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Evaluation of sampling methods for harvesting non-treated and hydrogen cyanamide treated kiwifruit vines
SClENTIA HORTICULTURIE
.... E LS EV I E R
Scientia Horticulturae 58 (1994) 17-30
Evaluation of sampling methods for harvesting nontreated and hydrogen cyanamide treated kiwifruit vines R.F. Henzell*, I.M. Gravett, P.A. Allison The Horticulture and Food Research Institute of New Zealand Ltd., Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand (Accepted 14 January 1994)
Abstract From 1986 through to 1992 kiwifruit (Actinidia deliciosa cultivar 'Hayward') from vines in the Bay of Plenty district of New Zealand, trained on a T-bar trellis with an upper wire to support renewal shoots, were harvested from various sections of vines and graded separately. For any variable, the effectiveness of grading only part of a vine was measured by R 2, the proportion of the variation in the true whole vine value that was accounted for by the estimate from the part vine. Grading fruit from ten long canes on the western side or all of the fruit on quarter vines gave R 2 values of approximately 0.6. R 2 values varied from 0.7 to 0.85 for half vines. Grading diagonal quarters was slightly better than using the east or west sides which were in turn marginally better than grading the north or south sides. In all of these eases the estimate was improved greatly when the part harvested was adjusted upwards by a scaling factor of the fruit weight on the whole vine divided by the fruit weight on the part graded. On hydrogen cyanamide treated vines, the west side of vines performed significantly better than the east side. This meant that a grading procedure based on one of these sides alone would be biased and could result in up to 22% error for vines growing on T-bars. Grading either the north or south side alone and adjusting by the fruit weight ratio was more satisfactory as the differences in fruit size at harvest were smaller between the north and south sides than between the east and west sides. In trials involving consecutive hydrogen cyanarnide treatment of vines over five seasons, significant differences between the north and south sides of vines were observed in only one season but scaling by fruit weight overcame the problem. Keywords: Actinidia deliciosa; Harvest sampling; Hydrogen cyanamide; Kiwifruit vines; Yields *Corresponding author. 0304-4238/94/$07.00 © 1994EIsevierScienceB.V. All rights reserved SSD10304-4238 (94)00630-X
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R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
1. Introduction Field trials investigating the effects of numerous vine management practices on the productivity and economic performance of kiwifruit ( A c t i n i d i a deliciosa cultivar 'Hayward') vines have been carried out in a commercial T-bar orchard in the Bay of Plenty district of New Zealand since the 1985/1986 season. The Tbars in the trial block were modified with an upper wire to support renewal shoots. Each season the trials have involved several hundred vines which require a high labour input, particularly at harvest, when all the fruit are picked. Fruit from each vine, and frequently those from parts of each vine, have been graded separately. Between 5000 and 6000 trays of kiwifruit have been processed each season using a two-lane electronic grader in the orchard packhouse. One of the aims of this work was to assess if there were any systematic trends in cropping within vines. This necessitated picking fruit from different parts on the vine at harvest and grading the fruit separately. Since resource and time constraints at harvest do not always allow this detailed sampling on the whole vine, a secondary aim was to identify a section of the vine which could cover any systematic trends and provide satisfactory estimates of yield variables for the whole vine. The data showed how fruit size and distribution varied within the vine in terms of fruit number, mean fruit weight and number of export trays produced. The relationship between fruit number and growth in different parts of the vine also has important plant physiological implications as fruit size and dry matter can decrease in the lower extremities of the canopy (Smith et al., 1993 ). Furthermore, a knowledge of the variation in yield performance within and between vines is useful for crop forecasting purposes.
2. Material and methods Over the trial period, the number of long canes (over 1.5 m long) changed from 55 (initially) to 40 per vine. The number of short canes (from over 0.5 to 1.5 m long) varied between ten and 15 per vine, and up to 20 spurs (less than or equal to 0.5-m long canes) per vine were tied down in winter. Fruit on the vines were harvested and graded separately for different parts of the vines. These included ten random long canes along the western side and the remainder of the vines, each quarter separately, or the north and south or east and west halves of each vine. Two-vine experimental plots were used throughout. At grading the fruit weights used for each tray count varied throughout the trial period in accordance with New Zealand Kiwifruit Marketing Board standards. There are eight size counts (Table 1 ) associated with moulded plastic trays (plixes) containing cavities of appropriate size to give between 25 and 46 fruit per tray with a m i n i m u m fruit weight of 3.5 kg per tray. In the first three seasons the minimum individual fruit weight for export was 70 g with fruit allocated to
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
19
Table 1 Weight ranges used over the 1985-1992 trial period for different kiwifruit tray sizes Tray count size
Weights (g) used for the 1986 and 1987 harvests
Weights (g) used for the 1989 harvest
Weights (g) used for and after the 1992 harvest
25 27 30 33 36 39 42 46
134-144 123-133 111-122 101-110 93-100 86-92 79-85 70-78
148-165 127-147 117-126 105-116 98-104 89-97 78-88 70-77
148-179 127-147 117-126 105-116 98-104 89-97 78-88 74-77
trays based on a firm fit into the plix cavity. For the 1986 to 1989 harvests, trial fruit in the 30-39 size counts were preferred for export. In subsequent seasons the 25-39 size counts were included in the preferred export category.
2. I. Quantitative and qualitative yield variables The grading information from each vine included quantitative (directly assessed ) yield variables (fruit number, fruit weight, export weight, trays per vine ) and qualitative (calculated) variables ( mean fruit weight and percentages of fruit in categories such as 'rejects' and 'preferred export fruit'). Since total fruit num= bet and total fruit weight are highly correlated, the quantitative variables can estimate whole vine yield by weighing the fruit on the remainder of the vine. An alternative estimate used in 1991 / 1992 only involved measuring the cordon length of the north and south sides and grading the north half only. The qualitative yield variables were derived from the graded parts only, as they could not be estimated.
2.2. Statistical analysis The effectiveness of grading part of a vine was measured by R 2, the proportion of the variation in the whole vine data accounted for by the estimate from the part, where R is the correlation coefficient between the whole and the part. This estimate can be improved by weighing fruit on the remaining part of the vine and adjusting by a scaling factor. If Wp, Wr are the fruit weights on the part graded and the remainder of the vine, respectively, and Np and Nr are the corresponding fruit numbers, then the estimate of total fruit per vine is Np ( Wp + Wr) / Wp. This scaling factor ratio (rather than a regression estimate) was also used for the other quantitative yield variables. It assumes that the mean fruit weight is the same for the different parts of the vine. In practice there will be differences but these are hopefully random and not systematic or physiological. Some orchard cultural practices (such as interplanting pollinators ) can involve systematic differences between north and south cordon lengths. In this case an
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R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
additional scaling factor (the ratio of the total cordon length of the vine to the cordon length of half vine graded) was also taken into account. Differences (West minus East) and (North minus South) were analysed to determine whether there were overall differences between vine sides and if so, consistent differences between treatments. A consistent bias would mean that the absolute estimates would be biased, but treatment comparisons would not be affected. An interaction with treatments would be far more serious. A Genstat 5 statistical package (Rothamstead Experimental Station, UK) was used for the analysis of variance and regression. Although two-vine plots generally were used, the relationships were based on single vines. 2.3. Trials
The evaluation of sampling methods was mainly carried out in conjunction with the hydrogen eyanamlde trial, described below, which continued on the same block of vines from 1985/1986 for six consecutive seasons. This level block measured 52 m across by 177 m long and contained about 280 vines planted 5.5 m apart in nine rows which were 4.5 m apart. The rows were oriented in a northsouth direction and at the start of the trials the vines were about 15 years from graft. The block was well sheltered on all sides with poplar trees that were 20 m high in 1985/1986. The eastern and western shelters were removed during the following season in spring and autumn, respectively. The northern and southern shelters were about 30 m high by the sixth season. Over the trial period, the number of vines treated with hydrogen eyanamide in a season varied between 82 and 120. The number of untreated vines varied between 30 and 48. From the 1986/1987 season onwards, generally fruit on the northern half of the vines were graded and on the southern half weighed. 2.4. 1 9 8 5 / 1 9 8 6 season
Fruit were harvested and graded from three trial blocks. The first experiment involved 40 untreated vines and 90 vines treated with different rates of hydrogen cyanamide at different times (ten vines per treatment combination). Six of these combinations increased crop loads at harvest by at least 30%. Fruit were sampled on ten long canes on the western side of each vine along with the remainder of the western side and the eastern side. Fruit from each of these sections were graded separately. In the second ( 105 vines, irrigation trial) and third (24 vines, gel pruning trial) experiments, the vines were not treated with hydrogen cyanamide. Fruit from the west and east sides were sampled and graded separately. 2.5. 1986~1987season
In this season, fruit on both the north and south sides were graded separately on ten vines that were treated with hydrogen cyanamide in late July for two consecutive seasons.
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
21
2.6. 1988/1989 season Sampling method evaluation in this season was carried out on a different block and involved 20 hydrogen cyanamide treated vines located in two alternate middie rows. Comparable winter bud numbers were tied down on each quarter of the trial vines and the fruit from each quarter were graded separately.
2. 7. 1991/1992 season This trial consisted of 80 vines located in three alternate rows in the middle of a block treated with hydrogen cyanamide. The block was the same as that used in the 1988/1989 trials, but the male vine layout had been modified. The three rows contained mature female vines 5.5 m apart with 1 m long male vines planted at 11-m intervals midway between the pairs of female vines. The cordons on female vines on either side of the male vines were pruned by about 0.5 m to accommodate the young male vine interplants. Crop loads were adjusted from the estimated flower numbers on whole vines at a few weeks before fruit set. Fruit on the northern side of each vine were harvested and graded while fruit on the southern side were weighed and counted.
3. Results and discussion
3.1. Efficiency of different sampling procedures In the first season of this study (1985/1986), the effect on vine phenology of the chemical treatment on canes in winter was determined by monitoring ten long canes on the western side of the vines throughout the season. These canes carded about one sixth of the total vine yield. At harvest fruit on these canes were combined and graded to determine if they were representative of fruit on the western side, or of the vine as a whole. Grading fruit on the ten long canes provided R e values of 0.59-0.67 for the quantitative yield variables for the whole vine and adjusting by fruit weight improved this to 0.84-0.98 (Table 2). Similarly, grading fruit on either the western or eastern sides alone gave R 2ffi0.80-0.91 for the quantitative variables and adjusting by fruit weight again gave a further improvement (R2ffi 0.96-0.99). The mean fruit weight based on the ten long canes gave R 2 - 0 . 8 6 and half-vine sampling improved this to 0.95-0.96. Figures 1 and 2 indicate the accuracy of predicting the numbers of trays per vine and mean fruit weight at harvest when based on sampling ten long canes, the east or west sides alone or after adjusting by the fruit weight on the remaining part of the vine. Each vine was partitioned and graded separately again in 1988/1989. In this season each quarter was graded and these were considered separately and in north/ south, east/west and diagonal combinations (Table 3). Sampling quarters alone
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R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
Table 2 Percentage harvest variation ( 100XR 2 values) on the whole vine accounted for by grading fruit on ten long canes (western side) or western and eastern sides alone and adjusted by the fruit weight ratio on the whole and graded part of the vine. Based on sampling 130 single vines grown on T-bars, 19851986 season Vine part sampled
Information (%) for variables Fruit per vine
Fruit weight per vine (k8)
Prof. export weight per vine
Trays per vine
Mean fruit weight (g)
Rejects (%)
67 90 89 97 80 97
86
82
96
94
95
93
(kg) Ten long canes Ten long canes, adjusted West West, adjusted East East, adjusted
62 98 91 99 90 99
59 100 88 100 85 100
67 84 90 96 82 96
gave results similar to those obtained using ten long canes. The results for the east and west halves were similar to those obtained in the 1985/1986 season. Sampling the north or south sides was inferior (R 2= 0.72 for fruit number) to sampling the east or west, and the diagonals gave the best results ( R 2 - - 0 . 8 8 ) . Adjusting by the fruit weight ratio reduced these differences and increased the R 2 values to a satisfactory level for almost all variables. Sampling half vines rather than quarters also improved the R 2 values for the qualitative variables. Sampling half or even quarter vines therefore gave more than half the information for the whole vine, which meant there was a positive correlation between parts of the vine. By contrast, in the 1991/1992 season sampling half the vine gave less than half the R 2 values (0.33-0.46 on fruit number) (Table 4). This was due to the male vine layout in the block which was different from that in the other trial blocks. Young male vines were interplanted between sets of two mature female vines down the rows. The cordon lengths of both female vines were shortened to accommodate the male vine. This meant that although the total cordon length of the female vines remained approximately equal, if the north cordon was long, then the south one tended to be short and vice versa, i.e. north and south cordon lengths were negatively correlated. This introduced negative correlations into total fruit number and total weight but not mean fruit weight. Scaling or using both vines in the plot could be used to overcome this systematic error. Adjusting by cordon length for single vines increased the R 2 o n total number from 0.46 to 0.57 for the north side and from 0.33 to 0.58 for the south side. Adjusting by fruit weight was better (0.97 for the north and south sides) (Table 4). Averaging data from the pairs of vines in plots gave R2=0.61 for the fruit number from half vines and adjusting by cordon length increased this slightly (0.64-0.71). The mean fruit weight results were consistent with half-vine sampling in previous trials and improved slightly by taking pairs of vines.
R.F. Henzell et al. I Scientia Horticulturae 58 (1994) 17-30 10 Canes x 6
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Fig. 1. Relationship between the predicted and actual number of trays per vine based on samplin8 ten western canes, the eastern or western sides of vines during the 1985/1986 season. Predictions are based on either the proportion of vine graded or scaled by the ratio of fruit weight on the whole vine to the weight on the graded part of the vine.
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24
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30 10 Canes
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R.F. Henzell et al. /Scientia Horticulturae 58 (1994) 17-30
25
Table 3 Percent harvest variation on the whole vine accounted for by grading quarter and half the vine alone and adjusted by the fruit weight ratio on the whole and graded part of the vine. Based on 20 single vines on T-bars and treated with hydrogen cyanamide, 1988/1989 season Fraction of vine
Mean of vine part sampled
Information (%) for variables Fruit per vine
Fruit weight (kg)
Pref. export weight (kg)
Trays per vine
Mean fruit weight
Rejects (%)
(g) Quarter Quarter Half Half Half Half Half Half
NE, NW, SE, SW NE, NW, SE, SW adjusted N, S N, S adjusted E, W E, W adjusted Diagonal Diagonal adjusted
60
57
63
59
97 72 99 84 99 88 99
100 68 100 85 100 88 100
76 71 82 90 91 92 93
90 67 95 90 97 91 97
74
58
85
68
91
85
93
88
Table 4 Percent harvest variation ( 100 × R 2) on the whole vine accounted for by counting and weighing fruit on the north or south half of the vine and adjusting either by the fruit weight or cordon length ratio on the whole and graded vine half. The estimates were based on 80 single vines on T-bars or 40 twovine plots treated with hydrogen cyanamide in the 1991/1992 season Vine half sampled
North North, adjusted (vet) North, adjusted (cordon) South South, adjusted (wt) South, adjusted (cordon)
Fruit per vine
Fruit weight per vine (kg)
Mean fruit weight (g)
Single vines
Two-vine plots
Single vines
Two-vine plots
Single vines
Two-vine plots
46 97 57 33 97 58
61 97 64 61 97 71
46 100 59 38 100 64
68 100 72 64 100 73
83
86
86
90
3.2. Systematic differences within vines In sampling vines at harvest for yield parameters the aim was to have a method which was an efficient estimator of both quantitative and qualitative variables. Since the latter are based entirely on the part of the vine graded, ideally there should be no bias between the graded and ungraded parts. Ifa slight bias is found, then this should be consistent over all treatments for comparative purposes. In the 1985/1986 season there was little difference between the yield variables for the east and west sides for the untreated vines, but there were large differences
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R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
for vines treated with hydrogen cyanamidc in lateJuly or mid-August (Tables 5 and 6). This inconsistency indicated that ifonly the east or west side was graded to estimate yield parameters for the whole vine then large errors could occur for hydrogen cyanamidc treated vines. For the mid-August treatment the correct result would have been under- or overestimated by 2.I trays per vine, and for the late July treatment the estimates would have been out by 3.2 trays per vine, or a difference of 6.4 trays between the cast and west estimates.This is about a 22% error, as treated vines on average carded about 29 trays per vine. These differcnccs were reduced greatlyby adjusting with the fruitweight ratio on the whole and graded part of the vine (Table 6). The sensitivityof the analysis of variance to differentiatebetween treatment means was not affectedby this adjustment (Table 7). For example, the F ratios based on the adjusted data for the various parts of vine sampled approximated Table 5 Harvest variable differences between the western and eastern sides of vines grown on T-bars ( 1985/ 1986 season). Means of 40 untreated vines and ten vines treated with hydrogen cyanarnide applied in late July or mid-August Variable (per half vine)
West minus east sides
Fruit number Fruit weight (kg) Preferred weight (kg) Number of trays Mean fruit weight (g) Rejects (%)
LSD* Untr. vs. other
Untreated
Late July
Mid-August
- 23 -0.95 - 0.17 0.03 1.03 0.10
128 I 1.67 8.73 3.05 2.68 - 1.55
129 9.73 3.78 1.73 0.03 0.01
106 7.8 4.80 1.65 6.80 2.62
*Least significant difference at P < 0.05. Table 6 The actual treatment means and the means obtained from grading the west or east sides alone and the means derived from adjusting by the fruit weight ratio on the whole and graded part of the vine. The vines were or were not treated with 3% hydrogen cyanamide in late July or mid-August 1985
Vine part sampled
Total (actual) East × 2 East adjusted West ×2 West adjusted Long canes adjusted
Preferred export weight (kg per vine)
Trays per vine
Control
Late July
MidAugust
Control
Late July
MidAugust
42.1 42.3 41.8 41.9 42.3 42.3
83.2 74.1 82.8 92.4 83.7 78.8
76.0 71.4 78.2 80.6 74.2 73.9
15.6 15.6 15.4 15.6 15.8 15.6
29.2 26.0 28.9 32.4 29.5 28.4
27.6 25.5 27.9 29.6 27.2 27.1
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
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Table 7 F-ratios from the Anova, CVs and selected treatment means for trays per vine data for the whole vine, individual parts and those parts adjusted up by the fruit weight ratio on the whole and graded part at harvest on untreated vines and vines treated with3% hydrogen cyanamide in late July or mid-August 1985 Statistical terms
Source of variation
Vine part sampled Total
F ratios
Control vs. treated Chemical rate Time of application Rate×time
CVs Treatment means
Control 3% late July 3% mid-Aug
East
West
Ten West canes
Alone
Adjusted
Alone
Adjusted
Alone
Adjusted
40.0 42.9
29.0 29.6
45.2 43.4
30.3 33.8
30.6 38.0
28.9 38.8
20.6 43.0
1.9 2.3
1.3 1.2
2.4 2.6
3.0 2.6
1.4 1.8
1.9 1.3
1.5 2.1
22.9
24.0
22.5
28.9
24.7
34.9
26.1
15.6 29.2 27.6
15.6 26.0 25.5
15.4 28.9 27.9
15.6 32.4 29.7
15.8 29.5 27.2
15.6 28.4 27.1
reasonably closely those for the whole vine, and would not have affected the interpretation of treatment effects. The data in Table 5 also show that even though both hydrogen cyanamide treatments had the same crop load difference, the vines treated in late July performed much better in that bigger fruit and more trays were obtained at harvest on the western side. This shows that fruit growth rate was different on different sides of the vine. There was no systematic linear trend from west to east across the block for the west side of vines, but there was a significant trend in the difference between the west and east sides for most variables (R=0.4 for trays per vine; R=0.46 for preferred trays per vine). This difference increased from west to east across the block ( P < 0.01 ). The favoured growth of the western side was only observed on vines treated with effective hydrogen cyanamide rates. For example, in the same 1985/1986 season, fruit on the west and cast sides of 105 nonhydrogen cyanamide treated vines were graded separately and no difference in fruit growth was apparent between the two sides of these vines. Because the differences between the east and west sides were not consistent over all treatments during the first season of the trials, the yield variables on the north and south halves also were compared in subsequent seasons. In 1986/1987, the north and south sides were graded separately on ten hydrogen cyanamide treated vines. The north side had 283 extra fruit and this led to the expected increase in the quantitative but not the qualitative harvest variables (Table 8 ). The north-south difference may have been due to a difference in cordon length between the vine halves, which were not measured in this season.
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R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
Table 8 Harvest variable differences between the north and south sides often vines on T-bars and treated with hydrogen cyanamide in late July 1986 Variable (per half vine )
North
South
North minus south
LSD
Fruit number Fruit weight (kg) Preferred export weight (kg) Number of trays Mean fruit weight (g) Rejects (%)
990 93.4 59.0 23.7 94.5 13.2
707 66.9 42.4 16.7 95.6 12.2
283 26.5 16.6 7.0 - 1.1 1.0
19.8 17.7 11.9 4.6 4.8 2.3
Table 9 Harvest variable differrences between means of north and south and west and east sides of 20 vines trained on T-bars and treated with hydrogen cyanamide in the 1988/1989 season Variable
Fruit number Fruit weight (kg) Preferred export wt (kg) Number of trays Mean fruit wt (g) Reject (%)
Variable differences between North minus south
LSD*
West minus east
LSD*
45.25 3.08 0.22 0.65 -2.11 1.37
76.90 6.09 2.88 1.39 4.03 8.36
51.85 5.18 2.97 1.31 4.73 -7.26
53.91 3.78 1.39 0.67 3.09 6.72
*Least significant difference at P< 0.05. Table I 0 Harvest variable differences between means of the north and south sides of 80 vines on T-bars. Vines were treated with hydogen cyanamide in the 1991/ 1992 season Variable per half vine
North
South
North minus south
LSD
Fruit number Fruit weight (kg) Mean fruit weight (g)
396 40.2 102.2
379 39.4 104.2
17 0.8 -2.0
50.0 5.1 1.69
Grading fruit on the east and west sides of vines was carried out for a second time during the 1988/1989 season. Significant differences and sampling bias again were apparent (Table 9 ). The north-south differences in the yield variables were lower than the west-east differences, but the latter had lower variances. This suggests that the west-east differences were due to physiological factors and the northsouth differences were due to random difference in cordon lengths. In contrast to the trial in 1986/1987, there was no significant north-south difference for any of the yield variables. The 1991 / 1992 results (Table 10 ) showed a significant but
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R.F. Henzell et al. /Scientia Horticulturae 58 (I 994) 17-30
Table 11 Differences between north and south crop weights on non-treated and 3% hydrogen cyanamide treated vines over five seasons. The two mid-August treatments involved different spray volumes, pollination, crop load and pruning methods
Season
No. vines sampled
North minus south fruit weight (kg)
Untreated
Untreated
Treated
Late July
MidAugust (1)
MidAugust (2)
40 24 40 40
40 24 40 10
1986/1987 1987/1988 1988/1989 1989/1990 1990/1991
40 48 40 40 30
10 34 40 40 90
1986/1987
LSD
Late July vs. others Mid-August (1,2) vs. untreated
1987/1988
LSD
Late July vs. others Mid-August ( 1,2 ) vs. untreated
1988/1989 1989/1990
LSD LSD
1990/1991
LSD
Mid-August ( 1) vs. untreated Mid-August (2) vs. untreated
7.0 0.0 4.5 6.2 6.7
Treated
Late July
MidAugust (1)
MidAugust (2)
26.0 14.2 3.3 3.3 10.0
-0.3 31.8 2.7 8.5
8.5 12.0 6.4 15.6
14.6 9.2 11.6 10.6 5.3 7.4 14.0 9.4
small north-south difference in mean fruitweight. This difference was consistent over all treatments, which allowed valid comparisons to be made between them and with only a slighterror in the absolute estimates for the harvest variables. Crop weight differences between the north and south halves of vines on the same block of vines involved in hydrogen cyanamidc trialsover five consecutive seasons arc summarised in Table I I. Inconsistent results over treatments were observed in 1987/1988, but in the four other seasons there was no difference between the north and south apart from the late July treatment in 1985/1986 which involvcd ten vines. Adjusting for the weight of fruiton the remaining part of the vine overcame these problems.
4. Conclusions
A n efficientsampling method to determine yield parameters on kiwifruit vines at harvest should be on a clearly identifiable part of the vine and accommodate most of the known systematic sources of variation in fruit size. These include fruit weight differences along a cane and along the cordon, and fruitdensity differences within the canopy. Sampling quarter or half vines would appear to meet these criteria.The main drawback in any sampling procedure is inconsistent diffcrcnces in qualitative variables, as these cannot bc adjusted. Sampling quarter
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R.F. Henzell et aL / Scientia Horticulturae 58 (1994) 17-30
vines and adjusting by the weight of fruit on the rest of the vine was satisfactory but about 25-30°/o of the information on mean fruit weight was lost, which would not be acceptable in research trials. Half vines are much better for field trials. Since significant differences occurred between north and south and east and west sides, it is definitely advisable to weigh the fruit on the ungraded half of the vine and adjust the quantitative yield variables. Some qualitative variables have shown significant differences between halves of vines, but these have been relatively consistent over treatments. For a typical New Zealand kiwifruit orchard which is on level ground with rows oriented in a north-south direction the best way to sample vines grown on T-bars consists of two diagonally opposite quarters. Failing this, either the north or south sides are recommended as the difference between the west and east sides is more likely to be a systematic physiological difference. For instance, in the 1985/1986 season there were high shelter belts on the east and west sides of the block and a systematic linear trend in the west-east differences from west to east across the block was observed. The actual differences in both the quantitative and qualitative variables on the north and south were almost always less than the east and west sides and any differences were relatively consistent over treatments. Adjusting by the fruit weight ratio for the whole and the graded part of vines was better than doing so by cordon length and appeared to counteract inconsistent differences between the graded and ungraded parts of the vine. Although adjusting was satisfactory, there are situations where vines are known to have systematic differences, for instance in north and south cordon lengths (Smith et al., 1993 ). Where this occurs it is safer for trial purposes to use pairs of vines in experimental plots with one of each type of vine in the plot. The yield performance data within and between vines are applicable to crop forecasting. For this purpose a bay which contains a different quarter of each of four female vines is a well defined unit. Differences in cordon length cancel out. From the above data it is estimated that sampling ten such bays to estimate fruit number per vine or percentage rejects would give the same information as that obtained by counting all the fruit on 24 vines. Reference Smith, G.S., Gravett, 1.M., Curtis, J.P. and Buwalda, J.G., 1994. Spatial analysis of the canopy of kiwifruit vines as it relates to the physical, chemical and post-harvest attributes of the fruit. Ann. Bot., 73:99-111.
.... E LS EV I E R
Scientia Horticulturae 58 (1994) 17-30
Evaluation of sampling methods for harvesting nontreated and hydrogen cyanamide treated kiwifruit vines R.F. Henzell*, I.M. Gravett, P.A. Allison The Horticulture and Food Research Institute of New Zealand Ltd., Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand (Accepted 14 January 1994)
Abstract From 1986 through to 1992 kiwifruit (Actinidia deliciosa cultivar 'Hayward') from vines in the Bay of Plenty district of New Zealand, trained on a T-bar trellis with an upper wire to support renewal shoots, were harvested from various sections of vines and graded separately. For any variable, the effectiveness of grading only part of a vine was measured by R 2, the proportion of the variation in the true whole vine value that was accounted for by the estimate from the part vine. Grading fruit from ten long canes on the western side or all of the fruit on quarter vines gave R 2 values of approximately 0.6. R 2 values varied from 0.7 to 0.85 for half vines. Grading diagonal quarters was slightly better than using the east or west sides which were in turn marginally better than grading the north or south sides. In all of these eases the estimate was improved greatly when the part harvested was adjusted upwards by a scaling factor of the fruit weight on the whole vine divided by the fruit weight on the part graded. On hydrogen cyanamide treated vines, the west side of vines performed significantly better than the east side. This meant that a grading procedure based on one of these sides alone would be biased and could result in up to 22% error for vines growing on T-bars. Grading either the north or south side alone and adjusting by the fruit weight ratio was more satisfactory as the differences in fruit size at harvest were smaller between the north and south sides than between the east and west sides. In trials involving consecutive hydrogen cyanarnide treatment of vines over five seasons, significant differences between the north and south sides of vines were observed in only one season but scaling by fruit weight overcame the problem. Keywords: Actinidia deliciosa; Harvest sampling; Hydrogen cyanamide; Kiwifruit vines; Yields *Corresponding author. 0304-4238/94/$07.00 © 1994EIsevierScienceB.V. All rights reserved SSD10304-4238 (94)00630-X
18
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
1. Introduction Field trials investigating the effects of numerous vine management practices on the productivity and economic performance of kiwifruit ( A c t i n i d i a deliciosa cultivar 'Hayward') vines have been carried out in a commercial T-bar orchard in the Bay of Plenty district of New Zealand since the 1985/1986 season. The Tbars in the trial block were modified with an upper wire to support renewal shoots. Each season the trials have involved several hundred vines which require a high labour input, particularly at harvest, when all the fruit are picked. Fruit from each vine, and frequently those from parts of each vine, have been graded separately. Between 5000 and 6000 trays of kiwifruit have been processed each season using a two-lane electronic grader in the orchard packhouse. One of the aims of this work was to assess if there were any systematic trends in cropping within vines. This necessitated picking fruit from different parts on the vine at harvest and grading the fruit separately. Since resource and time constraints at harvest do not always allow this detailed sampling on the whole vine, a secondary aim was to identify a section of the vine which could cover any systematic trends and provide satisfactory estimates of yield variables for the whole vine. The data showed how fruit size and distribution varied within the vine in terms of fruit number, mean fruit weight and number of export trays produced. The relationship between fruit number and growth in different parts of the vine also has important plant physiological implications as fruit size and dry matter can decrease in the lower extremities of the canopy (Smith et al., 1993 ). Furthermore, a knowledge of the variation in yield performance within and between vines is useful for crop forecasting purposes.
2. Material and methods Over the trial period, the number of long canes (over 1.5 m long) changed from 55 (initially) to 40 per vine. The number of short canes (from over 0.5 to 1.5 m long) varied between ten and 15 per vine, and up to 20 spurs (less than or equal to 0.5-m long canes) per vine were tied down in winter. Fruit on the vines were harvested and graded separately for different parts of the vines. These included ten random long canes along the western side and the remainder of the vines, each quarter separately, or the north and south or east and west halves of each vine. Two-vine experimental plots were used throughout. At grading the fruit weights used for each tray count varied throughout the trial period in accordance with New Zealand Kiwifruit Marketing Board standards. There are eight size counts (Table 1 ) associated with moulded plastic trays (plixes) containing cavities of appropriate size to give between 25 and 46 fruit per tray with a m i n i m u m fruit weight of 3.5 kg per tray. In the first three seasons the minimum individual fruit weight for export was 70 g with fruit allocated to
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
19
Table 1 Weight ranges used over the 1985-1992 trial period for different kiwifruit tray sizes Tray count size
Weights (g) used for the 1986 and 1987 harvests
Weights (g) used for the 1989 harvest
Weights (g) used for and after the 1992 harvest
25 27 30 33 36 39 42 46
134-144 123-133 111-122 101-110 93-100 86-92 79-85 70-78
148-165 127-147 117-126 105-116 98-104 89-97 78-88 70-77
148-179 127-147 117-126 105-116 98-104 89-97 78-88 74-77
trays based on a firm fit into the plix cavity. For the 1986 to 1989 harvests, trial fruit in the 30-39 size counts were preferred for export. In subsequent seasons the 25-39 size counts were included in the preferred export category.
2. I. Quantitative and qualitative yield variables The grading information from each vine included quantitative (directly assessed ) yield variables (fruit number, fruit weight, export weight, trays per vine ) and qualitative (calculated) variables ( mean fruit weight and percentages of fruit in categories such as 'rejects' and 'preferred export fruit'). Since total fruit num= bet and total fruit weight are highly correlated, the quantitative variables can estimate whole vine yield by weighing the fruit on the remainder of the vine. An alternative estimate used in 1991 / 1992 only involved measuring the cordon length of the north and south sides and grading the north half only. The qualitative yield variables were derived from the graded parts only, as they could not be estimated.
2.2. Statistical analysis The effectiveness of grading part of a vine was measured by R 2, the proportion of the variation in the whole vine data accounted for by the estimate from the part, where R is the correlation coefficient between the whole and the part. This estimate can be improved by weighing fruit on the remaining part of the vine and adjusting by a scaling factor. If Wp, Wr are the fruit weights on the part graded and the remainder of the vine, respectively, and Np and Nr are the corresponding fruit numbers, then the estimate of total fruit per vine is Np ( Wp + Wr) / Wp. This scaling factor ratio (rather than a regression estimate) was also used for the other quantitative yield variables. It assumes that the mean fruit weight is the same for the different parts of the vine. In practice there will be differences but these are hopefully random and not systematic or physiological. Some orchard cultural practices (such as interplanting pollinators ) can involve systematic differences between north and south cordon lengths. In this case an
20
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
additional scaling factor (the ratio of the total cordon length of the vine to the cordon length of half vine graded) was also taken into account. Differences (West minus East) and (North minus South) were analysed to determine whether there were overall differences between vine sides and if so, consistent differences between treatments. A consistent bias would mean that the absolute estimates would be biased, but treatment comparisons would not be affected. An interaction with treatments would be far more serious. A Genstat 5 statistical package (Rothamstead Experimental Station, UK) was used for the analysis of variance and regression. Although two-vine plots generally were used, the relationships were based on single vines. 2.3. Trials
The evaluation of sampling methods was mainly carried out in conjunction with the hydrogen eyanamlde trial, described below, which continued on the same block of vines from 1985/1986 for six consecutive seasons. This level block measured 52 m across by 177 m long and contained about 280 vines planted 5.5 m apart in nine rows which were 4.5 m apart. The rows were oriented in a northsouth direction and at the start of the trials the vines were about 15 years from graft. The block was well sheltered on all sides with poplar trees that were 20 m high in 1985/1986. The eastern and western shelters were removed during the following season in spring and autumn, respectively. The northern and southern shelters were about 30 m high by the sixth season. Over the trial period, the number of vines treated with hydrogen eyanamide in a season varied between 82 and 120. The number of untreated vines varied between 30 and 48. From the 1986/1987 season onwards, generally fruit on the northern half of the vines were graded and on the southern half weighed. 2.4. 1 9 8 5 / 1 9 8 6 season
Fruit were harvested and graded from three trial blocks. The first experiment involved 40 untreated vines and 90 vines treated with different rates of hydrogen cyanamide at different times (ten vines per treatment combination). Six of these combinations increased crop loads at harvest by at least 30%. Fruit were sampled on ten long canes on the western side of each vine along with the remainder of the western side and the eastern side. Fruit from each of these sections were graded separately. In the second ( 105 vines, irrigation trial) and third (24 vines, gel pruning trial) experiments, the vines were not treated with hydrogen cyanamide. Fruit from the west and east sides were sampled and graded separately. 2.5. 1986~1987season
In this season, fruit on both the north and south sides were graded separately on ten vines that were treated with hydrogen cyanamide in late July for two consecutive seasons.
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
21
2.6. 1988/1989 season Sampling method evaluation in this season was carried out on a different block and involved 20 hydrogen cyanamide treated vines located in two alternate middie rows. Comparable winter bud numbers were tied down on each quarter of the trial vines and the fruit from each quarter were graded separately.
2. 7. 1991/1992 season This trial consisted of 80 vines located in three alternate rows in the middle of a block treated with hydrogen cyanamide. The block was the same as that used in the 1988/1989 trials, but the male vine layout had been modified. The three rows contained mature female vines 5.5 m apart with 1 m long male vines planted at 11-m intervals midway between the pairs of female vines. The cordons on female vines on either side of the male vines were pruned by about 0.5 m to accommodate the young male vine interplants. Crop loads were adjusted from the estimated flower numbers on whole vines at a few weeks before fruit set. Fruit on the northern side of each vine were harvested and graded while fruit on the southern side were weighed and counted.
3. Results and discussion
3.1. Efficiency of different sampling procedures In the first season of this study (1985/1986), the effect on vine phenology of the chemical treatment on canes in winter was determined by monitoring ten long canes on the western side of the vines throughout the season. These canes carded about one sixth of the total vine yield. At harvest fruit on these canes were combined and graded to determine if they were representative of fruit on the western side, or of the vine as a whole. Grading fruit on the ten long canes provided R e values of 0.59-0.67 for the quantitative yield variables for the whole vine and adjusting by fruit weight improved this to 0.84-0.98 (Table 2). Similarly, grading fruit on either the western or eastern sides alone gave R 2ffi0.80-0.91 for the quantitative variables and adjusting by fruit weight again gave a further improvement (R2ffi 0.96-0.99). The mean fruit weight based on the ten long canes gave R 2 - 0 . 8 6 and half-vine sampling improved this to 0.95-0.96. Figures 1 and 2 indicate the accuracy of predicting the numbers of trays per vine and mean fruit weight at harvest when based on sampling ten long canes, the east or west sides alone or after adjusting by the fruit weight on the remaining part of the vine. Each vine was partitioned and graded separately again in 1988/1989. In this season each quarter was graded and these were considered separately and in north/ south, east/west and diagonal combinations (Table 3). Sampling quarters alone
22
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
Table 2 Percentage harvest variation ( 100XR 2 values) on the whole vine accounted for by grading fruit on ten long canes (western side) or western and eastern sides alone and adjusted by the fruit weight ratio on the whole and graded part of the vine. Based on sampling 130 single vines grown on T-bars, 19851986 season Vine part sampled
Information (%) for variables Fruit per vine
Fruit weight per vine (k8)
Prof. export weight per vine
Trays per vine
Mean fruit weight (g)
Rejects (%)
67 90 89 97 80 97
86
82
96
94
95
93
(kg) Ten long canes Ten long canes, adjusted West West, adjusted East East, adjusted
62 98 91 99 90 99
59 100 88 100 85 100
67 84 90 96 82 96
gave results similar to those obtained using ten long canes. The results for the east and west halves were similar to those obtained in the 1985/1986 season. Sampling the north or south sides was inferior (R 2= 0.72 for fruit number) to sampling the east or west, and the diagonals gave the best results ( R 2 - - 0 . 8 8 ) . Adjusting by the fruit weight ratio reduced these differences and increased the R 2 values to a satisfactory level for almost all variables. Sampling half vines rather than quarters also improved the R 2 values for the qualitative variables. Sampling half or even quarter vines therefore gave more than half the information for the whole vine, which meant there was a positive correlation between parts of the vine. By contrast, in the 1991/1992 season sampling half the vine gave less than half the R 2 values (0.33-0.46 on fruit number) (Table 4). This was due to the male vine layout in the block which was different from that in the other trial blocks. Young male vines were interplanted between sets of two mature female vines down the rows. The cordon lengths of both female vines were shortened to accommodate the male vine. This meant that although the total cordon length of the female vines remained approximately equal, if the north cordon was long, then the south one tended to be short and vice versa, i.e. north and south cordon lengths were negatively correlated. This introduced negative correlations into total fruit number and total weight but not mean fruit weight. Scaling or using both vines in the plot could be used to overcome this systematic error. Adjusting by cordon length for single vines increased the R 2 o n total number from 0.46 to 0.57 for the north side and from 0.33 to 0.58 for the south side. Adjusting by fruit weight was better (0.97 for the north and south sides) (Table 4). Averaging data from the pairs of vines in plots gave R2=0.61 for the fruit number from half vines and adjusting by cordon length increased this slightly (0.64-0.71). The mean fruit weight results were consistent with half-vine sampling in previous trials and improved slightly by taking pairs of vines.
R.F. Henzell et al. I Scientia Horticulturae 58 (1994) 17-30 10 Canes x 6
10 C a n e s
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Fig. 1. Relationship between the predicted and actual number of trays per vine based on samplin8 ten western canes, the eastern or western sides of vines during the 1985/1986 season. Predictions are based on either the proportion of vine graded or scaled by the ratio of fruit weight on the whole vine to the weight on the graded part of the vine.
60
24
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30 10 Canes
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Fig. 2. Relationship between the predicted and actual mean fruit weight (g) based on sampling ten western canes or the eastern or western sides of vines during the 1985/1986 season.
R.F. Henzell et al. /Scientia Horticulturae 58 (1994) 17-30
25
Table 3 Percent harvest variation on the whole vine accounted for by grading quarter and half the vine alone and adjusted by the fruit weight ratio on the whole and graded part of the vine. Based on 20 single vines on T-bars and treated with hydrogen cyanamide, 1988/1989 season Fraction of vine
Mean of vine part sampled
Information (%) for variables Fruit per vine
Fruit weight (kg)
Pref. export weight (kg)
Trays per vine
Mean fruit weight
Rejects (%)
(g) Quarter Quarter Half Half Half Half Half Half
NE, NW, SE, SW NE, NW, SE, SW adjusted N, S N, S adjusted E, W E, W adjusted Diagonal Diagonal adjusted
60
57
63
59
97 72 99 84 99 88 99
100 68 100 85 100 88 100
76 71 82 90 91 92 93
90 67 95 90 97 91 97
74
58
85
68
91
85
93
88
Table 4 Percent harvest variation ( 100 × R 2) on the whole vine accounted for by counting and weighing fruit on the north or south half of the vine and adjusting either by the fruit weight or cordon length ratio on the whole and graded vine half. The estimates were based on 80 single vines on T-bars or 40 twovine plots treated with hydrogen cyanamide in the 1991/1992 season Vine half sampled
North North, adjusted (vet) North, adjusted (cordon) South South, adjusted (wt) South, adjusted (cordon)
Fruit per vine
Fruit weight per vine (kg)
Mean fruit weight (g)
Single vines
Two-vine plots
Single vines
Two-vine plots
Single vines
Two-vine plots
46 97 57 33 97 58
61 97 64 61 97 71
46 100 59 38 100 64
68 100 72 64 100 73
83
86
86
90
3.2. Systematic differences within vines In sampling vines at harvest for yield parameters the aim was to have a method which was an efficient estimator of both quantitative and qualitative variables. Since the latter are based entirely on the part of the vine graded, ideally there should be no bias between the graded and ungraded parts. Ifa slight bias is found, then this should be consistent over all treatments for comparative purposes. In the 1985/1986 season there was little difference between the yield variables for the east and west sides for the untreated vines, but there were large differences
26
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
for vines treated with hydrogen cyanamidc in lateJuly or mid-August (Tables 5 and 6). This inconsistency indicated that ifonly the east or west side was graded to estimate yield parameters for the whole vine then large errors could occur for hydrogen cyanamidc treated vines. For the mid-August treatment the correct result would have been under- or overestimated by 2.I trays per vine, and for the late July treatment the estimates would have been out by 3.2 trays per vine, or a difference of 6.4 trays between the cast and west estimates.This is about a 22% error, as treated vines on average carded about 29 trays per vine. These differcnccs were reduced greatlyby adjusting with the fruitweight ratio on the whole and graded part of the vine (Table 6). The sensitivityof the analysis of variance to differentiatebetween treatment means was not affectedby this adjustment (Table 7). For example, the F ratios based on the adjusted data for the various parts of vine sampled approximated Table 5 Harvest variable differences between the western and eastern sides of vines grown on T-bars ( 1985/ 1986 season). Means of 40 untreated vines and ten vines treated with hydrogen cyanarnide applied in late July or mid-August Variable (per half vine)
West minus east sides
Fruit number Fruit weight (kg) Preferred weight (kg) Number of trays Mean fruit weight (g) Rejects (%)
LSD* Untr. vs. other
Untreated
Late July
Mid-August
- 23 -0.95 - 0.17 0.03 1.03 0.10
128 I 1.67 8.73 3.05 2.68 - 1.55
129 9.73 3.78 1.73 0.03 0.01
106 7.8 4.80 1.65 6.80 2.62
*Least significant difference at P < 0.05. Table 6 The actual treatment means and the means obtained from grading the west or east sides alone and the means derived from adjusting by the fruit weight ratio on the whole and graded part of the vine. The vines were or were not treated with 3% hydrogen cyanamide in late July or mid-August 1985
Vine part sampled
Total (actual) East × 2 East adjusted West ×2 West adjusted Long canes adjusted
Preferred export weight (kg per vine)
Trays per vine
Control
Late July
MidAugust
Control
Late July
MidAugust
42.1 42.3 41.8 41.9 42.3 42.3
83.2 74.1 82.8 92.4 83.7 78.8
76.0 71.4 78.2 80.6 74.2 73.9
15.6 15.6 15.4 15.6 15.8 15.6
29.2 26.0 28.9 32.4 29.5 28.4
27.6 25.5 27.9 29.6 27.2 27.1
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
27
Table 7 F-ratios from the Anova, CVs and selected treatment means for trays per vine data for the whole vine, individual parts and those parts adjusted up by the fruit weight ratio on the whole and graded part at harvest on untreated vines and vines treated with3% hydrogen cyanamide in late July or mid-August 1985 Statistical terms
Source of variation
Vine part sampled Total
F ratios
Control vs. treated Chemical rate Time of application Rate×time
CVs Treatment means
Control 3% late July 3% mid-Aug
East
West
Ten West canes
Alone
Adjusted
Alone
Adjusted
Alone
Adjusted
40.0 42.9
29.0 29.6
45.2 43.4
30.3 33.8
30.6 38.0
28.9 38.8
20.6 43.0
1.9 2.3
1.3 1.2
2.4 2.6
3.0 2.6
1.4 1.8
1.9 1.3
1.5 2.1
22.9
24.0
22.5
28.9
24.7
34.9
26.1
15.6 29.2 27.6
15.6 26.0 25.5
15.4 28.9 27.9
15.6 32.4 29.7
15.8 29.5 27.2
15.6 28.4 27.1
reasonably closely those for the whole vine, and would not have affected the interpretation of treatment effects. The data in Table 5 also show that even though both hydrogen cyanamide treatments had the same crop load difference, the vines treated in late July performed much better in that bigger fruit and more trays were obtained at harvest on the western side. This shows that fruit growth rate was different on different sides of the vine. There was no systematic linear trend from west to east across the block for the west side of vines, but there was a significant trend in the difference between the west and east sides for most variables (R=0.4 for trays per vine; R=0.46 for preferred trays per vine). This difference increased from west to east across the block ( P < 0.01 ). The favoured growth of the western side was only observed on vines treated with effective hydrogen cyanamide rates. For example, in the same 1985/1986 season, fruit on the west and cast sides of 105 nonhydrogen cyanamide treated vines were graded separately and no difference in fruit growth was apparent between the two sides of these vines. Because the differences between the east and west sides were not consistent over all treatments during the first season of the trials, the yield variables on the north and south halves also were compared in subsequent seasons. In 1986/1987, the north and south sides were graded separately on ten hydrogen cyanamide treated vines. The north side had 283 extra fruit and this led to the expected increase in the quantitative but not the qualitative harvest variables (Table 8 ). The north-south difference may have been due to a difference in cordon length between the vine halves, which were not measured in this season.
28
R.F. Henzell et al. / Scientia Horticulturae 58 (1994) 17-30
Table 8 Harvest variable differences between the north and south sides often vines on T-bars and treated with hydrogen cyanamide in late July 1986 Variable (per half vine )
North
South
North minus south
LSD
Fruit number Fruit weight (kg) Preferred export weight (kg) Number of trays Mean fruit weight (g) Rejects (%)
990 93.4 59.0 23.7 94.5 13.2
707 66.9 42.4 16.7 95.6 12.2
283 26.5 16.6 7.0 - 1.1 1.0
19.8 17.7 11.9 4.6 4.8 2.3
Table 9 Harvest variable differrences between means of north and south and west and east sides of 20 vines trained on T-bars and treated with hydrogen cyanamide in the 1988/1989 season Variable
Fruit number Fruit weight (kg) Preferred export wt (kg) Number of trays Mean fruit wt (g) Reject (%)
Variable differences between North minus south
LSD*
West minus east
LSD*
45.25 3.08 0.22 0.65 -2.11 1.37
76.90 6.09 2.88 1.39 4.03 8.36
51.85 5.18 2.97 1.31 4.73 -7.26
53.91 3.78 1.39 0.67 3.09 6.72
*Least significant difference at P< 0.05. Table I 0 Harvest variable differences between means of the north and south sides of 80 vines on T-bars. Vines were treated with hydogen cyanamide in the 1991/ 1992 season Variable per half vine
North
South
North minus south
LSD
Fruit number Fruit weight (kg) Mean fruit weight (g)
396 40.2 102.2
379 39.4 104.2
17 0.8 -2.0
50.0 5.1 1.69
Grading fruit on the east and west sides of vines was carried out for a second time during the 1988/1989 season. Significant differences and sampling bias again were apparent (Table 9 ). The north-south differences in the yield variables were lower than the west-east differences, but the latter had lower variances. This suggests that the west-east differences were due to physiological factors and the northsouth differences were due to random difference in cordon lengths. In contrast to the trial in 1986/1987, there was no significant north-south difference for any of the yield variables. The 1991 / 1992 results (Table 10 ) showed a significant but
29
R.F. Henzell et al. /Scientia Horticulturae 58 (I 994) 17-30
Table 11 Differences between north and south crop weights on non-treated and 3% hydrogen cyanamide treated vines over five seasons. The two mid-August treatments involved different spray volumes, pollination, crop load and pruning methods
Season
No. vines sampled
North minus south fruit weight (kg)
Untreated
Untreated
Treated
Late July
MidAugust (1)
MidAugust (2)
40 24 40 40
40 24 40 10
1986/1987 1987/1988 1988/1989 1989/1990 1990/1991
40 48 40 40 30
10 34 40 40 90
1986/1987
LSD
Late July vs. others Mid-August (1,2) vs. untreated
1987/1988
LSD
Late July vs. others Mid-August ( 1,2 ) vs. untreated
1988/1989 1989/1990
LSD LSD
1990/1991
LSD
Mid-August ( 1) vs. untreated Mid-August (2) vs. untreated
7.0 0.0 4.5 6.2 6.7
Treated
Late July
MidAugust (1)
MidAugust (2)
26.0 14.2 3.3 3.3 10.0
-0.3 31.8 2.7 8.5
8.5 12.0 6.4 15.6
14.6 9.2 11.6 10.6 5.3 7.4 14.0 9.4
small north-south difference in mean fruitweight. This difference was consistent over all treatments, which allowed valid comparisons to be made between them and with only a slighterror in the absolute estimates for the harvest variables. Crop weight differences between the north and south halves of vines on the same block of vines involved in hydrogen cyanamidc trialsover five consecutive seasons arc summarised in Table I I. Inconsistent results over treatments were observed in 1987/1988, but in the four other seasons there was no difference between the north and south apart from the late July treatment in 1985/1986 which involvcd ten vines. Adjusting for the weight of fruiton the remaining part of the vine overcame these problems.
4. Conclusions
A n efficientsampling method to determine yield parameters on kiwifruit vines at harvest should be on a clearly identifiable part of the vine and accommodate most of the known systematic sources of variation in fruit size. These include fruit weight differences along a cane and along the cordon, and fruitdensity differences within the canopy. Sampling quarter or half vines would appear to meet these criteria.The main drawback in any sampling procedure is inconsistent diffcrcnces in qualitative variables, as these cannot bc adjusted. Sampling quarter
30
R.F. Henzell et aL / Scientia Horticulturae 58 (1994) 17-30
vines and adjusting by the weight of fruit on the rest of the vine was satisfactory but about 25-30°/o of the information on mean fruit weight was lost, which would not be acceptable in research trials. Half vines are much better for field trials. Since significant differences occurred between north and south and east and west sides, it is definitely advisable to weigh the fruit on the ungraded half of the vine and adjust the quantitative yield variables. Some qualitative variables have shown significant differences between halves of vines, but these have been relatively consistent over treatments. For a typical New Zealand kiwifruit orchard which is on level ground with rows oriented in a north-south direction the best way to sample vines grown on T-bars consists of two diagonally opposite quarters. Failing this, either the north or south sides are recommended as the difference between the west and east sides is more likely to be a systematic physiological difference. For instance, in the 1985/1986 season there were high shelter belts on the east and west sides of the block and a systematic linear trend in the west-east differences from west to east across the block was observed. The actual differences in both the quantitative and qualitative variables on the north and south were almost always less than the east and west sides and any differences were relatively consistent over treatments. Adjusting by the fruit weight ratio for the whole and the graded part of vines was better than doing so by cordon length and appeared to counteract inconsistent differences between the graded and ungraded parts of the vine. Although adjusting was satisfactory, there are situations where vines are known to have systematic differences, for instance in north and south cordon lengths (Smith et al., 1993 ). Where this occurs it is safer for trial purposes to use pairs of vines in experimental plots with one of each type of vine in the plot. The yield performance data within and between vines are applicable to crop forecasting. For this purpose a bay which contains a different quarter of each of four female vines is a well defined unit. Differences in cordon length cancel out. From the above data it is estimated that sampling ten such bays to estimate fruit number per vine or percentage rejects would give the same information as that obtained by counting all the fruit on 24 vines. Reference Smith, G.S., Gravett, 1.M., Curtis, J.P. and Buwalda, J.G., 1994. Spatial analysis of the canopy of kiwifruit vines as it relates to the physical, chemical and post-harvest attributes of the fruit. Ann. Bot., 73:99-111.