The application of nitrogen (N) fertilizer to temperate pastures is an increasingly popular management tool for boosting pasture production on dairy farms in Australia. However, limited information is available about N fertilizer responses that can be obtained from pastures with varying levels of phosphorus (P) fertility. A field experiment examining the initial and residual response of pasture growth to urea was carried out within a large dairy farmlet study, in October 1998. The four P fertility treatments (Olsen P values) ranged from 9 to 32 mg/kg. Dry matter yields increased with increasing N rates in all treatments, at both harvests. Only pastures with Olsen P values of \u3c 12 mg/kg had a significantly lower response to N fertilizer

Frame, H.

Gourley, C. J. P.

Hall, M. E.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings XIX International Grassland Congress Responses to Nitrogen Fertilizer in Dairy Pastures with Differing Phosphorus Fertility in South Eastern Australia C. J. P. Gourley Agriculture Victoria, Australia H. Frame Agriculture Victoria, Australia M. E. Hall 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/19/4/9 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 # 04-09RESPONSES TO NITROGEN FERTILIZER IN DAIRY PASTURES WITH DIFFERINGPHOSPHORUS FERTILITY IN SOUTH EASTERN AUSTRALIAC.J.P. Gourley1, H. Frame2, and M.E. Hall3Department of Natural Resources and Environment1Agriculture Victoria, Hazeldean Rd, Ellinbank, Victoria 3821.2228 High St, Seymour, Victoria 3660.3225 Pakenham St, Echuca, Victoria 3564, Australia.AbstractThe application of nitrogen (N) fertilizer to temperate pastures is an increasingly popularmanagement tool for boosting pasture production on dairy farms in Australia.  However, limitedinformation is available about N fertilizer responses that can be obtained from pastures withvarying levels of phosphorus (P) fertility. A field experiment examining the initial and residualresponse of pasture growth to urea was carried out within a large dairy farmlet study, in October1998. The four P fertility treatments (Olsen P values) ranged from 9 to 32 mg/kg. Dry matteryields increased with increasing N rates in all treatments, at both harvests. Only pastures withOlsen P values of < 12 mg/kg had a significantly lower response to N fertilizer.Keywords: Farmlet study, Olsen P, pasture growth, ureaIntroductionStrategic applications of N fertilizer on pastures are now used by most dairy farmers inAustralia as an effective way of overcoming short-term seasonal feed deficits, especially whenlegume derived N is limiting pasture growth (Eckard and Franks 1998). A number of pot andfield studies have demonstrated an interaction between the response to N fertilizer and P fertilityof the pasture soil (Grant et al. 1981; Mouat and Nes 1983; Davison et al. 1997; Cayley et al.1998). These results have supported a common perception that high soil P fertility is required toachieve optimum N responses, and led to an increase in P fertilizer use on many dairy farms.However, responses to N fertilizer, obtained from pastures at various levels of soil P status havenot been well defined, particularly across the range found between most dairy farms in Australia.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 within all farmlets consisted of perennial ryegrass (Loliumperenne) (>60%) in association with white clover (Trifolium repens), annual grasses andbroadleaf weeds. Urea was applied to 2 x 10 m plots within 3 paddocks in all of the 10 farmletsin late winter, at rates of 0, 20, 40, 80 and 160 kg N/ha, in a randomised block design. Prior to Nfertilizer application, 150, soil cores (10 cm) were collected from each experimental area todetermine extractable P values (Olsen et al. 1954) and total N (Leco N analyser). Mixed pasturesamples were also analysed for P and N content using x-ray fluorescence spectroscopy. Pastureyields and compositions were examined after 28 days and again after a further 21 days. Nitrogenrates were log transformed to fit a linear model to the response relationship, and the slopedetermined.  All data were subjected to a one-way analysis of variance.Results and DiscussionThere was a significant effect (P<0.05) of P fertilizer rate on soil P levels (ranging from 9to 32 mg/kg) and pasture P content (ranging from 0.38 to 0.54%), but not soil or pasture N levels,prior to the N fertilizer application (Table 1). There was also a significant effect of stocking rate(P<0.05) on P% in pasture between the L2 and M2 farmlets.Pasture DM yields increased with N fertilizer in all farmlets, and at both harvests, butresponses diminished with increasing N fertilizer rates (Figure 1). The exception to this was asmall decrease in dry matter yield from 80 to 160 kg N/ha within the L2 farmlet (35 kg P/ha/yearand 2 cows/ha), at harvest one. In general, the treatments with the higher soil P levels producedthe most pasture (Figure 1). There was a significant effect of P fertility on response to Nfertilizer, as shown by the significant difference (P<0.05) between the slopes of the relationshipsbetween log N fertilizer applied and pasture DM (Table 1). The slopes were similar across all butthe lowest soil P levels (< 12 mg/kg), indicating no difference in response to N above an Olsen Pof 12 mg/kg.  There was no significant effect (P>0.05) of stocking rate. Dry matter yieldresponses in harvest 2 were substantially lower across all treatments, with no significant (P>0.05)effect of P fertilizer rates or stocking rates (data not shown).A number of previous field studies have also found greater pasture DM yield responses toN fertilizer at higher P status. Davison et al. (1997) found an N x P interaction on Green Panicbased pasture (Panicum maximum cv. Gatton) but this only occurred after 5 years, when the Pfertility of the two P treatments had separated markedly. Work in sheep pastures by Cayley et al.(1998) found that N responses increased with increasing P fertility, but the composition of thesepastures were substantially different between their different treatments. Grant et al. (1981)reported significant N x P interactions in ryegrass monoculture, but not for browntop (Agrostistenuis) in hill country in New Zealand. Our study supports these results, indicating that responsesto N fertilizer in dairy pastures were limited when P fertility was low (Olsen P values < 12mg/kg), but not where P fertility was moderate or high (between 12 – 32 mg/kg).The results from this study have indicated that DM yield response of dairy pastures to Nfertilizer may be restricted by low soil P fertility. Since the P fertility levels found on most dairyfarms in south eastern Australia are generally above 12 mg/kg, these results do not support theneed for higher soil P status, and therefore high P fertilizer inputs, to maximise the response to Nfertilizer.ReferencesCayley, J., McCaskill M.,Montgomery J., Lewis B., and Scholz T. (1998). Pasture response tonitrogen in late winter depends on phosphorus. Proceedings from the Victorian GrasslandsAssociation 39:149.Davison, T.M., Orr W.N., Silver B.A., Walker R.G., and Duncalfe F. (1997). Phosphorusfertilizer for nitrogen fertilized dairy pastures.  1. Long term effects on pasture, diet and soil.Journal of Agricultural Science, Cambridge 129:205-217.Eckard, R.J., and Franks D.R. (1998).  Strategic nitrogen fertilizer use on perennial ryegrassand white clover pasture in north-western Tasmania. Australian Journal of ExperimentalAgriculture 38:155-60.Grant, D.A., Luscombe P.C., and Thomas V.I. (1981).  Responses of ryegrass, browntop, andan unimproved resident pasture in hill country, to nitrogen, phosphorus and potassium fertilizers.1. Pasture production.  New Zealand Journal of Experimental Agriculture 9:227-236.Mouat, M.C.H., and Nes, P. (1983).  Effect of the interaction of nitrogen and phosphorus on thegrowth of ryegrass.  New Zealand Journal of Agricultural Research 26:333-336.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.Table 1 - Treatment combinations of stocking rate and P fertilizer rate in the farmlet study andnitrogen and phosphorus levels of the soil and pasture prior to urea application and response tonitrogen fertilizer, in October 1998.Farmlet P application Stocking Soil Pasture Slope1rate rate Olsen P Total N Total P Total N (kg DM/ha)/(kg P/ha) (cows/ha) (mg/kg) % (w/w) % (w/w) % (w/w) log (kg N/ha)L1 0 2 9 0.68 0.38 3.8 116.3M1 0 3 9 0.64 0.39 4.1 96.1L2 35 2 12 0.65 0.42 3.4 193.3M22 35 3 13 0.67 0.47 4.2 159.8M3 70 3 16 0.75 0.52 4.3 152.6H3 70 4 19 0.69 0.50 4.3 142.9M42 140 3 30 0.70 0.53 4.1 166.3H4 140 4 32 0.67 0.54 3.9 168.5l.s.d.(P=0.05) 3 4.14 0.15 0.05 0.5 88.2Phosphorus rate S4 NS S NS SStocking rate NS NS S NS NS1  Slopes of the relationship between DM yield and log transformed N fertilizer rates within each farmlet in harvestone2  Results are means of replicate farmlets3   Least significant difference4  S and NS are significant (P<0.05) and non significant (P>0.05) differences, respectivelyFigure 1 -  Effect of N fertilizer applications on pasture DM yield (kg DM/ha) in October 1998,when applied to dairy pastures with varying stocking rates of 2 (L), 3 (M) and 4 (H) cows/ha andP fertilizer rates of 0 (1), 35 (2), 70 (3) and 140 (4) kg P/ha/year.

Responses to Nitrogen Fertilizer in Dairy Pastures with Differing Phosphorus Fertility in South Eastern Australia

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Responses to Nitrogen Fertilizer in Dairy Pastures with Differing Phosphorus Fertility in South Eastern Australia

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