Fertiliser Index System

The recommendations in this section are using the RoI fertiliser classification system and are based on Teagasc research.

Due to slight differences between the RoI and NI classification systems, these recommendations are only a guide for Northern Ireland farmers. They can be converted between the RoI and NI classification systems using this Conversion Table

On a farm by farm basis your nutrient requirement programme will be determined by The Nitrate Directive (SI no 31 of 2014). “The Nitrates Directive”

All the recommendations given on this web site have been calculated using the Fertiliser Index System as laid out by Teagasc Johnstown Castle Co Wexford. This system is based on three main points:

  1. The results of a soil analysis to determine the levels of nutrients in the soil.
  2. The level of nutrients required to grow the proposed crop for the coming year.
  3. The pH of the soil i.e. the pH of the soil may need to be corrected to maximise the availability of the nutrients to the crop. At different pH ranges, soil nutrients may be locked and unavailable to the crop. Gran-Lime should be added to correct any unfavourable pH ranges.
The Soil Index System
Soil Index Index Description Response to Fertilisers
1 Very Low Definite
2 Low Likely
3 Medium Unlikely / Tenuous
4 High None

This gives the basis of the Fertiliser Index System on which our recommendations are made. In our recommendations section we firstly give a table of the crop requirements at all soil index levels.

Winter Wheat Nutrient Requirements (unit/acre)
Index N P K
1 Very Low 168 36 112
2 Low 144 28 100
3 Medium 96 20 88
4 High 64 0 0

From Table 4 we can see for example:

  • Where the soil is at index 2 for P we need to apply 28 units of P per acre.
  • Where the soil is at index 3 for K then we need to apply 88 units of K per acre.

We then give a table of suggested combinations of products that are most convenient to achieve these nutrient requirements.

Nitrogen Index System

Tillage
The Nitrogen recommendations are based on the requirement of each particular crop, taking into account the previous cropping, the manuring history of the field and the soil type:

Application rate (bags/acre)
Index K1 Very Low K2 Low K3 Medium K4 High
P1 Very Low 3 x (0-7-30)
+
2 x (18-6-12)
+
4½ x (CAN)
2 x (0-7-30)
+
3 x (18-6-12)
+
4 x (CAN)
3 x (0-10-20)
+
2 x (Replenish)
+
4¾ x (CAN)
1½ x (16% Superphos)
+
2 x (Classic NK)
+
4x (CAN)
P2 Low 3½ x (0-7-30)
+
1½ x (Richland)
+
5 x (CAN)
3 x (0-7-30)
+
1 x (18-6-12)
+
5½ x (CAN)
2 x (0-7-30)
+
2 x (18-6-12)
+
4 x (CAN)
1 x (16% Superphos)
+
2 x (Classic NP)
+
4 x (CAN)
P3 Medium 2½ x (0-7-30)
+
2½ x (Classic NK)
+
4x (CAN)
2 x (0-7-30)
+
3 x (Replenish)
+
4 x (CAN)
2 x (0-7-30)
+
2 x (Replenish)
+
4½ x (CAN)
½ x (16% Superphos)
+
2 x (Classic NP)
+
4 x (CAN)
P4 High 1½x (Muriate of Potash)
+
2 x (Classic NK)
+
4½ x (CAN)
1 x (Muriate of Potash)
+
3 x (Classic NK)
+
4 x (CAN)
1 x (Muriate of Potash)
+
2 x (Classic NK)
+
4½ x (CAN)
6 x (CAN)

If we look then at table 5 we can easily see the recommendation for index P2, K3 at the intersection of the rows and columns is:

  • 2 x 50kg bags of (0-7-30),
  • 2 x 50kg bags of (18-6-12)
  • And 4 x 50kg bags of (CAN)