Diagnosing Nutrient Deficiencies

Diagnosing Nutrient Deficiencies

Visual Symptoms of Deficiency

• Growth differences can indicate nutrient deficiencies, but are not always specific.
• Example: A field with two strips fertilized differently with nitrogen, showing larger plants on the right side where nitrogen supply is greater.

Nodules on Roots

• Healthy nodules on roots (e.g., Faber Bean) are a sign of nitrogen fixation, not deficiency.
• Nodule size: Approximately 4-5 millimeters in diameter.

Phosphorus Deficiency

• Narrow Leaf Lupine:
  • Growth improves with increasing phosphorus rates.
  • Interested in the transition zone where deficiency symptoms start to appear.
• Comparison of Lupine Species:
  • White lupine grows better than narrow leaf lupine at low phosphorus levels.
  • Conclusion: White lupine is efficient at accessing limited phosphorus in the soil; white lupine develops cluster roots when phosphorus deficient.
• Wheat:
  • Plants grown without phosphorus are much smaller.
  • A common symptom of phosphorus deficiency is reddening of stems due to anthocyanin accumulation.
  • However, this symptom is not specific to phosphorus deficiency; it can also occur with deficiencies in potassium or nitrogen.
  • Multiple deficiencies may produce similar symptoms, so visual appearance must be carefully considered.

Potassium Deficiency

• Potassium is a mobile nutrient in the phloem, so deficiency symptoms appear first on older leaves.
• Tips of older leaves become necrotic due to potassium remobilization from these tissues.
• Edges of older leaves are also affected due to being the oldest parts of those leaves.
• Example: Maize leaves showing necrosis at the tip and edges.
• Younger leaves at the upper stem generally appear unaffected, although physical damage can occur.
• Similar patterns occur in different plant species (e.g., barley, subclover, soybean, canola) regardless of leaf morphology (monocots vs. dicots).
• Yield and Quality:
  • Potassium deficiency affects yield quantity and quality.
  • Example: Maize ears are smaller and have fewer grains without sufficient potassium.
• Adding nitrogen and phosphorus makes no difference if potassium is deficient.
• The most deficient nutrient limits growth, regardless of the supply of other nutrients.
• Tip and margins of oldest leaves suffer first, with chlorosis initially, followed by necrosis under prolonged deficiency.
• Deficiency severity affects leaf size, with optimal control plants having much larger leaves.

Magnesium Deficiency

• Severe deficiency leads to chlorotic areas and eventual necrosis.
• Similar pattern to potassium deficiency: oldest parts of oldest leaves suffer first because magnesium is also highly mobile.
• Differentiating between deficiencies of mobile macronutrients can be difficult.
• Nutrient analysis is the most reliable measure of nutrient supply.
• Chlorotic areas appear between veins because magnesium is supplied close to veins.
• Striping effect on leaves: Can be confused with iron deficiency (yellow stripe transporter).
  • Magnesium deficiency occurs on older leaves, while iron deficiency occurs on younger leaves.
• Striping can occur in early growth of maize due to fast growth and insufficient magnesium uptake, but it usually remedies itself as growth slows and magnesium uptake increases.

Calcium Deficiency

• Bitter Pits in Apples: Fruits have pitted appearance and altered taste, reducing commercial value.
  • Calcium deficiency doesn't greatly affect fruit size.
• Calcium deficiency is hard to remedy because it is due to transport issues rather than calcium availability in soil.
• Fruits, young buds, and young leaves are predominantly supplied via the phloem, so calcium nutrition can be a problem.
• Blossom End Rot in Tomatoes and Capsicum (Peppers):
  • Occurs frequently in glasshouse-grown fruits due to high humidity slowing transpiration.
  • Calcium transport in the xylem is limited, and phloem transport is poor. The very end of the fruit suffers the most.
    *Blossom end rot is putrid and decomposing, unlike bitter pits in apples.

Boron Deficiency

• Grapes:
  • Some berries develop normally, while others do not develop at all (hen and chicken appearance).
  • Reduces commercial value.
• Pears:
  • Fruits are much smaller and harder compared to normal Williams Pears.
  • Consist mostly of sclerenchyma tissue and have no commercial value.
• Canola:
  • Grown under artificial conditions, showing significant differences between low and good boron supply.
  • Problems with both shoot and root growth.
  • Root system is underdeveloped, limiting nutrient scavenging.
• Leaves:
  • Tissue around the edges becomes chlorotic and then necrotic.
• Tobacco:
  • Very sensitive to boron deficiency.
  • Boron is required for normal vegetative growth and pollen grain growth.
• Pollen Grains:
  • Boron is crucial for pollen tube growth, which is required for fertilization.
  • Without sufficient boron, pollen grains do not germinate or grow healthy tubes, leading to sterility, which is a serious symptom.

Zinc Deficiency

• Severe deficiency causes middle leaves to lose mechanical strength and flop over.
• Remobilization of zinc from old leaves is insufficient to feed young leaves.
• Inducing zinc deficiency in nutrient solution is difficult due to zinc contamination.
• Requires specific conditions and chemicals to limit zinc availability.
• Wheat:
  • Flag leaf (last leaf to appear) is crucial for grain loading.
  • Zinc deficiency damages the middle part of the flag leaf.
  • Necrotic lesions develop all over the leaf.

Manganese Deficiency

• Barley leaves show chlorosis, necrosis, and brown spots on the underside.
• Must be distinguished from fungal infections (e.g., rust).
  • Rust can be identified by rubbing the spores off the leaf onto fingers.
• Nutrient analysis is necessary for accurate diagnosis.
• Lucerne: Shows extensive chlorosis when manganese deficient.
• Tobacco:
  • Manganese deficiency causes lots of chlorotic points on leaves.
  • Bacterial disease can cause similar white spots on leaves, requiring analysis to differentiate.
• Split Seed Narrow Leaf Lupin:
  • Embryo is exposed, leading to drying and death.
  • Commercial value decreases.
  • Farmers worry particularly if they lime, because this increases the soil PH, which decreases manganese availablity.

Copper Deficiency

• Causes problems with the flag leaf.
• Older parts of the leaf are almost completely gone.
• Symptom is called whip tail.
• Frost damage can cause similar symptoms, but the constriction point is more toward the tip of the leaf.

Iron Deficiency

• Grown in artificial conditions, all the leaves are still somewhat greenish, younger one are not.
• Younger leaves are chlorotic, and areas around veins are narrow.
• Older leaves may show some chlorosis, but younger leaves are severely affected.
• Severe deficiency can lead to necrosis.
• Can severely affect vineyards (e.g., in France) due to nutrient and clay leakage from the top of hills.

Toxicity

• Plants can suffer from problems when a particular nutrient is supplied in too high amounts.
• Various genotypes react differently to toxicity.
• Root growth suffers first, followed by shoot growth.

Boron Toxicity

• Problems occur at the leaf tip and margin.
• All tissues serve as rubbish bins, plants try to put material they do not want in said tissues.
• Older leaves and parts of leaves are sacrificed for the benefit of the plant: The oldest parts of the leaves suffer the most.
• Higher supply of zinc can protect plants from boron toxicity.

Nutrient Toxicity in Native Plants

• Native plants can suffer from nutrient toxicity as well.
• Boron toxicity in pine trees occurs mostly on older leaves.
• Symptoms start from the leaf tip toward the base.

Frequency of nutrient toxicity problems

• Not common because most nutrients cost money.
• The range between deficiency and toxicity is much wider for most nutrients than for boron.
• Boron can become toxic because the range is not so wide and is not difficult to accidentally induce a toxic concentration.
• High soil pH in South Australia causes boron toxicity.