Effects of Spacing on Sugar Beets in 30 Inch and Inch Rows

Transcription

1 Effects of Spacing on Sugar Beets in 3 Inch and Inch Rows F. J. HILLS! Receivedfor publication November 1,1972 Most sugar beets in California are grown on raised planting beds to facilitate furrow irrigation. The most common row arrangements are single rows centered on beds 3 inches apart or two rows 14 inches apart centered on beds that are 4 inches from center to center. The latter arrangement results in an alternating row spacing of inches (Figure 1). Increasing numbers of growers are planting to a stand. Because of hazards to emergence, the grower plants as many seeds as possible consistent with a plan to establish a stand that will not require thinning. It is common to find stands where plants average 4 inches and closer within the row. Such dense stands produce commercially acceptable crops, but critical comparisons show that stands spaced from 8 to 12 inches produce 2 to 4 tons more roots per acre (unpublished data). a. b. Figure l.-sugar beet row spacings on raised planting beds to provide furrows for irrigation: a) 3 inch rows, b) inch rows. There have been man y studies on the effects of plant population on sugar beet production. Early work was reviewed by Coons (l? in In a recent review, Hull and Jagga rd (3) point out tnat greatest sugar yields are given by populations of 26, to 34, plants per acre but that variations of several thousand per acre generally have only small effects on yield. In 1968, Robinson and Worker (7) confirmed earlier studies that a 12 inch square spacing (43,5 plants/acre) yielded maximum sucrose. Twenty-four inch square spacing yielded about 7% less sucrose; but a 3 inch spacing resulted in 5% Joss. Nelson (6), in Arizona, showed 6% loss in sucrose yield from plants spaced 5 inches in inch rows but only 2% loss from 5 inch spacing in 3 inch rows. I Extension Agronomist, Department or Agronomy & Range Science. University of California, Davis, Ca lifornia 'Numbers in parentheses refer to literature cited.

2 VOL. 17, No.4, OCTOBER The present experiment, cond ucted at Davis, California in 197 J, was done to assess the effects ofclose in-row spacings for the row spacings used in California to guide producers in final stand establishment. Materials and Methods The experimental treatments consisted of a factorial combination o f two row spacings (3 inch and inch), two dates of harvest, (7-8 September and Octobe r) planned to give mean root yields of approximately 2 and 3 tons per acre, and nine in-row spacings (1.5, 2, 3, 5, 7, 9, J I, 13 and 15 plants per 3 feet of row). The experimental design was a split-split plot with main plots as row spacings, sub plots dates of ha rvest, and sub-sub plots in-row spacings. The design allowed the main effect of in-row spacing and a ll interactions of in-row spacing with row width and harvest date to be determined with considerable precision but gave less precision for the main effects of row width and h arvest date. Seed of cultivar US H 9B, currently the most extensively used diploid h ybrid in California, was sown on 28 May with a Stanhay planter at I inch and furrow irrigated for germination. Emergence exceeded 8% and was virtually complete by 7 June. Spacings were established June when seedlings were in the two leaf stage by placing a 3- foot markn along a row and leavin g the required number of plants per 3 feet, spaced as evenly as possible. Post thinning cou nts indicated that the desired spacings were achieved. The first three columns of Table 1 indicate the final spacing in inches between plants, plants per 3 fe et of row, and plants per acre. Within a row spacing, population density increased in equal increments from 3 to 15 plants/3 feet of row, which allowed easy calculation of quadratic functions to fit yield s plotted against d ensity (4). At each harvest, 3 feet o f the center two rows of each sub-sub plot were dug by ha nd. Tops were weighed and one-quarter of each of ten tops composited to determine percent dry matter. Roots were separated into marketable (2 inches or more in diameter) and nonmarketable individuals and then counted and weighed. The average diameter of marketable beets was determined by measur ing ten randomly selected beets per plot. Two root samples, from eight to sixty beets per sample, depending upon root size, were taken from each plot for tare and sucrose analysis. Residual pulp from the two samples of each plot was comp osited to determine percent root dry matter. Coefficients o f variability for spacing and interactions involving spacing were 3. h, 6., and 5.9%, respectively, for percent sucrose, root, and sucrose yield. In determining the ratio of su crose to non-sucrose dry matter in marketable roots Cr a ble 1), non-sucrose dry matter was calculated as: (tons fresh roots/acre) (root % dry matter) (gross sucrose/acre).

3 '-> h:) Table I.-Effect of row width, spacing, and harvest date on marketable' sugar beet roots. Plant P~pulatio n Number Mean diameter, Fresh wt., Sucrose Sucrose/non- Gross sucrose Spacing, per 1' per 6 ft. inches tons I!er acre % sucrose dr~ matter tons/acre inches 3 feet per acre 7 Sept. 18 Oct. 7 Sept. 18 Oct. 7 Sept. 18 Oct. 7 Sept. 18 Oct. 7 Sept. 18 Oct. 7 Sept. 18 Oct. 3 inch rows: 2.4 I :, \I ,, A ~.IO inch ro"'s: l YO Stat istica lly Sx H*** significant RxS*** effects 'Roots 2 inches and more in d iameter at har vest R** S*** SxH' H** * S*** RxS*** H* S""' Sx H * H* S*** H *** S*** RxS*** '--< c " z ;, r ",.., ::r: '" ~ (/) (/) to ~

4 VOL. 17, No.4, O CTOBER Results and Discussion Plants grew well throughout the season and were essentially free of viruses and other diseases. Figure 2 characterizes the effects of changes in in-row plant density on root and sucrose yields for the two row spacings and illustrates the nature of the highly significant interactions of row width X spacing. Yields of roots and sucrose decreased more rapidly at densities above optimum but more slowly at densities below optimum for inch compared to 3 inch rows. The response curves indicate that seed should be sown or plants thinned to at ROOTS. TONS/ACRE ' _ 26 _INCH ROwS 2 o 3_ INCH ROW S " II PLANTS per 3 Fe T OF ROW '. J ' SPACING. INCHe s 1 2 LB. SUCROSE PHI ACR[ _INC M ROwS o 3D_INCH ROwS L-~~~--~~5--~~7--~~9--~~1I--~~/3--~~15~ PLANTS PER 3 FEU OF ROW SPACING. INCHES Figure 2.-Effects of in-row spacing on root and sucrose yield for row spacings of 3 and inches. Data points are means of four replications and two dates of harvest. Regression lines are quadratic functions of densities of from 3 to 15 plants per 3 feet of row, except for sucrose yield for inch rows where the fit is to from 5 to 15 plants per 3 feet. For densities less than 3/3 feet, the curves were extended by eye. Over the densities fitted, the quadratic function accounts for 95 to 99% of the variability in root and sucrose yield.

5 34 jocr:\al OF THE A. S. S. B. T. least 6 inches when the row spacing is inches but no closer than 4 inches on 3 inch rows. With commercial beet harvest it is quite possible that many roots 2 inches in diameter may not be recoverable. This would increase the rate of loss with dense stands, and thus spacings no closer than 7 and 5 inches, respectively, may be safer for commercial practice. With plants spaced 18 and 24 inches, the estimated reduction in sucrose yield for inch rows was 5 and 12% respectively but 13 and 23%, respectively, for 3 inch rows. Thus inch rows offer considerable safety from yield loss when poor emergence or mechanical thinning results in gappy stands. Tables 1 and 2 present results for both harvests; statistically significant effects are noted at the bottom of the tables. Interactions of row width X spacing x harvest date were not significant for any of the measurements presented except for total dry matter yield (Table 2), which was just significant at the 5% leve l. There were no significant interactions ofspacing x harvest with respect to root and sucrose yield despite an increase in marketable roots at the later harvest for spacings of 5 ir.ches and closer (Table I). Apparently the increase in yield of roots at wider spacings was equivalent to the yield increase resulting from the growth and increase in marketable roots for closer spacings. 5ucros{' concentration The significant spacing x harvest interaction with respect to fresh weight sucrose concentration appeared to be largely due to a red uction in pe,'cent sucrose in plants spaced 12 inches and further at the first harvest date, while six weeks later only plants spaced 18 inches and further were significantly lower in sucrose concentration. This was probably due to a differential response to nitrogen deficiency. At the first harvest, plants hadjust become nitrogen deficie nt and the smaller plants, those spaced 7.2 inches and closer, responded more quickly to the deficiency by increasing sucrose concentration. By the second harvest, sucrose perce ntage had, on the average, increased one pe.rcentage point and all plants had been deficient for a longer period. At this harvest, plants spaced 12 inches were not significantly different in sucrose concentration from closer spacings, but plants spaced 18 and 24 inches were still significantly lower in percent sucrose. Apparently the smaller roots were more responsive to nitrogen deficiency (5). Pe rcent water in roots decreased with in creasing plant population for both row spacings, thus increasing percent sucrose on a fresh weight basis as reported by Draycott, et al. (2). However, the re also was a decrease in the ratio of sucrose to non-sucrose dry matter for both row spacings as in-row spacing decreased (Table I). T he effects of spacing was highly significant and there were no significant interactions. Averaged over both row spacings and harvest dates, the ratio

6 Table 2.-Effect ofrow width, spacing, and date ofharvest on number and yield ofnon-marketable roots and dry matter yield ofall tops and roots. ~ ;=: Non-marketable roots '.-.1 Plants Number Fresh wt., All tops, dry wt.2 Total dry wt.; Ratio: Dry roots! Z Spacing, per per 6 ft. tons/acre tons/acre tons/acre dry tops2 :l inches 3 ft. 7 Sept. 18 O ct. 7 Sept. 18ct. 7 Sept. 18 Oct. 7 Sept. 18 Oct. 7 Sept. 18 Oct..*'" 3 inch rows: ("! , c., 3.3 II "" 7-l ' uo LSI inch rows: :; I I Slatistically R'" R** R** R* R* sig nificant 5*** S*** 5*** H*** H* ** effects RxS*** RxS*** S*** S*** RxSx H* 1 ROOLS less than 2 inches in d iamclcr at harvest. 2From marketabl e and no n-markefable roots. uo v'

7 36 JOClC\AL OF THE A. S. S. B. T. of sucrose to non-sucrose dry matter = X, where X is plants per 3 feet of row (r = -.956***). Thus, as in-row density increased a greater proportion of the photosynthate partitioned to roots went to non-sucrose dry matter which resulted in a decrease in dry weight sucrose concentration. Dry weight % sucrose was estimated as: [(fresh wt % sucrose) / (root % dry matter)] 1. As a linear function of plants/3 feet of row, dry weight percent sucrose = X (r = -.964***). Thus estimated dry weight sucrose concentrations for in-row spacings of 24, 12, 4, and 2.4 inches are, respectively: 68., 67.7, 66.3, and 64.9%. Dry matter production Top yield and total dry matter yield (tops plus storage roots, marketable and non-marketable) were greater for than for 3 inch rows and both increased asymptotically as in-row density increased to a maximum at about 13 plants per 3 feet of row (Table 2). The effect of in-row spacing on total dry matter yield is described well by fitting a quadratic to reciprocals of lb per plant as a function of plant population (8). The average effect of spacing over both harvest dates for each row width is shown in Figu re 3. As population increased there was a highly significant linear decline in the ratio of the dry yield of roots to tops for both row spacings (Table 2). Averaged over both harvests and row spacings, dry root yield/dry top yield = X, where X is plants/3 feet of row TOTA L DRy "AT TER TONS / ACRE 8. : o INCH ROWS PI,," lib "1./., i-'} i - ' } x i-'}X' o 3 INCH ROWS Plallis/ib dry wi. =3./ ) +S.489(/O - Z)X +6.99(1O- 5)X II PLANTS PER 3 F[U OF ROW ' PLANTS / ACRE. 3 INCH ROWS ' PLANTS ACRE INCH ROWS Figure 3.-Effect of plant population on the dry matter production of tops plus storage roots (marketable and nonmarketable). Data points are means of four replications and two harvest dates. Regression lines are calculated from quadratic functions of plants/pound fitted to plant population.

8 VOL. 17, No.4-,OCTOBER (r = -.98***). Thus, as population increased, an increasing proportion of photosynthate was partitioned to tops. This effect, in addition to the greater proportion of non-sucrose dry matter in roots as population increased, resulted in an increasin gly smaller proportion of photosynthate going to sucrose yield. Summary and Conclusions An experiment was cond ucted at Davis, California in 1971 to assay the effects ofin-row spacings on sugar beets grown in row widths of 3 and inches at two dates of harvest. Root and sucrose yield responses were characteri7.ed by quadratic functions of pl ant density. Root and sucrose yie lds declined at different rates for the two row widths at in-row densities higher and lmver than optimum. Yields d ecreased more rapidly at high in-row densities but more slowly at low in-row densities for compared to 3 inch rows. Near maximum yields occurred for inch rows at spacings of from 6 to 12 inches and on 3 inch rows at spacings o f from 4 to 1 inches. Increases in fresh weight sucrose concentration at high in-row densities are attributed to decreases in tissue water, but increases in non-sucrose dry matter also occur so that dry weight sucrose concentration decreases at high in-row densities. Total dry matter yield increased asymptotically for both row widths as in-row density increased but the ratio of roots to tops declined. As population increases an increasing proportion of photosynthate appears to be partitioned to tops, and a greater proportion of the photosynthate goin g to roots is partitioned to non-sucrose dry matter th an to sucrose. Acknow1edgements Appreciation is extended to Randolph Holme, Diane Hills, Gary Peterson, and Rodney Marble for their careful work in the arduous task of successfull y establishing the plant spac in gs reported in this experiment. Thanks also to Dr. T. M. Little for co nsultatioh in the design and analysis of the experiment. This study was aided by fin ancial assistance from the California Beet Growers Association and the sugar processors of California. (I) Literature Cited COONS, C. H Space relations hi ps as affecting yield and quality o f sugar beets. Proc. Am. Soc. Sugar Beet Techno!. 5: (2) DRAY COTT, A. P., M. J. D t ' RRANT, and P. J. LAST Effects ofcultural practices and fe rtilizers on Sligar beet quality. J. lnt. lnst. Sugar Beet Res. 5(3): (3) H r: LL, R. and K. W. JACCARD Recent developments in the establishment of sugar-beet stands. Field Crop,\bstracts. 24(3):

9 ~8 JOURNAL OF THE A. S. S. B. 1. (4) LITTLE, T. M Correlation and regression, a supplement to Experimental Methods for Exte nsion Workers. Univ. of Calif. Agric. Extension Service, pp. 62. (5) LOOMIS, R. S. and A. ULRICH Responses of sugarbeets to nitrogen deficiency as influenced by pl ant competition. Cro p Sci. 2:37-4. (6) NELSON,]. M Effect of row width, plant spacing, nitroge n rate, and time of harvest on yield and sucrose content of sugarbeets. J. Am. Soc. Sugar Beet Techno!. 15(6): (7) ROBI NSO N, F. E. and GEORGE F. WORKER, JR Plant density and yield of sugar beets in an arid environment. Agron. ]. 61: (8) WILLEY, R. W. and S. B. H EATH The quantative relationships between plant population and crop yield. Adva nces in Agronomy 21: