, PRGR , RRGR and NAR stand for plant crop growth rate, root crop.

Means of leaf number per plant as affected by genotype, low nitrogen fertilizer rates and interaction between genotype and nitrogen fertilizer (G x N) are presented in Table 1.The analysis of variance for leaf number per plant revealed significant differences among the studied genotypes at three sampling terms (4, 7 and 10 WAS), while at 13 and 16 WAS showed no significant differences. This implies that the studied genotypes had varietal difference in their response to the growing conditions for initiating leaves at the beginning of the season. However, this genotype significant effect disappeared when the maximum leaf number reached. The highest leaf number scored by G2 at 13 WAS although; it was not significantly different from the other genotypes at this stage. This indicates that the evaluated genotypes do not have same reaction to the local conditions at the beginning of season resulted in significant deviations on leaf number while non – significant at the end of the season, means that sugar beet compensated leaf initiation rate of growth during the growing season. This point of view was in agreement with ¹¹. On the other hand, nitrogen fertilizer level and interaction of genotype x nitrogen effects were insignificant on number of leaves per plant. These findings were in line with ^{12, 13}. Who had reported no significant effect of nitrogen and interaction (GXN) on the leaf number trait in the 1st year of their study.

The mean values of leaf area index (LAI) as affected by genotype, nitrogen and their interaction are presented in Table 1. LAI in the first growth stage was low for both treatments, but rapidly increased and reached a maximum at 10 WAS stage. The analysis of variance for mean values of LAI throughout the sampling terms exhibited insignificant difference at 4, 7and 16 WAS, while significant effect exhibited at 10 and13 WAS terms among the studied genotypes. The mean values of LAI increased gradually up to the 10 WAS term where reached the peak and then declined (highest was attained by G3, 5.645). There is a progressive increase in area of the successive early leaves that produced by the plant, but a point reached beyond which leaves subsequently grew progressively smaller and consequently LAI as shown in Table 1. This could be attributed to the phenomenon of genotype by environmental interaction causing genotype to produce different results and ranks under the local environmental conditions. Similar point of view was reported by ¹⁴. On the other hand, the nitrogen levels showed insignificant difference among the studied genotypes. This may indicate that none of the applied levels of nitrogen caused substantial effect on LAI. Due to low nitrogen available in the soil, there was neither variation in utilization of accumulated nitrogen nor variation in in uptake efficiency of nitrogen. Similarly ^{13, 15} stated that neither shortage nor excess of nitrogen at any stage of sugar beet growth affected its vigorousness’ while soil nitrogen was low. The genotype x nitrogen ii0interaction displayed insignificant effect; this is line with ¹⁶.

Means of fresh and dry weight of leaves per plant as affected by genotype, low nitrogen fertilizer levels and their interaction are shown in Table 2.The analysis of variance for fresh weight reflected insignificant difference among the studied genotypes at four sampling terms except at 7 WAS stage showed significant difference, at this stage the fresh weight reached the maximum fresh weight and the highest fresh weight scored by G2 (764-27 g/plant) .This may indicate that there was a high competition among the genotypes for growth requirements at this stage to attain the maximum weight that resulted in the variation. Then, gradually the fresh weight declined to reach the least amount of weight scored by G1 (170. g/plant) at 16 WAS stage with no significant difference. This is may be due to a progressive expansion and weight of leaves up to 7 WAS, but at 10, 13 and 16 WAS the leaf growth declined. This result is in harmony with ¹⁷. Nitrogen fertilizer and interaction between GXN gave insignificant effect on fresh weight of leaves per plant at all the 5 sampling stages. This may be due to low nitrogen fertilizer levels applied which not reached the extent of producing substantial effect on the fresh weight of leaves per plant. On the other hand, the analysis of variance for dry weight of leaves per plant gave statistically insignificant effect of genotype, nitrogen fertilizer and interaction between GXN at all sampling stages. Similar results were found by ^{18, 19}. Means of fresh and dry weight of foliage per plant as affected by genotype, nitrogen fertilizer and the interaction between genotype and nitrogen are presented in Table 3.The analysis of variance for fresh foliage weight exposed significant difference among the evaluated genotypes at 4 WAS and insignificant effect thereafter at 7, 10, 13, and 16 WAS. Thus the significant difference at 4 WAS could be attributed to different response of genotypes at the beginning of seedling growth before the 4-leaf stage to environmental conditions. Similar results were reported by ²⁰. Then the foliage weight reached its peak at 7 WAS and continued declining as the result of progressively produced smaller leaves but insignificantly different. Nitrogen fertilizer and the interaction G X N exhibited insignificant effect on foliage fresh weight per plant. This may be due to under applied nitrogen or lack of differences in nitrogen use efficiency. These findings were parallel with those reported by ²¹ who found that increasing nitrogen levels from 0, 35, 70, and 105 kg N/fed showed significant effect. Also ²² reported similar findings as found 60 and 80 kg N/ha gave significant effect. On the other hand, the analysis of variance for foliage dry weight at 4, 7, and 10 WAS stages indicate that the studied genotypes indifferently responded to growing conditions at the beginning of the growing season. The dry weight of foliage progressively increased up to maximum weight at 7 WAS, thereafter from 10 WAS stage onward the rate of dry matter accumulation declined, but with significant differences among the genotypes at 13 and 16 WAS. Similarly ¹⁹ reported significant results. Nitrogen fertilizer and interaction between genotype and nitrogen manifested insignificant effect at the sampling terms. This may be attributed to low nitrogen levels applied which failed to stimulate a substantial accumulation of dry matter on the foliage. These results were in harmony with those reported by ²³.

Mean values of root dimensions (length and diameter) obtained from the six sugar beet genotypes grown under low N fertilizer levels are shown in Table 4. Analysis of variance for mean values of root length reflected insignificant effect among the evaluated genotypes in four out five sampling stages but at 4WAS manifested significant effect. So this variation among the studied genotypes may be attributed to variation in seedling growth. While, thereafter, the non- significant effect at the other sampling stages indicates that the genotypes had very similar root length growth, and noted that root length from 7 WAS through 16 WAS became stable. These findings were in line with those reported by ²⁴. The different levels of N fertilizer and interaction between GxN exhibited non - significant effect on root length at all sampling stages. These results were in line with those detected by ²⁵. Also, ²⁶. The analysis of variance for root diameter means revealed non - significant effects at 4, 10 and 16 WAS sampling stages among the evaluated genotypes which indicate similar expansion of cells which enhance root diameter, while the sampling at 7 and 13 WAS reflected significant effect on the root diameter. This could be attributed to variation among the evaluated genotypes at the existing climatic conditions at these terms (7 and 13 WAS). Because various types of sugar beet genotypes may not have the same requirements and reactions to the local environmental effects. Such results were found by ¹⁶. Also, similar idea was reported by ²⁴. Regarding the significant and insignificant effect of the genotype at different growth stages were reported by ^{27, 19} found significant and non- significant effect among different cultivars. However, the different rates of N fertilizer and their interaction with the genotypes were non - significant. This indicates that N fertilizer rate and GXN had not ²⁸ who found insignificant effect on both root length and root diameter in the second season of their experiment.

Means of fresh and dry weight of root per plant as affected by genotype, nitrogen fertilizer rate and interaction between genotype and nitrogen fertilizer (GXN) are presented in Table 5.The analysis of variance for fresh weight of root per plant revealed significant difference among the evaluated genotypes at 4 and 10 WAS stages. The variation among the tested genotypes may be ascribed to the efficiency of utilization of growing conditions variability at these two stages. Similar results were observed by ^{29, 16}. The other three stages 7, 13, and 16 WAS showed non - significant effect which implies no genotypic variation on root fresh weight among the studied genotypes. Similarly ²⁷ reported significant and non - significant results in the first and second seasons of their experiments, respectively. It was noted that the fresh weight of root increased until reached its peak at 13WAS as it was increased at expense of the top growth then declined. Moreover, the N fertilizer levels and the interaction among genotypes and N fertilizer were non-significant which indicate similar response to low N fertilizer and no interaction (GXN) effect on the trait. In line to this, ¹³ found non - significant effect in the second season of their experiment also ³⁰ noted the same. The analysis of variance for mean values of root dry weight revealed highly significant effect at 4 and 10 WAS sampling stages among the evaluated genotypes. This indicates that at these two growth stages the evaluated genotypes showed variation in their response to the growing conditions in developing dry root weight accumulation. This is in line with ¹⁴. Who stated that the phenomenon of the genotype by environment interaction is always present in the crop production causing genotypes to have different results and ranks in various environmental conditions, also These findings were in line with those highly significant differences among the cultivars reported by ¹⁶. While at 4, 13 and 16 WAS the mean values reflected non-significant effect on root dry weight which implies that the genotypes had similar root development and in turn the root dry weight in early and late growth stages, similar results were found by ²⁷ in the second season of their experiment. This inconsistency could be attributed to the ability of sugar beet genotypes to compensate their growth throughout the growing stages especially in early stages of development. The N fertilizer levels and their interaction with genotypes produced no significant effect on root dry weight per plant. These findings were in agreement with ³¹. Who observed that root dry weight started accumulation of dry matter from 7 WAS increasingly to 16 WAS due to translocation of assimilates towards the root, which enhanced root length, diameter, root fresh weight as well as root dry weight.

Growth analysis as the first step in the analysis of primary production being a link between merely recoding plant productions and analyzing it by means of physiological methods. However, biomass increments in plant or root stands expressed in ground area basis (Crop growth rate = CGR), The rate of increase in biomass per unit of biomass present (Rate growth rate=RGR) and the rate of increase of dry weight per unit time per unit area of leaf surface (Net assimilation rate= NGR) are presented in Table 6.With regard to root and plant crop growth rate (RCGR and PCGR, respectively), data in Table 6 showed that crop growth rate was insignificantly increased with different applied treatments. Here, the highest plant crop growth rate values were 9.571, 9.150, 7.857 (g)/cm²/day; scored by G3, G1 and G2 at three different stages of growth namely 7-4, 10-7 and 13-10 WAS, respectively, while its highest values were 8.374, 6.264 and 6.694 g/cm²/day with nitrogen fertilizer level; No, N2 and No, respectively, at the same stage periods of growth season. Meanwhile the highest root crop growth rate mean values were; 0.005, 0.007 and 0.007 (g)/ cm² /day with G3&G2, G1 and G0 genotype, respectively and its highest values were 0.005, 0.005 and 0.006(g)/ cm² /day with No, N1 and No fertilizer level, respectively. At the same consecutive different periods of growth mentioned ahead. These results were in harmony with ^{32, 22} who found insignificant CGR at elect stages of growth.

Concerning relative growth rate (RGR) data in Table 6exhibited that relative growth rate was insignificantly increased with the studied treatments. The highest mean values were 0.045, 0.019 and 0.013 gg-1 day-1, scored by G2, G0 and G0 genotypes, respectively, meanwhile the highest mean values were 0.044, 0.018 and 0.010 obtained from No, N1 and N2 fertilizer levels, respectively, These values were determined at consecutive times of growth stages 7-4, 10-7 and 13-10 WAS, respectively. Similarly (2000) ³³ reported insignificant difference.

Moreover, with regard to Net assimilation rate (NAR), data in Table 6 reflected that Net assimilate rate was insignificantly increased with different applied treatments. Here, the highest net assimilate rate value was 0.010 g cm-2 day-1 determined at 7-4 WAS growth period, scored by G2 and its highest value was 0.009 g cm-2day-1, with N0 fertilizer level. This is in line with El-Zayat (2000) ³³ who reported non – significant effect.

In the light of the present study, it could be assumed that tested genotypes may have the same requirements and reactions to the local environmental effects genetically. Therefore, these physiological components indicated that the evaluated genotypes did not differ in the proportion of photosynthetates partitioned into dry weight. Moreover, the non – significant effect of the nitrogen fertilizer level on all the studied growth and some growth components indicates that the low nitrogen fertilizer levels applied may not enhanced the uptake of nitrogen increased (N1 & N2) and the slight unsubstantial variations among the levels could be due to utilization of accumulated nitrogen. This view is in agreement with who reported that the response of sugar beet depended on the N available in the soil. Nevertheless, no crossover interaction occurred for the fore mentioned parameters, there to be no specific suitability of the tested genotypes to environmental stress condition. The interaction between genotype and N fertilizer level effect on all the evaluated parameters was absent or insignificant. These findings were in line with those reported by ²⁴.

In this study of six sugar beet genotypes; the variation in root and plant growth rate, relative growth rate (RGR) and net assimilation rate (NAR) revealed no substantial differences among the genotypes or tested Nitrogen levels. This is probably arises because the beet is a vegetative storage organ and has no clear growth stages that particularly susceptible to unfavorable environmental conditions. Nevertheless, no significant interaction between genotype and N fertilizer level indicates a similar response of genotypes; not depending on N level. These findings were in line with those reported by ²⁴. Nonetheless, the growth evaluating techniques are good indicators for relating sugar beet growth to climatic conditions and information on crop growth during each growing stage is one of most important indexes of optimum cultivation and management, although, these results exhibited no significant difference at the different growth periods.

It has been noticed that sugar beet has ability of compensating its morphological growth components through the season. This could be fortified by the significant effects in some stages and insignificant in others among the studied genotypes.