Plant biomass nitrogen and effects on the risk of nitrate leaching of intercrops under organic farming in Eastern Austria

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1 EUROSOIL, Sept. th to th, Freiburg, Germny, Conference Proceeding Plnt biomss nitrogen nd effects on the risk of nitrte leching of intercrops under orgnic frming in Estern Austri Frthofer R., Friedel J.K., Pietsch G., Rinnofner,T., W. Loiskndl 5, Freyer B. 6,,, 6 Institute of Orgnic Frming, Deprtment of Sustinble Agriculturl Systems, University of Nturl Resources nd Applied Life Sciences, Vienn, Gregor-Mendel-Str., A-8 Vienn Institute of Orgnic Frming, Deprtment of Sustinble Agriculturl Systems, University of Nturl Resources nd Applied Life Sciences, Vienn, Gregor-Mendel-Str., A-8 Vienn, juergen.friedel@boku.c.t 5 Institute of Hydrulics nd Rurl Wter Mngement, Deprtment of Wter, Atmosphere, Environment, University of Nturl Resources nd Applied Life Sciences, Vienn, Gregor- Mendel-Str., A-8 Vienn Abstrct Dt on the potentil of intercrops to reduce soil nitrte contents, on their N ccumultion nd biologicl nitrogen fixtion (BNF) re lcking for orgnic frming in the dry, pnnonic region of Estern Austri. The effect of legumes, non-legumes, nd legumes + non-legumes used s intercrops on inorgnic soil nitrogen, crop yield nd biomss N, nd BNF were tested in comprison to bre fllow. Non-legumes nd legumes + non-legumes were more efficient thn legumes in reducing inorgnic soil N contents in utumn nd nitrte contents in soil solution from the subsoil in winter. This reduction in inorgnic soil N did not lst until Mrch of the following yer due to n N minerlistion from the mulch. The legume + non-legume mixture contined lrger mount of crop N thn both legumes nd non-legumes. This ws due to the combined effect of soil-n uptke by the non-legumes nd BNF by the legumes in the mixture. Introduction Intercrops re mjor tool in orgnic frming for preventing nitrte leching to the groundwter nd for trnsferring N to following crops. Due to pnnonic climte conditions (low precipittion 55 mm - ) in Estern Austri, sufficient wter supply plys n importnt role for gining dequte crop yield nd qulity. Studies on the N ccumultion in intercrop biomss (Sorensen, 99), on the biologicl N fixtion by intercrops (Jensen, 989; Müller und Thorup-Kristensen, ), on their effect on soil nitrte contents (Reents et l.,

2 EUROSOIL, Sept. th to th, Freiburg, Germny, Conference Proceeding 997; Miersch und Vetter, ) nd on succeeding crops (Jensen, 989; Biederbeck et l., 996; Reents et l., 997) hve been conducted in regions with higher precipittion. Respective results re not vilble for orgnic frming in the pnnonic region. The im of this study ws to optimise the use of intercrops with respect to soil inorgnic N contents in utumn nd winter, crop biomss nitrogen (N), nd effects on yield nd qulity of subsequent crops. The objectives were to test (i) if legumes + non-legumes re equivlent to non-legumes in reducing soil inorgnic N contents in utumn nd (ii) if crop biomss N in legumes + non-legumes surpsses the mount of N in non-legumes. Mteril nd Methods The experimentl fields, prt of n experimentl frm of the University of Nturl Resources nd Applied Life Sciences, Vienn, were converted to orgnic frming in 998. Soils re Clcric Pheozems from Loess (silty lom,. % TOC, ph 7.6). Men nnul precipittion is 55 mm, men temperture 9.8 C. Crop rottion ws winter whet / intercrop () potto () winter rye / intercrop () summer brley (5). Four vrints, including three different types of intercrops were tested in rndomised complete block design. Vrint : Legumes + non-legumes: ll mentioned legumes nd non-legume species; Vrint : Legumes: chickling vetch, common vetch, field pe; Vrint : Non-legumes: oil rdish, turnip, phceli; Vrint : Bre fllow. In, intercrops were sown fter hrvest of winter whet in erly August nd were mulched in lte October. The soil ws chiselled t the end of October. Pottoes were plnted in the mid of April of the following yer. Strting in August, inorgnic N (N in ) contents were monitored in cm depth every yer in spring, summer nd utumn. Soil solution ws collected by suction cups from cm depth nd nlysed for nitrte contents. Above-ground nd below-ground ( 6 cm) biomss production of the intercrops were determined. Below-ground crop biomss ws derived from smples tken with soil corer ( cm dim.) nd wshing roots out of the soil. Plnt nitrogen contents were nlysed by dry combustion nd gs chromtogrphy in LECO CN-Anlyzer. Biologicl nitrogen fixtion (BNF) of the legumes ws estimted by the extended difference method ccording to Stülpngel (98). Shoot, stubble nd root biomss N, nd soil N in

3 EUROSOIL, Sept. th to th, Freiburg, Germny, Conference Proceeding contents were tken into ccount (Eqution ). The non-legumes (vr. ) served s reference crop. Eqution : Clcultion of biologicl N fixtion (kg h - ) by the extended difference method. BNF = [(Shoot-N Leg + Stubble-N Leg + Root-N Leg ) (Shoot-N Ref + Stubble-N Ref +Root-N Ref )] + [N in(leg) N in(ref) ] Leg: legumes; Ref: reference crop = non-legumes Vrint effects were nlysed by two-wy nlysis of vrince (fctor : intercrop vrint, fctor : block) nd comprisons of the mens with Tukey test. Results nd Discussion Wether conditions Precipittion ws pprox. 8% bove the long-term verge in summer nd utumn. Februry to April nd June, however, were extremely dry. Crop biomss nd nitrogen At incorportion of the intercrops in lte October, the legumes + non-legumes yielded the lrgest bove-ground biomss (. t h - ), followed by the non-legumes (. t h - ) nd the legumes (.5 t h - ). Root biomss production ws gretest in the non-legumes (.6 t h - ), less in the legumes + non-legumes (. t h - ) nd lest in the legumes (. t h - ). Totl biomss production ws significntly higher in the legumes + non-legumes nd non-legumes thn in the legumes (Fig. ). The mount of totl crop N reched 5 kg N h - in the legumes + non-legumes. The totl mount of N in this vrint ws higher thn in the other two intercrop vrints, minly due to dditionl N derived from the ir by BNF (Fig. ). Plnt biomss nd N contents were negligible in the bre fllow tretment (dt not shown). Reents nd Möller () compred different intercrops following pes in orgnic frming t two sites in Upper Bvri (pprox. 7.7 C; 79 mm; lomy soils). Dry mtter yields decresed in the order winter vetch nd summer vetch + oil rdish > pes in pure crop nd + oil rdish > Persin clover. The N yield of the intercrops reched up to 5 kg N h - for sinter vetch nd summer vetch + oil rdish followed by pes in pure crop nd + oil rdish. They were lest for Persin clover. Sorensen (99) studied the N uptke of phceli, sunflower nd Itlin ryegrss in conventionl frming. Under optiml conditions up to 5 kg N h - could be stored in bove-ground biomss. Under bre fllow, on the opposite, N losses mounted to kg N h -.

4 EUROSOIL, Sept. th to th, Freiburg, Germny, Conference Proceeding Crop yield (t DM h - ) 6 b Nonlegumes, 5 boveground b b Legumes, boveground 5 V r i n t Beets (oilrdish, turnip) Roots N yield (kg N h - ) 5 V r i n t Legend: Vr. : Legumes + non-legumes; Vr. : Legumes; Vr. : Non-legumes Men vlues with the sme letter re not significntly different (Tukey, P <.5). Fig. : Biomss nd nitrogen yield of intercrops in lte October. Biologicl N fixtion nd N uptke from the soil BNF mounted to 8 kg N h - in the legumes + non-legumes nd to kg N h - in the legume vrint. This mens tht ll of the legume-n in the legumes + non-legumes nd bout 5 % of the legume-n in the legume vrint ws derived from the ir by BNF. The N derived from the soil thus mounted to pprox. 5 kg N h - in the legumes + non-legumes, to 6 kg N h - in the legume vrint nd to 7 kg N h - in the non-legumes. Müller nd Thorup-Kristensen (, Denmrk) found BNF of legume intercrops in orgnic frming of to 8 kg N h -. They concluded tht this is considerble contribution to N turnover. Inorgnic N in soil nd in soil solution Inorgnic N contents in the soil profile were reduced in ll intercrop vrints, but minly in the non-legumes nd the legumes + non-legumes compred to bre fllow in utumn (Fig. ). The two vrints contining non-legumes reduced N in contents by lmost 8 kg N h - within the observed soil depth of cm. The effect of the legumes mounted to pprox. kg N h - only. In ll intercrop vrints, the reduction in N in ws bout to 5 kg N h - less thn the crop N uptke from the soil. This difference indictes tht nitrte ws leched below cm in the bre fllow tretment, since plnt N uptke ws negligible here. In Mrch, differences in N in contents between the tretments were no longer significnt. N in contents incresed from October to Mrch by pprox. 5 kg N h - in the intercrop vrints, but only by 5 kg N h - under bre fllow. The min increse occurred in the

5 EUROSOIL, Sept. th to th, Freiburg, Germny, Conference Proceeding topsoil. The dditionl increse in N in contents in the intercrop vrints most probbly ws due to minerlistion of N from the green mnure. Topsoils were moist (pprox % of wter holding cpcity), thus enbling the decomposition of the mulch during winter. Nitrte leching my lso hve been lrger in bre fllow thn in the intercrop tretments. Nitrte contents in soil solution from cm depth were strongly reduced in intercrop vrints contining non-legumes (i.e. legumes + non-legumes nd non-legumes) compred to bre fllow (Fig. ). The legume vrint only hd minor potentil to reduce nitrte contents in soil solution. Intercrop Potto Bre fllow Winter rye Aug Oct Mr Aug Oct Apr b c 6 kg N in h cm 6-9 cm - 6 cm - cm Legend: see Fig.. Men vlues of one dte with the sme letter re not significntly different (Tukey, P <.5). Fig. : Inorgnic soil N contents during growth nd fter incorporting intercrops into the soil. Reents et l. (997) compred the effect of white clover nd mustrd intercrops on soil nitrte contents in orgnic frming (7.8 C, 8 mm, sndy to lomy soils). Mustrd reduced nitrte contents wheres white clover hd negligible effect. In ccordnce, nitrte contents were mostly lower in non-legume intercrop vrints thn with legume intercrops in the bove mentioned study of Reents und Möller (). A bre fllow tretment, however, ws not included. Soil nitrte contents fter dying off of intercrops in orgnic frming were lrger for

6 EUROSOIL, Sept. th to th, Freiburg, Germny, Conference Proceeding fb bens thn for non-legumes (Miersch nd Vetter,, SW Germny nd NO Frnce). At site with low wter holding cpcity included in this study, nitrte leching ws lower following fb ben thn bre fllow, but still lrger thn following non-legumes. In literture review, Miersch nd Vetter () lso found generl difference in N in contents before winter in the order legumes > mixtures > non-legumes used s intercrops. 5 mg NO-N L - b b b b b b b c VAR VAR VAR VAR Jn Feb Mr Apr Legend: see Fig.. Men vlues of one dte with the sme letter re not significntly different (Tukey, P <.5). Fig. : Nitrte contents in soil solution from cm depth fter incorporting intercrops into the soil. Conclusions nd outlook Non-legumes nd legumes + non-legumes showed n eqully gret reduction of N in contents in utumn nd of nitrte contents in solution from the subsoil in winter compred to blck fllow. The legume intercrop ws less effective. The mount of N minerlised during winter ws very high for ll intercrop vrints, presumbly due to unusully wet conditions in utumn. Therefore, the reducing effect of the intercrops on N in contents ws only trnsient nd did not lst until Mrch of the following yer. Soil wter blnces nd nitrte leching rtes re currently clculted to clrify the efficcy of the intercrop tretments on reducing leching losses. Totl biomss N in legumes + non-legumes exceeded the mount of crop N in non-legume intercrops due to dditionl N from biologicl N fixtion by the legumes. A higher precrop effect in terms of N cn be expected for legumes + non-legumes thn for nonlegumes. In the succeeding crop, potto, severe dmge due to Colordo beetles occurred. No yield effect of the intercrops ws found (dt not shown). In utumn the intercrop tretments will be repeted nd tested for their effect on succeeding summer brley.

7 References EUROSOIL, Sept. th to th, Freiburg, Germny, Conference Proceeding Biederbeck, V., Boumn, O., Cmpbell, C., Biley, L. und Winklemn, G. (996): Nitrogen benefits from four green-mnure legumes in drylnd cropping systems. Cndin Journl of Plnt Science, 76:, 7-5. Jensen, E. S. (989): The role of pe cultivtion in the nitrogen economy of soils nd succeeding crops. Legumes in frming systems [edited by Plncquert, P -5; ref. Dordrecht, Netherlnds; Kluwer Acdemic Publishers, Netherlnds. Miersch, M. nd Vetter, R. (): Stickstoffversorgung und -dynmik in Fruchtfolgen viehrmer Betriebe des ökologischen Lndbus. ITADA. Müllheim, Institut für umweltgerechte Lndbewirtschftung. Abschlußbericht zum Projekt A.5 des Grenzüberschreitenden Instituts zur rentblen umweltgerechten Lndbewirtschftung. Müller, T. nd Thorup-Kristensen, K. (): N-fixtion of selected green mnure plnts -- contribution to the N-turnover in soils under orgnic crop rottions. Mitt. Dtsch. Bodenkundl. Gesellsch. 95, Reents, H. J. nd Möller, D. (): Effects of different green mnure ctch crops grown fter pes on nitrte dynmics in soils nd on yield nd qulity of subsequent pottoes nd whet. Proceedings th Interntionl IFOAM Scientific Conference. T. Alföldi, W. Lockeretz, nd U. Niggli (Eds.). IFOAM, Zürich. p Reents, H. J., Möller, K., nd Midl, F. X. (997): Use of soil nitrte through differentited growing strtegies of cerels following pottoes. Köpke, U. nd Eisele, J.-A. (Eds.) Contributions to the th Scientific Meeting on Ecologicl Agriculture, p Berlin, Verlg Dr. Köster. Sorensen, N. (99): Effect of ctch crops on the content of soil minerl nitrogen before nd fter winter leching. Z. Pflnzenern. Bodenk. 55, Stülpngel, R. (98): Schätzung der von Ackerbohnen symbiotisch fixierten Stickstoffmenge im Feldversuch mit der erweiterten Differenzmethode. Zeitschrift für Acker- und Pflnzenbu 5, 6-58.