Late spring (mid-October to November) is the perfect time to tag new spring leaves in preparation for leaf analyses in summer, according to NSW Department of Primary Industries citrus development officer Steven Falivene.
Leaf analyses are used to help determine the nutrient status of trees and can be used to improve nutrient management and fertiliser decisions, which can lead to better yields, fruit quality and profits.
“By late summer to early autumn, February to March, the leaf nutrients will have stabilised so it is a good time to take samples,” said Steven. “In the first few months after the spring leaves come out their nutrient status fluctuates up and down so it’s not very helpful to do leaf analyses then.
“The best time is about four to seven months after the leaves have fully expanded, so leaves fully expanded in October are the ones you want to sample in late February to March.”
To the untrained eye, spring- and summer-emerging leaves look the same. The easiest way to be sure of sampling a spring leaf is to tag it in spring when it is clearly a new leaf.
“When I first started to select citrus leaves for analyses, they all looked the same,” said Steven. “To help learn how to recognise the difference between leaves that emerge in spring and those that emerge in summer I tagged the spring ones. It was a great learning tool.”
Tagging takes the guess-work out of the equation and ensures the leaf sampled was a spring leaf.
To help citrus growers sample leaves properly to obtain accurate data they can rely on, Steven has produced a fact sheet and a video series introducing how to identify and tag citrus leaves and how to get started on analyses.
“For most growers, the fact sheet and video series will be enough to help them identify spring leaves in navels accurately,” Steve said. “Mandarins are tricky because spring flush can look similar to summer flush in some varieties. However, there are some identifying characteristics like length of shoot.
“We can’t produce a fact sheet on every variety of mandarin but if you learn to recognise spring leaves in your own varieties by tagging the leaves, then you can learn how your own varieties grow.”
Steven tags leaves using pink flagging tape but adds, “If you are really desperate, use a hand staple like you use in nurseries. You go around and click hundreds of shoots so that when you want to pick leaves for analysis you are guaranteed you are getting the right ones.”
Agricultural supply stores, NSW DPI and others can provide a laboratory analysis service.
“Leaf analyses can cost as little as $30 a hectare, based on one analysis for a three-hectare block,” said Steven. “A grower can spend upwards of $800/ha on a fertiliser program, and with every extra tonne of yield per hectare worth between $400 and $1,000 it’s a good investment.
“Why wouldn’t you do it? The gains and losses are significant.”
While leaf analyses are a vital ingredient in shaping a fertiliser program, there are many other factors to consider to optimise tree nutrition. For growers wanting to deepen their understanding of citrus orchard nutrition, Steven runs a citrus nutrition masterclass every two years; the next one is scheduled to be held in 2018.