Phosphorus (P) fertilizer is required to sustain productive pastures in Australia, yet optimum P fertility is poorly defined. A large farmlet study involving 10 herds was established in 1995 to determine the relationship between milk production and pasture response to four different P fertilizer rates, at three stocking rates. Pasture growth significantly increased with increasing P fertilizer rate. Cumulative milk production from pasture over 4 years, was significantly affected by P fertilizer, but responses diminished with increasing P rate. The results from this study will enable a better targeting of P fertility levels for profitable milk production from temperate dairy pastures and minimise the environmental impact of excess P fertilizer use

Aarons, S. R.

Awty, I.

Gourley, C. J. P.

O\u27Doherty, M.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings XIX International Grassland Congress Phosphorus Fertilizer Requirements for Temperate Dairy Pastures and Milk Production in South Eastern Australia C. J. P. Gourley Agriculture Victoria, Australia I. Awty Agriculture Victoria, Australia M. O'Doherty Agriculture Victoria, Australia S. R. Aarons Agriculture Victoria, Australia Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/19/4/10 This collection is currently under construction. The XIX International Grassland Congress took place in São Pedro, São Paulo, Brazil from February 11 through February 21, 2001. Proceedings published by Fundacao de Estudos Agrarios Luiz de Queiroz This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. ID # 04-10PHOSPHORUS FERTILIZER REQUIREMENTS FOR TEMPERATE DAIRYPASTURES AND MILK PRODUCTION IN SOUTH EASTERN AUSTRALIAC.J.P. Gourley, I.Awty, M. O’Doherty, and S.R. AaronsDepartment of Natural Resources and Environment, Hazeldean Rd, Ellinbank,Victoria 3821, Australia.AbstractPhosphorus (P) fertilizer is required to sustain productive pastures in Australia, yetoptimum P fertility is poorly defined. A large farmlet study involving 10 herds was established in1995 to determine the relationship between milk production and pasture response to four differentP fertilizer rates, at three stocking rates. Pasture growth significantly increased with increasing Pfertilizer rate. Cumulative milk production from pasture over 4 years, was significantly affectedby P fertilizer, but responses diminished with increasing P rate. The results from this study willenable a better targeting of P fertility levels for profitable milk production from temperate dairypastures and minimise the environmental impact of excess P fertilizer use.Keywords: Pasture growth, farmlet study, stocking rates, Olsen P.IntroductionPhosphorus fertilizer use is well-entrenched in pasture based dairy systems in Australia.Despite this, the direct link between P fertilizer and milk production is poorly defined andrecommendations have been largely based on results from ungrazed pasture plots (Sparrow1993). Over the past decade, increasing stocking rates and pasture utilisation, have been used tojustify increases in P fertilizer recommendations. Recent studies highlighting the links between Pfertilizer applications and losses from dairy pastures (Nash and Halliwell, 1999) make it essentialthat current and future P fertilizer practices are based on scientifically sound information.Material and MethodsThe study was located at Agriculture Victoria Ellinbank in West Gippsland Victoria (38o15’ S; 145 o 93’E; mean annual rainfall of 1100 mm). The farmlet study involved 10 dairy herdsof 15 cows, in an incomplete factorial design, with 3 stocking rates of 2 (L), 3 (M) and 4 (H)cows/ha, and 4 phosphorus fertilizer rates of 0 (1), 35 (2), 70 (3), and 140 (4) kg P/ha/year. Twoof the treatment combinations, M2 and M4, were replicated twice. Each farmlet contained 13paddocks of uniform area, with total areas of 7.5, 5 or 3.9 ha, corresponding to the 3 differentstocking rates. Basal applications of 44 kg sulphur/ha/year and 30-60 kg potassium/ha/year wereapplied to all pastures with P fertilizer in autumn and spring. The soil type was a well-drained redclay loam (ferrasol). The permanent pasture consisted of perennial ryegrass (Lolium perenneL)(>60%) in association with white clover (Trifolium repens L), annual grasses and broadleafweeds.Cows were initially allocated to herds in June 1995, and at the end of each lactation 3heifers replaced cull cows. Each of the 4 lactation periods were between July and May, with cowsstaying in their respective paddocks during their dry period. At the beginning of each lactation, aprojected milk production curve for each herd was calculated, based on a yield of 180 kg milk fatper cow and accounting for the calving pattern. Milk production from each herd was measuredtwice daily. Supplementary feed requirements was determined by assessing current milkproduction against the projected production curve. Conserved fodder, and brought in hay andbarley, was fed when production fell below the projected curve.Pasture mass (kg DM/ha) was determined weekly in all paddocks and growth rates (PGRkg DM/ha/day) calculated. Pastures were grazed from approx. 2200 to 1350 kg DM/ha. Pasturein excess of cow demand was conserved as silage and fed back to corresponding herds. Soilswere sampled to 10 cm from all 130 paddocks in April of each year and P fertility measuredusing the Olsen P test (Olsen et al. 1954).Results and DiscussionPhosphorus fertility and pasture production. The average initial Olsen P values of allfarmlets in 1994 was 13 mg/kg. The addition of P fertilizer at 70 and 140 kg P/ha/year to the M3,H3, M4, H4 farmlets increased the P fertility over 4 years to 20 and 30 mg/kg, respectively. Thefarmlets receiving 35 kg P/ha/year (L2, M2) maintained their initial fertility and those receiving 0kg P/ha (L1, M1) declined to 7 mg/kg (Table 1). The high P sorption capacity of the soil clearlyimpacted on the rate of change in P fertility. Even after 560 kg P/ha had been applied over 4years (M4,H4), the Olsen P value had only changed from 13 to 30 mg/kg.Increasing P fertilizer rates significantly (P<0.05) increased pasture growth rates (Table1). At a uniform stocking rate of 3 cows/ha, the difference in pasture growth rates between the 0and 140 kg P/ha/year farmlets increased from 8% in 1995-6 to 16% in 1998-9. Stocking rate hadlittle effect on pasture growth rates or P fertility. The dry season in 1997-8 resulted in lowerpasture growth rates across all farmlets (Table 1) but an increase in the relative growth ratedifference between P fertilizer treatments. Work by Singh et al. (1999) on the same site duringthis dry period highlighted the improved performance of white clover when high P fertilizer rateswere applied and this effect is likely to be influencing overall pasture performance.Milk production. All herds had similar annual milk yields, producing around 74,000L/herd/year. Milk production/ha was therefore related to stocking rate, with herds averaging10,000, 15,000 and 19,000 L/ha, for the 3 stocking rates, respectively. When milk productionfrom brought in supplements was accounted for, there was a significant effect of P fertilizer rate(P<0.05) on milk produced from pasture (L/ha) over the 4 years (Figure 1). However, the milkproduction response diminished with increasing P fertilizer additions. The response to P fertilizerwas greatest between 0 and 35 kg P/ha and this effect increased each year. Milk production gainsfrom increasing the P fertilizer rate from 35 to 70 or 140, (corresponding to Olsen P values of 13,20 and 30 mg/kg respectively), were not significantly different (P>0.05), although a positivetrend is apparent with increasing years.These results are in contrast to reports from previous New Zealand farmlet studies whichsuggested increasing P rates up to 100 kg P/ha/year and Olsen P values in excess of 50 mg/kg,were economically justified (Thomson et al., 1993). However, these conclusions were based onthe last year of the 3 year study, and when differences between soil sampling depth, lactationlengths, and the inclusion of all years data are accounted for, the results appear similar.Given the financial costs and environmental implications of applying excess P fertilizerrates, it is important that dairy farmers optimise the P fertility of their farms. The results from thisstudy have quantified the benefits of P fertilizer on milk production and will enable farmers andadvisers to target soil P fertility for optimum milk production.ReferencesNash, D.M. and Halliwell D.J. (1999). Fertilizer and phosphorus losses from productive grazingsystems. Australian Journal of Soil Research. 37: 403-29 Olsen, S.R, Cole C.V., Watanabe F.S and Dean L.A. (1954). Estimation of availablephosphorus in soils by extraction with sodium bicarbonate. Circular No. 939. United StatesDepartment of Agriculture.Singh, D.K., Sale P.W.G, Gourley C.J.P and Hasthorpe C. (1999). High phosphorus supplyincreases persistence and growth of white clover in grazed dairy pastures during dry summerconditions. Australian J. Experimental Agriculture 39:579-85.Sparrow, L.A. (1993). Fertilizer advice in Australia. Proceedings of the 1st National Workshopon Soil and Plant Analysis. (Ed. D.R. Baigent). Australian Soil and Plant Analyses Council. pp.J.1 20.Thomson, N.A., Roberts A.H.C., McCallum A., Judd T.G. and Johnson R.J.  (1993).  Howmuch fertilizer is enough ?  Proceedings of the Ruakura Farmers Conference, Hamilton, NewZealand, June 1993.Table 1 - Average Olsen P soil test values (OP, mg/kg) and pasture growth rates (PRG, kgDM/ha/day) across all paddocks in each farmlet between 1995 and 1999.Farmlet and treatment 1995-6 1996-7 1997-8 1998-9OP1 PGR OP PG OP PG OP PGL1 (2 cows; 0 kg P/ha/year) 6 25 10 17 9 23 7 23L2 (2 cows; 35 kg P/ha/year) 8 28 14 19 12 28 13 25M1 (3 cows; 0 kg P/ha/year) 7 25 12 18 10 23 8 25M2 (3 cows; 35 kg P/ha/year) 3 9 26 13 20 11 25 14 27M3 (3 cows; 70 kg P/ha/year) 10 27 15 22 16 28 20 27M4 (3 cows; 140 kg P/ha/year) 3 12 27 24 22 24 28 30 29H3 (4 cows; 70 kg P/ha/year) 10 26 18 22 17 28 20 29H4 (4 cows; 140 kg P/ha/year) 13 27 23 23 25 27 29 301. Average for all 13 paddocks in each farmlet measured in April of each year2. Pasture growth rates determined weekly in ungrazed paddocks in each farmlet3. Results are means of replicate farmletsFigure 1 -  The cumulative effect of P fertilizer application and stocking rate on milk productionbetween 1995 and 1999. Error bars are 95% least significant intervals (LSIs) for comparingtreatment means. LSIs are defined such that intervals overlap when differences are notsignificant.

Phosphorus Fertilizer Requirements for Temperate Dairy Pastures and Milk Production in South Eastern Australia

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Phosphorus Fertilizer Requirements for Temperate Dairy Pastures and Milk Production in South Eastern Australia

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