III. MONITORING TURFGRASS RESPONSE TO N FERTILIZATION AND CLIPPING MANAGEMENT USING ANION EXCHANGE MEMBRANES:

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1 III. MONITORING TURFGRASS RESPONSE TO N FERTILIZATION AND CLIPPING MANAGEMENT USING ANION EXCHANGE MEMBRANES: A GREENHOUSE STUDY 3.1 ABSTRACT Anin exchange membranes (AEMs) hld prmise as a methd fr estimating the plant-available N status f sils, but their applicatin t turfgrass systems has nt been researched extensively. The main bjective f this experiment was t determine the relatinship between sil N3-N desrbed frm AEMs and grwth respnses in turf grass systems. A greenhuse experiment was cnducted with bentgrass and a bluegrassfescue-ryegrass mixture receiving fur rates fn (, 98, 196, 392 kg ha -1) with clippings returned r remved. Turfgrasses were established in pts and AEMs were inserted int the sil and exchanged weekly fr 29 weeks. Nitrate-N was desrbed frm the AEM strips and quantified. Clipping management, N rate, and grass species significantly (P <.1) affected the amunt fn3-n desrbed frm the AEMs. Higher sil N3-N levels were fund when clippings were returned (1 t 47% increase), as N rate increased, and with bentgrass. Returning grass clippings at 98 kg N ha -1 prduced statistically equivalent dry matter yields t remving clippings at 392 kg N ha -1 fr bth species. Linear plateau and Cate-Nelsn mdels were used t predict critical levels f sil N3-N desrbed frm AEMs necessary t ptimize yield, ttal N uptake, and ttal N cncentratin in turfgrasses. This technlgy hlds prmise fr determining relatinship between sil N3-N availability and grwth respnses in turfgrass systems. 23

2 INTRODUCTION Reliable determinatins f nitrate (N3 -) availability in sils beneath turfgrass are necessary t ptimize N fertilizatin rates fr maximum grass quality and minimizatin f nutrient pllutin. Sme traditinal methds emplyed t quantify the amunt f available N 3 - in the sil/plant system include chemical extractins, biassays, incubatins, and the use f exchange resins. Drawbacks f such techniques include the expense and lengthy time assciated with their use as well as the ptential fr excessive sil disturbance (Hubner et al., 1991; Subler et al., 1995). In additin, traditinal extractin methds nly prvide an index fn 3 - availability (Yang et al., 1991). Ideally, a technique fr determining available sil N 3 - in field situatins shuld impse minimal disturbance and shuld accunt fr the N dynamics f n-site cnditins. Anin exchange membranes (AEMs), which are flat, fiber-backed membranes that adsrb anins, prvide such a technique. Anin exchange membranes adsrb nutrients via exchange reactins that have the ptential t mimic rt activity in the sil (Abrams and Jarrell, 1992). The quantity f nutrient adsrbed n an AEM is related t and influenced by the cncentratin f that nutrient in the sil (Rbertsn et al., 1999). Anin exchange membranes have recently been examined as a tl fr measuring the availability fn3-n in varius field situatins. Anin exchange membranes generate minimal disturbance in the sil and accunt fr in situ cnditins (Cllins and Allinsn, 1999; Wander et al., 1995; Ziadi et al., 1999). Bth Ziadi et al. (1999) and Cllins and Allinsn (1999) fund psitive relatinships between the amunt f fertilizer N applied in grassland systems and the amunt fn3- desrbed frm AEMs. Cllins

3 25 and Allinsn (1999) als fund that N 3 - desrbed frm AEMs crrelated well with perennial grassland yield. Ziadi et al. (1999) fund that N 3 - desrbed frm AEMs crrelated well with yield and ttal N uptake in frage grasses. Wander et al. (1995) fund that AEMs were a better tl fr determining available sil N 3 - than sil extractin in a fall tillage/winter fallw crpping system. Anin exchange membranes were als used by Simard et al. (1998) n glf greens t estimate the relatinship between N cntent in grass clippings and desrbed N 3 - frm AEMs. The effective use f AEMs in field crp studies suggests their ptential fr applicatin in turfgrass studies. Therefre, the bjective f this study was t determine the relatinship between sil N 3 -N, desrbed frm AEMs, and grwth respnses in turfgrass systems. 3.3 MATERIALS AND METHODS Large, 7.5 L pts were filled with a fine, sandy lam tp sil (ph 6.1, mdified Mrgan extractable Ca, Mg, P, and K at medium levels) and arranged in a greenhuse in a 2 x 2 x 4 factrial in a randmized cmplete blck design with fur replicates. Pts were amended with lime and phsphrus as per sil test recmmendatins. Within blcks, pts were rtated weekly t accunt fr any within-blck variability. Experimental treatments included fur rates fn as ammnium nitrate fertilizer (equivalent t, 98, 196, and 392 kg N ha! yr -I) in 3 split applicatins, tw clipping treatments (returned and remved), and tw turfgrass stands: 1) bentgrass-agrstis palustris 'Prvidence', and 2) a bluegrass-fescue-ryegrass mixture [35/Cmmn Kentucky bluegrass (Pa pratensis), 35% cmmn creeping red fescue (Festuca rubra),

4 26 15% 'Cutter' perennial ryegrass (Llium perenne), and 15% 'Express' perennial ryegrass (Llium perenne)]. In additin t the abve N rates, at time f seeding, the equivalent f 49 kg N ha -1 in the frm f ammnium nitrate was applied t each pt t facilitate grass establishment. grass species. Pts were maintained with cultural practices apprpriate t each f the Bentgrass was maintained at a fairway height f 1.3 ern and the turfgrass mixture was maintained at a hme lawn height f 3.8 em. Fertilizer was applied during weeks 5, 12, and 2. Irrigatin was applied t prvide adequate misture but nt t induce leaching. The AEMs (type 24-U-386) used in this study are made f crss-linked vinyl cplymer reinfrcing fabric embedded with NH4+ anin exchange grups (Inics, 199). Individual membranes (6.25 x 2.5 em) were cut frm 61 x 122 em sheets f AEM material. As the grass became established and began t require clipping, a single AEM was inserted int each f the pts weekly t make in situ measurements f plant-available sil N 3 -N. A vertical slit was made in the sil with a masn's trwel and AEMs were inserted t a depth f 1 t 15 em. Cmplete cntact was established between the AEMs and the sil by pressing the slit tgether by hand. A mnfilament line was attached t each AEM t facilitate remval. After each AEM was remved frm the pts, a new AEM was inserted int a new slit. The specific methdlgy f preparing AEMs fr use fllwed Ziadi et al. (1999). This methd included rinsing AEMs with deinized water and then shaking fr 5 minutes in.5 M HCl. After shaking, AEMs were rinsed with deinized water (three times). The membranes were saturated with 1 M NaCI by shaking fr tw hurs, and received a final

5 27 deinized water rinse (three times). AEMs were stred in deinized water until use t prevent dessicatin. As AEMs were remved frm pts, they were lightly rinsed with deinized water t remve any adhering sil and were placed in 6 ml, lw-density plyethylene (LDPE) sample bttles cntaining 25 ml f 1 M NaCl. The AEMs were immediately remved t the labratry fr analysis. The sample bttles cntaining the AEMs were shaken fr 1 hur and the extracts filtered thrugh sil analysis papers (8-12 ~ retentin range, Schleicher and Schuell, Keene, NH). The extracts were analyzed fr N 3 -N cncentratin n a Scientific Instruments cntinuus flw analyzer (WESTCO, Danbury, CT) using a clrimetric, Cd-reductin methd. Clippings were cllected and dried in a frced-draft ven (7 C) until a cnstant weight was reached. Subsamples f clippings were analyzed using a LECO FP-2 CarbniNitrgen Analyzer fr the determinatin f ttal N cncentratin. The uptake f N was determined as clipping dry weight x N cncentratin. The experiment cntinued fr a ttal f 29 weeks-a perid f time equivalent t a typical grwing seasn in Cnnecticut. The effects f fertilizatin rate, clipping treatment, grass species, and all cmbinatins theref upn desrbed N 3 -N frm AEMs were determined by analysis f variance (AOV). The relatinships f dry matter yield (DMY), ttal N uptake (NUP), and final harvest perid tissue N cncentratin t the amunt fn 3 -N desrbed by the AEMs were determined by using linear plateau (LP) and Cate-Nelsn mdels. Linear plateau and Cate-Nelsn mdels were used t estimate critical levels f desrbed N 3 -N abve which additinal available N 3 -N wuld nt increase DMY, NUP, r tissue N.

6 28 cncentratin f clippings. Linear plateau mdels were generated using the NLIN prcedure f SAS (SAS Inst., 199). The calculatin f critical level and manual placement f a hrizntal plateau in the Cate-Nelsn plts were made t best divide the data pints int the upper right and lwer left quadrants f the plts. Because crrect predictins f the mdel ccur in the upper right and lwer left quadrants f Cate-Nelsn plts (Nelsn and Andersn, 1977), thse data pints falling utside these quadrants may be cnsidered in errr and an errr percentage may be determined. The ANOYA prcedure f SAS was used fr Cate-Nelsn determinatins (SAS Inst., 199). 3.4 RESULTS AND DISCUSSION Desrbed N 3 -N frm AEMs Fertilizatin rate, clipping treatment and species were fund t have significant effects (P<O.OOl) n desrbed N 3 -N frm AEMs (Table 3.1). Desrbed N 3 -N measured in bentgrass exhibited a linear respnse t N rate fr bth clipping treatments while desrbed N 3 -N measured in the mixed species exhibited a curvilinear respnse t N rate (Figs. la, B). Fr bentgrass, desrbed N 3 -N at 98 kg N ha- l (98 N) with clippings returned (CRT) was nt significantly different frm desrbed N 3 -N at 196 N with clippings either returned r remved (CRM) (Fig. 3.1A). In this case, reducing bentgrass fertilizatin by 5% did nt significantly change the amunt fn 3 -N desrbed frm AEMs regardless f clipping treatment. With mixed species, there was n significant difference in desrbed N3-N between 98 N with CRT r CRM and 196 N with CRM (Fig. 3.1B). Reducing fertilizatin by 5% did nt have a significant effect upn the amunt fn 3 -N desrbed frm AEMs in mixed species pts with CRT. In all instances but ne (mixed species at ON), returning clippings t the pts increased

7 29 desrbed N3-N frm AEMs. The increase varied frm 1 t 47/and was dependent n the experimental treatment (Figs. la, B). A direct cmparisn f these results t ther studies is difficult because nly ne turfgrass study using AEMs has been reprted. Hwever, ur findings crrbrate thse f Simard et al., (1998) wh reprted that AEMs respnded t varying N fertilizatin rates f bentgrass glf greens Dry Matter Yield. We bserved that fertilizatin rate and clipping treatment significantly (P<O.OOl) increased DMY (Table 3.1). Dry matter yield f bent grass exhibited linear and curvilinear respnses t N rate depending n clipping treatment (Fig. 3.1 C). Fr the mixed species, dry matter yield exhibited linear respnses t N rate fr bth clipping treatments (Fig. 3.1 D). Fr bentgrass, reducing N fertilizatin rates frm 5 t 75% did nt significantly decrease DMY when clippings were returned (Fig. 3.1 C). Fr mixed species, reducing fertilizatin up t 75/did nt significantly decrease clipping yield when clippings were returned (Fig. 3.1D). One ther study cnsidered the effect f returning turfgrass clippings n DMY. Starr and DeR (1981) bserved an increase in DMY (frm 15-55%) when they returned clippings at the N fertilizatin rates f 195 kg N ha -1 (first tw years) and 18 kg N ha -1 (final year) during their 3-year study. The increases in DMY that Starr and DeR (1981) bserved are cmparable t the increases that we bserved fr bentgrass (55%) and mixed species (52%) at the similar N rate f 196 kg N ha -1 when we returned clippings. Overall, we fund that returning clippings increased DMY frm 7 t 55% fr bentgrass and frm 36 t 89% fr mixed species, depending n N fertilizatin rate.

8 3 These findings suggest that clippings can be substituted, at least in part, fr N fertilizatin f turfgrass Ttal N Uptake We als bserved that N fertilizatin rate and clipping treatment significantly (P<O.OOl) increased NUP (Table 3.1). Depending n clipping treatment, NUP f bentgrass exhibited either a linear r a curvilinear respnse t N rate (Fig. 3.1E). Nitrgen uptake f the mixed species exhibited a linear respnse t N rate fr bth clipping treatments (Fig. 3.1F). This resulted in a 75% reductin in fertilizatin with n appreciable difference in NUP fr bentgrass when clippings were returned. Similar NUP relatinships were bserved fr mixed species. Reducing fertilizatin by up t 75% and returning clippings did nt significantly change the amunt fnup fr the mixed species. Returning clippings increased NUP frm 37 t 82% fr bentgrass and frm 38 t 112% fr mixed species depending n N fertilizatin rate. These increases in NUP were much higher than thse bserved by Starr and DeR (1981) wh bserved nly a 4% increase in NUP when they returned clippings Tissue N Cncentratin Fertilizatin rate, clipping treatment and the interactin fn rate and clipping treatment significantly (P<O.OOl,.1, and.1, respectively) increased tissue N cncentratin fr the final harvest perid (Table 3.1). Tissue N cncentratin in bentgrass exhibited a curvilinear respnse t N rate fr bth clipping treatments (Fig. 3.1 G). Tissue N cncentratin in mixed species exhibited either a linear r curvilinear respnse t N rate depending n clipping treatment (Fig. 3.1H). As N fertilizatin rate increased r with CRT, tissue N cncentratin als increased except at N (Fig. 3.1 G,

9 31 H). Fr bentgrass, reducing N fertilizatin frm 5 t 75% did nt significantly effect tissue N cncentratin when clippings were returned and in mixed species clippings, a 25% reductin in fertilizatin did nt significantly effect tissue N cncentratin when clippings were returned. Overall, returning clippings increased tissue N cncentratin frm t 31% fr bentgrass and frm t 13% fr mixed species, depending n N fertilizatin rate Relatinship f Grwth Respnses t Desrbed Sil N 3 -N Linear plateau and Cate- Nelsn mdels, which have lng been used t mdel grwth respnses f agrnmic crps, were successfully used t determine relatinships between turfgrass grwth and desrbed sil N 3 -N frm AEMs. Initial mdel analyses using LP and Cate- Nelsn mdels were perfrmed n bentgrass and mixed species data. Bth LP and Cate-Nelsn mdels had highly significant relatinships between desrbed N 3 -N and DMY, NUP, and tissue N cncentratin (Fig. 3.2). The linear plateau mdels generated greater critical levels f desrbed sil N 3 -N cmpared with Cate-Nelsn mdels fr all measured variables (Fig. 3.2). The percentage f data pints falling int the upper left and lwer right quadrants fcate-nelsn graphs describe the errr rate f the mdel and are cmmnly used t estimate the reliability f the methd. The errr rate f the Cate-Nelsn mdel fr DMY was 16%, fr NUP 14%, and fr tissue N cncentratin f clippings was %. These errr rates are mre indicative f the reliability f the Cate-Nelsn mdel than R 2 values. Our critical levels fr DMY using LP mdels (4.8 t 8.4 ug cm- 2 day") were greater than thse reprted by Cllins and Allinsn (1999) fr tw frage species (.66 t 3.8 ug em -2 day -1) using LP mdels. We expect that this difference is due t mre

10 32 intensive management regimens, i.e., frequent mwing, lw cutting height, that typically ccur with turfgrass cmpared with a frage grwn fr hay. Analyses using the LP and Cate-Nelsn mdels fdmy, NUP and tissue N cncentratin were als perfrmed n individual species data (Figs. 3, 4, and 5, respectively). Bth the LP and Cate-Nelsn mdels had highly significant relatinships fr DMY, NUP and tissue N cncentratin based n desrbed sil N 3 -N frm AEMs fr individual species data. Linear plateau mdels had greater critical levels fr bentgrass and mixed species DMY, NUP and tissue N cncentratin than Cate-Nelsn mdels (Fig. 3.3, 3.4, and 3.5, respectively). The errr rates f the Cate-Nelsn mdels were 19% fr DMY, 9% fr NUP, and 3% fr tissue N cncentratin f bent grass. Fr the mixed species, the errr rates f the Cate-Nelsn mdels were 6% fr DMY, 6/ fr NUP, and % fr tissue N cncentratin. We fund that the critical levels fr the grwth respnses measured were greater fr mixed species than fr bentgrass. One pssible explanatin fr this difference is that the N use efficiency f bentgrass is greater than the N use efficiency f the mixed species. Bentgrass has a higher percentage fleafn (4.9%) than Kentucky bluegrass (4.3%), creeping red fescue (3.9%), and perennial ryegrass (4.7%) (Hull, 1996) and tissue N cntent has been psitively crrelated with N use efficiency (Liu et al., 1993). In additin, creeping bentgrass has been shwn t have greater N recvery than perennial ryegrass and tall fescue (Bwman et ai., 1989). A secnd reasn fr the discrepancy in critical levels f bentgrass and mixed species may be the variable N requirements f the three grass species in the mixed species treatment and interspecific cmpetitin fr nutrients.

11 Relatinship f Grwth Respnses t Clipping Management Returning grass clippings was fund t significantly impact the measured variables and t increase them verall (Fig. 3.1). Therefre, LP and Cate-Nelsn mdels were als used t 'analyze the relatinships between CRT and CRM treatments and desrbed N 3 -N frm AEMs in terms DMY (Fig. 3.6), NUP f clippings (Fig. 3.7), and tissue N cncentratin (Fig. 3.8). Linear plateau and Cate-Nelsn mdels had highly significant relatinships fr DMY, NUP, and tissue N cncentratin based n desrbed N 3 -N fr CRM and CRT treatments, althugh LP mdels had greater critical levels than Cate-Nelsn mdels. In general, we fund greater critical levels f desrbed N 3 -N fr DMY and NUP when clippings were remved. This finding indicates that mre available sil N 3 -N was required t ptimize DMY and NUP when clippings were remved. This bservatin illustrates the effect f the practice f returning clippings. By returning grass clippings, the availability f sil N 3 -N as measured by AEMs was increased by t 43%. Therefre, the need fr fertilizer N was decreased. The errr rates f the Cate- Nelsn mdels were 19% fr DMY, 13% fr NUP, and % fr tissue N cncentratin fr the CRM treatment. Fr the CRT treatment, Cate- Nelsn errr rates were 6% fr DMY, 13% fr NUP, and % fr tissue N cncentratin. 3.5 CONCLUSIONS In ur study, AEMs were used t successfully determine the relatinship between sil N 3 -N availability t managed turfgrass and turfgrass grwth respnses. We were als able t use AEMs t determine the relatinship between clipping management and sil N 3 -N availability using AEMs. Fertilizatin rate, grass species, and clipping

12 34 treatment were all fund t have significant effects n desrbed N 3 -N frm AEMs. When clippings were returned, available sil N 3 -N measured by AEMs increased t 43%, clipping yield increased 7 t 89%, ttal N uptake increased 26 t 112%, and tissue N cncentratin increased t 31%. Reductins f 25 t 1% in N fertilizatin rate were fund t have n significant effect n DMY, NUP, and tissue N cncentratin fr sme experimental treatments when clippings were returned. Linear plateau and Cate-Nelsn mdels were used t estimate critical levels fr desrbed sil N 3 -N frm AEMs in relatin t DMY, NUP, and tissue N cncentratin. T ur knwledge, these are the first such critical levels t be determined fr turfgrass. Hwever, this experiment was perfrmed under the relatively cnsistent envirnmental cnditins f a greenhuse. Clearly, cnditins in the field will be much different. Therefre, future wrk invlving AEMs and turfgrass must be undertaken in field studies. With field research, the critical levels f desrbed N 3 -N that we determined fr DMY and NUP may be cmbined with turfgrass quality data t prvide an index and testing tl t help ptimize N management fr turfgrass systems in the future. 3.6 REFERENCES Abrams, M.M., and W.M. Jarrell Biavailability index fr phsphrus using in exchange resin-impregnated membranes. Sil Sci. Sc. Am. J. 56: Bwman, D. C., 1. L. Paul, W. B. Davis, and S. H. Nelsn Rapid depletin f nitrgen applied t Kentucky bluegrass turf. J. Am. Sc. Hrt. Sci. 114: Cate, R.B. and L.A. Nelsn A simple statistical prcedure fr partitining sil test crrelatin data int tw classes. Sil Sci. Sc. Am. Prc. 35:

13 35 Cllins, S.A. and D. W. Allinsn Use f anin exchange membranes t assess nitrgen needs f perennial grasslands. Cmmun. Sil Sci. Plant Anal. 3: Hubner, C., G. Redl, and F. Wurst In situ methdlgy fr studying N- mineralizatin in sils using anin exchange resins. Sil BiI. and Bichem. 23 : Hull, R. J., S. R. AIm, and N. Jacksn Tward sustainable lawn turf. p In Anne R. Leslie, USEP A (ed.) Handbk f Integrated Pest Management fr Turfgrass and Ornamentals. CRC Press, Inc. Lewis Publishers, U.S.A. Inics Prperties and characteristics f anin transfer membranes type 24-U Bulletin AR 24. O-D. Inics, Inc., Watertwn, MA. Liu, H., R.J. Hull, and D.T. Duff Cmparing cultivars f three cl-seasn turfgrasses fr nitrate uptake kinetics and nitrgen recvery in the field. In R.N. Carrw et al. (eds.) Int. Turf. Sc. Res. J.7. Intertec Pub. Crp., Overland Park, Kansas. Nelsn, L.A., and R.L. Andersn Partining f sil test-crp respnse prbability. p In T. R. Peck et al. (eds.) Sil testing: Crrelating and interpreting the analytical results. ASA Spec. Publ. 29. ASA, CSSA, and SSSA, Madisn, WI. Rbertsn, G.P., D. C. Cleman, C. S. Bledse, and P. Sllins (eds) Standard Sil Methds fr Lng-Term Eclgical Research. Oxfrd University Press. New Yrk. SAS Institute SAS/STAT User's Guide. Versin 6. 4th Ed. Cary, NC. U.S.A.

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15 37 eli' ~ <C E <.I:: Z Z I... V V ;:::$ ir: tr: : tr: C\l * Z Z Z Z I-< tr:... r/l 2 * * ~ " V.D I-< r/l V " t::: r/l,-...,... Z... ~ v 4-< tr: : ir: tr: ir: ;:::$ ~ V r/l Z Z Z Z * * Z Z v: V ~ U I-< ;:::$ '-" t::: tr:....s... t::: C\l ;>, C\l I-<... u a) t::: ~ > v.~ 2 u t::: (1) bij c,.[/j '" (1) >-... bij Z ~ : : tr: : : ", v Z Z Z Z Z a) C\l ;:::$ c * * > U tr: 2 ;:a.~... g C.- " : v t::: :l C\l.D t:::,-...,... C\l... c...~ ~ ZI ""' = :> Z 4-< '-" v "" tr: ~ Z v C\l " : tr: tr: : = :l... sr:... V ~.D Z * Z Z Z ;:::$ * * ~ - I-<.~ t::: Z ir: C\l V trl 4-<,-..., Cl >- (1) ~ I-< ~ C\l c 4-< ~ E '-" " M... M M " E -= :l ;:::$ a) U tr:.-,-..., ~,-...,!f: U,-..., I-< Z '-" : ir: = tjil V bij... '-" '-" X Ci3 M V v t::: sr: C\l... V v U... U : U E Jj I-< u tr: :: ;:::$ X v X X X C\l C... f--< Z [) " ir: Z tr: Z U Z *.

16 38 * * * * * * * * * * * * * * * * * * * * * * * I'-OOO\'DOOOOOOMO'DI'-O ~O\OOO\O\OOOOO\OO\OO\O\O

17 ZI 39 _ S.. I'D '» z " ::: I'D " ~ ~.. E(.) C'I ~ s ";"- " (5.~ C >-. C'I ~ I: I'D '5. E C» U - C'I - - I: ";" Q) _.8.!II: C.6.! '1 C - ::::>.4 z g' S ' :.2 {!!. U Bent rass 12~----~~~~~ O~--~--~r---~--~--~ B Mixed Species N Rate N Rate Clippings Remved Clippings Returned Figure Respnses f desrbed N3-N frm AEMs (A and B), clipping yield (C and D), ttal N uptake (E and F), and tissue N cncentratin in clippings (final harvest perid) (G and H) t N rate fr bentgrass and mixed species.

18 4..., 2 A Linear Plateau Mdels. Cate-Nelsn Mdels. CL= 1 ~ c..8 rn '-" Q).6.::t!.., 111 : -.4 z r (5.2 f- y=.9x +.4 if x < 6. y=.6 if x > 6. R2=.65*~ 6.::t! 'c>.3 5 c..g , ai 3 u c 8 2 y=7.98x if x < 3.2 z y=48.61 if x > 3.2 ~ 1 til til E F O~,-,-,-,-,-,-,-,-,-,-~~ Cate-Nelsn CL= <l-: em 2 day 1 R2=. 64 * * * F Desrbed N 3 -N (1J9 em - 2 day -1) Figure 3.2. Relatinship between clipping yield (A) and (B), ttal N uptake (C) and (D), and tissue N cncentratin (final harvest perid) (E) and (F) in clippings f bent grass (pen circles) and mixed species (clsed circles) pts and desrbed nitrate-n frm AEMs. ***Significant at P<O.OOI.

19 41..., Q.l r E ~ "C Cl Bentgrass Mixed Species 8 y=2.25x if x < if x < y=12.98 if x > 4.8 y=15 if x > "C Q3 >= Cl C s. ~ B Cale-Nelsn CL= Cale-Nelsn CL= 4 <I em -2 day 1 -.~<l em -2day 1 R 2 =.55*** R 2 =.52*** I I I I I I I Desrbed Nitrate (1-19 em day ) Figure 3.3. Relatinship between clipping yield f bentgrass and mixed species and desrbed nitrate-n frm AEMs; (A) and (B) are linear plateau mdels, (C) and (D) are Cate-Nelsn mdels. ***Significant at P<O.OOl).

20 Bentgrass.5 if x < 7.2 A y=.61 if x > 7.2 Mixed Species.6.4 ~.2 Q s.4 OCate-Nelsn CL=.2 <J em 2 day 1 R 2 =.64*** Cate-Nelsn CL= em 2 day 1 R2=. 6 * * * Oesrbed Nitrate (~g 2 em -1 day) Figure 3.4. Relatinship between ttal N uptake f bent grass and mixed species and desrbed nitrate-n frm AEMs; (A) and (B) are linear plateau mdels, (C) and (D) are Cate-Nelsn mdels. *** Signficant at P<O.OOl.

21 43 6 Bentgrass Mixed Species ') if x < :::,t. ) c ".;j C\'I I- +J C Q) U c 6 u Q) ::J (/) 4 F z 5.,,... (/) 3 2 Cate-Nelsn CL= Cate-Nelsn CL= 1 <l-- 1. J.l9 em 2 day 1 <l J.l9 em 2 day 1 R2=. 6 8 C R2=. 6 5 D Oesrbed Nitrate -2 1 (~g em day) Figure 3~5.Relatinship between tissue N cncentratin and desrbed nitrate-n frm AEMs; (A) and (B) are linear plateau mdels, (C) and (D) are Cate-Nelsn mdels. ***Significant at P<O.OOI.

22 Clippings Remved Clippings Returned,.. Ī 8 a. I- y=1.13x if x < 8.2 Q) +J 4 +J y=13.32 if x > 8.2 rn E R2 =.7 "' ~ > '--" "' 2 Q) >= > c 1 6 ' e Cate-Nelsn CL= 4 <r- 3.3 J.19 cm'2 day" 1 R2= y=2.93x if x <4.1 y=13.97 if x > 4.1 Cate-Nelsn CL= <r- 3.1 J.19 cm'2 day" 1 R2=. 5 Oesrbed N 3 -N frm AEMs (~g em -2 day -1) Figure 3.6, Relatinship between clipping yield f clippings remved and clippings returned treatments averaged acrss species and desrbed nitrate-n frm AEMs; (A) and (B) are linear plateau mdels, (C) and (D) are Cate-Nelsn mdels. ***Significant at P<O.OOl.

23 45 1 Clippings Remved y=.9x -.3 if x < y=.52 if x > ''.2 Q. R 2 =.8*** A Clippings Returned y=.13x +.1 if x < 4.5 y=.62 if x > r '.8 I-.6.2 Cate-Nelsn CL= 3.7 ~g cm 2 day' 1 R 2 =. 6 7 *c)* Q Cate-Nelsn CL= <J ~g cm 2 day 1 R2=. 5 5 * * * Desrbed N 3 N frm AEMs (JJg em 2 day 1) Figure 3.7. Relatinship between ttal N uptake f clippings remved and clippings returned treatments averaged acrss species and desrbed nitrate-n frm AEMs; (A) and (B) are linear plateau mdels, (C) and (D) are Cate-Nelsn mdels. ***Significant at P<O.OOl.

24 46 6 Clippings Remved Clippings Returned ') ~ ) c '';:; r~... c Q) c 8 z Q) :J (J) (J) ~ if x < 3. x > ~ apcfd y=9.3x if x-c 3.2 y=51.6 if x > 3.2 R 2 =.8***,-.. lit 2 1 Cate-Nelsn CL= <J--.1-,7 ~g em 2 day 1 R 2 =.6 C Cate-Nelsn CL= <J ~g em 2 day. 1 R2=.73 D Oesrbed Nitrate (ljg em day) Figure 3.8 Relatinship between tissue N cncentratin f clippings remved and clippings returned treatments averaged acrss species and desrbed nitrate-n frm AEMs fr the furth harvest perid; (A) and (B) are linear plateau mdels, (C) and (D) are Cate- Nelsn mdels. ***Significant at P<O.OOl.