THE EFFECTS OF UREA AND AMMONIUM SULPHATE NITRATE (ASN) ON THE PRODUCTION AND QUALITY OF IRRIGATED DAIRY PASTURES IN CANTERBURY, NEW ZEALAND

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1 THE EFFECTS OF UREA AND AMMONIUM SULPHATE NITRATE (ASN) ON THE PRODUCTION AND QUALITY OF IRRIGATED DAIRY PASTURES IN CANTERBURY, NEW ZEALAND Jim Mir l, Keith Camern l, H J Dil, Ants Rberts 2 and Wybe Kuperus 3 1 Centre fr Sil and Envirnmental Quality, PO Bx 84, Lincln University 2Ravensdwn Fertiliser C-perative Ltd, Pukekhe 3 Dexcel Ltd, Lincln Abstract This paper examines the effects f tw different frms f nitrgen (N) fertiliser, urea and ammnium sulphate nitrate (ASN) n the prductin and quality f spray irrigated dairy pastures in Canterbury. Pasture prductin and a wide range f pasture quality parameters were measured in a mwing trial f randmised design n the Lincln University dairy farm. Treatments cnsisted f three fertiliser frms (urea, urea plus sulphur (S) and ASN) applied at tw annual rates fn (150 and 250 kg N ha-i). Measurements included pasture dry matter (DM) yield, btanical cmpsitin, pasture Nand S uptakes, 'standard' pasture quality measurements, such as carbhydrate and prtein levels, and a detailed assessment f levels f individual prteins in the pasture. Under the cnditins f this trial representing typical centre-pivt irrigatin and high sil fertility, the ttal annual dry matter yield ranged frm 15.9 (Cntrl) t 19.4 (ASN 250) t DM ha- l and was strngly influenced by rate f N fertiliser applicatin but nt fertiliser type. ASN shwed a small significant yield advantage (P < 0.05) ver urea at the 150 N rate but nt at the 250 N rate. Clver levels did nt vary significantly with type r rate f fertiliser applied. Pasture quality, as measured by 'key' quality indicatrs was generally unaffected by fertiliser treatments thrughut the seasn, althugh sme differences in specific amin acid levels were detected. The implicatins f the impacts f N fertiliser use n pasture quality are discussed. Intrductin There is very little available research infrmatin in New Zealand that demnstrates the effect f fertiliser type n pasture quality. Mst research demnstrates the effects f fertiliser n pasture yield alne (Craighead et ai., 1997). Hwever, in cnjunctin with dry matter yield and animal intake, pasture quality is a critical factr influencing milk prductin and the health f the grazing dairy cw (Rgers and Stewart, 1982; Currie and Trigg, 1990). High yielding irrigated dairy pastures in Canterbury ften receive regular inputs f strategic fertiliser nitrgen (N) while sulphur (S) inputs are typically nly applied nce a year with phsphrus (P) fertiliser. Suth Island alluvial sils are inherently S deficient and have lw S retentin capabilities, and as a result sil sulphate S levels can drp dramatically even within ne seasn. Given these sil-plant cnditins it has been suggested that a cmbinatin S / N fertiliser may prvide pasture yield advantages ver strategic N alne. Hwever, there are n published research results available t supprt this r whether there is any influence f strategic N and S fertiliser use n the quality f irrigated dairy pastures thrugh the seasn. The bjective f this study was t determine and cmpare the effects f Ammnium Sulphate Nitrate (ASN) and urea n dry matter prductin and pasture quality f typically high prducing irrigated dairy pastures in Canterbury, New Zealand.

2 Materials and Methds This research was cnducted n the new Lincln University dairy farm, n free-draining Templetn (sandy) sils. The site was a recent cnversin (2001) frm lng-term sheep pastures t dairying and had high sil fertility status (Olsen P 30!lg Pg-I, Sulphate S 24!lg S g-t, ph 5.8). The trial was cnducted as a mwing trial under centre pivt irrigatin frm August 5 th 2002 t August 5 th 2003 with grazing animals excluded. Field plts (2 x 5 m) were laid dwn in a randmised blck design. Fertiliser treatments cnsisted f three fertiliser frms; ASN, Urea r Urea plus S (as gypsum), applied at tw rates f N: 150 r 250 kg N ha- 1 yfl ver six applicatins. A cntrl was included, and all treatments were replicated fur times. Basal nutrients and lime were applied in accrdance with current fertiliser plicy n the Lincln University dairy farm. All fertiliser applied t the main paddck area was excluded frm the trial area by cvering plts with plastic sheets at the time f applicatin. Irrigatin water (n effluent) was applied by the centre-pivt irrigatr (verhead spray) in accrdance with nrmal centre-pivt irrigatin practice in Canterbury. Centre-pivt irrigatrs are used n these dairy farms t supply small amunts f water n a regular rtatin arund the farm. During the 2002/03 seasn n the Lincln University dairy farm irrigatin water was applied frm late-september 2002 until May f 2003 at an equivalent rate f between 7 t 10 mm per applicatin (every hurs), depending n the farm requirements. Pasture was harvested apprximately every days, depending n the current farm grazing rtatin interval. A wide sickle-bar mwer was used t harvest plts which minimised any mechanical damage r bruising t herbage samples. Dry matter yield, btanical cmpsitin and dry matter respnse t fertilisers were measured at each harvest. Standard pasture quality analyses were als perfrmed at each harvest using near-infrared spectrscpy (NIR) and included quality parameters such as crude prtein, fibre, carbhydrate and metablisable energy cntents f samples. The N and S cntents f samples were als measured at each harvest. Detailed amin acid cmpsitin analyses were perfrmed n bth ryegrass and clver sward cmpnents at five times thrugh the seasn when pasture quality was cnsidered t be f high pririty. Amin acid analyses were perfrmed in: (1) September (early lactatin), (2) late-octber (peak milk prductin), (3) late-december, (4) early-february, and (5) mid-march. Results and Discussin Pasture Yield Ttal annual dry matter yield ranged frm 15.9 (Cntrl) t 19.4 (ASN 250) t DM ha- 1 (Figure 1). Pasture grwth was higher n fertilised treatments (P < 0.01) when cmpared with the cntrl, with the maximum (ASN 250) yield representing a 22 % yield increase. The '250 N' treatment significantly ut-yielded the lwer' 150 N' rate within the 'Urea' (P < 0.001), 'Urea+S' (P < 0.01) and 'ASN' (P < 0.05) fertiliser types. Annual yields n the ASN 150 N treated plts (18.06 t DM ha-i) were significantly higher (P < 0.05) than fr Urea (16.95 t DM ha-i) at the 150 N rate (Figure 1). Hwever, there was n significant difference in annual dry matter yield acrss fertiliser types at the 250 N rate. The higher annual yield f ASN 150 reflects a cumulative effect whereby the ASN 150 utyielded the Urea 150 treatment by a small nn-significant (P > 0.05) margin ver a number f harvests. The ASN 150 treatment als exhibited the largest difference in pasture grwth ver

3 ther 150 N fertiliser treatments (ns, P < 0.05) at the first harvest f the trial in September f 2002, perhaps shwing sme advantage ver ther fertiliser types at lwer sil temperatures. Hwever, the ASN 250 treatment shwed n pasture grwth advantage ver ther 250 N fertiliser treatments during this spring perid c "' c '1:J 10 'ii >= 5 I LSD5% Cntrl Urea 150 Urea 250 III Urea+S 150 murea+s 250 fziasn 150.ASN Figure 1. Ttal dry matter yield Nitrgen Respnse Pasture N respnses, expressed as kg DM grwn per kg f N applied as fertiliser are presented in Figure 2. N respnses ranged frm near 0 t 30:1, and reflected the variable and seasnal nature f pasture grwth respnses t N fertiliser. In general, N respnses were highest in early spring (August / September), with gd respnses in Autumn (April) and lwer respnses at ther times z _ , C).:.:: 15 C).:.:: - 10 c a. Cl) :2 _ASN250 -Urea+S Urea &l. ASN Urea+S ir-. Urea 150 O Aug Oct Dec Feb Apr Jun Figure 2. Pasture N respnse in the first harvest fllwing fertiliser applicatins

4 Pasture N respnse fllwing fertiliser applicatin in August was greater fr the ASN 150 treatment cmpared t the Urea 150 treatment, hwever the difference is nt statistically different (P > 0.05). Overall, the ASN 150 treatment appears t have a slightly higher 'mean' N respnse thrughut the seasn than ther treatments in this trial. Hwever, the variability f the data resulted in a nn-significant difference, and hence the verall level f pasture N respnse was nt significantly crrelated t fertiliser type, nr t rate fn fertilisatin. Btanical Cmpsitin Btanical separatins f pasture samples were cnducted at all harvests, and the seasnal clver cntents acrss treatments are represented in Figure 3. Clver cntents started at 15% f ttal dry matter in September f 2002, peaked at mean values f 45% in December, then fell slwly t lw levels «10%) acrss all treatments by the winter f2003 and reflected the seasnal nature f clver grwth. As expected, clver grwth was suppressed t sme extent by N fertilisatin. Clver prductin n cntrl plts was 5 t 10 % higher than n N fertilised treatments ver mst f the seasn. Hwever, given the mderate t high levels f N fertiliser rates applied in this trial, sward clver levels were significantly higher than expected thrughut the seasn. In this respect, all pastures were f very high quality. The data als indicate that there was n significant difference between the effects f ASN and urea n the clver cntent f the sward at either 150 r 250 N rates. Likewise, when verall N 'rates' were pled acrss all fertiliser types, the differences between the tw fertiliser rates n clver cntent culd nt be separated. - ::E C -;;e : Cntrl --it.- Urea Urea+S 150 -'-ASN Urea250 -Urea+S250 -ASN _-_+_--+_- +--_+_--I--- Aug Oct Dec Feb Apr Jun Figure 3. Clver cntent f pasture

5 Pasture Nand S Uptake Pasture N levels ranged frm 2.7 % w/w in Octber t 3.8 % w/w in late December (data nt shwn). In general pasture N cncentratin was highest in the 250 N treatments, but this trend was nt always clear. N ne fertiliser type appeared t shw any advantage in the elevatin f herbage N levels. Apprximately half f the amunt f N applied as fertiliser was apparently recvered by the pasture plants (e.g. N-uptake at the 250 kg N ha- I rate was 69 kg N ha- I minus N-uptake in the 'cntrl' (545 kg N ha-i) = 124 kg N ha-i). Sulphur levels in herbage were strngly influenced by fertiliser treatment. Values ranged frm 0.42 t 0.54 % w/w fr ASN and Urea+S treatments, and lwer levels f 0.36 t 0.43 % w/w n Urea treated and cntrl plts (data nt shwn). All bserved herbage S cncentratins were well abve the recgnised S deficiency level f 0.30 % w/w and reflect the high sulphate-s levels in the sil (24 /lg S g-\ These results suggest that luxury plant S uptake ccurred, which wuld explain why n pasture grwth respnse t S fertilisatin was apparent in this trial. Annual S uptake by pastures ranged frm 62 kg S ha-in the cntrl t 97 kg S ha- l fr the ASN 250 treatment. On S fertilised treatments, ttal plant S uptake was equivalent t apprximately 26 % f that applied as fertiliser at the 250 N rate. Pasture Quality (NIR Analyses) Standard pasture quality analyses were cnducted n all mixed pasture samples at all harvests t investigate the effects f the fertiliser treatments n feed quality. Quality indicatrs included crude prtein, carbhydrate, fibre and metablisable energy levels. Overall, fertiliser rate and type had negligible effect upn levels f the pasture quality indicatrs (e.g. metablisable energy cntent, Figure 4)...-; C C) W , , -c U W e ::::s 1;) C'\S a _--+--I_-_+--- Aug Oct Oec Feb Apr Jun -+-Cntrl Urea Urea250 -Urea+S150 -Urea+S 250 ASN 150 -ASN250 Figure 4. Pasture ME cntent thrugh the 2003 / 2004 seasn Mst pasture quality indicatrs, such as the critical 'metablisable energy' measurement gave nearly identical values acrss all treatments at each sampling (Figure 4). Much f the variatin in the levels f all measured quality indicatrs culd be attributed t seasnal variatin rather than treatment effect f fertiliser r N rate.

6 In summary, the tw N fertilisatin rates applied in this study had little if any effect n pasture quality indicatrs thrughut the seasn. This is an imprtant new finding because it demnstrates that at the 'typical' n-farm N rates used here, farmers culd use urea r ASN t grw up t 20 % mre dry matter with virtually n drp in pasture quality, given adequate sil fertility. Maintaining pasture quality will als depend n maintaining high levels f clver in the sward. Pasture Quality (Amin Acids) In additin t 'standard' pasture quality analyses, herbage samples als underwent HPLC analysis t determine the levels f a wide range f individual amin acids. These samples were selected frm five harvests representing key perids fr pasture quality thrugh the seasn. Samples were taken in September, Octber, Nvember, January and March. Amin acids such as methinine and lysine are critical prteins influencing milk prductin in dairy cattle (Schwab et al., 1992). The influence fn (and S) fertilisers n amin acid levels in pasture is therefre f real interest. Amin acids were determined separately n the grass and clver plant material and the results are presented here as a mixed pasture sward t represent that eaten by the grazing cws. The seasnal variatin in methinine cntent f mixed sward samples are given in Figure 5 belw as an example. Results indicate that the levels f sme amin acids can rise and fall quite dramatically thrugh the seasn. Amin acid levels acrss replicates were variable, and therefre the effects f fertiliser type and rate n prtein levels are difficult t separate. Therefre the data indicate that variatin f amin acid levels in the pasture samples due t fertiliser treatment is small, but in sme instances, may be ptentially significant. Mre detailed statistical analysis f these data sets wuld be required befre any definite cnclusins culd be drawn abut the influence f these fertiliser treatments n amin acid levels in pasture Cntrl._*...-Urea 150 c Urea 250 c -_. Urea+S150 -CD c '2 -Urea+S ASN 150.r:::: 0.20 CD ASN j Aug Oct Oec Feb Apr Jun Figure 5. Pasture methinine cntent ver the 2002 / 2003 seasn

7 Cnclusins The influence f ASN and urea at tw rates fn applicatin n the prductin and quality f irrigated dairy pastures in Canterbury, New Zealand was investigated. Under the cnditins f this trial representing typical frequent centre-pivt irrigatin and high sil fertility, pasture prductin ranged frm 15.9 (Cntrl) t 19.4 (ASN 250) t DM ha- 1 y(l and was strngly influenced by the rate f N fertiliser applicatin. ASN shwed a small significant yield advantage (P < 0.05) ver urea applied at the 150 N rate but nt at the 250 N rate. The clver cntent f the sward did nt vary significantly with the type, r rate f fertilisers. Seasnal variatin in sward clver levels was high, and mderately high clver cntents were maintained n fertiliser treated pastures (frm 10-45%). Clver levels in the pastures were 5-10% lwer n fertilised plts cmpared t the cntrl. The fertiliser types and tw N fertilisatin rates applied in this study had little if any effect n key pasture quality indicatrs thrughut the seasn. This is an imprtant new finding because it demnstrates that at the N rates used here farmers culd use urea r ASN fertiliser t grw up t % mre dry matter with virtually n drp in pasture quality. Further pasture quality analyses revealed that amin acid cncentratins in the herbage varied widely ver the seasn. The data indicate that the variatin f amin acid levels in the pasture samples due t fertiliser treatment is hwever small. Acknwledgements The authrs wish t thank Ravensdwn C-p Ltd fr funding this study, and Carle Barlw, Hamish Masters, Trevr Hendry and Kleighne Frd fr field and technical assistance. References Craighead, M.D.; Hayward, I.A; Hwie, AM. 1997: Evaluatin f nitrate fertilisers as nitrgen surces fr spring pasture. Prceedings f the New Zealand Grassland Assciatin 59: Currie, R.; Trigg; T.E. 1990: Effects f pasture and supplement quality n the respnses f lactating dairy cws t high energy supplements. Australian Jurnal f Experimental Agriculture 30(1) : Rgers, G.L.; Stewart, la 1982: The effects f sme nutritinal and nn-nutritinal factrs n milk prtein cncentratin and yield. Australian Jurnal f Dairy Technlgy 37(1) : Schwab, e.g.; Bzak, C.K.; Whitehuse, N.L. 1992: Amin acid limitatin and flw t dudenum at fur stages flactatin. Jurnal f Dairy Science 75: