ARCHIVE: Fertiliser Manual (RB209)

Sheep Production – Nitrogen Requirements


The recommendations for promoting the growth of grass for animal production are based on knowledge of grass response to fertiliser nitrogen, under conditions where growth is not limited by supplies of other nutrients. The recommendations are based on the need to produce the amount of home grown forage necessary to maintain a target intensity of production, rather than the optimal amount relative to the cost of fertiliser. This enables farmers who may be operating at widely different stocking rates and feeding different levels of concentrates to obtain relevant recommendations for whole season nitrogen requirements. Nitrogen requirements have been calculated using commonly accepted values for feed intake, liveweight gain, proportions of available land devoted to cutting and grazing and efficiencies with which home-grown forage can be utilised under the two harvesting regimes (cutting and grazing). If hay is used to supplement feeding in the winter months, refer to the Table on page 213 for recommendations on nitrogen requirement.

The N recommendations for sheep are based on supplying sufficient home grown forage and concentrate to maintain target annual intake at 3 levels of production. Ewes are fed concentrates during lambing in the intensively and moderately grazed systems (1.0 and 0.5 kg/ewe/d, respectively). They also receive conserved forage at this time. Lambs may also need to be fed concentrates to maintain the higher stocking rates. Assumptions regarding LU are as follows: 1 ewe + lambs = 0.17 LU in the intensively and moderately grazed systems, and 0.14 LU in the extensively grazed system. As with dairy and beef, silage production is optimised at relatively high levels of N requirement, and hence in the moderately grazed system there is a significant N requirement for cut grass, and little or none for grazed grass. Note, the whole season total N requirement can be provided through contributions from SNS, clover and applied organic manures, as well as fertiliser. If your system is markedly different from this, then you may need to seek FACTS qualified advice about interpretation of N recommendations.

Three Grass Growth Classes have been defined earlier (see page 188): Very good/Good, Average and Poor/Very poor. Their definition depends on the water holding capacity of the soil and amount of summer rainfall.

There are three tables for sheep production; one for nitrogen requirements for cutting and grazing for Grass Growth Class Very good/Good (Table 8.6), one for the Average Grass Growth Class (Table 8.7), and one for the Poor/Very poor Grass Growth Class (Table 8.8). Therefore the first step is to identify the Grass Growth Class of your land to direct you to the correct table. Within each table there are total nitrogen requirement values given for three different levels of production intensity according to stocking rate to enable most of the systems operating in UK grassland farming to be matched as closely as possible.

Adjustments can be made (indicated above the tables) for high or low soil nitrogen supply (SNS – see page 188), and for nitrogen from applied manures. Suggestions for the percentage splits and their timing for each total fertiliser amount are also given within the tables and accompanying notes.

To use the recommendations, first identify the Grass Growth Class of your land to direct you to the correct table. Within the sheep tables some intensive, moderate and extensive systems are identified, which are then each subdivided according to stocking rate.

First Actions:

  • Identify whether your land is Very good/Good, Average or Poor/Very poor Grass Growth Class (page 188)
  • Choose Table 8.6 (Good/Very good), Table 8.7 (Average) or Table 8.8 (Poor/Very poor)
  • Identify the SNS of the land (Low Moderate, High) (page 188)
  • Find the stocking rate division most appropriate to your management

Table 8.6 provides the whole season total nitrogen requirements for cutting and grazing in the Very good/Good Grass Growth Class. Values in the table are for a moderate SNS situation. Reduce total fertiliser nitrogen input by 30 kg N/ha for high SNS. Increase total fertiliser nitrogen input by 30 kg N/ha for low SNS (uncommon for dairy production).

Table 8.6 Sheep: Grass Growth Class Very good/Good. Whole-season total nitrogen requirement for cut and grazed grass (kg N/ha).

SHEEP Grass Growth Class Very good/Good

Total N requirement

 

Stocking rate Cut Grazed
  LU/ha kg/ha Indicative
yield*(t DM/ha)
kg/ha
Moderately to Intensively grazed 2.1 370 11.3 280
1.7 340 10.9 170
1.2 300 10.3 70
Extensively to Moderately grazed 1.0 280 10.1 40
0.7 260 9.6 0
0.5 240 9.3 0
Extensively grazed 0.2 210 8.9 0
0.1 200 8.8 0
0.05 200 8.5 0
  • Values in the above table are total annual nitrogen requirement. To obtain your fertiliser requirement, DON’T FORGET to consider nitrogen supply from SNS (page 188), clover (page 208) and applied organic manures (Section 2)
  • *Average dry matter yields for cut grass should be achievable in most seasons.
  • For estimation of LU for sheep systems, use an average of 0.17 LU per ewe plus lambs. Stocking rates >2.0 increase the risk of high worm burden with consequences for animal productivity.
  • For stocking rates that are intermediate between values in the table, assume a proportional difference in nitrogen requirement between two values.

The total nitrogen requirement should be split into 3-6 applications during the growing season if > 150 kg N/ha. Three applications would be appropriate only where the total requirement is less than or equal to 150 kg N/ha. Applications need not be of equal size and advantage can be taken of the relatively high grass growth rate in late spring. For example, the recommended split of N application could be; for first cut; 40% (could be split further, Feb-March 15%, April 25%), for second cut; 35% (could be split further, May 20%, June 15%); for subsequent cuts; 25% (could be split further, July 15%, August 10%).

In mild areas where earlier grazing is possible, nitrogen may be applied from early-mid February. In upland areas, apply nitrogen from mid-late March. Typically, nitrogen would be applied around one month before normal turn-out date.

Cutting after early spring grazing

Following early spring grazing, reduce the 1st cut recommendation by 25 kg/ha. For grazing after cutting, see recommendations in the Grazing and cutting section later in the sheep section.

Table 8.7 provides the whole season total nitrogen requirements for cutting and grazing in the Average Grass Growth Class. Values in the table are for a moderate SNS situation. Reduce total fertiliser nitrogen input by 30 kg N/ha for high SNS. Increase total fertiliser nitrogen input by 30 kg N/ha for low SNS (uncommon for dairy production).

Table 8.7 Sheep: Grass Growth Class Average. Whole-season total nitrogen requirement for cut and grazed grass (kg N/ha).

SHEEP Grass Growth Class Average

Total N requirement

 

Stocking rate Cut Grazed
  LU/ha kg/ha Indicative
yield*(t DM/ha)
kg/ha
Moderately to Intensively grazed 2.0 340 9.7 350
1.5 300 9.3 170
1.0 270 8.8 50
Extensively to Moderately grazed 0.9 260 8.8 30
0.7 250 8.6 0
0.5 230 8.3 0
Extensively grazed 0.2 210 7.9 0
0.1 200 7.7 0
0.05 200 7.6 0
  • Values in the above table are total annual nitrogen requirement. To obtain your fertiliser requirement, DON’T FORGET to consider nitrogen supply from SNS (page 188), clover (page 208) and applied organic manures (Section 2)
  • *Average dry matter yields for cut grass should be achievable in most seasons.
  • For estimation of LU for sheep systems, use an average of 0.17 LU per ewe plus lambs. Stocking rates >2.0 increase the risk of high worm burden with consequences for animal productivity.
  • For stocking rates that are intermediate between values in the table, assume a proportional difference in nitrogen requirement between two values.

The total nitrogen requirement should be split into 3-6 applications during the growing season if > 150 kg N/ha. Three applications would be appropriate only where the total requirement is less than or equal to 150 kg N/ha. Applications need not be of equal size and advantage can be taken of the relatively high grass growth rate in late spring. For example, the recommended split of N application could be; for first cut; 40% (could be split further, Feb-March 15%, April 25%), for second cut; 35% (could be split further, May 20%, June 15%); for subsequent cuts; 25% (could be split further, July 15%, August 10%).

In mild areas where earlier grazing is possible, nitrogen may be applied from early-mid February. In upland areas, apply nitrogen from mid-late March. Typically, nitrogen would be applied around one month before normal turn-out date.

Cutting after early spring grazing

Following early spring grazing, reduce the 1st cut recommendation by 25 kg/ha. For grazing after cutting, see recommendations in the Grazing and cutting section later in the sheep section.

Table 8.8 provides the whole season total nitrogen requirements for cutting and grazing in the Very poor/Poor Grass Growth Class. Values in the table are for a moderate SNS situation. Reduce total fertiliser nitrogen input by 30 kg N/ha for high SNS. Increase total fertiliser nitrogen input by 30 kg N/ha for low SNS (uncommon for dairy production).

Table 8.8 Sheep: Grass Growth Class Very poor/Poor. Whole-season total nitrogen requirement for cut and grazed grass (kg N/ha).

SHEEP Grass Growth Class Very poor/Poor

Total N requirement

 

Stocking rate Cut Grazed
  LU/ha kg/ha Indicative
yield*(t DM/ha)
kg/ha
Moderately to Intensively grazed 1.4 280 7.0 270
1.2 270 6.9 190
1.0 260 6.7 140
Extensively to Moderately grazed 0.9 250 6.8 120
0.7 240 6.5 70
0.5 230 6.3 30
Extensively grazed 0.2 210 6.0 0
0.1 200 5.8 0
0.05 200 5.8 0
  • Values in the above table are total annual nitrogen requirement. To obtain your fertiliser requirement, DON’T FORGET to consider nitrogen supply from SNS (page 188), clover (page 208) and applied organic manures (Section 2)
  • *Average dry matter yields for cut grass should be achievable in most seasons.
  • For estimation of LU for sheep systems, use an average of 0.17 LU per ewe plus lambs. Stocking rates >2.0 increase the risk of high worm burden with consequences for animal productivity.
  • For stocking rates that are intermediate between values in the table, assume a proportional difference in nitrogen requirement between two values.

The total nitrogen requirement should be split into 3-6 applications during the growing season if > 150 kg N/ha. Three applications would be appropriate only where the total requirement is less than or equal to 150 kg N/ha. Applications need not be of equal size and advantage can be taken of the relatively high grass growth rate in late spring. For example, the recommended split of N application could be; for first cut; 40% (could be split further, Feb-March 15%, April 25%), for second cut; 35% (could be split further, May 20%, June 15%); for subsequent cuts; 25% (could be split further, July 15%, August 10%).

In mild areas where earlier grazing is possible, nitrogen may be applied from early-mid February. In upland areas, apply nitrogen from mid-late March. Typically, nitrogen would be applied around one month before normal turn-out date.

Cutting after early spring grazing

Following early spring grazing, reduce the 1st cut recommendation by 25 kg/ha. For grazing after cutting, see recommendations in the Grazing and cutting section below.

Grazing and cutting systems

Where cut grass is followed by grazing, farmers should obtain the two total N requirement values (cut and grazed) for their chosen system. For cut grass, the recommended split of N application could be; For first cut; 40% (could be split further, Feb-March 15%, April 25%), For second cut; 35% (could be further split May 20%, June 15%); subsequent cuts 25% (could be further split July 15%, August 10%). For grazed grass the recommended split could be: Feb-March 15%, April 25%, May 20%, June 15%; July 15%, August 10%.

Then, for example in the case of a 1 cut system followed by grazing; follow the guidance on proportional total N split for 1st cut, i.e. 40% of the total value. Then revert to 20% proportional split of grazed grass total value (starting May) and follow grazing split accordingly.

Similarly, for a 2 cut system followed by grazing; follow the guidance on the proportional total N split for 1st and 2nd cuts, i.e. 40% for 1st cut and 35% for 2nd cut. Then revert to the 15% proportion split of the grazed grass total value (starting July) and follow grazing split accordingly.

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