Yield and tenderometer reading relationships for
smooth- and wrinkled-seeded processing pea cultivars
A.P. Everaarts
*, W. Sukkel
Applied Research for Arable Farming and Field Production of Vegetables, PO Box 430, 8200 AK Lelystad, Netherlands
Accepted 1 December 1999
Abstract
An analysis was made of the relationship between yield and tenderometer readings of smooth-and wrinkled-seeded types of pea (Pisum sativumL.) cultivars. The analysis involved 13 smooth-seeded cultivars and 31 wrinkled-smooth-seeded cultivars in 16 cultivar trials that were carried out at two locations during ®ve seasons with varying sowing periods. The results showed that for the two types of cultivars a distinction could be made in the relationship between yield and tenderometer readings in the relevant range for processing (90±150). At tenderometer readings lower than 120 the relative yield of wrinkled-seeded cultivars is higher than that of the smooth-seeded types, while at tenderometer readings above 120, the relative yield is lower. Consequences for a sliding price scale are indicated.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Peas;Pisum sativum; Yield; Relative yield; Tenderometer readings; Wrinkled-seeded cultivars; Smooth-seeded cultivars
1. Introduction
During the harvest period of peas (Pisum sativum L.) for processing, yield increases while tenderness decreases. The aim is to harvest at an optimum tenderness for processing. As it is not the grower who decides the moment of harvesting, but the processing company, the processing companies pay the growers according to a sliding scale. At a lower than optimum tenderness a higher
*
Corresponding author. Tel.:31-320-291-111; fax:31-320-230-479.
E-mail address: [email protected] (A.P. Everaarts)
price is paid, while at a higher than optimum tenderness a lower price is paid. The sliding price is based on the relationship between yield and tenderness. Tenderness is determined with a tenderometer, an instrument which measures the force needed to shear and press a sample of peas through a standard grid. The less tender a sample, the higher the required force. The relation between yield and tenderometer reading is usually a curvilinear one, in which the increase in yield per unit increase in tenderometer reading decreases with increasing tenderometer readings. In the past, several examples of such a relationship have been published (Hagedorn et al., 1955; Ottosson, 1958; Berry, 1965; Anderson and White, 1974; Pumphrey et al., 1975). In the Netherlands a general sliding price scale for peas was proposed and accepted in 1982 (Neuvel, 1992). Recent questions from growers about the validity of this scale for wrinkled-seeded cultivars and the availability of data on yield and tenderometer readings of both smooth- and wrinkled-seeded cultivars from cultivar trials prompted an evaluation of the relationship between yield and tenderometer readings of peas. The present paper describes the relationship between yield and tenderometer readings for smooth-and wrinkled-seeded cultivars.
2. Materials and methods
Sixteen cultivar trials with peas were carried out from 1990 to 1994 at two locations, Lelystad and Westmaas, the Netherlands, with three sowing periods (Table 1). Experiments were laid out as randomized complete block designs with two or three replicates and three to six harvests. Towards maturity the crop was sampled to measure the tenderness of the peas with the aim of having the ®rst harvest at a tenderometer reading between 90 and 100. At each harvest the net yield and the tenderometer reading of the ungraded product were determined. Fertiliser application, weed, pest and disease control in the trials were according to commercial practice.
A total of 31 observations (that is, the number of times a type of cultivar was evaluated in the trials) on smooth-seeded cultivars and 114 observations on wrinkled-seeded cultivars were used in the present study (Table 2). The observations involved 13 smooth-seeded cultivars and 31 wrinkled-seeded cultivars. The smooth-seeded cultivars were mostly in the early sowing period, the wrinkled-seeded cultivars were better represented in the later sowing periods, as is the case in practice.
Table 1
The sowing dates and the number of cultivars (in italics) at each sowing date at two locations (Lelystad, Westmaas) and the sowing periods, Early, Medium and Late
Year Lelystad Westmaas
Early Medium Late Early Medium Late
1990 March 20 15 ± May 16 4 ± ± May 21 5
1991 March 28 10 ± May 15/17 8 April 3 10 ± May 14 7
1992 ± April 23 20 ± ± April 23 10 May 19 10
1993 March 19 6 ± May 17 9 March 17 6 ± May 14 9
1994 ± April 21 8 ± ± May 4 8 ±
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harvest and the relation between tenderometer reading and number of days after the ®rst harvest was described with a quadratic relationship of the type:
yabxgx2 (1)
where y is the yield or tenderometer reading and x is the days after the ®rst harvest. The relation between yield and tenderometer reading was described with a similar equation. The type of cultivar, smooth- or wrinkled-seeded, was taken as a ®xed term by estimating a, b, and g for each type of cultivar after residual maximum likelihood (REML) analysis to account for the unequal number of observations for smooth- and wrinkled-seeded cultivars. The signi®cance of the difference between both type of cultivars for the estimates ofa,bandgwas tested with a Wald test.
An analysis of variance on b and g for the relationship between yield and tenderometer reading for the wrinkled-seeded cultivars in each experiment (Table 1) showed no signi®cant difference between sowing periods (data not shown). No such analysis was carried out for the smooth-seeded cultivars because of the limited number of observations in the medium and late sowing periods (Table 2).
3. Results and discussion
The wrinkled-seeded cultivars in the experiments had higher yields (Fig. 1). Although the slopes of the yield±time response curves for both cultivars were not statistically signi®cantly different (Table 3), the wrinkled-seeded cultivars never-theless showed a faster decrease in the rate of yield increase during the harvest period (Fig. 2). Tenderometer readings for both type of cultivars increased during the harvest period (Fig. 3), but only the level of the response curves for both type of cultivars differed signi®cantly (Table 3). In terms of tenderometer reading, the smooth-seeded cultivars thus were slightly earlier during the harvest period.
The relationships between yield and tenderometer readings differed signi®-cantly for the two types of cultivars (Table 3). At tenderometer reading 90, at the beginning of the relevant range (90±150) of tenderometer readings for processing (Neuvel, 1992), the yield of the wrinkled-seeded cultivars was higher as
Table 2
The number of observations for smooth-seeded and wrinkled-seeded cultivars in the three sowing periods
Sowing period
Early Medium Late
Smooth-seeded 22 8 1
Wrinkled-seeded 25 38 51
Fig. 1. The calculated yield of the smooth- and the wrinkled-seeded cultivars in the harvest period.
Table 3
Estimates fora,bandgfor the relationships (Eq. (1)) between yield and days after the ®rst harvest (DAFH), tenderometer reading (TR) and DAFH, and yield and TR and the signi®cance of the difference between the smooth- and wrinkled-seeded type of cultivars
Relationship Cultivar type a b g
Yield±DAFH Smooth 3.855 0.6176 ÿ0.01791
Wrinkled 5.286 0.6613 ÿ0.02893 Significance p<0.001 n.s. n.s. TR±DAFH Smooth 102.80 9.834 ÿ0.1616
Wrinkled 93.97 10.070 ÿ0.1506 Significance p0.05 n.s. n.s. Yield±TR Smooth ÿ12.70 0.2410 ÿ0.0007534
Wrinkled ÿ8.39 0.2114 ÿ0.0006864
Significance p<0.00l p<0.001 n.s.
compared to the smooth-seeded ones (Fig. 4). The increase in yield with an increase in tenderometer reading of the wrinkled-seeded cultivars, however, was less than that of the smooth-seeded cultivars.
This is more clearly expressed in the relative yield when the yield at tenderometer reading 120 is put at 100% (Neuvel, 1992) (Table 4). The relative yields for the smooth-seeded cultivars compare well with the relative yields previously established in 1982 (Neuvel, 1992). The relative yields of the wrinkled-seeded cultivars at tenderometer readings lower than 120, however, are higher as compared to those of the smooth-seeded cultivars, while at
Fig. 3. The calculated tenderometer readings (TR) of the smooth- and the wrinkled-seeded cultivars in the harvest period.
Fig. 4. The relation between the yield and the tenderometer readings (TR) of the smooth- and the wrinkled-seeded cultivars.
Table 4
Relative yield (TR 120100%) at different tenderometer readings (TR) according to the 1982 scale (Neuvel, 1992) and according to the present results for the smooth- and wrinkled-seeded cultivars
TR ungraded product
90 100 110 120 130 140 150
1982 scale 50 70 86 100 110 117 123
Present results
Smooth-seeded 54 72 87 100 110 117 121 Wrinkled-seeded 72 83 92 100 106 109 111
tenderometer readings above 120, they are lower. This difference in the relation between tenderometer reading and relative yield is likewise expressed in the sliding price scale (Table 5). With this scale the product price the farmer receives is put at 100% for tenderometer reading 120. The price at tenderometer readings lower than 120 is higher than 100% of that at tenderometer reading 120 to compensate for the lower yields when harvesting takes place at tenderometer readings below 120. At tenderometer readings above 120 the price is less than 100% of that at tenderometer reading 120, because of the higher yields. The results of the present study now show that at tenderometer readings below 120, the relative price for wrinkled-seeded cultivars should be lower than that for the smooth-seeded ones. While at tenderometer readings above 120, the relative price for wrinkled-seeded cultivars should be higher than that for the smooth-seeded ones. Ottosson (1958) has already drawn attention to differences in maturation pattern between one smooth-seeded and three wrinkled-seeded cultivars. Berry (1965) stated that his model of the relation between yield and tenderometer readings would be suited for the wrinkled-seeded cultivars, but no conclusion on its suitability for the smooth-seeded cultivars could be reached because of lack of testing on such cultivars. No reference was found to a study involving an appreciable number of both types of cultivars. The present investigation, considering 13 smooth-seeded and 31 wrinkled-seeded cultivars studied in 16 trials during ®ve seasons, shows that it is justi®ed to distinguish in the relationship between yield and tenderometer readings for the smooth- and wrinkled-seeded cultivars. Accordingly, separate sliding price scales should be used for the two types of cultivars.
Acknowledgements
We thank W. Van Den Berg (PAV, Lelystad) for statistical assistance and Dr. C. Knott (PGRO, Thornhaugh) and C.L.M. De Visser (PAV, Lelystad) for reading the manuscript.
Table 5
Relative price (TR 120100%) at different tenderometer readings (TR) according to the 1982 scale (Neuvel, 1992) and according to the present results for the smooth- and wrinkled-seeded cultivars
TR ungraded product
90 100 110 120 130 140 150 1982 scale 200 143 116 100 91 85 81
Present results
References
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