Within Row Plant Spacing in Processing Tomatoes

Gene Miyao, Farm Advisor, Yolo, Solano & Sacramento Counties

DIRECT SEEDED TOMATOES:
Tomatoes yield well over a wide range of plant populations. Direct seeded plants are very opportunistic in compensating for thin as well as thick stands. Field evaluations demonstrate maximum yields are achievable with plants spaced from 6 to 18 inches apart. In a few trials, yields did not plummet even when spaced 30 inches apart. A target of 9 inches between clumps has been an aim for most growers.

This benchmark does not need strong adherence. As the price of seed increases, movement toward lower plant populations by seeding toward final stand targets of 10 to 12 inches would not compromise yields. During prime planting periods, local variety trial evaluation of stand counts indicates emergence is approximately 50% of seeded rates. Unfortunately, the distribution of seedling emergence is not uniform, thus complicating formulating an optimal seeding rate.

The primary economic justification for seeding at a high rate is to overcome obstacles such as: poor weather conditions during emergence, soil crusting, losses to insects, diseases and bird feeding, frost and hail. During the expected poor weather conditions, high seeding rates help buffer against thin stands. While high seeding rate plantings don't guarantee an adequate stand, it helps.

Bottom Line: Final stands of 1 to 3 plants per clump spaced any where between 8 to 15 inches between clumps could be a target under many situations. A final stand of 12 inches between clumps is a conservative goal. With double seed lines per bed, the distance between plants can be increased over that of single seed lines per bed.

Clumps of plants yield slightly more than similarly spaced stands thinned to singles. Conversely, once a stand is established, only those fields with seedlings crowded with about 8 or more plants per foot in a single seed line should be candidates for thinning.

TRANSPLANTED TOMATOES:
What is the ideal distance to transplant plugs down the row? While the answer would be filled with many qualifiers (soil quality, variety selection, time of year, field history, etc.), field tests conducted in Yolo County in the mid 80's suggested that transplants did not compensate for lower plant populations as well as direct seeded plants. Based on these few tests, the recommended transplant spatial target was less than 20 inches between plugs. Most growers in the area first began transplanting to 12 inches and many gradually increased the distance to 15 to 16 inches between plugs. Later, some growers opted to spread their transplants across a double-'seed' line configuration.

Transplant Spacing Study: With renewed interest a transplant spacing study was conducted in 2001 in the western part of Yolo County near the town of Madison. The grower cooperator was Blake Harlan of Harlan and Dumars. The soil type was a class 2, Tehama loam. The variety, Halley 3155, was planted on March 30th using the grower's mechanical transplanting equipment and crew. Plants were placed on single lines per bed centered on 5 feet. The field was initially irrigated with sprinklers for a single time and thereafter with furrows.

The spatial treatments were distances between transplanted plugs ranging from 8 to 28 inches apart in 4-inch incremental steps (8, 12, 16, 20, 24 and 28 inches). Individual plots were planted in a single row for the entire field length, approximately 1/2 mile long. The trial design was a randomized complete block with 6 replications. The trial area was composed of 36 beds (6 treatments x 6 reps). After planting, the study area was confined to 3 consecutive 200-foot sections of each row near the headland in order to more easily monitor the plants and manage the harvest.

Over the course of the season, an average of 4% of the plants was killed, mainly to root rot. The loss of plants was uniform across treatments, but the resulting 'bare-ground' gaps between plants were higher in the low population treatments. In the wide spacing, the accumulated gap averaged less than 3 feet over a 200-foot distance.

Results: Ten days before mechanical harvest, a 10-foot length of each row was hand harvested to assess fruit maturity. Fruit were separated into categories of red, pink or green by weight. Fruit size as estimated by weighing a batch sample of 50 red fruit. There were no statistically significant differences among the treatments for percent pink or green fruit (Table 1).

Table 1. Influence of transplant population on pre-harvest fruit maturity of variety Halley, 2001.

The grower mechanically harvested the plots into GT carts equipped with weigh sensors to measure yields on August 16th. Yields were higher in plots with wider spacing between plugs (Figure 1), positively correlated to increased spatial distance. Soluble solids and fruit color were reduced slightly with the wider spacing while pH was unaffected (Table 2). For soluble solids and color, the plug spacing of 16 to 20 inches produced similar quality to the closer spacing treatment. Mold levels were elevated with closer spacing. As expected, fruit 'size' was increased with the wider spacing.

Summary: Placing plugs 12 inches apart and closer is costly at both ends of the season: initial higher investment in plants and lower yield at harvest. While it would be very bold to rec-ommend that transplants be spaced over 2 feet between plants,

a more conservative transplanting strategy should be adopted from our research results. Growers should be comfortable with transplanting to distances at or slightly above 15 inches between plants.

This field research effort will continue with funding support for the 2002 season through the California Tomato Research Institute (CTRI).

Table 2. Influence of transplant population on yield and quality of variety Halley, 2001.

Figure 1. Influence of plant spacing on
yield of processing tomato variety Halley.

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