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Agronomy Journal 92:152-159 (2000)
© 2000 American Society of Agronomy

FIELD-GROWN TOMATO

Growth and Canopy Characteristics of Field-Grown Tomato

Johannes Scholberga, Brian L. McNeala, James W. Jonesb, Kenneth J. Bootec, Craig D. Stanleyd and Thomas A. Obrezae

a Soil and Water Science Dep., Univ. of Florida, Gainesville, FL 32611-0510 USA
b Agric. & Biol. Engineering Dep., Univ. of Florida, Gainesville, FL 32611-0570 USA
c Agronomy Dep., Univ. of Florida, Gainesville, FL 32611-0500 USA
d Gulf Coast Res. & Educ. Center, 5007 60 St. E, Bradenton, FL 34203-9324 USA
e Southwest Florida Res. & Educ. Center, PO Box 5127, Immokalee, FL 33934-9716 USA

blm{at}gnv.ifas.ufl.edu


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
Although detailed growth studies and yield analysis are common for agronomic crops, their application to horticultural crops is limited. Detailed growth measurements of field-grown tomato (Lycopersicon esculentum Mill.) were conducted at four Florida locations for two irrigation methods. Maximum rate of main-stem node development was {approx}0.5 nodes d-1 and leaf area index (LAI) increased exponentially with main-stem node number. Maximum LAI was attained 11 wk after transplanting, with values ranging from 1.5 to 3.0 and from 3.2 to 6.0 for drip-irrigated and subirrigated crops, respectively. Lower LAI values with drip irrigation were only partially related to wider row spacings. Final biomass (dry weight) ranged from 6 to 12 Mg ha-1 and fruit dry weight harvest indices (fruit biomass/total above-ground biomass) ranged from 0.53 to 0.71. Average dry matter accumulation by roots, stems, and leaves accounted for {approx}3, 23, and 17% of final biomass, respectively. Estimated radiation use efficiency (RUE) for tomato averaged 1.05 g dry weight MJ-1 m-2, with 50 to 60% light interception in the crop production area at LAI values of 4 to 5. At 11000 plants per ha, the rate of dry matter accumulation averaged 17.8 g d-1 m-2 during the linear growth phase, with instantaneous dry matter partitioning to fruits averaging 0.70 during the fruit-growth phase. Relationships between degree days, estimated cumulative intercepted radiation, and fruit yield accounted for much of the variation in fruit yields for these different seasons and locations throughout Florida.

Abbreviations: HI, harvest index • LAI, leaf area index • RUE, radiation use efficiency • °Cd, degree day


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
TOMATO is one of the world's most important vegetable crops, with a worldwide fresh-weight production of 80 million Mg and a total cropped area of {approx}3 million ha (Food and Agricultural Organization, 1995). In Florida, 23000 ha of tomato are grown annually, with a total yield of 730 x 103 Mg and a crop value of $460 million (Florida Agricultural Statistics Service, 1996). The crop is typically grown on shallow watertable (flatwoods) sites, using raised plastic-mulched production beds along with large quantities of water and fertilizer. The most commonly used irrigation systems are drip and subsurface (seepage) irrigation, with commercial growers typically applying N fertilizer in amounts of {approx}300 to 400 kg N ha-1 (McNeal et al., 1995).

Growth characteristics of tomato are governed by genetic traits and management practices (McNeal et al., 1995; Rick, 1978). For field production in Florida the use of containerized transplants is common. Transplants are typically 5 wk old, having 3 to 5 leaf-bearing nodes, an initial leaf area of 15 to 40 cm2, and a dry weight of 0.20 to 0.30 g plant-1 (Scholberg, 1996). Most of the production areas in Florida are planted with semi-determinate cultivars, in most cases axillary shoots formed below the first fruit cluster are removed a few weeks into the growing season, and plants are typically staked (Olson, 1989). Approximately 4 wk after transplanting, plants are tied with nylon string at a height of 25 to 30 cm. Additional strings are then placed periodically at 25 to 30 cm intervals, constraining the canopy to a width of 90 to 120 cm. Average marketable fruit yields are {approx}40 Mg ha-1 fresh weight but, under optimal conditions, yields in excess of 100 Mg ha-1 may be possible (Scholberg, 1996). Although existing knowledge on the effects of growth factors on fruit yield of field-grown tomato is appreciable (Bar-Yosef et al., 1980; Locascio et al., 1992; Marlowe et al., 1983), detailed studies of crop and canopy characteristics appear to be lacking. Teasdale and Abdul-Baki (1997) outlined some growth characteristics of field-grown tomato for one location and season, but more detailed studies of crop and canopy characteristics are required to define general trends across seasons and locations, particularly in support of modeling approaches for field-grown tomato. Our current understanding of growth characteristics for field-grown tomato appears to lag behind comparable knowledge for several other crops.

The research presented here outlines the general growth characteristics of field-grown tomato in Florida across locations and seasons for two irrigation systems (subirrigation and drip irrigation) under near-optimal conditions. Since observed plant growth appeared to be affected by irrigation mode, separate growth analyses are presented for the two types of irrigation systems. It was hypothesized that, due to potential differences in water and nutrient management, actual plant growth might be different for these two irrigation systems.


   Materials and methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results and discussion
 Conclusions
 REFERENCES
 
Experiments with subirrigated tomato cultivar `Sunny' were initiated during the spring of 1991 at the Gulf Coast Research and Education Center in Bradenton, FL and were repeated during the spring growing seasons of 1992, 1994, and 1995. Additional experiments using drip irrigation and cultivar `Agriset 761' were conducted at the Southwest Florida Research and Education Center in Immokalee and at the North Florida Research and Education Center in Quincy during the spring season of 1995 and at the Univ. of Florida Horticultural Unit in Gainesville during the 1996 spring season. Row spacings were 1.37 m (Bradenton 1991), 1.52 m (Bradenton 1992–1995), and 1.83 m for the drip-irrigated crops. Planting dates were mid-January for Immokalee, late February to mid-March for Bradenton, and mid- through late-March for Gainesville and Quincy. Planting densities ranged between 9000 and 12000 plants ha-1.

At Bradenton, a subirrigation (fully enclosed seepage) system (Stanley and Clark, 1995) was used with the watertable maintained at a depth of {approx}45 cm. All of the fertilizer was applied preplant in two surface bands located 15 to 20 cm to either side of the tomato row. With drip irrigation, 20% (Immokalee) and 40% (Gainesville) to 100% (Quincy) of the fertilizer was broadcast preplant. The remaining fertilizer was applied periodically with the irrigation water (i.e., via fertigation). Water supply for the drip-irrigated crops was based on crop evapotranspiration estimates and/or on readings from tensiometers placed in the production beds. Schematic overviews of the drip-irrigated and subirrigated production systems are presented in Fig. 1 .



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  		Fig. 1 Schematics of a typical drip irrigation system and a fully enclosed seepage irrigation (subirrigation) system in Florida

 
Weather data were collected daily from on-site stations (Bradenton, Immokalee, and Quincy) or from a nearby weather station (Gainesville). Average seasonal maximum daily temperature values ranged from 25.7°C (Immokalee) to 30.3°C (Gainesville), with corresponding average seasonal minimum daily temperature values ranging from 13.5°C (Immokalee) to 19.3°C (Bradenton 1991). Average seasonal total radiation values ranged from 18.4 to 22.0 MJ m-2 d-1. Soils at Bradenton and Immokalee were mapped as Eaugallie fine sand (sandy, siliceous, hyperthermic Alfic Alaquods) and Myakka fine sand (sandy, siliceous, hyperthermic Aeric Alaquods), respectively. Soils at Gainesville and Quincy were mapped as Millhopper fine sand (loamy, siliceous, hyperthermic Grossarenic Paleudults) and Orangeburg loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults), respectively.

At Bradenton, representative plants from the guard rows of subirrigated tomato were sampled every other week during the 1991 and 1992 growing seasons. A total of four plants were sampled destructively on each sampling date. After selection, plant height and canopy width were recorded and, subsequently, plants were severed at the bed surface. Main-stem nodes, branches, leaves, and flower clusters were counted before measuring total fresh weights of leaves (leaf blades plus petioles), stems, and fruits. A representative leaf subsample ({approx}100 g) was taken, leaf blades were separated from petioles, and blades were run through a leaf-area meter to calculate LAI. Subsamples of petioles, leaf blades, stems, and fruits were dried at 65°C prior to grinding and dry weight determinations. During the 1991, 1992, and 1995 growing seasons root measurements were taken, either early in the season by excavating plants to a soil depth of 30 cm using a spade or by washing all of the soil away from roots in bulk samples taken from prescribed sections of the production bed.

During the 1994 and 1995 growing seasons at Bradenton, plants were obtained from fertilizer-trial research plots with two or three representative plants, respectively, being sampled per fertilizer treatment. Atypical plants, plants near previously sampled plants, or plants planted later to fill gaps were not sampled. Sampling procedures for drip-irrigated crops were the same as those outlined above, except that two plants were sampled at Gainesville (1996) and three at Immokalee (1995) and Quincy (1995). Sampling intervals varied from 2 wk (Immokalee 1995) or 3 wk (Gainesville 1996 and Quincy fall 1995) to {approx}4 wk (Quincy spring 1995). Results presented here include only N-fertilizer treatments for which the applied amount was expected to be adequate for optimal plant growth. This generally corresponds to application of 180 to 240 kg N ha-1.

For growth analysis of tomato keyed to degree days, a base temperature of 10°C was used (Wolf et al., 1986; Jones et al., 1989). Thermal time (used to normalize the results from different experiments) was calculated by subtracting 10 from the mean daily air temperature. If the resulting averages were negative, thermal time increments for that day were set to zero. Radiation interception was calculated using a hedge-row light interception model (Boote and Pickering, 1994) based on measured canopy height, canopy width, LAI, the assumption of an ellipsoid plant shape, plant spacing, time of day, day of year, latitude, and row azimuth. This approach computes direct-beam extinction coefficients hourly as a function of solar elevation and approximate leaf-angle distribution among three angle classes. Once the canopy shadow has been factored in, the model considers sunlit and shaded LAI similar to the corresponding approach for a horizontally uniform canopy. Earlier computations (Scholberg, 1996) had been based on a single-leaf canopy-photosynthesis model, but the hedgerow model was felt to be more appropriate for settings such as these where the crops are grown in distinct rows, with leaves clumped around the main axis of the plant. Subsequently, dry weight accumulation was plotted versus either thermal time or cumulative intercepted daily radiation (Bennett et al., 1993). The RUE was calculated by regression analysis of biomass dry weight accumulation vs. cumulative intercepted radiation as calculated from the hedgerow light interception model. Experimental data were fitted using the linear and nonlinear SAS/STAT least-squares LIN and NLIN procedures (SAS Institute, 1989).


   Results and discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
Conclusions
 REFERENCES
 
Although water use is typically lower with drip irrigation than with subirrigation (Locascio and Smajstrla, 1993), parts of the bed (especially for coarse-textured soils) may remain dry with drip irrigation. Nutrients also are more prone to leach or may accumulate in the dry portions of the bed, thereby becoming unavailable for plant uptake. As a result, drip irrigation requires better water- and fertilizer-management skills.

Node Development
At transplanting, plant node number ranged from 3.1 to 6.3. Initial flowering typically occurred {approx}4 wk after transplanting, when a total of 8 to 10 main-stem nodes had been formed. This time also coincided with more pronounced growth of axillary shoots. For these semi-determinate cultivars, fruit clusters alternate with two leaf nodes and main-stem node formation terminates after the formation of a terminal fruit cluster. Thereafter, node formation and proliferation of leaves continue via lateral shoots only. Main-stem node numbers measured during the second part of the 1992 growing season at Bradenton appeared to be high (McNeal et al., 1995) and it was probable that continued node growth on some lateral branches was inadvertently included in the main-stem node number for this particular data set. A slight reduction in apparent node number towards the end of the 1995 Immokalee growing season (data not presented) was probably due to undetected senescence of lower leaves, with associated nodes then no longer being counted.

The overall rate of node development for tomato was calculated by plotting node number formed after transplanting vs. thermal time (Fig. 2) . The initial slope for the fitted line [°Cd (degree day) < 530] was 0.027 nodes °Cd-1. Assuming a base temperature of 10°C and a maximum node development rate at 28°C, this translates into an average node-development rate of 0.49 nodes d-1. This agrees well with the value of 0.5 nodes d-1 reported by Jones et al. (1989) for greenhouse tomato. Main-stem node formation typically ceased to increase appreciably (tailed off) after the accumulation of 530 °Cd and the formation of 15.7 nodes. This is a genetic trait, with formation of the terminal fruit cluster inhibiting further main-stem node formation. Since plants at transplanting had already formed 3 to 5 nodes, the total maximum number of main-stem nodes thus ranged from {approx}19 to 21, as shown in Tables 1 and 2 .



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  		Fig. 2 Node formation of tomato as a function of thermal time with subirrigation (Sub-I) and drip irrigation (Drip-I). Data points were fitted using nonlinear regression, resulting in a linear plateau (Lin. Plat.) form

 

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  		Table 1 Summarized growth measurements for subirrigated tomato crops, Bradenton spring seasons of 1994 and 1995

 

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  		Table 2 Summarized growth measurements for drip-irrigated tomato crops, Gainesville 1996 and Quincy 1995

 
Canopy Development
The LAI values at transplanting ranged from 0.002 to 0.004. Maximum LAI values ranged from 3.19 to 6.00 with subirrigation and from 1.54 to 2.99 in drip-irrigated plots, which were planted at a lower density and also represented a different cultivar (Tables 1 and 2). Plotting LAI values for subirrigated crops versus real time yielded distinct curves, with canopy build-up appearing to be more rapid for later planting dates (Scholberg, 1996). The use of thermal time resulted in a relatively uniform canopy-development curve for all sites and seasons (Fig. 3) . Though the data have been fitted here using linear segments, a sigmoidal relationship could have been used as well, but the linear-segments approach was adopted for relative consistency among the figures for the various plant-growth parameters, including Fig. 2 and 6 , where no lag phase was evident for one or more of the relationships. After an initial lag phase of 225 °Cd, LAI values also increased linearly (until 795 °Cd), resulting in an average maximum LAI value of 3.8 (Fig. 3). The lag phase during initial growth could be related to transplant shock coupled with the crop being either sink-limited (due to limited axillary branching) and/or source-limited (due to incomplete light interception). The tailing off later in the season appeared to be related to a shift from vegetative to reproductive growth (discussed below), coupled with increased leaf senescence at lower positions in the canopy. Due to staking and tying of the crop, leaves and branches were often confined to a land area and light regime smaller than that which existed during initial growth. This may have resulted in undetected late-season leaf senescence.



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  		Fig. 3 Leaf area index (LAI) of tomato as a function of thermal time with subirrigation (Sub-I) and drip irrigation (Drip-I). Data points were fitted using nonlinear regression, resulting in a linear plateau (Lin. Plat.) form

 


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  		Fig. 6 Total dry weight (Biom) and fruit dry weight (Fruit) accumulation over time as a function of estimated cumulative intercepted radiation with subirrigation (Sub-I) and drip irrigation (Drip-I). Data points were fitted using a linear regression model

 
The lower LAI values with drip irrigation may have been related to the relatively wide row-spacings used in these studies (1.8 m, compared with 1.5 m for the subirrigated crops), in large part because our LAI values are based on total production area (including between-bed walkways but excluding in-field ditches and drive paths). Peak LAI values below 2 or 3 could alternatively be attributed to poor crop growth due to incidence of moderate water or N stress (Gainesville and Immokalee 1995; data not shown) or to rapid canopy senescence due to incidence of plant pests and/or diseases (Immokalee 1992; see McNeal et al., 1995; Bradenton 1995). Previously reported LAI values for subirrigated field tomato and drip-irrigated greenhouse tomato were {approx}5.5 to 6.5 and 7 to 8, respectively (Jones et al., 1989; Marlowe et al., 1983). The LAI values reported here for drip-irrigated tomato are similar, however, to those reported for other drip-irrigated settings (e.g., an LAImax of {approx}3.25 for the study of Teasdale and Abdul-Baki, 1997).

The linear relationship between log-transformed leaf area measurements and main-stem node number shown in Fig. 4 appears to apply to both irrigation systems. This general relation also was evident for greenhouse tomato, although slopes and intercepts were slightly different (Scholberg, 1996). The linear log-scale increase shown in Fig. 4 suggests a season-long exponential relationship between LAI and main-stem node number. This is related to the formation of both primary and secondary axillary branches as the main-stem node number increases, with an associated exponential increase in leaf sites. Plotting actual LAI values versus real time resulted in a logistic curve instead (data not shown).



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  		Fig. 4 Leaf area index as a function of main-stem node number with subirrigation (Sub-I) and drip irrigation (Drip-I). Data points were fitted using a log-linear regression model

 
The relationship of growth to radiation interception as calculated from the hedgerow light interception model was decidedly nonlinear throughout the growing season, with approximate light extinction coefficients ranging from {approx}1 early in the season to {approx}0.2 late in the season. Estimated light interception in the tomato production area (as defined previously) averaged {approx}50 to 60% during the period of maximum seasonal fruit development for drip-irrigated and subirrigated culture, respectively.

Maximum fruit yields for tomato appeared to be attained with LAI values of 4 to 5. Lower LAI values would reduce light interception and also typically increase yield losses due to sunburn. Higher LAI values are generally indicative of excessive vegetative growth, which may delay the onset of fruit production and can reduce the effectiveness of foliar pesticides. Jones (1979) reported that a reduction in canopy area of subirrigated tomato by 10 to 20% did not significantly affect fruit yield. It is interesting to note that higher LAI values for subirrigated crops also coincided with a smaller inter-row spacing. This plant arrangement resulted in increased light interception, with tomato plants typically proving capable of adapting their canopy architecture according to specific plant arrangements. According to hedge-row light interception calculations (Boote and Pickering, 1994), near-optimal light interception within the row for field-grown tomato appeared to be attained within 4 to 6 wk at intra-row spacings of 45 and 60 cm, respectively. Canopy closure between rows, however, typically does not occur. Based on a maximum observed canopy width of 1.0 m, the percentage ground area covered by the crop would be {approx}83, 67, and 55% for row spacings of 1.2, 1.5, and 1.8 m, respectively. Increasing intra-row spacings (at Bradenton) may thus have delayed interplant competition for light and, along with narrower inter-row spacing, may have resulted in increased light interception and yield increases of {approx}15 to 25%. This is consistent with observations in the field, where a row spacing of 1.2 m for a drip-irrigated crop resulted in marketable fruit yields of {approx}110 Mg ha-1 (Hochmuth, 1996) compared with fruit yields of 60 to 90 Mg ha-1 (Locascio and Smajstrla, 1996; Rhoads et al., 1996) with a row spacing of 1.8 m. However, fungicide applications and harvesting operations may become difficult with row spacings <1.8 m.

Dry Matter Accumulation
During initial growth, weights of leaf blades were typically higher than weights of stems (including leaf petioles), but towards the end of the growing season the reverse was true (Tables 1 and 2). Total plant dry weight increased from 0.15 to 0.20 g dry wt. plant-1 at transplanting to {approx}900 and 500 g dry wt. plant-1 at harvest for subirrigation and drip irrigation, respectively. A decrease in total plant dry weight near the end of the 1995 growing season at Bradenton (Table 1) appeared to be related to premature crop senescence due to the incidence of diseases. Lower weights per plant at Gainesville compared with Quincy (Table 2) appeared to be related to higher plant densities (9042 vs. 11960 plants ha-1) and/or differences in crop management and soil type. Root weight increased from {approx}0.07 g dry wt. plant-1 at transplanting to {approx}8 to 20 g dry wt. plant-1 at crop maturity. Values for maximum root weights were similar to those reported by Stoffella (1983), but appeared to be low compared with those reported for deep watertable conditions (Jackson and Bloom, 1990). This may be related to more pronounced root senescence under frequently anaerobic conditions near the bottom of the rooting zone for subirrigated sites in Florida.

Fruit dry weights were {approx}600 g dry wt. plant-1 and 400 g dry wt. plant-1 with subirrigated and drip-irrigated crops, respectively. Teasdale and Abdul-Baki (1997) reported values on the order of 300 g dry wt. plant-1 for another drip-irrigated crop. Assuming a dry matter percentage for tomato fruits of {approx}5% (Scholberg, 1996), fresh fruit yield would be {approx}50 to 100 Mg ha-1 and 24 to 60 Mg ha-1 for subirrigated and drip-irrigated crops, respectively. Overall biomass (dry matter) production was {approx}9 and 6 Mg ha-1 for subirrigated and drip-irrigated crops, respectively. Under optimal management conditions, marketable fruit yield (fresh weight basis) and total biomass (dry weight basis) for drip-irrigated crops in Florida should be {approx}90 Mg ha-1 (Hochmuth, 1996) and 8 Mg ha-1 (Scholberg, 1996), respectively.

In Fig. 5 , biomass and fruit dry accumulation are presented as a function of thermal time. The approach presented here is similar to that used by Goudriaan and van Laar (1994) and normalizes the results from different locations and cropping seasons, thereby allowing for establishment of overall growth relationships independent of season and location. During the initial growth phase, biomass accumulation by tomato plants was limited by low canopy interception of photosynthetically active radiation (Hsiao, 1990). This phase was followed by a linear growth phase, which starts around 300 °Cd (Fig. 5). At that age, LAI values were {approx}0.6 (Fig. 3), which corresponds to near-complete bed-area coverage by the canopy (the bed area typically covers {approx}50 to 60% of the production area). The slope of this line is the average potential growth rate expressed in units of thermal time (g dry wt. m-2 °Cd-1). Respective values for potential growth rate with respect to total dry weight and fruit dry weight were {approx}0.98 and 0.80 g dry wt. m-2 °Cd-1, respectively. Assuming a base temperature of 10°C and an optimal temperature for crop growth of 28°C (Jones et al., 1989), this translates into average growth rates during the linear growth phase of {approx}18.0 and 14.4 g dry wt. m-2 d-1 for total dry weight and fruit dry weight, respectively. Similar values have been reported for faba bean (Vicia faba var. faba) and sorghum [Sorghum bicolor (L.) Moench] (Goudriaan and Monteith, 1990). Actual peak values may be around 20 to 25 g dry wt. m-2 d-1 (Scholberg, 1996), which is consistent with results for greenhouse-grown tomato (Heuvelink, 1995). Growth rates during initial crop development were relatively low (0.07 to 0.13 g dry wt. m-2 d-1), due to incomplete light interception.



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  		Fig. 5 Total dry weight (Biom) and fruit dry weight (Fruit) accumulation over time as a function of thermal time with subirrigation (Sub-I) and drip irrigation (Drip-I). Data points were fitted using a linear regression model

 
In Fig. 6, biomass and fruit dry weight accumulation also are shown to be linearly related to the estimated cumulative intercepted radiation. Average RUE for total dry matter was 1.05 g MJ-1 of total radiation (which translates to 2.10 g MJ-1 on a photosynthetically active radiation basis). This is higher than the value of 0.76 g MJ-1 reported for peanut (Arachis hypogaea L.) (Bennett et al., 1993), but is lower than the value of 1.18 g MJ-1 reported for potato (Solanum tuberosum subsp. tuberosum) (Kooman, 1995). The estimated slope (analogous to RUE) for fruit dry matter increase was 0.73 g MJ-1 (Fig. 5). The very short lag-phase (indicated by a negative intercept on the y-axis) for total dry weight accumulation may be related to transplant shock (which delays subsequent growth by {approx}4 to 7 d). The corresponding delay in fruit production is related in turn to the onset of initial flowering, which occurs {approx}4 wk after transplanting. Initial fruit growth rates were slow (Scholberg, 1996), requiring up to 6 wk after transplanting (100 to 120 MJ m-2 of intercepted radiation) before a substantial number of fruits entered into their linear growth phase. Lower overall dry matter accumulation for drip-irrigated crops could be attributed to lower LAI values (Fig. 3), resulting in less-complete interception of solar radiation. This seems to provide support for the hypothesis that crop yields of drip-irrigated tomato could be increased by reducing row spacing and increasing plant densities. Effects of N-stress on RUE will be presented elsewhere.

Dry Matter Distribution
The apparent fractions of current dry matter in selected plant parts over time are shown in Fig. 7 . An overview of the empirical functional relationships fitted through the data using SAS linear and nonlinear regression analysis of the experimental data is presented in Table 3 . After the onset of reproductive growth (which occurred after the accumulation of 395 °Cd), the fraction of dry matter accumulated by vegetative plant parts decreased appreciably. Dry matter accumulation by roots accounted for up to 30% of total biomass during initial growth, but decreased exponentially to values of only 2 to 3% by the end of the growing season. Dry matter accumulation by leaves accounted for up to 70% of the total biomass during initial growth, but also decreased exponentially to values averaging 17% near the end of the growing season. The fraction of dry matter accumulated in stems initially increased, typically ranging between 25 and 35%, but then decreased once more after the onset of fruit growth. Decreases in the respective weight fractions can be caused by a decrease in actual partitioning (Scholberg, 1996) and/or by aging (and senescence) of previously formed plant material. The rather pronounced decrease in leaf and root dry weight fractions was probably related to increased incremental allocation to stems and fruit as well as to greater concurrent senescence rates of leaves and roots (Scholberg et al., 1997). Based on field observations, leaf senescence typically begins 30 to 50 d after leaf formation, whereas senescence of stems occurs only near the end of the growing season.



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  		Fig. 7 Fraction of total dry weight accumulated in selected plant parts for field-grown tomato plants. Data points were fitted using SAS in the nonlinear regression mode, with the respective regression equations as outlined in Table 5

 

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  		Table 3 Overview of the fraction of total dry matter accumulated by selected plant organs

 
Final fruit harvest indices [HI values, expressed as the ratio of fruit biomass to total above-ground biomass (both on a dry-weight basis)] ranged from 0.53 to 0.71, with an average of 0.58 (linear plateau for the "fruit" line in Fig. 7). Respective HI values for drip-irrigated and subirrigated crops were 0.60 and 0.53, respectively. However, it was observed that higher HI values were often associated with better crop management and that high-yielding crops typically had HI values of {approx}0.65 regardless of the irrigation system. It should be noted that the ratio between RUE values for fruit dry weight and total dry weight was {approx}0.70 (Fig. 5). This may be considered an estimate of the actual average instantaneous partitioning of dry weight to fruit for field-grown tomato.


   Conclusions
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
REFERENCES
 
Based on the results presented here it may be concluded that, for the included locations and seasons, general relations appear definable for spring-grown crops that predict LAI development and dry matter production over time for a number of seasons and locations in Florida. After an initial lag phase of {approx}225 °Cd (or {approx}3 wk assuming an average temperature of 21°C), leaf area increases linearly with °Cd. The linear growth phase for dry matter began when LAI values exceeded {approx}0.6 and, for typical production systems, near-complete light interception within the cropped area should occur at LAI values of 4 to 5. Plant growth was generally less vigorous with drip irrigation compared with subirrigation. With the use of wider row spacings at these drip-irrigated sites, yield reductions should have occurred (though only on the order of 20% for the row-spacing combinations evaluated). Yield reductions are exacerbated if fertilization and irrigation management is suboptimal. The average RUE value for total dry matter accumulation by a tomato crop was 1.05 g MJ-1 and the calculated seasonal average for the fruit partitioning coefficient was 0.7. The final ratio of fruit dry matter to total above-ground dry matter was 0.58 and would be lower at some sites due to poor fruit set and suboptimal growth conditions. The relatively low R-square values for regression analysis of dry weight accumulation vs. thermal time may be related to extended periods of warm and overcast weather. Under these conditions, estimates of intercepted radiation appear to be more closely related to fruit dry matter production instead (R-square values of 0.79 and 0.84 for thermal time and estimated cumulative intercepted radiation, respectively). The relationship to radiation interception was decidedly nonlinear throughout the growing season, so the strong correlation could not be ascribed solely to an interdependence of LAI and fruit production. The general relationships between degree days, estimated cumulative intercepted radiation and fruit yield outlined here appear useful, as they accounted for much of the variation in fruit yields for these different seasons and locations throughout Florida.


   ACKNOWLEDGMENTS
 
Growth analysis of tomato plants was possible through collaboration with the following additional scientists: Dr. A.A. Csizinszky (Gulf Coast Research and Education Center in Bradenton, FL); Dr. S.J. Locascio (Horticultural Science Dep., Univ. of Florida in Gainesville, FL); and Dr. S.M. Olson (North Florida Research and Education Center in Quincy, FL). This research was supported by joint contributions of the Florida Agricultural Experiment Station and the USDA (ES/SCS/ASCS) via the Lake Manatee Demonstration Project and USDA Special Grant in Tropical Agriculture No. 9-34-34-34135-0641 (Decision Support Systems for Vegetable Production).


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
Florida. Agric. Exp. Stn. Journal Series no. R-06445.

Received for publication February 22, 1999.
   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 




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