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Ten ways to cut fertilizer N costs on the farm

By James Humphreys


  1. Apply 23 units/acre (29 kg/ha) for the first application in spring (mid-Jan to early March depending on location and soil type etc.). Urea is more cost effective than CAN in spring.

  2. Replace the first application of fertilizer N by an application of watery slurry. 1000 gals watery slurry = 8 to 10 units of N/acre. At Solohead around 2,500 gals/acre are applied on two-thirds of the farm on 1 Feb. using an umbilical system. The other one-third is grazed during Feb and early March. Allow around six weeks between application and expected date of grazing. You get the best response to the nutrients in slurry when it is applied in the spring (late Jan. to April).

  3. Apply the second application of fertilizer N between 6 and 4 weeks after the first. A 6-week interval should be allowed with earlier start dates (mid-Jan) and a 4-week interval with later application dates (mid-Feb). The second application should take place sometime during March. The third application should roughly coincide with closing up for silage in April. Match fertilizer N applications to stocking rates on the farm at various times of the year (see table 2).

  4. Replace some of the fertilizer N for first cut silage by slurry. If 92 units/acre (115 kg/ha) is applied for first cut silage, this can be lowered to around 69 units/acre (85 kg/ha) along with an application of 3000 gals slurry/acre. At Solohead 3000 gals/acre is applied to around two-thirds of the first-cut silage area on 1 April (this is the proportion of the silage area that will have been grazed at that stage). The slurry is applied allowing at least 6-weeks between application and expected silage harvest date. An interval of around one week is allowed between application of slurry and the application of fertilizer N for first-cut silage. Don’t apply the fertilizer N immediately before or shortly after the slurry because this leads to losses by denitrification.

  5. Try to make as much of your silage as possible as first cut. Firstly work out how much silage is required. Secondly, depending on requirements, aim to maximise stocking rate on the grazing area during April and May. This makes as large an area as possible available for first-cut silage. There is a very high response to fertilizer N during April and May. First cut silage yields will be at least 20% higher than second cut for more-or-less the same input costs. High grazing pressure on the grazing area during April and May is good for grass quality later in the season.

  6. Diluting slurry with dirty water will increase the efficiency of utilization of N in the slurry when it is applied to silage stubble after first cut silage. Although dilution will lower the DM and N content of the slurry, it will increase the efficiency of N utilization (lower volatilization losses).

  7. Avoid making second cut silage, if possible. Having the whole farm available for grazing from June onwards lowers the requirement for fertilizer N. Apply fertilizer N in line with stocking rate (Table 2) and also pasture cover. If pasture cover is above target, lower the amount - or increase the interval between applications - of fertilizer N. Do not skip applications.

  8. Plan to build pasture cover by extending out the rotation from mid to late July depending on stocking rate and location (later on higher stocked farms in more favourable locations and vice-versa). Fertilizer N applied in July and August has greater bearing on grass supply in Nov./Dec. and in the following spring than applications later in the autumn. Cease applying fertilizer N by mid-September (earlier under more restricted conditions – wet soils, northerly location and aspect etc.)

  9. KEEP RECORDS of quantities and dates of application – and study them. Blanket spreading of fertilizer N simplifies record keeping and this helps to keep overall fertilizer N use on the farm under control (this can bring about a considerable saving in annual fertilizer N use while also lowering baled surpluses). The first three applications during the spring (during calving) and applications during August and September can be blanket spread with no loss of production. Blanket spreading during the summer months can result in slight (3.5%) lowering of production.

  10. WHITE CLOVER has the potential to halve the amount of fertilizer N used on the majority of grassland farms in Ireland. Annual savings on expenditure on fertilizer N of between €2,000 and €4,000 per farm are currently being achieved on commercial dairy and beef farms in Ireland by making greater use of white clover.