The Effect of Salinity on Nitrate Leaching from Turfgrass

Transcription

1 The Effect f Salinity n Nitrate Leaching frm Turfgrass by DR. DANIEL C. BOWMAN, DR. DALE A. DEVITT and WALLY W. MILLER University f Nevada, Ren Clumn lysimeters planted t tall fescue r bermudagrass used t cllect leachate in the greenhuse prtin f the study. SOIL SALINITY is a prblem in the western United States due t the ccurrence f sluble salts in many desert sils and irrigatin with mderately saline water. In suthern Nevada, irrigatin has leached native salts belw the rt zne, creating a perched saline aquifer estimated at apprximately 1, acre feet. Having an electrcnductivity (EC) f 9 ds m' (apprximately ne fifth f seawater), this aquifer represents a ptential threat t the deeper primary aquifer. As a resurce, hwever, this aquifer cntains enugh water t satisfy the irrigatin needs f many f the existing glf curses in Las Vegas fr the next years. If prperly managed, this water supply culd be used as an alternative r supplemental irrigatin surce, decreasing the demand n high-quality water while reducing the ptential fr cntaminatin f the primary aquifer. One cncern abut the use f saline water fr turf irrigatin, and the fcus f ur study, is that salinity might increase nitrate (N) leaching frm turf. Since nitrgen is the mst heavily used nutrient in turfgrass management, this cncern is justified. In the case where N applicatin exceeds the ability f the turfgrass t absrb the nitrgen, excess N culd mve frm the sil-plant system int water supplies. The degradatin f lakes and streams, the pssible permanent cntaminatin f grundwaters, and pssible health hazards related t waters high in nitrate are all cnsequences f inefficient r imprper use f nitrgen fertilizers. Numerus studies have dcumented the effects f envirnmental factrs and management practices n nitrate leaching frm turfgrasses. Fr example, Brwn et al. () measured cncentratins f nitrate as high as 7 ppm N in the leachate belw bermudagrass fllwing applicatin f ammnium nitrate, with ttal leaching lss f % f the applied N. Fr cmparisn, 1 ppm N -N is cnsidered the maximum fr safe drinking water. Snyder et al. (9) fund peak N -N cncentratins between and ppm N in JANUARY/FEBRUARY

2 Table 1 Nitrgen Uptake Efficiency fr and at Three N Applicatin Rates Efficiency is calculated as average daily N remved in clippings (based n regressin analysis) divided by the average daily N additin (mnthly divided by, amunting t 1.5,., and.55 mg N/clumn/day fr the lw, medium, and high N rates, respectively). Species NRate Lw Medium High Lw Medium High the sil slutin belw the turf rtzne 5 t 1 days after applying 1 lb N/1 sq ft as NH N. Up t 56% f the applied N was lst during a -week perid. Hwever, minimizing the dwnward mvement f water by carefully cntrlling irrigatin with tensimeters reduced lsses frm 56% t % (1). In cntrast t these findings, Rieke and Ellis (8) reprted little effect f fertilizatin n nitrate leaching fllwing applicatin f 6 lbs N/1 sq ft per year t a mixed turf. Starr and Der (11) fund similar lw leaching lsses. Mancin and Trll (7) investigated nitrate leaching frm a creeping bentgrass turf under cnditins favring heavy leaching lsses (sand rtzne, sluble nitrate-based fertilizers, and 6% leaching fractin). When the fertilizers were applied weekly at a rate f. lb N/1 sq ft, nitrate leaching averaged less than.5% f the applied nitrgen. Even at the rate f 1 lb N/1 sq ft, cumulative lsses averaged nly.5% fr the nitrate surces. Gld et al. (6) reprted a maximum flwrated N cncentratin f 1.6 ppm N in the leachate frm a hme lawn fertilized with 5 lbs N/1 sq ft per year. Apprximately half f the leachate samples had N cncentratins at r belw.1 ppm N. Chen et al. () mnitred N -N in wells at fur glf curses n Cape Cd ver a tw-year perid. Nitrate cncentratins in the shallw grundwater increased ver backgrund in respnse t turfgrass fertilizatin at three f the fur curses. Hwever, average cncentratins were all belw 1 ppm N -N. Bwman et al. (1) presented data indicating that rapid bilgical immbilizatin, bth by the turf and sil micrrganisms, may reduce leaching lsses by limiting the perid f time that the fertilizer N is resident in the N Remved in Clippings (mg N/clumn/day) N Uptake Efficiency sil. Hwever, n studies have investigated the effects f salinity n nitrate leaching. Since salinity inhibits nitrgen uptake in a number f species, the use f saline irrigatin water n turfgrasses culd increase nitrate leaching and cntaminatin f grundwaters. The bjectives f this research were 1) t determine the effects f salinity and N applicatin rate n nitrate leaching and N mass emissin frm turfgrass under greenhuse cnditins, and ) t determine the effects f salinity and leaching fractin n nitrate leaching and N mass emissin frm a bermudagrass and tall fescue turf under field cnditins. Tw experiments were cnducted t examine the effects f salinity n N leaching frm turfgrasses. The first was a greenhuse study cnducted frm February thrugh December, 199, t address the bjectives under tightly cntrlled envirnment cnditins. Mnarch tall fescue and NuMex Sahara bermudagrass were grwn in PVC clumns filled with a lamy sand and utfitted with a vacuum sampling system t cllect drainage. Treatments cnsisted f three N levels (.5, 1, and 1.5 lbs N/1 sq ft per mnth applied as NH N ) and three irrigatin salinity levels (ECs f,1.5, and ds nr 1 fr tall fescue and,, and 6 ds nr 1 fr bermudagrass) in a x factrial arrangement. The salinity ranges were chsen as being ptentially stressful but nn-lethal. Irrigatin was scheduled twice each week t prvide a relatively high leaching fractin f %. This leaching fractin was impsed t rapidly equilibrate rtzne salinity while increasing the ptential fr N leaching. Leachate was cllected after every irrigatin and analyzed fr salts and N -N. Clippings were cllected and analyzed fr ttal N. Salt cntent f the leachate rse steadily during the first fur mnths f the experiment and then leveled ff, indicating that a cnstant salt prfile had been attained. Leachate ECs fr the.1, 1.5,., and 6. ds m' salt treatments stabilized at apprximately.,.5,9, and 15 ds nr 1, respectively. These values are clse t thse predicted based n a leaching fractin f %. Ttal mnthly irrigatin data fr the April thrugh September perid were used t examine the effects f N and salinity n irrigatin requirement. In bth grasses, the high salinity treatments reduced irrigatin by 9% cmpared t the lw salinity treatments, whereas high N increased irrigatin 1-1% relative t lw-n treatments. Similar effects f N rate () and salinity (5) have been reprted fr water use by bermudagrass turf. Average mnthly N -N cncentratins in the leachate ranged frm less than.1 t 1. ppm N in the bermudagrass (Figure 1) and frm less than.1 t. ppm in the tall fescue (Figure ). Highest N cncentratins ccurred during February and April, whereas cnsistently lw values were fund frm June thrugh December. Since the tw grasses were grwing slwly during late winter/early spring, the high values culd be due t a lwer grwth demand fr N. Expressing the N -N cncentratin as an average based n the ttal vlume f leachate, apprximately.-.5 ppm N is calculated fr the bermudagrass leachate and ppm N fr the tall fescue leachate. When cmpared t the tap water, which cntained.1-. ppm N -N, it is apparent that N applied t bermudagrass cntributed very little t net N leaching. While greater amunts f applied N leached frm the tall fescue, the average cncentratins were very lw, cnsiderably belw the critical 1 ppm N level. There were n bvius effects f either salinity r N applicatin rate n the cncentratin f N in the leachate frm either grass. Significantly, f the nearly 1 samples analyzed during this study, nne was abve the critical level f 1 ppm N. These data are cnsistent with previus results demnstrating the ability f turfgrass systems t rapidly immbilize applied N (1) but further suggest that the N uptake systems f turf rts and assciated micrrganisms were nt appreciably impaired by the mderate salinity levels used in this study. Cumulative nitrate-n leached ver the 11-mnth experimental perid amunted t apprximately 1 mg N/clumn fr the tall fescue and - mg N/clumn fr the bermudagrass, representing 1.% and.% f the applied N, respectively. This des nt cnsider the amunts f N present in the irrigatin water. Much f the ttal lss 6 USGA GREEN SECTION RECORD

3 ccurred during March thrugh May, with very little additinal lss recrded thereafter. This pattern was prbably due t the unintentinally high vlumes f leachate cllected during March and May. Again, there was n apparent r cnsistent effect f salinity r N applicatin rate n nitrate leaching in either species. Clipping dry weight and percent N in the tissue were used t calculate the amunt f N partitined t leaf tissue and remved in clippings (Table 1). Nitrgen remval increased with increasing N applicatin rate, but there was n effect f salinity. The average daily N allcatins t leaf tissue Figure 1 Mnthly Average N Cncentratin in the Leachate frm Thrf (Study 1) Fertilized with Three Rates f N and Irrigated with Three Levels f Salinity Figure Mnthly Average N Cncentratin in the Leachate frm Thrf (Study 1) Fertilized with Three Rates f N and Irrigated with Three Levels f Salinity Lw Salt -- LawN --MediumN A--6.HighN Lw Salt -- LwN --MediumN A--6.HighN Z 1.5 S.. 1. S...,.9 1) I:':l I-<.6 >. :a 1::. Medium Salt Z S.. S g..., Ol) I:':l I-< >. :a 1:: 1 Medium Salt. 1.5 High Salt High Salt J OND J FMAMJ JA Mnth JANUARYIFEBRUARY

4 were cmpared t the N additin rates and used t estimate lng-term uptake efficiency. Uptake efficiency decreased in bth turf species with increasing N rate (Table 1). At the lw N rate, N recvery in clippings was greater than 9% fr bth species, whereas at the medium and high N rates, bermudagrass clippings cntained apprximately 1% mre f the applied N than the tall fescue clippings. These values indicate very efficient absrptin f applied N by the turfgrasses, and suggest that ver the lng term, a mature turf allcates mst acquired N t new leaf tissues. It must be cnsidered that this research was perfrmed n a yung turf system with clippings remved, and in which very little sil rganic N is likely t have accumulated. Cnsequently, mineralizatin f rganic N wuld supply little N t the turf. If mineralizatin f sil rganic N cntributed significantly t the N nutritin f the turf, as might be the case in an lder turf system, it is prbable that additinal applied N wuld nt be absrbed as efficiently. Under such cnditins, N leaching might be higher than fund in this study. The results f the first study indicate that irrigatin f tall fescue and bermudagrass turf with mderately saline water shuld nt increase N leaching as lng as adequate leaching prevents salts accumulating t txic levels in the rt zne. Measures f grwth, such as clipping prductin r N allcatin t leaf grwth, were nt affected by mderate salinity. This indicates that the grasses were under relatively lw stress, and may explain why there was n effect f salinity n N leaching. If salinity stress were greater, r if multiple stresses were impsed, it is pssible that N use efficiency wuld decline and N leaching increase. This questin is addressed in the field study discussed next. The secnd phase f this prject was cnducted frm April 1991 thrugh December 199 at Hrseman's Park, Las Vegas, t examine the effects f salinity and irrigatin regime n N leaching frm turfgrasses. This was part f a larger study examining the individual and cmbined effects f nitrgen applicatin rate, salinity, and drught n turfgrass perfrmance. The plt area measured 11by ft, with half planted t bermudagrass and half t tall fescue. The present study was cnfmed t thse sub-plts at the east and west end f the field receiving NH N at the rate f 1 lb N/lOOOsq ft per mnth. Seed f NuMex Sahara bermudagrass and Mnarch tall fescue was swn June -7, 1991, at lib and 81bs/1 sq ft, respectively, and the turfgrasses established by accepted prcedures. Gd quality water (EC less than 1. ds/m) was used t irrigate the turfgrass during establishment. was verseeded with Palmer Prelude perennial ryegrass (Llium perenne L.) in early Octber. A linear gradient irrigatin system (LIGIS) supplied the irrigatin treatments, with a gradient ranging frm 15% f ptential evaptranspiratin t O.Briefly, 6 parallel irrigatin lines were installed feet apart, with heads spaced at feet (duble verlap) n each line. The three lines at the east end f the field supplied gd quality municipal water while the three lines at the west end supplied saline water (during turf establishment all lines supplied fresh water). Water frm the saline aquifer was blended with fresh water t an EC f 6. ds mland stred in an n-site reservir frm which it was pumped fr irrigatin. The established turf was irrigated with all lines fr 1 mnths f the year. The irrigatin gradient treatment was impsed fr a 6-day perid beginning July 8, 199, and July 7, 199, by shutting ff the utide irrigatin line n bth the freshwater (east) and saline water (west) sides f the plt. This prvided a water gradient n the fresh side and a cmbined water/salt gradient n the saline side. The experiment thus cnsisted f fur separate treatment cmbinatins, with tw species and tw salinity levels cmbined in a factrial arrangement. Outside irrigatin lines were turned n again after the 6-day treatment perid, reestablishing cnstant vlume irrigatin acrss the plts. Irrigatin was scheduled t 5 days per week t supply 15% f tall fescue ET. Prir t planting, lysimeters (" diameter by " deep) were installed at grund level either clse t the gradient irrigatin line (full irrigatin, nn-stressed) r tward the utside f the gradient (deficit irrigatin, drught stressed). Lysimeters were equipped with suctin extractin cups buried at the bttm. After each irrigatin, a vacuum was applied t the extractin cups t cllect leachate. Leachate samples were then analyzed fr N cncentratin, with mass emissin f nitrgen calculated as the prduct f cncentratin and vlume. Ttal N cntent f clippings was used t estimate nitrgen absrptin by the plant. The data presented are frm the secnd year f measurements and represent the mre significant leaching data in terms f cncentratin and amunt. Hwever, it is helpful t understand the cnditin f the turf fllwing the first year f treatment. Turfgrass grwing in the lysimeters receiving adequate irrigatin did nt exhibit stress symptms during the 6-day dry-dwn perid. irrigated with fresh water but grwing in the utside lysimeters (drught stressed) was significantly impaired by water deficit, with cnsiderable thinning t apprximately 5% cver ging int the fall f 199. The cmbined stresses f drught and salinity (utside lysimeters, saline water) had a similar effect n the bermudagrass, with 5% cver at the end f the 199 grwing seasn. Tall fescue in the utside lysimeters was severely affected by bth drught and the cmbined stresses t the extent that very few if any individual plants survived the 6-day stress perid. Cnsequently, the utside lysimeters were sdded in late Octber, 199, t reestablish the turf. Nitrate leaching frm bermudagrass irrigated with fresh water peaked during January and February, 199, with cncentratins exceeding 1 ppm N (Figure, left). It must be nted that the bermudagrass was drmant during this perid, and it is unlikely that the verseeded perennial rye grass had develped an extensive rt system. Frm March thrugh September, leachate N cncentratins frm bermudagrass irrigated with fresh water were lw, ranging frm t 6 ppm N. Salinity increased N cncentratins in the leachate up t 6 fld, with the highest values measured in February and then again in August and Octber. The highest N cncentratins (nearly 6 ppm N) were assciated with the inside saline lysimeters (adequate irrigatin), althugh the bermudagrass appeared healthy and under little stress. It is pssible that salinity affected rting depth r density withut appreciably inhibiting sht grwth, thus reducing plant uptake and increasing leaching ptential. The mnthly pattern fn leaching frm tall fescue differed frm that f bermudagrass (Figure, right). Nitrate cncentratins were generally lw in turf irrigated with adequate amunts f fresh water. Cncentratins were higher in turf irrigated with adequate amunts f saline water, with peaks during December, 199, and then again in late summer, 199. In bth cases, the turf appeared t be under little stress. Hwever, it is pssible that heat stress alne r in cmbinatin with salinity affected either rt activity r sht demand fr N, resulting in lwer N absrptin and greater leaching. Very high N cncentratins (up t 1 ppm N) were fund in the utside lysimeters (drught stress) during the winter mnths, regardless f water quality. Hwever, it must be remembered that the turf in these lysimeters died in 199, and the new sd likely had nt develped a deep rt system. Further, mnthly N applicatins cntinued in spite f the turf cnditin. Cupled with mineralizatin f the dead rt system, it seems likely that there was cnsiderable inrganic N present in the sil. This N wuld be easily leached when full irrigatin was reestablished. Nitrate cncentratins frm the utside lysimeters irrigated with fresh water declined rapidly during January 8 USGA GREEN SECTION RECORD

5 Figure Mnthly Average N? Cncentrtin in.the Leachate frm (left) and Turf (right) fr Inside and Outside Lyslmeters Irrigated with Fresh r Saline Water in Study 1 -- Fresh, clse.--. Fresh, far -- Saline, clse A--A Saline, far 1 thrugh March, leveling ff at apprximately 1 ppm N. This may reflect the establishment f a deeper rt system in the newly sdded turf, resulting in mre efficient N absrptin. Cncentratins als declined in the utside lysimeters irrigated with saline water, but at a much slwer rate. Again, the decline in cncentratin may be due t new rt grwth and better N absrptin by the all.fescue. The slwer rate f decline might mdicate that rtzne salinity was restricting nrmal rt grwth r that N absrptin was affected directly. Mass emissin f N was calculated based n the average daily N applicatin rate and expressed as N leached relative t applied. Over the curse f 199, apprximately 15-5% f the applied N leached frm bermudagrass irrigated with fresh water, while 75-1% f the applied N leached frm the saline treatments. This cmpares t apprximately 5% f the applied N leaching frm the inside, freshwater lysimeters planted t tall fescue. Hwever, salinity alne r in cmbinatin with drught increased leaching frm the tall fescue t -1% f applied N..Cmparing the results f the field study WIth the greenhuse clumn study, it is apparent that much higher cncentratins and amunts f N are leached under the field cnditins. This may be the result f higher rtzne salinity in the field, the severe impact f drught, r bth. Based n grwth data, the turf in the greenhuse study was under very little stress, in spite f sil slutin salt cncentratins appraching 9 and 18 ds ml fr the tall fescue and bermudagrass, respectively. These salt cncentratins, hwever, are lw t mderate cmpared t thse develping in the field under deficit irrigatin (in excess f ds m'l). Cllectively, the data suggest that where rtzne salinity is maintained at mderate levels and in the absence f ther stresses, N leaching frm turf is unlikely t be a cncern. Hwever, where salts build up in the sil t high levels, r when ther stresses such as drught r heat are limiting tu grwth, N leaching may be a very senus prblem. Under such cnditins careful fertilizer and irrigatin managemen may help t reduce the ptential fr N cntaminatin f grundwater. References 1. Bwman, D. C., J. L. Paul, W B. Davis, and S. H. Nelsn Rapid Depletin f Nitrgen Applied t Kentucky Bluegrass Twf 1. Amer. Sc. Hrt. Sci. 11:9-.. Brwn, K. W., 1. C. Thmas, and R. L. DubIe Nitrgen Surce Effect n Nitrate and Ammnium Leaching and Runff Lsses frm Greens. Agrn. J. 7: Chen, S. Z., S. Nickersn, R. Maxey, A Dupuy Jr., and 1. A Senita A Grund Water Mnitring Study fr Pesticides and Nitrates Assciated with Glf Curses n Cape Cd. Grund Water Mnitr. Rev. 1: Devitt, D. A, and R. L. Mrris Grwth f Cmmn as Influenced by Plant Grwth Regulatrs, Sil Type, and Nitrgen Fertility. J. Envirn. Hrt 7: Devitt, D. A, D. C. Bwman, and R. L. Mrris Effects f Irrigatin Frequency, Salinity f Irrigatin Wate}; and Sil Type n Grwth and Respnse f. Arid Sil Res. Rehab. 5: Gld, A 1., W R. DeRagn, W. M. Sullivan, and J. L. Lemunyn Nitrate-Nitrgen Lsses t Grundwaterfrm Rural and Suburban Land Uses. J. Sil and Water Cnserv. 5: Mancin, C. F., and 1. Trll Nitrate and Ammnium Leaching Lsses frm N Fertilizers Applied t Penncrss Creeping Bentgrass. HrtSci. 5: Rieke, P. E., and B. G. Ellis Effects f Nitrgen Fertilizatin n Nitrate Mvements Under Twfgrass. p In E. C. Rberts (ed.) Prc. nd Int. Turfgrass Res. Cnf. Blacksburg, VA Amer. Sc. f Agrn., Madisn, WI. 9. Snyder, G. H., E.. Burt, and J. M. Davidsn Nitrgen Leaching in TUJf' Effect f Nitrgen Surces and Rates. p. 1-. In R. W. Sheard (ed.) Prc. th Int. Turfgrass Res. Cnf. University f Guelph, Guelph, Ontari. 1. Snyder, G. H., B. 1. Augustin, and 1. M. Davidsn Misture Sensr-Cntrlled Irrigatin fr Reducing N Leaching in Twf Agrn : Starr., J. L., and H. C. DeR The Fate f Nitrgen Fertilizer Applied t TUJfgrass. Crp Sci.1: JANUARYIFEBRUARY