Urea and composted cattle manure affect forage yield and nutritive value in sandy soils of south-central Vietnam

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1 Received: 18 My 2016 Revised: 15 Ferury 2017 DOI: /gfs ORIGINAL ARTICLE Ure nd composted cttle mnure ffect forge yield nd nutritive vlue in sndy soils of south-centrl Vietnm K. C. McRoerts 1 D. Prsons 2,3 Q. M. Ketterings 1 T. T. Hi 4 N. H. Qun 4 N. X. B 4 C. F. Nicholson 5 D. J. R. Cherney 1 1 Deprtment of Animl Science, Cornell University, Ithc, NY, USA 2 School of Lnd nd Food, University of Tsmni, Tsmni, Austrli 3 Deprtment of Agriculturl Reserch for Northern Sweden, Swedish University of Agriculturl Sciences, Ume, Sweden 4 Hue University of Agriculture nd Forestry, Hue City, Vietnm 5 Deprtment of Supply Chin nd Informtion Systems, The Pennsylvni Stte University, University Prk, PA, USA Correspondence K. C. McRoerts, Deprtment of Animl Science, Cornell University, Ithc, NY, USA. Emil: kcm45@cornell.edu Funding informtion Fulright-Hys Doctorl Disserttion Reserch Arod Fellowship; Richrd Brdfield Reserch Awrds; Cornell University Grdute School Trvel Grnts; Mrio Einudi Center for Interntionl Studies Interntionl Reserch Trvel Grnts; Gerld O. Mott Scholrship for Meritorious Grdute Students in Crop Science; Andrew W. Mellon Awrds; Wilson G. Pond Interntionl Trvel Awrd; Clinton-Dewitt- Smith Fellowship Astrct Improved forge mngement cn support incresed production in smllholder eef systems. Our ojective ws to evlute the effects of minerl nitrogen (ure) nd composted cttle mnure on Brchiri cv. Multo II yield nd nutritive vlue in south-centrl costl Vietnm. Study design ws rndomized complete lock on six frms (locks), with tretments derived from the fctoril comintion of five rtes of composted cttle mnure (0, 4, 8, 12 nd 24 Mg DM h 1 yer 1 ) nd three ure rtes (0, 60 nd 120 kg N h 1 yer 1 ), split into six yerly pplictions. Yield ws mesured from 2011 to 2013 with 36-dy verge hrvest intervls. Forge nutritive vlue ws mesured in Septemer 2011 nd Decemer Highest yields were chieved when oth compost nd ure were pplied t high rtes. The initil yield nd tiller responses to ure ppliction were not sustined over the durtion of the study when no compost ws pplied. Compost pplied in isoltion did not increse yield. Compost ppliction incresed sh concentrtion. Ure incresed nutrient yield for ll forge nutritive vlue prmeters mesured. Composted cttle mnure comined with ure enefits grss yield, ut high ppliction rtes re needed for sustined high yields on sndy soils. KEYWORDS composted cttle mnure, cultivted forge yield, fertiliztion, smllholder crop livestock system, tropicl grss nutritive vlue, ure 1 INTRODUCTION Animls rised on smllholder crop livestock frms (one to five heds of cttle per household) in south-centrl costl Vietnm supply prt of the growing demnd for eef in urn res (Prsons et l., 2013). Cttle systems in the region re predomintely semi-intensive (grzing nd stll feeding) or extensive (grzing of communl lnd), with few household opertions prctising only intensive stll feeding. Typicl cttle mngement consists of supervised or unsupervised grzing on communl (nd sometimes privte) lnd nd supplementry stll feeding with sl diet of rice strw, penut strw, concentrtes, nd cultivted forge (e.g., Pennisetum purpureum Schumch.) or cut-nd-crry ntive grsses nd legumes from privte nd communl lnd (Prsons et l., 2013). In recent yers, progressive frmers hve initited the trnsition towrds semi-intensive opertions to increse niml productivity (dily gin) y improving the quntity nd nutritive vlue of forges nd reducing mintennce energy expenditures incurred from wlking to open grzing res. A key component of this trnsition is cultivtion of high-yielding, high-qulity forges tht re well dpted to locl climtic nd soil conditions (B et l., 2013, 2014; Prsons et l., 2013; St ur, Khnh, & Duncn, 2013). Production of improved forges in ckyrd plots lso enefits frmers y reducing lour required for cttle production (Khnh et l., 2014; St ur et l., 2013). Supplementry forges used in pproprite comintion with existing John Wiley & Sons Ltd wileyonlinelirry.com/journl/gfs Grss Forge Sci. 2018;73:

2 MCROBERTS et l. 133 low-cost ingredients (e.g., rice strw) ply n importnt role in niml productivity nd income gins. Sndy soils cover 900 million h worldwide, with the mjority locted in Afric (51%; sndy soils cover 13% of su-shrn Afric), Austrlsi (21%) nd South nd Southest Asi (10%) (Hrtemink & Huting, 2005). Sndy soils in the tropics present numerous chllenges for griculturl production, ut well-mnged sndy soils with timely ccess to wter nd pproprite fertiliztion cn e productive. Cultivtion of these soils is less common thn other soil types, nd consequently, reserch nd informtion supporting mngement decisions in these soils re limited. Furthermore, informtion on the effect of mngement decisions on yield nd nutritive vlue of forges in sndy, tropicl, rin-fed systems such s those locted in the south-centrl Vietnm cost nd in other regions of Southest Asi is scnt (Devendr, 2002; St ur, Horne, Gund, Phengsvnh, & Kerridge, 2002). Importnt frm mngement decisions include forge species, estlishment (vi seed or vegettive mteril), hrvest intervls, cutting height, irrigtion nd fertiliztion. Frmers in the south-centrl costl region of Vietnm prefer grsses over legumes due to higher yield potentil for smll plot production (St ur et l., 2013). Yer-round growth of perennil forge grsses with high nutrient uptke potentil cn contriute to productivity of the cttle herd while reducing nutrient loss to the environment. Hrvesting for high nutritive vlue is n importnt secondry ojective for frmers in the study region of Vietnm, ut is more difficult to mnge thn yield. Chnges in forge nutritive vlue re often dependent on climte-relted fctors with rpid dy-to-dy nd intrdiurnl vrition. These effects re typiclly smller in the tropics due to lower fluctution in photoperiod nd temperture reltive to temperte regions (Vn Soest, 1994). In the tropics, high tempertures nd reltively constnt dy length drive n inconsistent reltionship etween digestiility nd fire, due to the poor reltionship etween cellulose nd lignin (Buxton & Fles, 1994; Vn Soest, 1994). Thus, hrvest mngement decisions re complicted, ecuse fire concentrtion is less effective in predicting niml response (Vn Soest, 1994). Furthermore, high tempertures nd prevlence of C 4 grsses promote high concentrtion of cell wll components, lignifiction nd poor digestiility (Vn Soest, 1994). Wter vilility is more importnt in the tropics, nd sesonl precipittion ptterns in rin-fed forge systems ffect forge yield nd nutritive vlue (Buxton & Fles, 1994; Vn Soest, 1994); drought cn improve forge digestiility t the expense of yield due to slower plnt development nd mturtion, while excess rinfll tends to cuse lignifiction (Vn Soest, 1994, 1996). Fertiliztion with loclly ville orgnic nd inorgnic fertilizers nd soil mendments is criticl to otining nd sustining high yields in the region. Specificlly, nitrogen (N) fertiliztion is essentil to otin higher yields nd cn increse crude protein concentrtions in forge s well (Peyrud & Astigrrg, 1998). Nitrogen-fertilized grsses lso tend to grow fster, generting more lignified plnt fster due to more rpid plnt growth nd mturity (Vn Soest, 1994, 1996). Plnt ville N is key to short-term high yields of perennil forge grsses. Slower relese forms of N nd other mcro- nd micronutrients from minerliztion of composted cttle mnure nd crop residues could e importnt to supply other nutrients criticl to sustined growth nd high nutritive vlue (Plm, Myers, & Nndw, 1997). Consequently, we evluted the effects of fertiliztion with ure nd composted cttle mnure on forge yield nd forge nutritive vlue vi multiyer (29-month) on-frm field experiment. The effects of ure nd composted cttle mnure in the study on soil fertility nd prtil nutrient lnces were reported in McRoerts et l. (2016). 2 MATERIALS AND METHODS 2.1 Ct Trinh commune chrcteristics The experiment ws conducted etween 2010 nd 2013 in Ct Trinh Commune, Phu Ct District, Bınh Dịnh Province in south-centrl costl Vietnm. Ct Trinh orders the district cpitl of Ng^o M^y ( N, E) on the north nd est. Sndy soils in the commune elong to the Arenosols Group (IUSS Working Group WRB, 2014). Annul rinfll in the region is out 1,200 mm, with over 70% flling during the riny seson (Septemer to Decemer; Tle S1). Averge monthly tempertures rnge from 23 to 31 C (Tle S1). Precipittion during the experiment period ws generlly consistent with recent ptterns in the study region (Tle S1). Rinfll ws ove verge in Novemer 2010, cusing flooding nd plnt loss during the plnt estlishment period on one of the frms. Rinfll ws elow verge in Septemer 2011 nd Octoer nd Novemer 2012, contriuting to overll elow-verge nnul precipittion. Dry seson rinfll ws low nd consistent with historicl ptterns. Most rinfll occurred during the Septemer to Decemer riny seson in 2011 (76%) nd 2012 (55%). Tempertures were within norml rnges. Loction selection ws sed on the presence of the Austrlin Centre for Interntionl Agriculturl Reserch-funded Project SMCN/2007/109, entitled, Sustinle nd Profitle Crop nd Livestock Systems for South-centrl Costl Vietnm. Project presence simplified ccess to commune frms, including provincil nd commune permission requirements. It furthermore incresed the likelihood of dequte trcking of the experiment nd eventul dissemintion of results due to close nd frequent contct with commune extension eductors nd rurl development professionls operting in the region. This experiment complemented existing reserch nd extension inititives nd responded directly to prolems identified y smllholder frmers nd priorities reveled during seline project surveys (Ho, 2009; Prsons et l., 2013). The field experiment ws estlished on smllholder frms in collortion with frmers nd locl extension eductors to ensure frmer prticiption in the experiment nd potentilly higher cceptnce of reserch results, which hs een noted prolem in Southest Asi (Devendr, 2002; St ur et l., 2002). Frmers contriuted to implementtion nd experiment mngement decisions nd mnged weed control nd plot irrigtion s needed. Frmer prctice ws dopted for most spects of experiment mngement.

3 134 MCROBERTS et l. 2.2 Frm selection nd experiment preprtion Commune extension stff recommended six cttle owners sed on the following criteri: (i) non-prticipnts in previous Austrlin Centre for Interntionl Agriculturl Reserch-funded inititives, (ii) interest in prticiption, (iii) vilility of well-drined, level prcel ner the household (13 m 9 13 m or equivlent) nd (iv) ccess to irrigtion. Recent frm field histories included the following: (i) Pennisetum purpureum Schumch. cultivtion, (ii) vcnt with household wste nd sh ccumultion, (iii) cssv nd eggplnt production, (iv) cssv production, (v) penut production nd (vi) vcnt. Consequently, the six fields represented sndy soils vrying in soil fertility levels (McRoerts et l., 2016). Pre-experiment (2010) soil smples t depth of cm indicted low orgnic mtter (3.5 g/kg with SD 2.07), low ction exchnge cpcity (1.3 cmol + kg ), low nutrient concentrtions (NO 3 N = 3 mg/kg 2.6; Mehlich 3- extrcted P = 37 mg/kg 27.3; K = 36 mg/kg 36.2; S = 9.1 mg/ kg 4.47; Mg = 29 mg/kg 23.3; N = 23 mg/kg 13.1; C = 176 mg/kg 68.3; Mn = 7 mg/kg 7.5) nd cidic soils (ph (1:1 soil:wter) = ) (McRoerts et l., 2016). [Correction dded on 02 My 2017 fter first online puliction: The mesurement for ction exchnge cpcity ws previously incorrect nd hs now een mended in this version] In July 2010, experimentl res were prepred for plnting, ccording to frmer prctice, using niml trction nd hndheld hoes. Weeds were controlled with hndheld hoes s needed (one to two times per month) throughout the experiment. A 1.2-m-high woven wire fence ws plced round ech experimentl re to prevent niml entry. No pesticides were pplied during the experiment. Preliminry reviews from Ct Trinh frmers prticipting in forge vrietl selection experiments suggested Brchiri cv. Multo II (B. ruziziensis 9 B. decumens 9 B. riznth) ws the most pproprite grss given its populrity mong frmers (B et l., 2013, 2014), drought tolernce, dpttion to cid soils nd high nutritive vlue reltive to other C 4 forges (Argel, Miles, Guiot, Cudrdo, & Lscno, 2007; Inyng et l., 2010; Vendrmini et l., 2012). A high-density Multo II seeded (>500 plnts per m 2, covered) ws estlished t Frm 3 in August Young plnts (15 30 cm mximum height) were trnsplnted into experimentl res pproximtely 4 weeks fter seeded estlishment. Strter fertilizer ( ; N P 2 O 5 K 2 O) ws pplied t 175 kg/h just efore trnsplnting (erly Septemer 2010), nd gin in Octoer 2010 fter trnsplnting. Twenty Multo II plnts were estlished in ech m plot (50 cm row spcing nd 40 cm plnt spcing). Interplot uffers (1 m) nd outer orders of experimentl res contined single row of Multo II (40 cm spcing etween plnts). Replnting occurred where needed during the first 2 months fter estlishment (Septemer nd Octoer 2010) to otin the desired density in the m plots (50,000 plnts h 1 ). 2.3 Experimentl design The rndomized complete lock design on six smllholder frms (locks) included fifteen tretments derived from the fctoril comintion of five composted mnure rtes (0, 4, 8, 12 nd 24 Mg DM h 1 yer 1 ) nd three ure rtes (0, 60 nd 120 kg N h 1 yer 1 ). Tretment 16 consisted of the highest compost rte nd 80 kg K 2 Oh 1 yer 1 in The highest ure rte ws dded to this tretment from Jnury 2012 onwrds. Buffers received 4 Mg DM h 1 yer 1 compost. Frm 3 provided ll the composted mnure to ensure consistency of compost tretments cross ll six frms. Preprtion consisted of dily removl of cttle mnure nd rice strw orts from stlls nd plcement in n uncovered pile for pproximtely 45 dys. The pile ws turned t lest twice prior to use. Compost ws pplied t rtes tht imed to provide 0, 40, 80, 120 nd 240 kg N h 1 yer 1 sed on n initil ssessment of verge compost nutrient content. Actul N rtes were slightly higher (0, 46, 92, 138 nd 276 kg N h 1 yer 1 ) due to vrition in compost DM nd N concentrtions nd were reported long with full compost tretment composition in McRoerts et l. (2016). Compost tretments were selected to meet Multo II N requirements (240 kg N h 1 yer 1 ) with the highest compost ppliction rte (nd without ure ppliction). Yerly tretments were split into six pplictions pplied y hnd t pproximtely 2-mo intervls directly fter hrvest. Tretments were surfce-pplied in yer one nd incorported (top 0 to 15 cm) with hndheld hoes from yer two onwrds to reduce potentil for nutrient trnsfer cross plots nd to prevent nutrient loss. Incorportion should not impct yield sed on mnure ppliction method experiment in the sme region (Vn et l., 2014), lthough positive yield response to incorportion vs. surfce ppliction to sndy soils hs een oserved for orgnic mendments in other regions (Cstillo et l., 2011). Two months post-trnsplnting (Novemer 2010), ll plnts were cut uniformly t 25 cm ove ground level using hndheld sickle to promote the development of verticl tillers. Initil fertiliztion tretments were pplied t tht time. 2.4 Smpling protocols Composted cttle mnure smples Representtive composted cttle mnure smples (three susmples t 150 g ech for ech ppliction period) were collected, dried t 60 C in forced-ir oven nd ground to pss 2-mm screen in Retsch cutting mill (Germny). Susmples were nlysed t Brookside Lortories, Inc. (New Bremen, OH) using procedures descried in Peters et l. (2003). Determintion of totl N ws performed using n Elementr vrio MAX (Elementr Anlysensysteme, Hnu, Germny), nd determintion of minerls ws undertken using CEM Mrs Express microwve (CEM Corportion, Mtthews, NC, USA) with digest nlysed in Thermo Scientific icap 6500 inductively coupled plsm-tomic emission spectrometer (Thermo Electron Corp., Wlthm, MA, USA). Determintion of NO 4 -N nd NO 3 -N ws performed using Lcht QuickChem 8000 flow injection clorimetric nlyser (Lcht Instruments, Lovelnd, CO, USA). Orgnic mtter (OM) ws determined y loss on ignition t 550 C for 2 hr (Peters et l., 2003). Minerl mtter ws clculted ccording to 100 %OM.

4 MCROBERTS et l Forge smples A 30-dy cutting intervl nd 15 cm cutting height were trgeted to chieve high yield nd nutritive vlue without negtively impcting persistence (Inyng et l., 2010; Vendrmini et l., 2014). Plots were hrvested (24 totl hrvest events) t pproximtely monthly intervls (36 dys with SD 8.6 dys) using hndheld sickles eginning in Jnury Cutting height incresed from 15 cm to pproximtely 25 cm over the course of the experiment s crowns thickened. Frms were hrvested within 2 4 dys nd in the sme sequence t ech hrvest window. The cutting intervls in 2011 (39 dys with SD 12.3 dys) were longer nd more vrile thn intervls for the rest of the experiment (33 dys with SD 3.3 dys), due to missed Octoer 2011 hrvest ecuse of flooding in the study re (mximum hrvest intervl = 63 dys). For ech plot, ll fresh forge iomss ws collected nd weighed. Susmples ( g) were collected every other hrvest to mesure forge nutritive vlue, while smller susmples (20 50 g) were collected to determine DM concentrtion during lternte hrvests. Dry-mtter concentrtion ws determined y drying smples to stle weight t 60 C in forced-ir oven. Susmples for forge nutritive vlue were ground to pss 4-mm screen in Retsch cutting mill (Hn, Germny) nd divided using smple seprtor. Only smples tht were not visily dmged y het or wter during the post-hrvest trnsporttion nd storge process were reground to pss 1-mm screen in UDY Cyclone Mill (UDY Corp., Fort Collins, CO, USA). Dirylnd Lortories, Inc. (Arcdi, WI, USA) determined nutritive vlue for smples collected in Septemer 2011 nd Decemer 2012 using ner-infrred spectroscopy (Mrten, Shenk, & Brton, 1989) with Foss model 5000 (Foss-NIR System, Silver Spring, MD, USA). Nutritive vlue prmeters included crude protein, cid detergent fire (ADF), neutrl detergent fire (NDF), lignin, cid detergent-insolule crude protein, neutrl detergent-insolule crude protein, solule protein, ft, sh, C, P, Mg, K, S, sugr (wter-solule crohydrtes), non-fire crohydrtes 1 nd totl ftty cids. Septemer 2011 nutritive vlue smples were collected t the eginning of the riny seson efore the onset of hevy rinfll. Decemer 2012 smples were collected t the eginning of the dry seson. Totl rinfll in Septemer 2011 hrvest (49-dy cutting intervl) ws higher thn in Decemer 2012 (33-dy cutting intervl). Men temperture ws 3 C higher in the growth period ssocited with the Septemer 2011 hrvest. Nutrient yields were clculted y multiplying DM yield y nutrient concentrtion in Septemer 2011 nd Decemer 2012 hrvests. Nitrogen nutrition index (NNI) ws clculted s NNI = N /N c nd N c = W, where N is ctul N concentrtion, N c is criticl N concentrtion, W is DM yield (Mg h 1 ), nd nd re species-specific constnts for C 4 perennil grsses (3.6 nd 0.34, respectively; Aldermn, Boote, & Sollenerger, 2011; Lemire, Jeuffroy, & Gstl, 1 Non-fire crohydrtes were clculted s follows: 100 (crude protein + neutrl detergent fier + ft + sh) (Hll, 2013). 2008). Luxury N consumption ws ssumed for NNI vlues >1 (Lemire et l., 2008). At hrvest, live tillers from three plnts per plot were counted y sudividing crowns into four equl prts nd counting live tillers in one qurter. The sme plnts were mesured throughout the experiment. Grss mximum height (tllest extended grss lde), cnopy height nd plnts per plot were recorded. The recording of plnt vigour (10-point scle from 1 = lest vigorous to 10 = most vigorous), wter logging (6-point scle from 0 = no stnding wter to 5 = severe plnt deth due to extreme inundtion for prolonged periods) nd lef ttrition (6-point scle from 0 = no deth to 5 = 80% 100% of leves nd tillers ded) egn in the 2011 riny seson (Octoer) nd ws completed for 15 dt collection periods. Other fctors potentilly impcting plot growth during given hrvest were recorded (e.g., chicken dmge, cttle dmge, cttle urine run-off into plots, ccidentl cutting). Flooding destroyed some plots on Frm 2 in fll 2010 nd gin in Replnting ws required, nd there were missing yield dt during nd fter these periods for the ffected frm. 2.5 Sttisticl methods Mixed model procedures nlysed results from the multiyer experiment using PROC MIXED (SAS Institute Inc., 2011). Men differences mong tretments were declred t p.05 using Tukey s sttistic to control the fmily-wise error rte for multiple comprisons. Models included fixed effects of compost rte, ure rte nd their interction, nd lock (frm) s rndom effect. Models with repeted mesures (DM yield, live tiller count, grss mximum height, grss cnopy height, grss vigour, lef ttrition, DM concentrtion) were selected with lock nd lock 9 tretment rndom effects to ccount for dependence of oservtions within frms nd within plots over time. Repeted-mesures models were selected with fixed-effect covrites including rinfll (cumultive rinfll in ech growth period), men temperture (men dily temperture during growth period, computed s mid-point etween mximum nd minimum temperture) nd hrvest intervl (dys from previous hrvest to current hrvest). Additionl cndidte fixed-effect covrites included the numer of plnts in ech plot (plnt count) nd principl components derived from pre-experiment soil fertility fctors (McRoerts et l., 2016) generted in JMP PRO (SAS Institute Inc., 2013) from individully significnt soil fertility fctors in selected yield model. The first principl component ws used s cndidte covrite in mixed models nd ws clculted s follows: Soil PC1 = Ction Exchnge Cpcity Field ph C N Mn NO 3 -N. Fixed-effect covrites nd interctions (up to two-fctor interctions) were individully removed from the model t p >.05 in stepwise mnner, nd the model ws run gin until only min tretment effects, significnt covrite effects nd interctions remined. Kenwrd Roger s pproximtion ws used to clculte denomintor degrees of freedom for models with repeted mesures. Min effect

5 136 MCROBERTS et l. interctions were lso evluted using the slice option in the lsmens sttement of PROC MIXED, which uses n F test to ssess interction slices, ut does not control for fmily-wise error. Nonnorml distriutions (e.g., DM yield, live tiller count, cnopy height nd mximum height) were identified y visul ssessment of quntile quntile plots nd distriution of model residuls. Log trnsformtion ws pplied for DM yield, while squre root trnsformtion ws used for live tiller count, cnopy height nd mximum height. Geometric mens nd 95% confidence intervls were clculted for trnsformed dt in lieu of true mens nd stndrd errors. Frm yield mens were extrcted from the selected yield model, ut with lock s fixed effect nd without the lock 9 tretment interction. Yield decline ws tested y compring pired mens etween the first nd second experiment yers with t test nd vi ssessment of the yield difference etween yers one nd two. Two rekdowns were evluted: nnul DM yield from Novemer 2010 to Novemer 2011 vs. nnul DM yield from Novemer 2011 to Novemer 2012, nd April 2011 to April 2012 vs. April 2012 to April Men differences were clculted s DM yield yer 2 DM yield yer 1. Sesonl yield vrition ws tested with tretment 9 seson interction in model with seson in lieu of hrvest period nd wether vriles. Sesonl vrition in live tiller count ws evluted using model with yer nd hrvest period nested in yer in lieu of hrvest intervl, climtic fctors nd the soil principl component. Nutritive vlue models included fixed effects of compost rte, ure rte nd their interction, nd lock (frm) s rndom effect. Hrvest period ws included s covrite when Septemer 2011 nd Decemer 2012 dt were nlysed together. These dt were lso nlysed seprtely. Compost nd compost 9 ure interction were not significnt in nutrient yield models nd were excluded from nlyses. Thus, nutrient yield models contined fixed effects of ure nd hrvest period (Septemer 2011 nd Decemer 2012), nd lock s rndom effect. Nutrient yield responses were log- or squre root-trnsformed. 3 RESULTS 3.1 Multo II yield nd development Dry-mtter yield Dry-mtter yield ws impcted y ure 9 compost interction (Tle S2). Climtic effects (rinfll nd temperture), plnt count, hrvest intervl, pre-experiment soil fertility nd significnt interctions impcted yield, ut not yield responsiveness to the fertility tretments (Tle S2). Ure ppliction lone (without compost ddition) did not increse DM yield (p =.6528; Tle S3). Similrly, yield did not increse with compost ppliction (p =.9167) if no ure ws pplied (Tle S3). Ure did increse yield when compost ws pplied t 4, 12 nd 24 Mg DM h 1 yer 1, nd compost ppliction incresed yield when ure ws pplied t 60 kg N h 1 yer 1, with similr trend t 120 kg N h 1 yer 1 (Tle S3). The highest comined rte of compost nd ure resulted in higher yield thn the no compost or ure control, the plots where compost ws pplied t 12 or 24 Mg DM h 1 yer 1 without ure ppliction, where the highest rte of compost ws pplied ut only 60 kg N h 1 yer 1 s ure, nd where 60 kg N h 1 yer 1 ws pplied s ure without compost ddition (Figure 1). In generl, lowest numericl yields were otined for compost-only tretments or ure-only tretments (Figure 1). Results were similr for model tht included hrvest period in lieu of wether fctors nd hrvest intervl. However, differences were not detected for the compost 9 ure interction (p =.2058). Tretment differences or lck thereof did not vry mong hrvest periods. Yield declined from the first to second yer of the experiment (p <.0001) independent of compost or ure tretments. Highest forge yields occurred during the lte dry seson from pproximtely April to August when some rinfll occurred nd tempertures were t pek levels. Yield declined throughout the riny seson nd initil stges of the dry seson. Overll yield differences were higher etween April 2012 to April 2013 nd April 2011 to April 2012 ( 4.1 Mg DM h 1 yer 1 ) thn etween Novemer 2011 to Novemer 2012 nd Novemer 2010 to 2011 ( 3.6 Mg DM h 1 yer 1 ). All frms except one experienced yield decline in the April comprison, while ll frms ut two experienced yield decline in the Novemer comprison. For two frms, the yield decline ws lrge (April to April: Frm 3 = 8.3 Mg DM h 1 yer 1 nd Frm 6 = 10.6 Mg DM h 1 yer 1 ; Novemer to Novemer: Frm 6 = 9.9 Mg DM h 1 yer 1 nd Frm 3 = 11.1 Mg DM h 1 yer 1 ). At Frm 2, where flooding occurred in fll 2010 nd fll 2011, yield in yer 2 ws higher thn the first-yer yield, perhps due to the lter re-estlishment period for ffected plots (less nutrient depletion from plnt growth) nd potentil soil nutrient trnsfer during flooding. Sesonl differences in yield mgnitude were oserved, ut tretment effects did not depend on seson (riny or dry; p =.9848). The 16th tretment contining potssium yielded numericlly lower thn the highest compost 9 ure tretment comintion, ut the men yield ws not different from the men yield of ny other DM yield (Mg h 1 yer 1 ) Ure = 0 kg N h yer Ure = 60 kg N h yer Ure = 120 kg N h yer Composted mnure rte (Mg DM h 1 yer 1 ) FIGURE 1 Bck-trnsformed Brchiri cv. Multo II dry-mtter (DM) yield lest squre mens (geometric mens) with 95% confidence intervls for composted mnure 9 ure tretment comintions. Tretments not connected y the sme letter re significntly different (p.05)

6 MCROBERTS et l. 137 tretment. This ws consistent for ll response vriles, nd therefore, results for this tretment will not e reported or discussed further. Lrge yield differences were oserved mong frms (Tle 1), rnging from n verge totl yield of Mg DM h 1 yer 1. Frm-to-frm vrition explined lrge proportion of residul vrince (51% in yield model, 34% in live tiller count, 37% in cnopy height, 45% in mximum height nd 18% in vigour model). Lrge differences in frm yields cn e ttriuted to vrile frm plot histories nd pre-experiment soil fertility levels (McRoerts et l., 2016). High frm-to-frm vriility generted results tht re potentilly more representtive of vrition in sndy Vietnmese soils nd sndy tropicl soils, nd more generlizle over the study re. Despite frm-to-frm vrition, tretment effects were consistent s determined y the sence of interctions with compost nd ure min effects. Furthermore, lock 9 tretment (plot) explined only 6% of residul vrince in the yield model, 8% in the tiller count model, 2% in the cnopy height model, 4% in the mximum height model nd 5% in the vigour model Live tiller count Live tiller counts responded similrly to tretments s did DM yield (Tle S4). Pirwise correltion etween live tiller count nd DM yield ws strong nd positive (r =.65). Live tiller count incresed with ure ppliction, ut not compost, nd there ws trend (p =.0616) for compost 9 ure interction. Live tiller count for the highest ure rte (120 kg N h 1 yer 1 ) ws higher thn where no ure hd een pplied (Figure 2). Tests of effect slices (Tle S5) indicted tht, similr to DM yield, live tiller count did not respond to compost ppliction when no ure ws dded, nor to ure when no compost ws pplied. Live tiller count incresed with ure ppliction t the highest compost rte, with similr trend oserved when compost ws pplied t 4 nd 12 Mg DM h 1 yer 1. Live tiller count responded to compost only t the intermedite ure rte (60 kg N h 1 yer 1 ), ut response ws inconsistent nd driven y high tiller counts when compost ws pplied t 4MgDMh 1 yer 1. TABLE 1 Bck-trnsformed Brchiri cv. Multo II dry-mtter yield lest squre mens (geometric mens) nd 95% confidence intervls for lock (frm) Frm Geometric men (Mg DM h 1 yer 1 ) Lower 95% CI (Mg DM h 1 yer 1 ) Upper 95% CI (Mg DM h 1 yer 1 ) c d e Mens not connected y the sme letter re significntly different (p.05). Live ller count ( llers/plnt) Ure rte (kg N h 1 yer 1 ) FIGURE 2 Bck-trnsformed live tiller count lest squre mens (geometric mens) nd 95% confidence intervls for ure tretments in plots estlished to Brchiri cv. Multo II. Tretments not connected y the sme letter re significntly different (p.05) Live tiller count incresed throughout the yer until Septemer, efore declining from Octoer to erly in the susequent yer (Figure 3). Riny seson negtively impcted tiller count, which recovered during the dry seson in the two full yers oserved. The rnge in tiller count declined from the first yer of the experiment to the second yer, ut overll live tiller count did not decline from the first yer to second yer of the experiment Cnopy nd mximum height, nd plnt vigour Cnopy height nd mximum height responded to compost nd ure (Tles S6 nd S7). A ure 9 compost interction effect ws not detected. Cnopy height nd mximum height models were similr, lthough covrite interctions differed. Cnopy height ws higher for the two highest rtes of compost thn without compost, nd mximum height ws higher in the highest compost rte thn without compost nd t the intermedite rte (8 Mg DM h 1 yer 1 ; Tle 2). Cnopy height ws higher for the highest rte of ure thn Live tiller count (tillers/plnt) Jn Fe Mr Apr My Jun Aug Sep Nov Jn Fe Mr Apr My Jun Jul Aug Sep Oct Nov Dec Jn Mr Apr FIGURE 3 Bck-trnsformed Brchiri cv. Multo II lest squre mens (geometric mens) with 95% confidence intervls for live tiller count y hrvest period during the experiment

7 138 MCROBERTS et l. TABLE 2 Bck-trnsformed lest squre mens (geometric mens) for Brchiri cv. Multo II cnopy height nd mximum extended lef height, sorted y cnopy height mens Cnopy height, (cm) Mximum height, (cm) Compost rte (Mg DM h 1 yer 1 ) Ure rte (kg N h 1 yer 1 ) Mens not connected y the sme letter re significntly different (p.05). Men comprisons for compost nd ure re independent. TABLE 3 Lest squre mens for on Brchiri cv. Multo II plnt vigour. Vigour ws ssessed on 10-point continuous scle from 1 = lest vigorous to 10 = most vigorous Men, SE Compost rte (Mg DM h 1 yer 1 ) Ure rte (kg N h 1 yer 1 ) Mens not connected y the sme letter re significntly different (p.05). Men comprisons for composted mnure nd ure re independent. without ure, while ure ppliction rte did not impct mximum height. Compost nd ure ddition explined differences in plnt vigour (Tle S8). The highest comined rte of compost nd ure resulted in greter plnt vigour thn for the no-compost or ure control, plots where compost ws pplied t 4 Mg DM h 1 yer 1 without ure, where ure ws pplied t 60 kg N h 1 yer 1 without compost, nd where ure ws pplied t 60 kg N h 1 yer 1 nd compost t 8MgDMh 1 yer 1 (Tle 3). Lef ttrition did not respond to compost nd ure tretments. Yield ws positively correlted with live tiller count (r =.65), mximum height (r =.63), cnopy height (r =.56) nd vigour (r =.53). Cnopy height, mximum height nd vigour were the only plnt indictors tht responded directly to compost tretments (Tles S6, S7 nd S8). Grss in plots receiving high compost rtes grew tller nd ws more vigorous thn grss grown with low rtes of compost nd ure. The tllest, most vigorous plnts occurred in the highest compost 9 ure tretment comintion. 3.2 Forge nutritive vlue Plnt tissue smples for the two representtive hrvest periods (n = 96 for ech period) indicted high nutritive vlue s forge for cttle (Tle 4). Nutritive vlues in Septemer 2011 (eginning of riny seson) nd Decemer 2012 hrvests (eginning of dry seson) were similr, ut notle differences were higher sugr nd non-fire crohydrte levels in Septemer 2011 nd higher crude protein in Decemer Cooler, wetter, cloudier conditions ner Decemer 2012 hrvest reltive to the Septemer 2011 hrvest could explin these differences (Vn Soest, 1996). Septemer 2011 smples were collected t the eginning of the riny seson (prior to hevy rinfll). Decemer 2012 smples were collected t the eginning of the dry seson. Rinfll ws higher, cutting intervl longer, nd men temperture ws higher during the Septemer 2011 period thn Decemer 2012 (Tle 4). Compost nd ure ppliction ffected few nutritive vlue prmeters, nd results were inconsistent for the Septemer 2011 nd Decemer 2012 hrvest periods (Tle S9). Nutritive vlue tretment mens for the compost 9 ure interction re lso ville (Tle S10). Compost ddition decresed DM concentrtion in pooled nlysis of smples collected in Septemer 2011 nd Decemer 2012 (n = 180; Figure 4). Dry mtter in the highest compost ppliction rte ws lower thn where 8 Mg DM h 1 yer 1 or no compost hd een pplied. Compost ppliction incresed sh concentrtion (Figure 4). The highest sh concentrtion ws mesured when compost ws pplied t 24 Mg h 1 yer 1, which ws significntly higher thn for plots receiving 12 or 8 Mg DM h 1 yer 1 or plots tht hd not received ny compost. Compost lso incresed K concentrtion of smples collected in Septemer 2011 nd Mg concentrtion of smples from Decemer The K nd Mg concentrtions of forge fertilized with the highest compost rte were higher thn for forge tht did not receive ny compost (Figure 4, Tle S9). Compost ppliction tended to increse P concentrtion of forge hrvested in Septemer 2011; P when compost ws pplied t 24 Mg DM h 1 yer 1 ws higher thn for plots tht hd not received compost (Figure 4, Tle S9). Compost tended to decrese the sugr content of smples collected in Septemer 2011, ut men differences were not significnt (Figure 4, Tle S9). Compost lso impcted non-fire crohydrtes in Decemer 2012, ut results were inconsistent nd men differences were not significnt. Ure incresed NNI vlues in pooled Septemer 2011 nd Decemer 2012 smples, with NNI in plots receiving the highest ure ppliction rte (0.819) higher thn the intermedite rte nd without ure (Figure 5). Nitrogen nutrition index mens were <1, indicting tht criticl N levels were not reched, reflecting n N deficiency for ll tretments. The ure tretment did not ffect crude

8 MCROBERTS et l. 139 TABLE 4 Hrvest period chrcteriztion nd nutritive vlue prmeters for Brchiri cv. Multo II forge hrvests in Septemer 2011 nd Decemer 2012 on six frms (16 plots per frm) Sept 2011 (n = 96) Dec 2012 (n = 96) Vrile Men SD Men SD n Hrvest intervl (d) Rinfll (mm) Men temperture ( C) Dry-mtter (DM) yield (Mg h 1 ) Dry mtter (%) Crude protein (g kg 1 DM) Nitrogen nutrition index Acid detergent fire (g kg 1 DM) Neutrl detergent fire (g kg 1 DM) Lignin (g kg 1 DM) Acid detergent-insolule crude protein (g kg 1 DM) Neutrl detergent-insolule crude protein (g kg 1 DM) Solule protein (g kg 1 CP) Ft (g kg 1 DM) Ash (g kg 1 DM) C (g kg 1 DM) P(gkg 1 DM) Mg (g kg 1 DM) K(gkg 1 DM) S(gkg 1 DM) Sugr (g kg 1 DM) Non-fire crohydrtes (g kg 1 DM) Totl ftty cids (g kg 1 DM) Nitrogen nutrition index (NNI) ws clculted s NNI = N /N c nd N c = W, where N is ctul N concentrtion, N c is criticl N concentrtion, W is DM yield (Mg h 1 ), nd nd re species-specific constnts for C 4 perennil grsses (3.6 nd 0.34, respectively; Aldermn et l., 2011; Lemire et l., 2008). Luxury N consumption ws ssumed for NNI vlues >1 (Lemire et l., 2008). protein concentrtion in hrvested iomss. Ure incresed lignin concentrtion in Septemer 2011 (Figure 5), with lignin in the highest ure ppliction rte (46.8 g kg 1 DM) higher thn in plots tht hd not received ure (45.6 g kg 1 DM). Forge DM ws higher during dry periods nd periods with longer hrvest intervls. Temperture, rinfll nd hrvest intervl effects on DM concentrtion were stronger nd more importnt thn the impct of compost ddition s demonstrted y the significnce nd effect size of wether effects in the full DM model from ll hrvests (n = 24). Fixed effects included compost rte (p =.0975), cumultive rinfll in ech growth period (p <.0001), hrvest intervl (p <.0001), men dily temperture in hrvest intervl (p <.0001) nd the numer of plnts in ech plot (p =.0108). Dry-mtter concentrtion decresed slightly with compost ppliction, from 22.1% when no compost ws dded, to 21.3% when 24 Mg DM h 1 yer 1 of compost ws pplied. Dry-mtter concentrtion incresed y 0.33% for every 1 C increse in men temperture nd y 0.15% for ech dditionl dy etween hrvests nd decresed y 0.191% for ech dditionl plnt in the plot nd y % for ech 1 mm increse in rinfll. Block (frm) explined 31% of residul vrince, while plot explined less thn 1%, suggesting reltively lrge frm differences ut consistent response to min effects. 3.3 Nutrient yield Dry-mtter yield in Septemer 2011 ws nerly three times higher thn in Decemer Nutrient yield for mesured nutritive vlue prmeters incresed with ure ppliction nd ws primrily function of DM yield response to ure during Septemer 2011 nd Decemer 2012 (Tle 5). Compost ppliction did not impct nutrient yield, nd compost 9 ure interction ws not detected. Nutrient yield ws higher for the highest ure ppliction rte thn for plots receiving the intermedite ure rte nd those not receiving ure. The only exception ws K yield, which ws higher for the highest ure ppliction rte thn without ure. Potssium yield for plots receiving ure t 60 kg N h 1 yer 1 did not differ from other ure ppliction rtes.

9 140 MCROBERTS et l. P (g/kg DM) K (g/kg DM) Dry mtter (%) () 120 () Composted mnure rte (Mg DM h 1 yer 1 ) Composted mnure rte (Mg DM h 1 yer 1 ) Ash (g/kg DM) (c) 4 5 (d) Composted mnure rte (Mg DM h 1 yer 1 ) Composted mnure rte (Mg DM h 1 yer 1 ) (e) Mg (g/kg DM) Sugr (g/kg DM) Composted mnure rte (Mg DM h 1 yer 1 ) Composted mnure rte (Mg DM h 1 yer 1 ) (f) FIGURE 4 Lest squre mens for effect of compost on Brchiri cv. Multo II dry mtter (, n = 180, p =.0060) nd sh (, p =.0072) in Septemer 2011 nd Decemer 2012 smples, K in Septemer 2011 smples (c, n = 90, p =.0231), Mg in Decemer 2012 smples (d, n = 90, p =.0010), P in Septemer 2011 smples (e, n = 90, p =.0583) nd sugr in Septemer 2011 smples (f, n = 90, p =.0577). Error rs re 1 SE of the men. Brs connected y the sme letter in ech r grph re not significntly different (p.05) NNI () () Ure rte (kg N h 1 yer 1 ) Ure rte (kg N h 1 yer 1 ) Lignin (g/kg DM) FIGURE 5 Lest squre mens for effect of ure on nitrogen nutrition index (NNI,, p =.0065) nd lignin (, p =.0469) in Multo II forge smples collected in Septemer 2011 nd Decemer 2012 (n = 180). Error rs re 1 SE of the men. Brs connected y the sme letter in ech r grph re not significntly different (p.05)

10 MCROBERTS et l DISCUSSION 4.1 Yield nd gronomic components Appliction of ure ws most effective when comined with compost ppliction, possily reflecting oth greter overll N vilility nd relese of P, K, secondry mcro- nd micronutrients during compost minerliztion. The comintion of highest yields when oth compost nd ure were pplied t the highest rtes nd lck of response to ure where no compost ws pplied suggests tht (i) not only N ut lso other nutrients re yield limiting in these sndy soils nd (ii) compost ppliction t the rtes in this study supplied insufficient mounts of N. Furthermore, s suggested y Cstillo et l. (2010), N minerliztion of compost my hve een higher when comined with inorgnic N. The overll yield decline over time is consistent with decrese in ville N s well, reflecting negtive prtil N lnces (McRoerts et l., 2016). Such lck of N is lso supported y NNI levels tht were consistently elow 1. Pek Multo II yields in this experiment were higher or equivlent to those reported elsewhere in the literture for reserch plots (Gonzlez, Arzol, Morgn, River, & Rmırez, 2011; Pizrro, Hre, Mutimur, & Chngjun, 2013), ut lower thn oserved for Multo II in forge vrietl selection experiment in the sme region (25.7 Mg DM h 1 yer 1 ; B et l., 2013), nd lower thn the yield verge of 29.1 Mg DM h 1 yer 1 for three south-centrl costl provinces in Vietnm (B et l., 2014). Higher inorgnic N fertiliztion nd shorter experiment durtion my e responsile for higher yields in the B et l. (2013, 2014) experiments. Crude protein concentrtions in Multo II reported y B et l. (2013) (137 g kg 1 DM) nd B et l. (2014) (122 g kg 1 DM) were in the sme rnge s levels oserved in our experiment. Tiller counts were more ccurte indictor of sesonl vrition in plnt condition thn yield given non-constnt cutting intervls. Riny seson tiller decline my hve occurred due to decresed photosynthetic opportunities (cloudy, cool conditions), comined with plnt stress from wter logging nd flooding, nd high tiller senescence nd competition mong geing plnts. The lrge decline in tiller count t the end of 2011 my explin lower yields in yer 2 of the experiment. 4.2 Nutritive vlue nd nutrient yield Forge nutritive vlue ws consistent with results reported in the literture for Multo II (Argel et l., 2007; B et l., 2013, 2014; Inyng et l., 2010). Cooler, wetter, cloudier conditions in Decemer 2012 compred to Septemer 2011 could explin higher sugr nd non-fire crohydrte levels in Septemer 2011 nd higher crude protein in Decemer 2012 (Vn Soest, 1996). The effect of compost on sh, K nd Mg concentrtions is consistent with work y Gonzlez et l. (2011) tht reported positive K response to cttle mnure. These effects could e importnt for formultion of cttle rtions. Most frmers in south-centrl costl Vietnm supply slt, ut only out 40% of frmers in the study re provide supplementl minerls (Prsons et l., 2013). Trnsition to semi-intensive opertions with less grzing limits the opportunities for minerl intke through wter, herge intke nd soil ingested while grzing, TABLE 5 Geometric mens (ck-trnsformed lest squre mens from log- or squre root-trnsformed responses) for Multo II nutrient yield s impcted y ure (n = 180). Models include ure min effect, hrvest period covrite nd lock s rndom effect Ure ppliction rte kg N h 1 yer 1 Nutrient yield Units p Crude protein Mg h 1 yer Acid detergent fire Mg h 1 yer Neutrl detergent fire Mg h 1 yer Digestile dry mtter Mg h 1 yer Sugr Mg h 1 yer Ash Mg h 1 yer Non-fire crohydrtes Mg h 1 yer Lignin Mg h 1 yer Ft Mg h 1 yer C Mg h 1 yer P Mg h 1 yer Mg Mg h 1 yer K Mg h 1 yer S Mg h 1 yer 1 < Totl ftty cids Mg h 1 yer Mens connected y the sme letter in ech row re not significntly different (p.05).

11 142 MCROBERTS et l. mking minerl supplementtion even more importnt. Minerl concentrtion of Multo II could e dequte to fulfil cttle requirements (Vn Soest, 1994), ut should e verified during rtion formultion. The sence of Multo II crude protein response to the ure tretment differs from crude protein response to inorgnic N fertiliztion in experiments with other species (Aldermn et l., 2011; Cmpos et l., 2013). This could e ttriuted to dilution effect of higher yield with dded N or insufficient inorgnic N for luxury consumption (NNI < 1). The effect of ure ppliction on lignin my e product of mturtion, s N increses reltive mturity due to fster growth (lrger plnts; Vn Soest, 1996). This is lso reflected in lower wter content in smples collected in Septemer 2011 (longer hrvest intervl) reltive to Decemer This effect on lignin is unlikely to e consistent from hrvest to hrvest, especilly with shorter cutting intervls in which reltive mturity levels re less divergent s demonstrted y the lck of tretment effect in Decemer Nutrient yield from Multo II could e sufficient to support supplementtion of smllholder cttle production with forge produced in ckyrd plots (Tle 5). Precise rtion lncing comining Multo II supplementtion with other ville diet components will e necessry to ensure dequte nutrient supply for cttle production in these systems. 4.3 Implictions Lnd nd lour vilility nd yield potentil in ckyrd plots Lnd nd lour my e more limiting thn nutrient vilility for forge production in smllholder systems in the study region. Prsons et l. (2013) reported 2.4 people per household with SD 1.6 in ville lour nd h with SD in griculturl lnd. Bckyrd lndholdings tht could e llocted to forge production re often scrce. However, such ckyrd forge plots could ese pressure on lour resources (B et l., 2013; Khnh et l., 2014; St ur et l., 2013). Thus, frmer interest in production of well-mnged, smll, ckyrd forge plots could increse in the study region. St ur et l. (2013) demonstrted in Vietnm s Centrl Highlnds tht frms dopting forge production invested 3 hr/dy in cttle production lour vs. 6.8 hr/dy for non-dopters. Returns to cttle-relted lour were clculted t $0.73 hr 1 for dopters nd $0.16 hr 1 for non-dopters (2005 rtes). They concluded tht lour ws key reson for doption of cultivted forge technology nd tht lour contriuted to oserved expnsion of cultivted forge res over time. An environmentl enefit of ckyrd forge production is decresed pressure on communl grzing lnds in the semi-intensive system. Therefore, doption of ckyrd forge systems like the one used in our experiment t commune-wide scle could decrese the risk of overgrzing in nd ner nturl res. Furthermore, grzing shortflls likely occur during the lte dry seson, nd potentil for high yields for cultivted forges during this time, especilly on irrigted ground, would coincide with periods of pek supplementtion demnd. Prticipting frmers in this experiment owned n verge of 0.85 h of lnd, 7% (603 m 2 ) of which ws llocted to forge production for cttle diet supplementtion. Forge plots were locted ner the household nd cttle shed, which simplified dily mngement. An verge household plot could produce 1.2 Mg forge DM yer 1 (ssumed production of 20 Mg DM h 1 yer 1 ), enough to supplement five nimls with pproximtely 241 kg DM niml 1 yer 1. Further ssuming 175 kg men odyweight (0.7 tropicl livestock units (Jhnke, 1982)) nd 2% odyweight per d in DM intke, Multo II could fulfil pproximtely 19% of dily DM intke (sesonlly vrile) for ech niml. This is potentilly importnt contriution to supplementry green fodder, the implictions of which merit further investigtion with rtion lncing softwre nd economic models. Expnsion of productive res could further increse ville DM per niml nd resulting production potentil. For exmple, expnsion to 0.1 h would increse supplementtion potentil to pproximtely 31% of dily DM intke requirements Mnging for high yield nd high nutritive vlue Hrvest intervls for the periods nlysed for nutritive vlue in this experiment (49 nd 33 dys) produced high nutritive vlue forge for supplementry cttle consumption. A fvourle pproch to hrvest high nutritive vlue forges my e the ppliction of short cutting intervls to hrvest t erlier developmentl stges (stem elongtion or oot stges), lthough intervls less thn 3 weeks cn negtively impct persistence nd should e voided (Vendrmini et l., 2014). Future field reserch should trget the hrvest intervl component in the study region. With limited resources in smllholder systems, our results suggest tht it will e more fesile to mnge forges for high yield with compost nd ure fertiliztion thn for high nutritive vlue. Further supporting this conclusion, review of psturelnd studies demonstrted tht 60% 90% of vrition in verge dily gin is due to forge quntity in pstures with high vrition in forge mss (Sollenerger & Vnznt, 2011) such s those in rin-fed forge systems of south-centrl Vietnm. In the study region, ville Multo II cn e supplemented y redily ville sources of protein (penut ckes) nd energy (cssv) to lnce cttle rtions Cttle mnure vilility, fertilizer equivlence nd mngement If we ssume 700 kg mnure DM niml 1 yer 1 (1,000 kg per tropicl livestock unit per yer; de Hn, Steinfeld, & Blckurn, 1999), herd size of five nimls nd 525 kg ville mnure DM niml 1 yer 1 (6 hr grzing per dy removed), the mount of cttle mnure ville mounts to 2,625 kg mnure DM yer 1, nd 26 kg N frm 1 yer 1. Assuming no N losses, composted mnure could e pplied t or ner frmer-desired rtes for ckyrd 0.1-