GRAZG ALFALFA WTH SHEEP: DES T EFFECT YELD R STAD LFE? Bruce Rberts C. Frate V. arble University f Califrnia Cperative Extensin Farm Advisrs and Specialist Abstract: Field trials in the Sacrament and suthern San Jaquin Valley were cnducted t investigate effects f winter grazing n stand life and frage yield. Results frm the Sacrament Valley study using an intermediate drmant variety that included different grazing intensities shwed n reductin in hay yields frm selected cuttings cmpared t machine harvested cntrls. Tw years f data frm the San Jaquin Valley study using a nn-winter drmant variety shwed an average reductin in winter grazed and mwed plts f.4 tn per acre during the hay seasn cmpared t nn-harvested cntrls; hwever ttal frage {hay plus winter frage) was nt reduced. n bth studies n change in sil bulk densities frm sheep grazing ccurred. Reductin in stand density was nt bserved in either trial. Keywrds: alfalfa. grazing. sheep sil cmpactin. winter harvest TRDUCT Alfalfa varieties grwn in the Central Valley f Califrnia belng t drmancy grups which prduce frage in late fall and winter under mderate temperature cnditins. Several ptins are available t farmers fr managing this winter grwth when pr drying cnditins prevent making hay. Standard practices in this area are greenchpping fr dairy use r grazing by sheep. Anther ptin is t leave alfalfa unharvested until the first spring cutting. With this last ptin grwers trying t prduce ptimum quality hay are cncerned abut the ld ver-wintered grwth affecting first cutting hay quality. Cmmn questins cncerning these management ptins relate t impact n yield in the fllwing seasn sil cmpactin and ecnmic return. Trials have been cnducted in the Sacrament and the suthern San Jaquin Valley t investigate the impact f fall r winter sheep grazing n alfalfa stands and prductivity. A reprt n sheep grazing in the mperial Valley was presented at the 1987 Califrnia/Arizna Alfalfa Sympsium. UCD TRAL -The grazing trial in the Sacrament Valley which is reprted in the 1988 September-ctber issue f CALFRA AGRCULTURE Peltn et al. was cnducted at the University f Califrnia Davis n a Yl lam sil. The alfalfa variety was an intermediate drmant type typical f varieties planted in that area and grazing ccurred in mid-september r ctber instead f a hay harvest. Grazing treatments cnsisted f tw intensities: llsevere" grazed by the equivalent f 34 head per acre fr an average f 3 days; and "partial" 17 head fr an average f 2.5 days. These were cmpared t machine harvested plts. Sil misture cntent ranged frm 2 t 22% just prir t grazing each year. During three years f the trial yields frm selected cuttings were btained using a Carter frage plt harvester. Sil bulk densities measured with a Trxler Duble-Density Prbe at depths frm 2 t 8 inches were taken befre the initiatin f grazing and then each spring befre the first cutting. Yield results (Table 1) did nt shwany differences amng machine harvested severely grazed and partially grazed treatments fr any f the cuttings taken. There were n significant differences in sil bulk density measurements between grazed and nn-grazed treatments (Table 2). SUTHER SA JAQU VALLEY TRAL -This grazing trial was cnducted in a cmmercial alfalfa field in Tulare Cuntyn a Traver fine sandy lam sil. Treatments included a cntrl which was nt harvested during late fall r winter a treatment which was grazed when the cmmercial field was grazed and a treatment that was mwed with a plt mwer at the same time as grazing. This latter treatment was included t help separate the impact f remving frage frm the effects f sheep grazing. When the field was cmmercially grazed nngrazed plts were fenced t keep sheep ut. Grazing intensity and duratin in grazed plts were the same as that used in the rest f the field which was apprximately 85 ewes plus lambs in 4 acre blcks fr 7 t 8 days (apprximately 23 grazing units per acre). n 1984 grazing ccurred in the latter part f December; in 1985 sheep were present during the last week f vember. Rainfall in the tw
} eks prir t the first year f grazing ttaled 1.3 inches with anther.9 inches ccurrwhile sheep were in the field. n 1985 2.8 inches f rain fell in the 15 days preceding grazing with an additinal.15 inches during the grazing perid. S ii misture cntent at the time sheep were intrduced was 11 and 18.5% respectively fr the tw years. Yields were determined during the seasn by mwing a strip thrugh each plt with a plt harvester measuring fresh weights and taking misture samples t calculate dry weights. Sil bulk density was measured with a Trxler uble-ensity Prbe. easurements were made at depths f 2 6 and 1 inches. Samples frm the first cutting in 1985 were analyzed fr ttal digestible nutrients (T) and percent prtein. n the first year f the trial 1 tn f dry matter was harvested frm the mwed treatment at the time f grazing and presumed t be the same amunt f frage available fr grazing (Table 3). f the seven hay cuttings that year there was nly ne (early June) in which yields differed between treatments. At this cutting the grazed treatment yielded lwer than bth the cntrl and the winter mwed treatments. Ttals fr the seven hay cuttings that year shwed that the grazed treatment yielded significantly less than the cntrl but nt less than the mwed treatment. When frage remved by mwing r grazing in ecember is added t hay seasn ttals grazed and mwed plts yielded similar t cntrl plts. Quality samples cllected frm the first cutting indicated a slightly higher T value fr grazed and mwed treatments cmpared t the unmwed cntrl (Table 4). There were n differences in percent prtein amng treatments. n 1986 half a tn f dry matter was harvested frm the treatment mwed in late vember when grazing ccurred. n this year bth grazed and mwed plts had reduced yields cmpared t the cntrl at first cutting. n the next six cuttings n differences ccurred. n the last cutting hwever the mwed treatment prduced significantly less than the cntrl and the grazed treatments. Ttal hay prductin fr that year did nt differ significantly amng treatments. When frage remved during the time f grazing is added t hay ttals mwed and grazed treatments prduced as much as cntrls. Analysis f cmbined data ver the tw years indicates bth grazed and mwed plts yielded significantly less hay than cntrls but did nt differ between each ther (Table 5). Grazing r mwing reduced hay prductin by an average f.4 tn per acre. Hwever when the yield frm the harvest taken at the time f grazing is added t hay ttals the grazed treatment prduced as much as the cntrl and the mwed treatment yielded significantly mre than the cntrl. Sil bulk density measurements shwed n (Table 6). difference between grazed and ungrazed plts DSCUSS n bth the Davis and suthern San Jaquin Valley trials grazing with sheep did nt increase sil cmpactin as measured by bulk density. n bth trials yields frm grazing treatments were equal t treatments mwed at the time f grazing. t is imprtant t nte that mwed treatments were nt meant t simulate cmmercial greenchpping as small plt harvesters used in these trials d nt have the same ptential fr crwn damage and sil cmpactin that field-scale equipment wuld have. The suthern San Jaquin Valley trial demnstrated a reductin in hay seasn yields f.4 tn per acre when plts were either grazed r mwed in late fall/early winter cmpared t unharvested plts. Ttal dry matter prduced fr the year was nt affected hwever. Alfalfa hay prducers shuld decide if incme and ther advantages frm late fall/winter grazing r greenchpping are wrth the apprximately.4 tn/acre (dry weight) reductin in alfalfa prduced during the "hay seasn." A special acknwledgement and thank yu g t r. Jeff Curti f Curti Farms in Waukena CA fr cperatin and assistance n the sheep grazing trial in the suthern San Jaquin Valley. We als want t thank Dr. Burl eeks ancy Gdell and Je unes frm the U.S.D.A. Cttn Research Center at Shafter Califrnia. -2-
TABLE 1. VEL RESULTS FR ALFALFA SHEEP GRAZG TRAL. U.C. DAVS. 1985-19871 Vield2 4/4/85 5/16/85 4/17/86 6/3/86 1/15/86 4/16/87 7/24/87 j/9/87 Severe Graze 1. 1.6.7 1.3 1.6 1. Partial Graze 1.6 1..1 "" 1. 1 Grazing ccurred during ctber in 1984 and 1985 and in mid-september in 1986 2 Differences amng treatments were nt significant {LSD.5) TABLE 2. EFFECT F GRAZG SHEEP SL BULK DESTY. U.C. DAVS TRAL. 1985-87 Sil Bulk Density Pre-graze Treatment Fall Fall Spring Spring and epth f achine -2 2-4 4-6 6-8 Harvest Severe -2 2-4 4-6 6-8! Graze 1.6 1.6 1.6 2.6 1 6 Partial -2 2-4 4-6 6-8 Graze TE: Data nt reprted fr spring f 1985 due t malfunctin f density prbe. measurements were repeated again that year just befre the fall grazing. * verall treatment fr 1985. '86 and '87. Within each year. n statisticlly significant treatment effects were bserved. Cefficient f variatin n verall data: 5.5. -3-
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. { TABLE 4. QUALTY AALYSS FR APRL 1985 HARVEST SA JAQU VALLEY ALFALFA SHEEP GRAZG TRAL Cntrl 41. 21. wed When Grazed 47.5 21.1 Grazed 48. 2 TABLE 5. CBED 1985 AD 1986 AVERAGE YELDS FR SUTHER SA JAQU VALLEY ALFALFA SHEEP GRAZG TRAL Yield --Tns Dry atter Per Acre f Hay Seasn Fall/Winter Ttal Dry atter Yields Harvest Prductin Cntrl 8.9 8.9 b wed When Grazed 8.6.7 9.4a Grazed 8.41 (.7)1 (9.2}2 LSD.5 CV%.3 7.4.3 7.2 rthgnal cmparisn fr hay seasn yields: Cntrl vs grazed and mwed when grazed (P =.1). 1 Assumed yield based n yield f plt harvested at the time f grazing. 2 mean separatin is given fr this value because it is an assumed value based n the winter mwed treatment and was nt included in the analysis. (- 5-
# TABLE 6. SL BULK DESTY EASUREETS FR THE SUTHER SA JAQU VALLEY AlFAlFA SHEEP GRAZG TRAL DATE 2/15/85 3/4/86 n-grazed 2 inches 6 inches 1 inches Grazed 2 inches 6 inches 1 inches 6 7 1.64 9 9 9 S 5 7 1.6 7 5 1.6 S easurements made with a Trxler Duble-Density Prbe -6-