• Farm-gate nitrogen balances on intensive dairy farms in the south west of Ireland

      Treacy, Mark; Humphreys, James; McNamara, Kevin; Browne, R.; Watson, C. J.; Teagasc Walsh Fellowship Programme; European Union; Dairy Levy Research Trust (Teagasc, Oak Park, Carlow, Ireland, 2008)
      Nitrogen management and farm-gate N balances were evaluated on 21 intensive dairy farms in the south west of Ireland for each of four years (2003 to 2006). The mean annual stocking density was equivalent to 202 kg/ha (s.d. 29.6) of N excreted by livestock on the farm. The mean annual farm-gate N surplus (imports – exports) declined between 2003 and 2006 (277 to 232 kg/ha, s.e. 6.8; P < 0.001) due to a decline in annual N imports (fertilizer, feed and imported manures; 335 to 288 kg/ha, s.e. 6.9; P < 0.001). Overall annual fertilizer N use on the farms decreased during the study period (266 to 223 kg/ha, s.e. 6.5; P < 0.001) mainly due to lower inputs for the first application in spring and for the production of first-cut silage. These decreases were partly offset by applying more slurry in spring for early grazing and for first-cut silage. The introduction of white clover resulted in lower N imports on four farms. Export of N from farms was unaffected by reductions in N imports. The mean efficiency of N use tended to increase over time (0.18 in 2003 to 0.20 in 2006). The large variation in quantities of fertilizer N applied on farms with similar stocking densities suggests potential for further improvements in the efficiency of N use. In terms of fertilizer N use, complying with S.I. No. 378 of 2006 did not require major changes in the N management practiceson 19 of the farms.
    • Farm-gate phosphorus balances and soil phosphorus concentrations on intensive dairy farms in the south-west of Ireland

      Ruane, E. M.; Treacy, Mark; McNamara, Kevin; Humphreys, James (Teagasc (Agriculture and Food Development Authority), Ireland, 2014)
      Phosphorus (P) loss to water is a significant threat to water quality in Ireland. Agriculture is an important source of this P. There is concern about balancing agronomic requirements and environmental protection in regulations prescribing P management on farms. This study examined farm-gate (P) balances and soil test P (STP) concentrations on 21 dairy farms in the south west of Ireland over four years, from 2003 to 2006 inclusive. Stocking density on the farms averaged 2.4 (s.d. = 0.4) livestock units (LU) per ha. Annual mean import of P onto farms was 21.6 (1.9) kg P/ha. Fertilizer P accounted for 47% (0.041), concentrates 35% (0.060) and organic manures 18% (0.034) of imported P. The mean annual P balance per farm was 9.4 (1.2) kg/ha, ranging from –3 to 47 kg/ha and mean P use efficiency was 0.71 (0.05) ranging from 0.24 to 1.37. The mean STP per farm following extraction using Morgan’s solution was 8.15 (2.9) mg/L of soil and ranged from 4.4 (2.2) to 14.7 (6.4) mg/L. There was a positive relationship (R2 = 0.34; P < 0.01) between STP and P balance; farms with a deficit of P tended to have agronomically sub-optimal STP and vice versa. The high between- and withinfarm variation in STP indicates that farmers were either unaware or were not making efficient use of STP results, and consequently there was agronomically sub-optimal soil P status in some fields and potentially environmentally damaging excesses on others (often within one farm). There was considerable potential to improve P management practices on these farms with clear agronomic and environmental benefits.
    • Nutrient management on intensive dairy farms in the southwest of Ireland

      Humphreys, James; Treacy, Mark; McNamara, Kevin (Teagasc, 2006-08-01)
      Intensive grass-based dairy farming relies on high inputs of nutrients that are now regulated under SI 378, 2006 (Good Agricultural Practice for Protection of Waters). This project studied nutrient management practices on twenty-one intensive dairy farms in the south-west of Ireland between 2003 and 2006. Mean stocking rate was 202 kg organic-N/ha deposited by grazing livestock. Overall fertiliser-N use on the farms decreased from 266 to 223 kg N/ha/yr during the study, with the rate of fertiliser-N in the first application each year decreasing from 49 to 33 kg N/ha, while the rate of fertiliser-N applied for first cut silage production also fell from 106 to 96 kg N/ha. These decreases were partly achieved by applying more slurry in springtime and by the introduction of white clover on five of the farms. While the limits on fertiliser-N use under SI 378 were exceeded on ten farms in 2003, the limits were exceeded on only two farms in 2006. Fertiliser-P usage declined from 12.0 to 10.2 kg P/ha/yr, and complied with the limits of SI 378 on thirteen of the farms in 2006. Mean Morgan’s extractable soil P concentration (STP) exceeded 10 mg/l on five farms, while the mean concentration exceeded 8 mg/l on ten farms. Phosphorus management, therefore, was close to that required by SI 378 on most farms. Slurry storage capacity met or exceeded the minimum requirements of SI 378 on eight farms; substantial investment in slurry storage facilities was necessary on thirteen farms. The mean N surplus on the farms declined from 277 to 232 kg N/ha/yr during the study due to a decline in total N input from 335 to 288 kg N/ha/yr over the same period. The mean efficiency of N-use increased from 17.9 to 20.2 %. The large variation in rates of fertiliser-N applied on farms with similar stocking rates suggests potential for further improvements in N use efficiency on some farms. Decreases in nutrient input levels can be partly attributed to increased farmer awareness, due to advice and record keeping from this study and the introduction of SI 378, and the increasing cost of nutrient inputs relative to output prices. In terms of fertiliser N and P use and soil P concentrations, complying with the limits in SI 378 does not require major changes in nutrient management practices on the majority of these intensive dairy farms.