ARCHIVE: Fertiliser Manual (RB209)

Dairy 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 energy conversion to milk, proportions of available land devoted to cutting and grazing and efficiencies with which home-grown forage can be utilised under the two harvesting regimes (cut and grazed grass).

The N recommendations for dairy production are based on feeding a herd of Holstein-Friesian animals (where 1 adult = 650 kg liveweight = 1 LU) producing standard milk composition (4.0% fat and 3.3% protein). Concentrate use ranges from 0.5t to 4.4t/cow/yr. It is assumed that 40% of the forage DM comes from cut grass, the remainder from grazed grass, and that silage production is optimised, whatever the overall level of production, resulting in (in general) higher levels of N requirement under cutting than grazing. A 3-cut system is assumed – but advice is provided about how to operate with fewer cuts. Note, the whole season total N requirement can be provided through contributions from SNS, clover and applied organic manures, as well as fertiliser. If you operate a markedly different system to this, you may need to seek FACTS qualified advice about interpretation of the 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 two tables for dairy production; one for nitrogen requirements for cutting and grazing on Grass Growth Class Very Good/Good (Table 8.1) and a second table for nitrogen requirements for cutting and grazing on Average Grass Growth Class (Table 8.2). Therefore, the first step is to identify the Grass Growth Class of your land to direct you to the correct table. It is assumed that dairy farming requires a Grass Growth Class of at least Average. Within each table there are total whole season nitrogen requirement values given, according to level of production, concentrate use and 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 each of the dairy tables the system is first fixed by the average annual milk yield per cow. Each of these milk yields is then subdivided according to concentrate use and each of these further subdivided according to stocking rate. Thus, systems are grouped in sets of three according to milk yield and concentrate use with a range of stocking rates. The maximum stocking rate which can be supported for each milk yield/concentrate combination is given in the top line of each set of three.

First Actions:

  • Identify whether your land is Very good/Good or Average Grass Growth Class (page 188)
  • Choose Table 8.1 (Good/Very good) or Table 8.2 (Average)
  • Identify the SNS of the land (Low, Moderate, High) (page 188)
  • Find the milk yield/concentrate/stocking rate division most appropriate to your management.

Table 8.1 provides the whole season total nitrogen requirements for cutting and grazing in the Good/Very good Grass Growth Class (most dairy enterprises). Values in the table are for a moderate SNS. 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 8.1 Dairy: Grass Growth Class Very Good / Good. Whole-season total nitrogen requirement for cut and grazed grass (kg N/ha).

DAIRY Grass Growth Class Very Good / Good

 

    Total N Requirement
Milk yield Concentrate use Stocking rate Cut Grazed
l/cow/yr t/cow/yr LU/ha kg/ha Indicative yield*
(t DM/ha)
kg/ha
8,000 to
10,000
4.4 4.0 360 11.2 280
3.5 310 10.6 210
3.0 260 9.7 150
8,000 to
10,000
3.7 3.0 370 11.3 300
2.6 310 10.5 210
2.2 240 9.4 150
6,000 to
8,000
2.2 2.6 360 11.2 320
2.2 280 10.1 210
1.8 200 8.5 140
6,000 to
8,000
1.5 2.2 360 11.2 340
1.8 260 9.9 210
1.6 210 8.8 170
6,000 to
8,000
0.9 1.9 330 10.9 320
1.7 280 10.1 240
1.5 230 9.1 190
4,000 to
6,000
0.9 2.4 350 11.0 330
2.1 280 10.1 240
1.8 210 8.8 180
4,000 to
6,000
0.5 2.1 320 10.7 290
1.9 270 9.9 230
1.7 220 8.9 190
< 5,000
extended
grazing
0.5 2.5 350 11.1 340
2.2 310 10.6 240
2.0 270 9.9 200

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.

  • concentrate use is based on that used per lactating cow over a calendar year
  • stocking rate is based on all dairy animals (lactating cows plus followers), 1 cow = 1 LU
  • To interpolate between stocking rates at a given milk yield/concentrate use combination, assume a proportional difference in nitrogen requirement between two values.
  • To interpolate between concentrate use within a given milk yield/stocking rate combination:
    • add 10 kg N/ha for every reduction of 0.1 tonnes concentrate/year/animal
    • subtract 10 kg N/ha for every increase of 0.1 tonnes concentrate/year/animal.
  • Seek additional help from a FACTS qualified advisor if you have difficulty in matching your system to those in the table.

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/equal to150 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 dairy section.

Table 8.2 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 in a high SNS situation. Increase total fertiliser nitrogen input by 30 kg N/ha in a low SNS situation (uncommon for dairy production).

Table 8.2 Dairy: Grass Growth Class Average. Whole-season total nitrogen requirement for cut and grazed grass (kg N/ha).

DAIRY Grass Growth Class Average

 

    Total N Requirement
Milk yield Concentrate use Stocking rate Cut Grazed
l/cow/yr t/cow/yr LU/ha kg/ha Indicative yield*
(t DM/ha)
kg/ha
8,000 to
10,000
4.4 3.5 340 9.7 290
3.1 300 9.3 210
2.8 260 8.8 170
8,000 to
10,000
3.7 2.6 330 9.7 290
2.4 300 9.3 240
2.2 270 8.8 200
6,000 to
8,000
2.2 2.3 320 9.6 340
2.1 290 9.1 260
1.8 230 8.2 180
6,000 to
8,000
1.5 1.9 310 9.4 340
1.7 260 8.8 240
1.5 220 8.0 190
6,000 to
8,000
0.9 1.7 300 9.4 340
1.5 250 8.6 240
1.3 200 7.6 180
4,000 to
6,000
0.9 2.1 300 9.4 330
1.9 260 8.8 250
1.7 220 8.0 200
4,000 to
6,000
0.5 1.9 290 9.2 330
1.7 250 8.5 240
1.5 200 7.7 190
< 5,000
extended
grazing
0.5 2.2 340 9.7 340
2.0 300 9.3 250
1.8 270 8.9 200
  • 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.
  • concentrate use is based on that used per lactating cow over a calendar year
  • stocking rate is based on all dairy animals (lactating cows plus followers), 1 cow = 1 LU
  • To interpolate between stocking rates at a given milk yield/concentrate use combination, assume a proportional difference in nitrogen requirement between two values.
  • To interpolate between concentrate use within a given milk yield/stocking rate combination:
    • add 10 kg N/ha for every reduction of 0.1 tonnes concentrate/year/animal
    • subtract 10 kg N/ha for every increase of 0.1 tonnes concentrate/year/animal.
  • Seek additional help from a FACTS qualified advisor if you have difficulty in matching your system to those in the table.

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/equal to150 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 see below.

Grazing and cutting systems

Where cut grass is followed by grazing, you should obtain the two total N requirement values (cut and grazed) for your 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%); for 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.

ADLib logo Content provided by the Agricultural Document Library
© University of Hertfordshire, 2011