Shoot Growth Chrcteristics Following Mechnicl Hedging nd High Lim Pruning in Tulre Wlnuts on Two Rootstocks t Two Spcings B.D. Lmpinen, S.G. Metclf, V. Gmle, K. Moore nd W. Reil University of Cliforni Dept. of Pomology One Shields Avenue Dvis, CA 951 USA D. Rmos Wlnut Mrketing Bord 15 River Prk Drive Scrmento, CA 95815 USA Keywords: cnopy mngement, Juglns regi, mechnicl hedging, photosyntheticlly ctive rdition, shoot growth, wlnut Astrct Shoot re-growth following mechnicl hedging ws mesured in 1 yer old Tulre wlnut orchrd plnted t two tree spcings on two rootstocks. In ddition to the mechnicl hedging tretment, high lim pruning, designed to lower overll tree height, ws performed on su-plots ech yer y selectively removing 1-3 lims of 5 to 1 cm dimeter high in the cnopy. The gretest terminl shoot growth occurred in the yer following hedging, while the gretest overll growth, including lterls, occurred in the second yer following hedging. The numer of new rnching points formed incresed for the second nd third yer fter hedging ut decresed y the fourth yer. Terminl shoot growth ws significntly greter for the wider compred to nrrower spced trees in the first yer fter hedging nd therefter there were no significnt differences. The only impct of the high lim pruning tretments ws significntly greter terminl shoot growth for the high lim pruned trees versus the non-high lim pruned trees t the nrrow tree spcing. These results suggest tht less frequent pruning is likely to increse productivity. In ddition, it suggests tht culturl prctices in the yer fter hedging hve the most potentil to control cnopy development. INTRODUCTION There is trend towrd higher density plntings in wlnut with mny new orchrds eing plnted s hedgerows. Reserch on high density plntings hs een done in the United Sttes (Rmos et l., 1), Spin (Alet nd Ninot, ) nd Chile (Lemus, 1). However, s these high-density plntings mture, shding in the lower cnopy frequently ecomes prolem. This results in shift in production higher up into the cnopy nd dieck of lower lims (Olson et l., 3). There is concern tht this could result in loss of nut production nd/or nut qulity over time. In ddition, s production shifts higher up into the cnopy, it cn e difficult to get good spry coverge leding to incresed insect nd disese pressure. In n ttempt to remedy these prolems, hedging nd/or hnd pruning regimes re implemented ut these hve hd mixed success, generlly resulting in decreses in production. The ojective of this study ws to mesure shoot growth responses to mechnicl hedging nd hnd thinning of high lims s influenced y rootstock nd tree spcing nd to investigte the reltion of the shoot growth to cnopy light ion nd yield. MATERIALS AND METHODS The orchrd ws plnted to Tulre wlnuts in 199 on Yolo silty cly lom soil. There were four replictions of ech rootstock (Northern Cliforni Blck nd Prdox nd tree spcing (3.5 x 7.3 nd.7 x 7.3 m) nd two replictions of the high lim pruning tretments. Mechnicl hedging ws done on lternte rows in Jnury nd Jnury Proc. V th Int. Wlnut Symp. Eds. M.E. Mlvolti nd D. Avnzto Act Hort. 75, ISHS 51
1. High lim pruning consisted of removing one to two of the most upright nd/or most crowded lims pproximtely 5 to 1 cm in dimeter from the upper cnopy. Cuts were mde just ove sustntil side rnch (i.e. thinning cuts) to minimize excessive vegettive growth tht would e formed from heding cuts. High lim removl ws continued for three dormnt pruning sesons (Jnury 1,, nd 3). Photosyntheticlly ctive rdition () ion ws mesured through the seson using n 8 cm light r (Accupr, Decgon Devices). One hundred mesurements were tken in grid pttern covering the re in the center of the plot on the rows from ech hedging dte for ech repliction. Shoot growth ws mesured from pruning tower during lte winter in the lleywys pruned 3 nd yers previously. Shoots chosen were from heights of 1.5 to 5.7 meters ove the ground on the sides of the hedged wll. Shoot growth ws seprted into ctegories of 1,, 3, or yers fter hedging nd the numer of new rnching points formed ech yer ws tllied s well s shoot lengths. Plots were hrvested y mechnicl shking nd dry yield s well s nut qulity fctors were evluted in through 3. s were collected seprtely within ech plot for the rows tht hd een mechniclly hedged in the winter of 1999- nd those hedged in the winter of -1. RESULTS AND DISCUSSION A digrmmtic representtion of the shoot growth ptterns for the four yers following hedging is shown in Figure 1. Primry shoot re-growth following mechnicl hedging ws gretest in the first growing seson while overll shoot growth ws gretest in the second growing seson following hedging. Rootstock There were no significnt differences etween the two rootstocks in ny of the shoot growth chrcteristics mesured (Fig. -e). Growth of the primry shoot ws gretest in the yer following hedging, nd then decresed in the second through fourth yers fter hedging for oth rootstocks (Fig. ). The numer of rnching points formed incresed in oth rootstocks during the second nd third yers fter hedging nd then egn to decrese (Fig. ). The totl numer of rnching points incresed t slowing rte in yers two through four (Fig. c). The totl yerly growth, including the terminl nd lterls, ws gretest in the second yer following hedging nd then decresed for the 3rd nd th yers (Fig. d). The cumultive growth ws gretest the yer fter hedging nd then the rte slowed. Spcing Trees t the wider spcing hd significntly greter growth of the primry shoot in the first yer following hedging compred to those t the closer spcing (Fig. 3). After the first yer, there were no significnt differences etween the tree spcings in growth ptterns of the primry shoot. The numer of rnching points formed nd the totl numer of growing points ws similr for the two tree spcings (Fig. 3,c). The totl yerly growth ws significntly greter for the wider compred to the closer spcing for the first yer following hedging ut not in yers two through four (Fig. 3d). The cumultive growth ws greter for ll four yers (3d), most likely due to the significnt difference in the first yer primry shoot growth (Fig. 3). High Lim Pruning There ws tendency towrd incresed primry shoot growth for the high lim pruned tretment ut the effect ws only significnt for the first yer for the closely spced trees (dt not shown). There were no differences cnopy light ion, rnching ptterns or cumultive growth for the high lim pruning tretment compred to the non-high lim pruned tretment (dt not shown). These dt suggest tht the high lim pruning strtegy my e effective for mnging crowded orchrds without impcting yields. In vocdo, more severe high lim pruning tretment led to decresed yields 5
while less severe tretment (Thorp nd Stowell, 1). The lck of negtive impct of this tretment ws likely ecuse it did not generte sustntil vegettive growth s result of cuts since ll cuts were mde to sustntil side rnch. Light Interception nd Light ion incresed significntly in the second nd third yer following hedging for ll rootstock nd spcing comintions (Tle 1,). By the fourth yer fter hedging, light ion ws no longer incresing for ny rootstock nd spcing comintion. s followed similr pttern to light ion incresing significntly in etween yers one nd two nd then incresing slightly etween yers two nd three (Tle 1,). The decrese in yield seen in the fourth seson following hedging occurred cross the entire orchrd nd ws likely due to poor pollintion conditions comined with incresing dmge from Phytophthor root rot in prts of the orchrd. Rows tht were hedged either three or four yers efore oth hd similr decreses in yield this yer, gin suggesting n orchrd wide fctor impcting yield rther thn hedging tretments. There were no significnt differences in ion or yield y rootstock or spcing for ny yer (Tle 1,). These dt gree with previous reports suggesting tht mechnicl hedging leds to decresed yields (Siett nd Rmos, 197; Rmos et l., 1983) or hs no effect on yields (Olson et l., 3). CONCLUSIONS In generl, primry shoot growth ws gretest in the yer following hedging while overll growth (including lterls) ws gretest in the second yer following hedging. This two yer period of refilling the cnopy removed y the mechnicl hedging likely explins the negtive impcts of hedging on yield. Cnopy light ion nd yield for the first yer following hedging were significntly lower in ll cses nd it ws not until the third yer following hedging tht mximum light ion nd yields ppered to e reched. This suggests tht hedging regimes tht cut on less frequent sis re likely to hve the lest negtive impcts on yield. There were no significnt effects of rootstock on ny of the mesured shoot growth chrcteristics, ion or yield. Wider spced trees hd significntly more primry shoot growth s well s totl yerly growth the yer following hedging. Cumultive growth (including primry nd lterl growth) ws significntly greter for the wider spced trees in ll yers. Although there ws tendency towrds higher yields in the wider compred to nrrower spced trees, there ws not significnt yield difference in ny yer. The high lim pruning tretment did not significntly impct light ion or yield suggesting this my e useful strtegy to mnge crowded hedgerow plntings. These results suggest tht if there is n interest in ttempting to control vegettive growth with culturl prctices such s deficit irrigtion, the first nd second yer fter mechnicl hedging should e the periods to trget. Literture Cited Alet, N. nd Ninot, A.. Hedgerow wlnut plnting system: experiences in Spin. FAO-CIHEAM- Nucis-Newsletter 9:33-37. Lemus, G. 1. Chilen experience on trining wlnut trees in centrl leder system. Act Hort. 5:3-7. Olson, B.B., Lmpinen, S., Metclf, J., Wlton nd Miller, S. Comprisons etween mechnicl hedging tretments nd the non-hedged check- 3.. Wlnut Reserch Reports- 3, Wlnut Mrketing Bord, 15 River Prk Drive, #3, Scrmento, CA 95815. pp. 171-179. Rmos, D., Kelley, K., Reil, W., Siett, G.S. nd Snyder, R. 1. Estlishment nd mngement considertions for wlnut hedgerow orchrds. Act Hort. 5:7-35. Rmos, D., Ryugo, K., Olson, W., Osgood, J., Siett, S., Reil, W. nd Snyder, R. 1983. Mngement systems for high density wlnut orchrds. Wlnut Reserch Reports- 1983, Wlnut Mrketing Bord, 15 River Prk Drive, #3, Scrmento, CA 95815. pp. 9-31. 53
Siett, S. nd Rmos, D. 197. Mechnized pruning. Dimond Wlnut News. 5():1-18. Thorp, T.G. nd Stowell, B. 1. Pruning height nd selective lim removl ffect yield of lrge Hss vocdo trees. Hortscience 3:99-7. Tles Tle 1. Averge photosyntheticlly ctive rdition () ion nd yields for Tulre wlnuts y hedging yer nd rootstock. Yer fter hedging Overll oth rootstocks (t h -1 ) By rootstock NCB Prdox lsd (t h -1 ) (t h -1 ) (t h -1 ) 1 1 8 3 393 3 91 77 5987 7 595 78 79 5 87 3 8 81 13 381 83 8 5813 318 8 8 7 5 78 115 lsd 3 1 9 5 73 Tle. Averge photosyntheticlly ctive rdition () ion nd yields for Tulre wlnuts y hedging yer nd spcing. Yer fter hedging By spcing Overll oth spcings 3.5m x 7.3 m spcing.7m x 7.3 m spcing lsd (t h -1 ) (t h -1 ) (t h -1 ) (t h -1 ) 1 1 8 377 8 3 958 77 5988 75 55 79 7 788 3 8 13 81 5 8 81 3 853 81 381 8 313 8 31 11 lsd 3 1 5 855 3 98 5
Figurese ~.8 m cut 1 3 1 3 Yers fter hedging Fig. 1. Pttern of shoot growth following mechnicl hedging. 55
Primry shoot yerly # new rnching points 1 8 5 3 1 Totl growing points 1 1 1 8 NCB Prdox c 1 8 d Totl yerly 3 5 e Cumultive 15 1 5 1 3 5 Yer fter hedging Fig.. Pttern of () primry shoot growth, () numer of rnching points, (c) totl growing points, (d) totl yerly growth including side rnching, nd (e) cumultive totl growth y yer nd rootstock. 5
Primry shoot yerly 1 8 # rnching points 5 3 1 Totl growing points Totl yerly 1 1 1 8 1 1 8 3.5 m spcing.7 m spcing c d Cumultive 35 3 5 15 1 5 e 1 3 5 Yer fter hedging Fig. 3. Pttern of () primry shoot growth, () numer of rnching points, (c) totl growing points, (d) totl yerly growth including side rnching, nd (e) cumultive totl growth y yer nd tree spcing. 57