Purpose of Plant Analysis
Plant analysis (leaves, fruit, etc.) aims to relate the mineral content of the plant (or part thereof) with its physical appearance, growth rate, yield or quality of the harvested product, and the nutrient content of the soil. Precise sampling procedures—regarding the selected plant part and the growth phase (time of sampling)—are required. Interpretation of results assumes a significant biological relationship exists between the elemental content of the soil, the plant, and its growth or production.
The purposes of plant analysis are:
- To evaluate the nutrient-supplying capacity of the soil.
- To evaluate the plant’s response to fertilizer applications.
- To assess the nutritional status of the plant as an aid to estimate fertilizer requirements (e.g., to diagnose deficiencies).
Sampling Protocol
- Plants are complex and their elemental composition is not homogeneous.
- Leaves, stems, shoots, fruit, and their positions on the plant differ in elemental composition.
- Do not mix different organs in a compound sample. Select the correct plant part for sampling.
- Refer to the table below to ensure the correct plant part and number of leaves are sampled at the most appropriate time.
General guidelines:
- Do not sample trees/plants at the edge of the block or at the end of rows (may be coated with soil/dust or differ in nutrient status/irrigation).
- Do not sample diseased, insect-damaged, or dead leaves.
- Do not sample during the hottest part of the day (can influence leaf composition). Collect samples in the morning.
- Place leaves in a clean plastic or paper bag and keep cool until delivered to the laboratory. Do not freeze.
- Sample problem spots and adjacent healthy plants separately.
- For perennial crops, collect routine samples from the same marked trees to identify seasonal trends.
Table 1. Protocol for Leaf Sampling by Crop Type
| Crop Type | Organ to be Sampled | Time of Sampling | Sample Size & Comments |
|---|---|---|---|
| VEGETABLE CROPS, GRAINS & HERBS | |||
| All crops not specified | Youngest mature leaves | Vegetative phase; for fruiting crops, just before flowering | 30 leaves per sample. Indicate growth phase. |
| Asparagus | Spears: Entire above ground part. Ferns: Youngest mature frond. | Vegetative phase | 20–30 plants. 20 fronds per sample. Plant 10 cm length. |
| Canola | Youngest mature leaf | Prior to flowering | 40 leaves. |
| Ginger | Youngest mature leaves | 105 days after planting (around mid-December) | 30 leaves per sample. |
| Onion | Entire above ground portion | Vegetative stage | 20–30 plants. |
| Peanut | Most recently mature trifoliate leaf | Pre-flowering to early flowering | 40–50 leaves. |
| Potato | Entire 4th leaf (petiole and leaflets) or only petiole | Mid-season | 30–40 leaves or petioles. Separate leaves from petioles immediately—analyze either one. |
| Soybean | Most recently mature trifoliate leaf | Early flowering to early pod set | 30–40 leaves. |
| Sweet corn & Maize | Youngest mature leaves | Plant 60 cm height or just before flowering/tasseling | 30 leaves per sample. |
| Sunflower | Third mature leaf from the top | Month before bloom | 20–30 leaves. |
| Wheat, oats, rye, barley | Youngest mature leaves; flag leaves when they appear | 5–6 leaf stage or just before flowering | 60–80 leaves. |
| FRUIT, OLIVES AND NUTS | |||
| Pome & stone fruit | Leaves at shoulder height, middle of current season’s growth, both sides of row | Mid-season, just before fruit ripening (late Jan–early Feb) | At least 50 leaves per sample. |
| Wine & table grapes | Leaf opposite the bunch, or on a bearing shoot between nodes 3–5 | At set or veraison (indicate time) | 30–40 leaves or petioles. Separate leaves from petioles immediately—analyze either one. |
| Citrus | Spring cycle leaves from 4–6 month old non-fruiting shoots | March–April before autumn fertilization | 40–50 leaves per sample. |
| Avocado | 6–8 month old leaves in the middle of the tree | February–April | 40–50 leaves per sample. |
| Almonds | Leaves at shoulder height, middle of current season’s growth, both sides of row | Mid-season, just before fruit ripening | At least 50 leaves per sample. |
| Bananas | Third youngest leaf from the top | October–April when 50% of orchard has flowered | One leaf of at least 1 m long. |
| Blackberry & Raspberry | Mature leaves from middle of non-fruiting canes | Mid-season, 4–6 weeks after bloom | 50–60 leaves per sample. |
| Blueberry | Mature leaves in middle of non-fruiting branches | Mid-season, 4–6 weeks after bloom or after harvest (end Jan–end Feb) | 50–60 leaves per sample. |
| Cherries | Fully expanded mature leaves (2–5 months old) from non-fruiting spurs | January–February | 50–60 leaves per sample. |
| Coffee | Fourth pair of leaves from the tip of a primary branch (mid-canopy, cropping region) | Full bloom (Oct–Nov) | Four pairs per tree, at least 10 trees (80 leaves). |
| Figs | Youngest fully expanded, exposed leaves on non-fruiting branches, perimeter of tree at 1.5–1.8 m height | Mid to late summer (Jan–Feb) | 30–40 leaves. |
| Granadilla | Mature leaves from non-bearing shoots | September–December | 40–50 leaves per sample. |
| Guava | Young, fully developed leaves directly behind the largest fruit | Five months after pruning (Jan–Mar) | 40–50 leaves per sample. |
| Kiwi’s | Youngest mature leaf (early); second leaf past final fruit cluster (mid-summer, non-terminated female vines) | Before fruit-set (Oct–Nov) or late summer (Dec–Feb) | 40–50 leaves per sample. |
| Litchi | Second last leaflet pairs on terminal shoots | September–November | 40–50 leaves per sample. |
| Macadamia | Mature, three month old leaves (third & fourth from terminal end of new shoot) | Three month old leaves (Oct–Nov) | 40–50 leaves per sample. |
| Mangoes | 7-month-old, fully developed, hardened-off leaves from fruit-bearing twigs | Mid-summer to onset of ripening | 30–40 leaves per sample. |
| Olives | Mature leaves from middle of non-bearing, current season shoots | Mid-summer (late Dec–end Jan) | 80–100 mature leaves per sample. |
| Papaya | Mature leaves (petiole removed—analyze petiole) | Two weeks before harvest | 20 petioles required. |
| Pecan nuts | Middle leaflet pairs from mature leaves on terminal shoots | Mid-season, 6–8 weeks after bloom | 40–60 leaves per sample. |
| Pineapple | D-leaves: a whorl of three leaves, including the tallest | — | 10–15 leaves per sample. |
| Pomegranate | Mature spring cycle leaves from non-fruiting shoots, middle third of branch | Mid-summer (Dec–Jan) | 90–100 mature leaves per sample. |
| Strawberries | Youngest fully mature tri-foliate leaf | Vegetative to fruiting stages | 50–60 leaves per sample. Separate leaves from petioles immediately—analyze either one. |
| Sweet melon & watermelon | 9th petiole and leaf blade from growing tip | Early bloom | 30–40 leaves or petioles. Separate leaves from petioles immediately—analyze both. |
| PASTURES, SUGAR CANE & TURF | |||
| Lucerne/Alfalfa | Top 20 cm of the plant | Shortly before bloom | ~300 g of leaves required. |
| Sugar cane | Second fully mature leaf | Mid-season | 20–30 leaves required. |
| Turf | Leaves, clipped by hand | Early to mid-summer | ~200 g of leaves required. |