Cover Crop and Mulching Effects on Yield and Fruit Quality in Unsprayed Organic Apple Production

Transcription

1 Europ.J.Hort.Si., 74 (6). S , 2009, ISSN Verlg Eugen Ulmer KG, Stuttgrt Cover Crop nd Mulhing Effets on Yield nd Fruit Qulity in Upryed Orgni Apple Prodution B.F. Kühn nd H. Lindhrd Pedersen (Arhus University, Fulty of Agriulturl Sienes, Deprtment of Hortiulture, Arslev, Denmrk) Summry To determine the optiml growing system for orgni pple prodution three different over rop mngement prtises were estlished for two s resistnt pple ultivrs; ultivr A Prim nd ultivr B Vnd. The mngement prties inluded: Tretment 1: A permnent grss mixture in the lley wy, Tretment 2: A permnent lover grss mixture in the lley wy nd Tretment 3: An nnul mixture of grss nd lover ws sown every yer in erly July nd mulhed down the following yer in April. Mehnil weed ontrol in the tree rows ws rried out yerly from April to July. No dditionl fertilizer, irrigtion or pest nd disese ontrol were rried out. A mulhing su tril ws onduted in the over rops: fter mowing the over rops in Tretment 1 nd 2: lippings were mulhed into the tree row (Tretment A) or lippings were left in the lley wy (Tretment B). The permnent grss lley wy system (Tretment 1) resulted in the lowest shoot growth, the lowest level of nitrogen in lef dry mtter nd fruit with the highest perentge of skin olour. The permnent lover grss mixture (Tretment 2) inresed the nitrogen level in the leves nd deresed the perentge of skin olour, moreover the pple s nd fly spek infetion on the fruit skin inresed ompred to fruits produed in Tretment 1. The nnul over rop growing system (Tretment 1) produed vigorous tree growth, high level of nitrogen in the leves, high soil wter ontent in the lley wy, the highest yield of lrge fruits nd low perentge of skin olour. The mulhing tril showed tht leving lippings of grss in the lley wy (Tretment B) resulted in lower yield of oloured fruit ompred with fruit hrvested following mulhing of the lippings into the tree row (Tretment B). This effet ws not only otined for grss (Tretment 1) ut lso for lover grss lippings (Tretment 2). The soil wter ontent in the tree row ws highest following mulhing lover grss. For the permnent grss system the highest ontent of soil wter in the tree row ws otined for re soil. Key words. orgni pple prodution growing system pple s resistnt pple ultivrs N-supply soil wter pest nd diseses fruit qulity Introdution In orgni pple prodution it is importnt to determine the est soil mngement system tht optimizes fruit prodution nd fruit qulity. Apple trees hve shllow root systems nd re found to e poor ompetitors for wter nd nutrients from weeds or over rop speies (MARSH et l. 1996; WALSH et l. 1996). Therefore it is importnt to redue the ompetition for wter nd nutrients from other plnts in the zone lose to the tree trunk. Cover rops or mulhes my utilise or supply the fruit trees with nitrogen (N). Nitrogen is the most moile of the essentil plnt nutrients (KOEHN et l. 2002) nd is very importnt for plnt growth. Uptke of N y roots of pple trees s well s y over rops or weeds will derese the onentrtion of N in the soil (KOEHN et l. 2002). Cover rops my, y ompetition for moisture nd N, ffet tree growth nd dely fruit prodution (HAYNES nd GOH 1980). It hs een shown tht orgni mulhes inrese soil wter ontent (HOUGE nd NIELSEN 1987; WALSH et l. 1996) nd mulhing tretments result in stronger tree growth nd redued need for irrigtion nd fertiliztion with N. Choie of ultivr in orgni pple prodution is lso very importnt. It is essentil to e quinted with the hrteristis of the different pple ultivrs when hoosing ultivrs for orgni growing. The use of pple s resistnt pple ultivrs is essentil to redue infetio of pple s, whih is the most signifint disese on pples t mny lotio. However, it is well known tht pple s resistne, espeilly in the monogeni sed pple s resistnt ultivrs, is not persistent nd my e roken (DUREL et l. 2000; GUERIN nd LE CAM 2004). The im of the this reserh ws to investigte the impt of soil mngement prtises on soil moisture, nitrogen in soil, lef nutrients levels, pple tree growth, fruit yield nd qulity y evluting three different lley wy over rop mngement prtises nd two different mulhing methods on the prodution nd qulity of two s resistnt pple ultivrs under n orgni prodution system.

2 248 Kühn nd Lindhrd Pedersen: Cover Crop nd Mulhing Effets in Orgni Apple Prodution Mteril nd Methods Tril design nd orhrd mngement The experimentl reserh orhrd is loted t the Deprtment of Hortiulture, Arhus University, Arslev Reserh Centre (10 27 E, N), on sndy lom soil, with ly ontent of %. In Jnury 1995, three seprte over rop tretments of two s resistnt pple ultivrs; ultivr A Prim nd ultivr B Vnd, grfted on rootstok M9 nd trined s free spindle were estlished in n orgni prodution system. Eh of the three over rop tretments oisted of 2 rows per ultivrs, with 23 trees in eh row. The plnting distne ws 3.3 x 1.6 m. The distne etween over rop tretments ws 6 m. The over rop mngement systems estlished in the lley wys were: Tretment 1: Grss: A permnent wek grss mixture of red fesue (Festu rutr) nd medow grss (Po prteis). Tretment 2: Clover grss: A permnent lover grss mixture oisting of white lover (Trifolium repe) nd perennil ryegrss (Lollium perénne). Tretment 3: Annul: An nnul over rop oisting of Itlin ryegrss (Lollium multiflorum) nd persin lover (Trifolium resupintum) sown every yer in July nd mulhed down the next yer in April nd mehnil weed lening from April to July. In tree rows (1 m width) weed ontrol ws rried out mehnilly. The trees were kept unfertilized nd upryed. Fruit thinning ws rried out y hnd when needed. Detiled studies of soil wter, ontent of lef nutrients, tree growth, fruit prodution, fruit qulity nd suseptiility to pest nd diseses were rried out in 18 single trees per over rop tretment of eh ultivr. A su-tril ws estlished in Tretment 1 nd Tretment 2 where, fter mowing the over rops, the following tretments were onduted: Tretment A. Mulhing; lippings were mulhed into the tree row; nd Tretment B. Bre soil; lippings were left in the lley wy. Three replites per tretment were estlished nd the plot size inluded three trees. Soil nd lef nlysis nd tree growth Inorgni nitrogen (Nmin) ontent in the soil ws mesured in the 0 50 m soil lyer in mid April, June nd Septemer in 1999, 2000, nd Nitrte-N nd mmonium-n were determined olorimetrilly ording to slightly modified method of CROOKE nd SIMPSON (1971) nd BEST (1976), respetively. The soil moisture ws mesured in the 50 m top soil in the entre of the tree row nd in the entre of the lley wy in June Septemer Mesurements were rried out 3 11 times per yer. Soil moisture ws determined using Tre system tht mesured soil moisture y time domin refletometry (TDR), Model 6050XI. Lef smples were olleted in August 1998, 2000, nd 2001 nd nlysed for nitrogen (N), potssium (K) nd lium (C) ontent. Annul shoot growth ws mesured during winter for eh of the 18 trees of eh ultivr per over rop tretment during the period For eh tree the totl shoot prodution per growing seson ws lulted. Fruit prodution nd fruit qulity Fruit prodution ws ssessed from 1996 to Fruits were olour grded with MAF RODA grder. From 1999 to 2001 fruit were grded in to three lsses: Clss 1: Fruit overed with more thn 75 % red skin olour, Clss 2: Fruit overed with % red skin olour nd Clss 3: Fruit overed with less thn 25 % red skin olour. Furthermore the fruits were hnd grded into mrketle nd unmrketle fruit ording to ommeril rules for fruit size nd skin disorders using the UN/ECE Stndrds for Apples (Deemer 2000). Clsses 1 nd 2 fruit re mrketle s Clss 1 orgni pple prodution in Denmrk. Twenty-five rndom fruits per tree were exmined for skin dmge used y pple s (Venturi inqulis), fly spek (Leptothyrium pomi), sooty loth (Gloedes pomigen), tortrix (different speies), odling moth (Cydi pomonell) nd pple swfly (Hoplomp testudine). The perentge of dmged fruit ws lulted per yer in 1996 to Sttistil method Sttistil nlyses of dt were performed using SAS (Version 8 The effets of the over rop tretments were nlysed with the Generl Liner Models (GLM) proedure. Dt for ompring the three over rop tretments inluded trees reeiving the su tretment B. Bre soil, nd dt for ompring the mulhing su tretments inluded trees in over rop tretment 1. Permnent grss nd 2. Permnent lover grss. Dt oisting of whole numers (hrter vlues) were rsine trformed to fit norml distriution efore onduting sttistil nlysis. Me were seprted with n LSD test nd sttistil signifine ws defined t P<0.05. Whenever signifint intertio were determined, the results for individul intertio re presented. Although the two ultivrs were very different in their mesured qulities, their respoe to the tretments ws pproximtely similr. Therefore ultivr verge ws used for the sttistil lultio. Results Soil nd lef nlysis nd tree growth The nnul rinfll nd evportion t the reserh site vried mm nd mm, respetively, in the period 1998 to The highest ontent of ville nitrogen (Nmin) in the soil ws oistently found in the nnul system (Tretment 3, Tle 1). By Septemer, nd on verge over the growing seson, the nitrogen ontent of the soil ws signifintly higher in the nnul system ompred with the two perennil systems. Lef nlyses showed tht the lowest nitrogen (N) nd lium (C) ontent nd the highest ontent of potssium (K) ws present in leves from trees grown in the permnent grss over rop (Tle 2). Almost ll lef smples were found to e within the optimum rnges; whih in Denmrk re oidered to e N: % dry mtter nd K: % dry mtter. Lef C ontent ws found to e higher thn the optimum rnge: % dry mtter; no symptoms of the physiologil C defiieny disor-

3 Kühn nd Lindhrd Pedersen: Cover Crop nd Mulhing Effets in Orgni Apple Prodution 249 Tle 1. Effet of over rop mngement prtises on soil nitrogen ontent (N-min), determined three times during the growing seson, verge over two pple ultivrs; Prim nd Vnd from Cover rop system 15 Apr 15 Jun 15 Sep Averge (kg N h 1 ) Grss * 14.1 Clover grss Annul P > F LSD * different letters within olumn denotes signifint differene (P < 0.05). Tle 2. Effets of over rops on lef Clium (C), potssium (K) nd nitrogen (N) levels in lef dry mtter, nd soil wter ontent in tree row nd lley wy nd shoot growth of two pple ultivrs Prim nd Vnd from (lef nutrients not mesured in 1999). Cover rop system Lef nutrients (% dry weight) Wter ontent in soil (Vol. %) Shoot growth N K C in tree row in lleywy (m tree 1 ) Grss * Clover grss Annul P > F < < < < < LSD * different letters within olumn denotes signifint differene (P < 0.05). der, itter pit, were oserved in ny fruit smples. The soil wter ontent in the tree rows ws not influened y the over rop system (Tle 2). However, in the lley wys the soil wter ontent ws signifintly highest in the nnul system nd lowest in the permnent lover grss system (Tle 2). Totl shoot growth ws influened y the over rop system (Tle 2). The most vigorously growing trees were found in the nnul system, while the wekest shoot growth ws oserved in the permnent grss system. Lef smples from the two mulhing methods showed tht mulhing lover grss hd no effet on lef nutrients. However, mulhing grss inresed the ontent of N nd C nd deresed the K ontent (Tle 3). Mulhing orgni mteril from the grss lley wy into the tree row resulted in lower soil wter ontent in the tree row in omprison to re soil. However, mulhing the lover grss into the tree row hd n opposite nd positive effet on the soil wter ontent (Tle 3). Mulhing mowed grss mteril into the tree row resulted in higher shoot growth thn when leving the lippings in the lley wys (Tle 3). However, in the lover grss system no differenes in shoot growth were found when mulhing the lippings into the tree row or leving lippings in the lley wy (Tle 3). Fruit prodution nd fruit qulity The highest totl yield ws otined in the nnul system (Tle 4A), however; the highest perentge of fruits with more thn 75 % red olour ws otined in the permnent grss system. Fruit produed in the nnul system were slightly lrger thn fruit from the two other over rop systems (Tle 4A). In the permnent grss system the highest yield nd the lowest perentge of oloured fruit >75 % olour were found when mulhing lippings into the tree row (Tle 4B). For the lover grss system no signifint differenes etween mulhing methods were found. Hrvested fruit were grded ording to skin dmge used y the different pests nd diseses (Tle 5). Fruit grown on the permnent grss system hd on verge less fruit with pple s nd fly spek infetio (Tle 5). Although the ultivrs were s resistnt when plnted, their resistne ws roken during the experimentl period. Prim mintined s resistne for only 2 yers fter plnting, while Vnd retined s resistnt for 4 yers fter plnting. The loss of pple s resistne ws severe in Prim. On verge, 4.2 % of the hrvested Prim fruits were infeted with pple s in 1998 nd this inresed to 93.4 % in 2001 (Fig. 1). After loss of the pple s resistne the most severe symptoms were found in the lover grss system. The mngement system signifintly influened the inidene of pple s dmges on the ultivr Prim. The highest perentge pple s dmged fruit ourred in the lover grss system (Fig. 1). Vnd hd on verge very few (. 0.5 %) fruits with pple s dmge irrespetive of mngement system.

4 250 Kühn nd Lindhrd Pedersen: Cover Crop nd Mulhing Effets in Orgni Apple Prodution Tle 3. Effets of mulhing on soil wter ontent, shoot growth nd lef nutrients in two pple ultivrs Prim nd Vnd, where nutrient nlysis is given for lium (C), potssium (K) nd nitrogen (N) in 1998, 2000 nd Mulh tretment Permnent grss system Clover grss system Soil Shoot Soil Shoot Lef nutrients (% dry weight) wter growth Lef nutrients (% dry weight) wter growth C K N (Vol. %) (m tree 1 ) C K N (Vol.%) (mtree 1 ) Mulhing * Bre soil P > F < < LSD * different letters within olumn denotes signifint differene (P < 0.05). Tle 4A. Effets of over rop mngement system nd mulh tretments on fruit yield nd fruit olour, verge of two pple ultivrs Prim nd Vnd from 1999 to Cover rop system Yield (kg tree 1 ) Fruits < 25 % red olour (%) Fruits > 75 % red olour (%) Fruit size (g fruit 1 ) Grss 13.3 * Clover grss Annul P > F < < < < LSD * different letters within olumn denotes signifint differene (P < 0.05). Tle 4B. Effets of mulh tretment in two over rop tretments on fruit olour, verge of two pple ultivrs Prim nd Vnd from 1999 to Mulh tretment Yield (kg tree 1 ) Permnent grss over rop system Fruits < 25 % red olour (%) Fruits > 75 % red olour (%) Yield (kg tree 1 ) Clover grss over rop system Fruits < 25 % red olour (%) Fruits > 75 % red olour (%) Mulhing 15.7 * Bre soil P > F > > > LSD * different letters within olumn denotes signifint differene (P < 0.05). In 2000, for the ultivr Vnd, 0.5 % pple s infeted fruits were reorded on hrvested fruit, in 2001 the inidene of infeted fruits inresed to 2.5 % (dt not shown). Fruit grown in the nnul system hd the lowest inidene of sooty loth. The most severe dmges from fly spek nd sooty loth were oserved in the ultivr Vnd tht hs the most light-oloured pples. The pples were grded one to two months fter hrvest, iide tht period no post hrvest diseses ourred. Different tortrix speies lso used severe dmge to fruit, with the most dmge eing oserved on fruit from the lover grss system (Tle 5). Codling moth used no serious dmge in either ultivr or mngement system. Apple swfly dmge ws generlly limited to nd most prevlent in the nnul grss system. Mulhing lippings into the tree row did not influene the inidene of dmge used y pest nd diseses (Tle 5). On verge ( ) mrketle yield ws signifintly higher for Vnd (8.9 kg tree 1 ) thn Prim (7.7 kg tree 1 ). The differene etween the ultivrs in the perentge of mrketle fruit inresed during the tril, mostly due to the loss of pple s resistne of Prim (Fig. 2). In 2001 Prim hd on verge only 23.0 % nd Vnd hd 71.8 % mrketle fruit.

5 Kühn nd Lindhrd Pedersen: Cover Crop nd Mulhing Effets in Orgni Apple Prodution 251 % Fruit with pple s dmge Yer Grss Clover grss Annul Fig. 1. Apple ultivr Prim with pple s dmges grown in three different over rop systems: grss, lover grss nd nnul. Tretments with different letters within yer re signifintly different t P<0.05. = not signifintly different. Disussion Cover rop mngement system The over rop tretments hd signifint influene on the level of Nmin in the soil. The different mngement tretments influened the levels of ville nitrogen in the soil. Bre soil normlly releses round 45 kg plnt ville N h 1 during the growing seson in Denmrk (POULSEN nd HANSEN 1962). In this tril the highest levels of inorgni N in the soil were otined in the nnul system t 26.2 kg plnt ville N h 1 (Tle 1), this resulted from the dditionl N relesed y the deomposing orgni mteril nd proly euse there ws no N uptke y the permnent over rop in the lley wy. The N ontent in the soil remi more or less unhnged during the growing seson in the grss nd the lover grss systems ompred to the nnul system, this is likely ttriuted to N uptke from the over rop in the lley wy. The rther low level of inorgni N in the grss over rop mngement system ws expeted s grss is stronger N ompetitor thn pple trees, similr results hve een otined y MARSH et l. (1996). In oth the lover grss nd grss lover rop systems the inorgni soil N ontents were stle t 13.1 nd 14.1kg plnt ville N h 1 (Tle 1). However, pple lef smples showed high ontent of nitrogen in trees grown with permnent lover grss over (Tle 2). This is proly ttriutle to relese of N from the deomposing orgni mteril nd rther high N uptke of the pple tree roots. The high N fixtion pity nd relese in the lover grss system is likely to e linked to the high N in lover leves s reported y MARSH et l. (1996) nd HORNIG nd BÜNEMANN (1996). These pple trees hd high ontent of N in the leves, higher thn tht reommended in Denmrk. In the nnul system the plnt ville N inresed during the seson due to the high N relese, higher thn the potentil uptke y the pple tree roots (Tle 1). It ws oserved tht when N levels in pple lef dry mtter were low, K levels were high (Tle 2). This is in greement with MARSH et l. (1996). The high level of K in lef dry mtter in trees grown in grss over Tle 5. Fruit with skin dmge used y pple s, fly spek, sooty loth, tortrix, odling moth nd pple sw fly, verge of two pple ultivrs Prim nd Vnd from nd mrketle yield from Cover rop system Apple s Fly spek Sooty loth Tortrix Codling moth Apple sw fly Mrketle yield (% fruit with dmge) (kg tree 1 ) Grss 10.0 * Clover grss Annul P > F < < < < LSD Mulh tretment Mulhing Bre soil P > F * different letters within olumn denotes signifint differene (P < 0.05).

6 252 Kühn nd Lindhrd Pedersen: Cover Crop nd Mulhing Effets in Orgni Apple Prodution Mketle yield, % Yer Prim - Grss Prim - Clovergrss Prim - Annul Vnd - Grss Vnd - Clovergrss Vnd - Annul Fig. 2. Perent mrketle fruit for Prim nd Vnd pple ultivrs for three different over rop systems from Tretments with different letters within yer re signifintly different t P<0.05. rops my lso e due to high ontent of K in the grss, whih is quikly ville to the trees due to fst deomposion. If the orgni mteril is moved to the tree row (mulhing) the K vlues re deresing (Tle 3). This my e due to slower deomposion. The soil wter ontent ws signifintly highest in the nnul system. This ws likely due to higher ontent of orgni mtter used y the nnul mulhed over rop nd due to smll uptke y the nnul over rop. HORNIG nd BÜNE- MANN (1996) reported high soil moisture ontent in lover system moreover the soil moisture in the grss mixture tretment ws reltively low. In the present experiment this tendeny ould not e seen in the tree row (Tle 2). The over rop system ffeted tree growth signifintly y influening the soil wter ontent nd the soil N-ontent (Tle 1 nd 2). It ws onfirmed here s in relted studies (MERVIN nd STILES 1994; HORNIG nd BÜNEMANN 1995; MARSH et l. 1996) tht shoot growth vigour depends on the soil wter ontent nd the N vilility, nd reltiohip exists etween tree vigour nd N ontent in lef dry mtter. The highest shoot growth ws oserved in the nnul system. Additionlly, high soil wter ontent, high level of ville soil N-min ontent nd high level of N in lef dry mtter were found in the nnul system (Tle 1 nd 2). It is ovious from this tril tht grss is very strong ompetitor to the pple trees for oth nutrients nd wter, this grees with reports y WALSH et l. (1996) tht grss over rop hs tendeny to redue shoot growth. The over rop system influened the yield s well s the fruit size nd qulity (Tle 4A). During , when fruit yield hd stilized, the highest yield nd fruit size were otined from the nnul system; the highest shoot growth ws lso reorded in this tretment (Tle 2). However, for this prodution system fruit qulity results were poor. The nnul system resulted in only 32.5 % of the fruit developing full olour, wheres for the N limited trees grown in the grss system, s muh s 68.7 % of the fruit were well oloured (Tle 4). Aording to these results, use of grss system gve limited soil N vilility (Tle 1) resulting in limited lef dry mtter N ontent, high perentge K in lef dry mtter (Tle 2) nd high perentge of well oloured fruits (Tle4A). In generl systems tht resulted in high lef N lso hd low perentge of well oloured fruits (Tle 2 nd 4). The reltion etween the fruit olour nd N supplement hs een disussed in other reserh (OLAND 1960; RAESE nd WILLIAMS 1974; VANG-PETERSEN et l. 1977; NEILSEN et l. 1984; HORNIG nd BÜNEMANN 1995). Even though the yield in the permnent grss system ws lower, the high perentge of oloured fruit t 9.1 kg tree 1 on verge per yer, ompred to the nnul system tht produed only 5.6 kg tree 1 ment tht greter proportion of the rop ws mrketle. However it should e noted tht fruit grown in the permnent grss system were slightly smller thn those from the nnul system. Dmges on fruit skin used y pest nd diseses were very vrile. Results depended on the vried kinds of pests or diseses (Tle 5). The lowest perent pple s dmges ws seen in the permnent grss system nd ws relted to limited shoot growth nd low nitrogen relese pttern (Tle 1, 2 nd 5). In the pple s resistnt ultivr Prim no severe pple s dmge ws reported on the fruits until fifth yer (2000) fter plnting (Fig. 1). At this time dmge ws most severe in the lover grss system. The dmge ontinued to e more severe on the pples grown in the lover grss system from (Fig. 1). This tretment lso resulted in the lrgest uptke of N in the trees (Tle 2). BUCHTER-WEISBRODT (1996) found tht high N supply redues the phenol synthesis in the trees nd this my e one of the mehnisms to the inresed suseptiility to pple s. Trees grown in high N relesing soil systems hd more vigorous shoot growth whih fvoured the development of diseses suh s pple s nd fly spek. In these high N relesing systems the monogeni pple s resistne ws roken. The smllest mrketle yield ws oserved in the lover grss system (Tle 5). Furthermore the highest perentges of fruits with pple s dmges were found in this system. Mulh tretment Mny reports hve suggested tht mulhing lippings ould preserve soil moisture levels, primrily due to redution in evportion (SKROCH nd SHRIBBS 1986 nd Hogue et l. 2002). However, this tendeny ws only just pprent in the lover grss system (Tle 3). The expl-

7 Kühn nd Lindhrd Pedersen: Cover Crop nd Mulhing Effets in Orgni Apple Prodution 253 ntion of the overll low soil wter ontent in the grss system my ttriute to the ft tht the mount of lippings ws rther low or the ft tht higher shoot growth ws otined in the mulhing tretment, whih indites tht soil moisture ws tken up y the trees nd used for shoot growth (Tle 3). Other reports hve lso demotrted tht mulhing ffets the rte of tree growth (WALSH et l. 1996). A higher N ontent in lef dry mtter nd higher yield were oserved following mulhing of the permnent grss lippings into the rows however the resulting fruit were less oloured t hrvest (Tle 3 nd 4B), likely result of higher N-uptke. Although MARSH et l. (1996) demotrted positive effet of mulhing on soil nd lef nutrient levels, this reserh found no signifint effets following the pplition of mulh s lippings (Tle 3). In generl the lover grss system resulted in higher lef N ontent thn the grss with fewer well oloured fruits t hrvest (Tle 4B). In generl the mulhing tretment hd no effet on the inidene of fruit skin dmges used y different pests nd diseses (Tle 5). Cultivrs Vnd nd Prim were very different in growth hit, prodution nd fruit qulity. The s resistne ws roken in oth ultivrs during the experimentl period; however Vnd kept s resistne longer thn Prim. The perentge mrketle fruit ws lso different for the two ultivrs; in 2001 Vnd hd more mrketle fruit thn Prim (Fig. 2), n explntion for this ws tht Prim hd lower yield with more s infeted fruit. Conlusion To redue the likelihood of pple s development nd inrese the olour development of the fruit it is importnt to hoose over rop system tht supports the pple trees with dequte N, resulting in lef dry mtter ontent round 2.1 %. Limited N supply redues tree growth nd to some extent the yield, ut inreses fruit olour development, nd dereses the inidene of diseses in upryed orgni prodution systems. The level of mrketle fruit ws omprle to those grown under higher N supply. None of the over rop systems evluted resulted in defiieny of potssium or lium. The effet of mulhing lippings from over rop depends on the over rop mteril. Mulhing lover inresed the soil wter ontent, ut no other effets were oserved. Mulhing grss inresed lef N, shoot growth nd yield, while the proportion of well oloured fruit deresed. For sustinle orgni pple prodution it is ritil to oider pple s resistnt ultivrs tht hve polygeni resistne to void loss of resistne. Aknowledgement The present study ws mde possile through funding from The Dnish Reserh Centre for Orgni Frming. Thnk to Anette Søreen, Stig Søreen nd Kim Nielsen for vlule tehnil ssistne. Referenes BEST, E.K. 1976: An utomted method for determining nitrte-nitrogen in soil extrts. Queelnd J. Agr. nd Animl Si. 32, BUCHTER-WEISBRODT, H. 1996: Phenole gegen Shorf. Ostu. 2, CROOKE, W.M. nd W.E. SIMPSON 1971: Determintion of mmonium in Kjeldhl digests of rops y n utomted proedure. J. Si. Food Agr. 22, DUREL, C.E., L. PARISI, L. LAURENS, F. VENISSE nd M.F. JOURJON 2000: Does the Vf gene mintin residul resistne to pple s despite its rekdown y Venturi inequlis re 6 stri? At Hort. 538, GUERIN, F. nd B. LE CAM 2004: Brekdown of the s resistne gene Vf in pple leds to founder effet in popultio of the fungl pthogen Venturi inqulis. Phytopthology. 94, HAYNES, R.J. nd K.M. GOH 1980: Some effets of orhrd soil mngement on swrd omposition, levels of ville nutrients in the soil, nd lef nutrient ontent of mture Golden Deliious pple trees. Si. Horti. 13, HORNIG, R. nd G. BÜNEMANN 1995: Ground overs nd fertigtion in pple orhrds with integrted prodution. 1. Growth, yield, nd fruit qulity. Grtenuwissehft 60, HORNIG, R. nd G. BÜNEMANN 1996: Ground overs nd fertigtion in IP pple orhrds. 2. Nutrient sttus of the pple trees. Grtenuwissehft 61, 1 7. HORNIG, R. nd G. BÜNEMANN 1996: Ground overs nd fertigtion in IP pple orhrds. 3. Biomss yield nd nutrient uptke of the ground overs nd influene on soil moisture nd nutrients in the soil. Grtenuwissehft 61, HOGUE, E.J. nd H.G. NEILSEN 1987: Orhrd floor vegettion mngement. In: Jnik, J. (ed.): Hort. Rev. 9, KOEHN, A.C., F.J. PERYEA, D. NEILSEN nd E.J. HOGUE 2002: Temporl hnges in nitrte sttus of orhrd soils with vrying mngement prties. Comm. Soil Si. Plnt Anl. 33, MARSH, K.B., M.J. DALY nd T.P. MCCARTHY 1996: The effet of under storey mngement on soil fertility, tree nutrition, fruit prodution nd pple fruit qulity. Biol. Agri. & Hort. 13, MERWIN, I.A. nd W.C. STILES 1994: Orhrd groundover mngement impts on pple tree growth nd yield, nd nutrient vilility nd uptke. J. Am. So. Horti. Si. 119, NEILSEN, G.H., M. MEHERIUK nd E.J. HOGUE 1984: The effet of orhrd floor mngement nd nitrogen fertiliztion on nutrient uptke nd fruit qulity of Golden Deliious pple trees. HortSi. 19, OLAND, K. 1960: Nitrogen feeding of pple trees y post hrvest ure sprys. Nture POULSEN, R. nd P. HANSEN 1962: Undersøgelser over jorde nitrtindhold. Tidsskr. Plntevl. 65, (in Dnish). RAESE, J.T. nd M.W. WILLIAMS 1974: The reltiohip etween fruit olour of Golden Deliious pples nd nitrogen ontent nd olour of leves. J. Am. So. Hort. Si. 99, SKROCH, W.A. nd J.M. SHRIBBS 1986: Orhrd floor mngement: An overview. HortSi. 21, VANG-PETERSEN, O., K. KAACK nd P.M. RASMUSSEN 1977: Kvælstof til frugttræer. iii Effekt på frugte frve og indhold f syre, sukker og romstoffer. Tidsskr. Plntevl. 81, (in Dnish). WALSH, B.D., A.F. MACKENZIE nd D.J. BUSZARD 1996: Soil nitrte levels s influened y pple orhrd floor mngement systems. Cn. J. Soil Si. 76, WALSH, B.D., S. SALMINS, D.J. BUSZARD nd A.F. MACKENZIE 1996: Impt of soil mngement systems on orgni dwrf pple orhrds nd soil ggregte stility, ulk deity, temperture nd wter ontent. Cn. J. Soil Si. 76, Reeived Otoer 28, 2008 / Aepted June 25, 2009 Addresses of uthors: B. F. Kühn nd H. Lindhrd Pedersen (orresponding uthor), Arhus University, Fulty of Agriulturl Sienes, Deprtment of Hortiulture, Kirstinejergvej 10, DK 5792 Arslev, Denmrk, emil: Hnne.Lindhrd@grsi.dk.