• NITROGEN DEFICIENCY
• PHOSPHORUS DEFICIENCY
• POTASSIUM DEFICIENCY
• CALCIUM DEFICIENCY
• MAGNESIUM DEFICIENCY
• SULPHUR DEFICIENCY
• MICRONUTRIENTS
• SOIL pH AND LIME REQUIREMENTS

The first part of this section describes the general conditions likely to result in nutrient deficiency or toxicity symptoms in vegetable crops. Methods of overcoming nutrient disorders are included.

The specific symptoms and nutrient requirements are then listed for each of the main species or families of vegetables.

NITROGEN DEFICIENCY

Occurrence

Depends on the N supplying power of soils, N losses by leaching and N fertiliser use. Nitrogen deficiency is more common on soils:

• with little organic matter;
• after repeated cropping with non-leguminous species;
• after heavy rain and irrigation causes either leaching in freely drained soils or waterlogging in heavier soils;
• when fresh organic residues have been incorporated into the soil;
• at low temperatures and with excessive plant populations (close spacing or weeds).

Species susceptibility

Nearly all species are susceptible. Exceptions are well nodulated legumes although green beans may require fertiliser N even when nodulated. Requirements vary and are listed under each crop described. The requirements given are both the results of New Zealand experiments and from overseas. Where a range of values is given, the greatest rates are for maximum yields on the most responsive soils.

More fertiliser N is needed for winter crops than for summer ones. This is because of the cold conditions in winter and greater leaching losses at this time.

When large rates must be applied, it is usual to apply half at or before sowing and the remainder as a side dressing. In sandy soils where leaching is severe, frequent small dressings will be used more efficiently.

Treatment

If a deficiency is diagnosed, sidedress with a soluble N fertiliser (ammonium nitrate or urea) and water in if possible, or spray with 500-1000 litres/ha of urea solution (2 kg/100 l).

PHOSPHORUS DEFICIENCY

Occurrence

Acid or calcareous soils; high phosphate retention soils; peats; dry or cold conditions, especially at emergence.

Species susceptibility

Species vary in susceptibility. Olsen soil test values required at sowing time are given for each crop species. These can be achieved by applying the rates of P fertilisers indicated in Table 1. Asparagus appears to have the lowest P requirements and winter crops such as winter lettuce, spinach and early potatoes the greatest. Leeks and celery also require P-rich soils.

Treatment

The main requirement occurs at early stages of growth and should be met with pre-planting applications of phosphorus fertilisers. Deficiency is avoided by starter fertilisers applied at rates to achieve the desired soil test status. These are used most efficiently in banded close to, but not in touch with the seed. If this is done, application rates can be decreased by 25-50%. The rates of fertiliser in Table 1 refer to water or citric soluble phosphates. Greater rates of water insoluble materials will be needed, but these are generally unsuitable where a rapid and large increase in soil test value is required. Target test values are achieved about four weeks after fertiliser has been applied. Subsequently, test values will decline so that if the interval between topdressing and sowing is extended, fertiliser applications should be greater than indicated in Table 1.

If a deficiency is diagnosed in mid growth stages, foliar sprays with specific products may partly alleviate symptoms.

Table 1: Increase of Olsen P units in the top 15 cm of soil as a result of broadcast application and incorporation of 1 tonne of superphosphate per hectare (10% P; 8% water soluble P). P retention values are given in brackets.

3 - 5 Units	6 - 10 Units	11 - 15 Units	16 - 30 Units
Levin silt loam (76) Egmont brown loam (93) New Plymouth black loam (98) Ohakune loam (90) Katikati sandy loam (95)	Karaka (88) Kumeu peat (96) Takapau sandy loam (69) Muriwai sand (42) Patumahoe clay loam (56) Westmere silt loam (53) Kiwitea silt loam (64) Pukepuke sand (31) Hastings silt loam (30) Temuka black silt loam (34) Waimauku sand (41) Kumeu clay (51) Tikokino (51)	Kumeu clay (Trig Road) (45) Mapua loam (Nelson) (12) Templeton Eyre & Paparua (84) Hastings clay loam (14) Waimakiriri sandy silt loam (Waimate) (3) Waimea silt loam (Nelson) (13) Havelock sandy loam on clay pan (19) Templeton silt loam (Waimate) (7) Waimakiriri silt loam (Blh) (10) Kaiapoi silt loam (8) Twyford silt loam (11) Twyford sandy loam Otiake silt loam (1) Takapau stoney loam (26) Ranzau stoney clay loam (30) Barrhill sandy loam (6) Putiki sandy loam (33) Pakowhai silt loam	Templeton silt loam (CH) (9) Taitapu silt loam (5) Ranzau gravelly silt loam (19) Waimakiriri silt loam (CH) (6) Putiki sandy loam (33) Kawhatau stoney loam (57) Meeanee Makaraka heavy silt loam Makaraka clay loam Matawhero heavy silt loam Matawhero clay loam Waipaoa silt loam

POTASSIUM DEFICIENCY

Occurrence

On any heavily cropped soil with the possible exception of recent alluvial soils and some soils in the drier areas of the South Island (Brown-grey earths, dry yellow-grey earths, dry brown granular loams and clays and rendzinas). On other soils, soil test K values give a reasonable indication of supply. Large amounts of Mg or ammonium -N can decrease K availability.

Species susceptibility

Target soil K test requirements are listed under each crop. They are influenced by soil texture. Relatively large amounts of potassium are taken up by crops, and required in fertiliser on responsive soils, typically 100-250 kg/ha of this element is required for each crop. Corn and peas have relatively small requirements whereas celery, potatoes and tomatoes require considerably more. Target soil K test values can be achieved by applying rates of fertilisers calculated from data in Table 2.

Treatment

Potassium fertilisers are normally broadcast before sowing. Application rates can be decreased by 20-30% if the fertiliser is banded adjacent to seeds. Potassium chloride is often used but potassium sulphate is preferable for chloride sensitive crops such as tomatoes, potatoes, celery, lettuce, beans and cauliflower. This is particularly important on light soils in low rainfall areas.

CALCIUM DEFICIENCY

Occurrence

Erratic and fairly rare. Can occur with soil test values less than 10. Other conditions include excessively wet or dry soils, high humidity and when available K, Mg or ammonium-N concentrations are very large. Uptake is dependent on water uptake for transpiration, and in periods of good growth, and limited transpiration, deficiencies can be found on leafy vegetables such as lettuce, cauliflower and spinach.

Species susceptibility

Celery and lettuce are most sensitive while brussel sprouts, cabbage and sweetcorn are rarely affected.

Treatment

Liming to required pH (see separate crops) is usually adequate. Avoid excessive soluble salts and soil compaction and irrigate regularly in dry conditions. Blackheart in celery, and tipburn on leafy vegetables can be controlled by spraying calcium nitrate (16 kg/1000 i/ha) or calcium chloride (8 kg/1000 i/ha) fortnightly, or specific commercial products as recommended.

MAGNESIUM DEFICIENCY

Occurrence

Symptoms tend to occur approaching maturity when yields may not be affected. Commonest on sandy soils and in wet conditions. Can be induced by excessive K in soils. Soil test values of 12-15 are adequate for most species but susceptible crops require 20+, especially where soil K levels are high.

Species susceptibility

Tomatoes, potatoes, cauliflowers and beans are sensitive to Mg deficiency.

Treatment

Diagnosed deficiencies can be treated by spraying with magnesium sulphate solution (2 kg/100 i), or specific commercial products.

SULPHUR DEFICIENCY

Occurrence

Rare in New Zealand although the continued use of high analysis fertilisers could result in deficiencies developing in soils prone to leaching and with little organic matter.

Species susceptibility

UK data indicate that brassica crops, leeks and radishes are most susceptible and beans, carrots, parsnips and celery are least likely to respond.

Treatment

Use S containing fertilisers such as ammonium sulphate and superphosphate. Elemental S can be used in areas prone to excessive leaching but it becomes available slowly and will acidify the soil.

MICRONUTRIENTS

The inclusion of micronutrients in the fertliser programme is not routine for most vegetables. The most common deficiencies encountered are those of B and Mo in brassica crops. The deficiency occurs because soils contain inadequate supplies of these nutrients or because of pH affecting availability. Deficiencies of Mn, Fe, Zn or Cu are uncommon and are usually related to specific soils or situations.

Diagnosis of deficiency is not reliable from soil testing. Plant analysis is the recommended method of confirming a deficiency. Visual symptoms can be confusing in most cases and only a few situations have clear-cut symptoms.

To determine the need for a micronutrient to be added to a fertiliser programme, knowledge of the soil involved, susceptible crops and conditions conducive to deficiency is needed. This is summarised below.

Where a deficiency is diagnosed during crop growth, foliar applications usually give a good response. Rates of fertilisers to use are included below, and there is a range of commercial products with single or multiple element compositions, use as recommended for these products where the need is diagnosed.

Excessive use of micronutrients should be avoided because toxicities can occur affecting plants or livestock grazed on cropping areas.

Boron

Susceptible soils:

Sands, loamy sands, sandy loams, high pH areas.

Susceptible crops:

Turnip, red beet, carrot, celery, cauliflower, broccoli, cabbage, tomato, asparagus, beans.

Treatment:

cultivate 1-2.5 kg B/ha into soil prior to sowing/planting.
Foliar - apply borax 0.2-0.5 kg/100 i (may need hot water to dissolve) or use an equivalent amount of sodium borate which is more soluble (see Table 10 under Introductory section 'Trace element materials').

Copper

Susceptible soils:

Organic soils

Susceptible crops:

Onion, carrot, corn, cauliflower, lettuce, spinach, broad beans.

Treatment:

Soil - apply copper sulphate at 25-50 kg/ha when first cropped.
Foliar - spray with copper sulphate 200-500 g/100 i/ha.

Iron

Susceptible soils:

Organic and podzolic soils, calcareous soils, soil pH greater than 6.7.

Susceptible crops:

Tomato, potato, beans, spinach.

Treatment

Soil - apply ferrous sulphate at 20 kg/ha.
Foliar - iron chelates at 75-100 g/100 i

Manganese

Susceptible soils:

Podzols, organic soils, soil pH greater than 6.7.

Susceptible crops:

Tomato, beans, cucumber, squash, corn, red beet, radish, lettuce, peas.

Treatment:

Cultivate manganese sulphate into soil at 20-30 kg/ha on mineral soils and 150-300 kg/ha on organic soils.
Foliar - spray with manganese sulphate(200-400 g MnSO₄/100 i/ha).

Molybdenum

Susceptible soils:

Compacted sands, yellow-brown earths from greywacke, yellow-grey earths, soil pH less than 5.4.

Susceptible crops:

Brassicas, cucurbits, tomato, spinach, legumes.

Treatment:

Soil - correct soil pH; apply sodium molybdate at 0.5-2.0 kg/ha.
Foliar - spray with sodium molybdate at 25-50 g/100 i/ha.

Zinc