Looking for the perfect tree planting density to meet all of your objectives for citrus fruit quality and yield? That may not be possible, University of California Cooperative Extension’s Craig Kallsen said in a recent talk about planting density’s impact on navel orange yield and quality.
The citrus and pistachio farm advisor for Kern County gave the example of a grower wanting to maximize profits by adjusting spacing for an early-maturing mandarin. For early and more intense fruit color, as well as high early fruit sugar/acid ratio, low tree density is suggested. But for small/moderate fruit size along with high early yields, high tree density is called for. There isn’t a one-size-fits all tree density to meet all objectives.
Kallsen said very little research has been done in California on the effect of planting density on yield and fruit quality. He cited results from a navel orange on Troyer rootstock tree-spacing trial conducted in Kern County from 1961 to 1971. In that trial, the highest density was a planting of 9 feet between trees in a row and 15 feet between rows (9 x 15). The lowest density was a planting of 22 feet between trees in a row and 22 feet between rows (22 x 22).
Kallsen summarized results regarding color, fruit size, sugar/acid ratio and yield:
COLOR
Orange color developed first and was more intense in the lowest density (22 x 22) spacing, Kallsen reported. He said fruit color was delayed as much as 45 days after reaching legal maturity in closer tree spacings. Kallsen’s take-home message: For earlier and more intense color development, plant trees farther apart.
FRUIT SIZE
Individual navel orange fruit size was larger in the wider 22 x 22 spacing. The take-home message: For larger fruit size, plant trees farther apart. For reduced fruit size, plant trees closer together.
SUGAR/ACID RATIO
Higher sugar/acid ratios were produced earlier in the fall in wider spacings like 22 x 22. Trees spaced 9 x 15 were 11 days later in reaching a sugar/acid ratio of 8. The take-home message: For faster development of a higher sugar/acid ratio, plant trees farther apart. In general, to increase the rate of fruit maturation, plant trees farther apart. To decrease the rate of fruit maturation, plant trees closer together.
YIELD
More densely planted orchards had greater total accumulated yield after 10 years than less dense plantings, Kallsen said. The take-home message: Higher planting density increases early yield per acre but comes with increased cultural costs such as more pruning, which may or may not result in increased net income.
Kallsen said profitability should be improved by matching the tree-density strategy with the right cultivar and rootstock. For example, if later maturity is desired, start with something like a late Australian navel grafted onto a trifoliate rootstock.
Kallsen’s talk was the first of the Citrus Research Board of California’s 2023 Citrus Growers Educational Webinar Series.
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