ARCHIVE: Fertiliser Manual (RB209)

Top Fruit, Established Orchards

The nitrogen recommendations are based on the soil management system and soil type. The recommendations are intended as a guide and should be varied according to variety, rootstock, vigour, leaf or fruit analysis and appearance of foliage. Nitrogen dressings can be split across the growing season. The largest demand for nitrogen is between blossom and late July which corresponds with the rapid shoot growth phase and nitrogen applications should reflect this. No application should be made during and after leaf drop.

The results of leaf and fruit analysis are particularly important. The width of the herbicide strip and the effectiveness of the herbicide programme and use of mulches (e.g. straw) can also influence nitrogen requirements. Straw and composted green waste mulches release potash which can antagonise calcium uptake, which in extreme cases can cause physiological fruit disorders where soil calcium availability is low. Guidance on the use of leaf analysis to modify nitrogen and other minerals recommendations is given on pages 166-168.

Applying excess nitrogen encourages vegetative growth with large, dark green leaves. This may adversely affect fruit quality, especially taste, firmness and storage quality. Increasing nitrogen reduces the amount of red colour and intensifies the green colour of apples. This effect is detrimental to crop appearance and value in red coloured varieties, but can be beneficial in culinary varieties such as Bramley. Excess nitrogen can also reduce the storage life of fruit. However, autumn foliar application of nitrogen can improve blossom quality in the following spring.
When nitrogen is deficient, the leaves of fruit crops tend to be small and pale green, the bark of fruit trees may be reddish in colour and shoot growth restricted. Yields are reduced due to the decrease in the number and size of fruit, which may also be highly coloured.

In grass alley herbicide strip orchards, the tree roots are largely confined to the strip and fertiliser should be applied to the herbicide strip only. The nutrient recommendation given in the table are for the complete orchard area and should be reduced pro-rata where nitrogen is applied to the bare soil area only.

Where soil pH is high, consideration should be given to using ammonium sulphate which will help lower the soil pH. Calcium nitrate will have little effect on the soil pH but the calcium applied may improve the storage quality of apples.

Fertigation of young trees

The addition of nutrients to the irrigation water (fertigation) can improve the growth and early cropping of young apple trees planted on sites previously cropped with apples, and may help overcome replant problems. A benefit is more likely where the soil organic matter level and nitrogen reserves have been depleted by long-term use of herbicides intended to maintain a bare soil surface. The rate of nitrogen addition should be about 10 g N/tree in the first growing year, increasing to 15–20 g N/tree in the second and third years. Fertigation will allow fertiliser rates to be reduced by up to 50%of that used for broadcast applications in orchards older than three years. It can also help correct nutrient deficiencies such as phosphate because nutrients in solution are more rapidly moved down the soil profile. Again leaf analysis should be used regularly to provide feedback on adjusting nutrition to appropriate levels.

Care should be taken to ensure soils are not completely wetted to minimise the risk of nitrate leaching.

Biennial fertiliser application

For established crops, the timing of phosphate, potash and magnesium application is not critical.

Established Top Fruit – nitrogen

Crop

Grass/herbicide strip a

Overall grass

 

kg/ha

Dessert apples b
Light sand and shallow soils

 80

 120

Deep silty soils

 30

 70

Clays

 40

 80

Other mineral soils

 60

 100

Cinary and Cider apples
Light sand and shallow soils

 110

 150

Deep silty soils

 60

 100

Clays

 70

 110

Other mineral soils

 90

 130

Pears, Cherries and Plums
Light sand and shallow soils

 140

 180

Deep silty soils

 90

 130

Clays

 100

 140

Other mineral soils

 120

 160

a. The recommended rates are for the complete orchard area and should be reduced pro-rata where nitrogen is applied to the herbicide strip area only.
b. Larger nitrogen rates may be needed on varieties with regular heavy cropping potential (i.e. >40 t/ha).

Refer to pages 166-168 for guidelines on modifying nitrogen rate according to leaf analysis.

Established top fruit – phosphate, potash and magnesium

 

SNS, P, K or Mg Index

 

0

1

2

3

4 & Over

P mg/l (Olsen's)

0-9

10-15

16-25

26-45

>46

K mg/l

0-60

61-120

121-240

241-400

>401

Mg mg/l

0-25

26-50

51-100

101-175

>176

kg/ha

All top fruit, annually
Phosphate (P2O5)

80

40

20

20

0

Potash (K2O)

220

150

80

0

0

Magnesium (MgO)

100

65

50

0

0

a. Pears require an additional 70 kg K2O/ha up to Index 3, but no addition at Index 4, cider apples also respond to larger application rates of potash.

The recommended rates are for the complete orchard area. In grass/herbicide strip orchards, the recommended rates should be reduced pro-rata where fertiliser is applied to the herbicide strip area only.

For apples, soil K Index should not be built up above 2 because excessively large potash applications can adversely affect storage quality.

To avoid inducing magnesium deficiency, the soil K: Mg ratio (based on soil mg/litre K and Mg) should be no greater than 3:1. For example, if soil K is 240 mg/litre soil Mg should not exceed 80 mg/litre.

Where the yields of apples and pears are regularly above 40 t/ha, maintenance applications of potash may need to be increased by 20 kg K2O/ha for every additional 10 t/ha in yield.

When applying phosphate fertilisers, only use those that contain a large proportion of water-soluble phosphate.

 

Don’t forget to deduct nutrients applied as organic manures (see Section 2)

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