Methodological aspects of determination of biological N-fixation of different forage legumes [Methodische Aspekte der Bestimmung der biologischen N-Fixierung verschiedener Futterleguminosen]

Knowledge about the amount of fixed nitrogen of different legume crops is very important for calculation of farm N balances. According to literature the choice of determination method may have an impact on the estimated amount of N fixed by a legume sward. The aim of the study was to compare the three most important field methods for determination of nitrogen fixation under different sward management systems. In the present study the natural 15N abundance method gave lower fixation rates than the two alternative methods (total-N-difference method and 15N enrichment technique). The determination of N fixation based only on N in harvestable plant material underestimated the amount of fixed N on average by 70 kg × ha-1 compared to techniques including also the amount of N in non harvestable plant parts

Dinitrogen fixation and residue nitrogen of different managed legumes and nitrogen uptake of subsequent winter wheat [N2-Fixierung und residualer Stickstoff verschiedener Futterleguminosen sowie N-Aufnahme der Folgefrucht Winterweizen.]

Fixed nitrogen accumulated by legumes is the main nitrogen source for organic farming systems. Knowledge about the amount of fixed nitrogen, its pathways into forage yield, crop residues, soil-N and yield formation of the following crop is needed for designing crop rotations. Two field experiments were conducted in Northern Germany with differently managed (cut, mulched) legumes (red clover, alfalfa, white clover) in pure stands and various mixtures with two companion grasses (Lolium multiflorum, Lolium perenne) have been grown to determine N2-fixation, residue nitrogen and N-uptake of subsequent crops. Cropped grass/legume reached higher N2-fixation than mulched. While green manure grass/legume left up to 280 kg ha-1 of N in mulch, stubble and roots on the field, most cropped grass/legume mixtures left less than 110 kg N ha-1 in crop residues. Pure legume swards or legume rich mixtures showed higher N2-fixation than grass rich mixtures. N-uptake in late autumn and at maturity of the subsequent wheat was strongly correlated to the legume content in DM-yield

Methodological aspects of determining nitrogen fixation of different forage legumes

Knowledge about the amount of fixed nitrogen of different legume crops is very important for calculation of farm N balances. According to literature the choice of determination method may have an impact on the estimated amount of N fixed by a legume sward. The aim of the study was to compare the three most important field methods for determination of nitrogen fixation under different sward management systems. In the present study the natural 15N abundance method gave lower fixation rates than the two alternative methods (total-N-difference method and 15N enrichment technique). The determination of N fixation based only on N in harvestable plant material underestimated the amount of fixed N on average by 70 kg ha-1 compared to techniques including also the amount of N in non harvestable plant part

Yield, forage quality, residue nitrogen and nitrogen fixation of different forage legumes

Fixed nitrogen accumulated by legumes is the main nitrogen source for organic farming systems. Knowledge about the amount of fixed nitrogen, its pathways into forage yield, crop residues, soil-N and yield formation of the following crop is needed for designing crop rotations. In a field experiment conducted in Northern Germany differently managed (cut, mulched) legumes (red clover, alfalfa, white clover) in pure stands and in mixture with a companion grass (Lolium perenne) have been grown to determine Yield, forage-quality, N2-fixation and residue nitrogen. Cropped grass/legume reached higher N2-fixation than mulched. While green manure grass/legume left up to 296 kg ha-1 of N in mulch, stubble and roots on the field, most cropped grass/legume mixtures left less than 120 kg N ha-1 in crop residues. Cropped swards showed higher N2-fixation than the mulched mixtures. Swards with red clover or alfalfa reached higher legume contents and harvestable biomass than swards with white clover. Conclusions The results show that biomass production, forage yields, residue nitrogen and N fixation of grass/legume mixtures can be influenced by various combinations of legume species and management. The factors listed have to be considered carefully when planning crop rotations

The contribution of grass and clover root turnover to N leaching

Sources of inorganic and organic N leaching from grass-clover mixtures at field sites in Denmark, Germany and Iceland were investigated. Grass or clover was labelled with 15N-urea four times (autumn 2007, spring, summer and autumn 2008) prior to the leaching season in autumn and winter 2008. Soil water was sampled at 30 cm depth and analyzed for 15N-enrichment of dissolved inorganic N (DIN) and dissolved organic N (DON). Most 15N was recovered in DON for both labelled grass and clover at all sites. At the Danish site, grass and clover contributed more to the DON pool than the DIN whereas the opposite was observed at the German and Icelandic sites. The results show that both clover and grass contribute directly to N leaching from the root zone in mixtures, and that clover contribution is higher than grass. Furthermore, the present study indicates that roots active in the growth season prior to the drainage period contribute more to N leaching than roots active in the growth season the previous year, which is consistent with estimates of root longevity at the three sites

Ertrag, Futterqualität, N2-Fixierungsleistung und Vorfruchtwert von Rotklee- und Rotkleegrasbeständen

Zusammenfassung: In einem Feldversuch im Rahmen des Sonderforschungsbereiches 192 wurde in den Jahren 1994 und 1995 der Einfluß der Faktoren Klee/Gras-Saatmischungsverhältnis (Prüfglieder: 100% Rotklee, 67 % Rotklee + 33 % Gras, 33 % Rotklee + 67 % Gras, 100% Gras), Begleitgrasart (Prüfglieder: Deutsches Weidelgras, Welsches Weidelgras) und Bestandstyp (Prüfglieder: 1-jähriger Futterbau, 2-jähriger Futterbau, 1-jährige Gründüngung) auf die Parameter Ertrag, Futterqualität, N2-Fixierungsleistung sowie Menge und Zusammensetzung der Ernterückstände untersucht. Durchgeführt wurden die Untersuchungen an jeweils im August der Jahre 1993 und 1994 durch Blanksaat etablierten Klee/Gras-Beständen. Nach dem Umbruch der Klee/Gras-Bestände im Herbst 1995 wurden im Versuchsjahr 1996 Erhebungen zu ausgewählten Parametern des N-Haushaltes und der Ertragsleistung von Winterweizen in Abhängigkeit der genannten Faktoren der Klee/Gras-Periode sowie des Umbruchzeitpunktes (Prüfglieder: Früherbst, Spätherbst) durchgeführt. Die Ergebnisse lassen sich wie folgt zusammenfassen: 1. Eine Steigerung des Saatmischungsanteiles des Klees führt bei futterbaulich genutzten Klee/Gras-Beständen über zunehmende Klee-Erträge bzw. Klee-Anteile am TM-Ertrag zu deutlich zunehmenden N-Erträgen, RP-Gehalten im TM-Ertrag, N2-Fixierungsleistungen sowie Ernterückstands-N-Konzentrationen. Im folgenden Weizen zeigt sich mit steigendem Kleeanteil in der Vorfruchtsaatmischung eine steigende N-Freisetzung aus den Ernterückständen im Herbst sowie eine steigende N-Aufnahme des Weizens und eine Zunahme der Korn-RP-Gehalte. Die Parameter TM- bzw. Energieertrag, Nettoenergiegehalt des Erntegutes sowie N-Menge der Ernterückstände der futterbaulich genutzten Bestände mit Klee wie auch der Kornertrag der Nachfrucht Weizen bleiben vom Klee/Gras-Saatmischungsverhältnis weitgehend unbeeinflußt. 2. Die Klee/Gras-Bestände mit Deutschem Weidelgras als Begleitgras erzielen bei geringeren Begleitgras- und Nettoenergieerträgen, höhere Klee- und RP-Erträge, höhere RP-Gehalte im TM-Ertrag sowie höhere N2-Fixierungsleistungen als die Bestände mit Welschem Weidelgras. Auf die Ertragsleistung der Nachfrucht hat die Wahl der Begleitgrasart nur geringen Einfluß. 3. Gründüngung führt im Vergleich zu Schnittnutzung bei geringeren TM-Erträgen und N2-Fixierungsleistungen zu höheren Ernterückstands-N-Mengen. Bei höheren Klee-Erträgen erzielen die Bestände im 2. Hauptnutzungsjahr deutlich höhere Ertrags- sowie N2-Fixierungsleistungen als die Bestände im 1. Hauptnutzungsjahr. Von der Nutzungsart bzw. -dauer des Kleegrases geht nur ein geringer Effekt auf den Ertrag der Folgefrucht aus. 4. Bedingt durch die ausgeprägte Trockenheit im Herbst 1995 beeinflußt der Umbruchzeitpunkt der Klee/Gras-Bestände die Boden-N-Gehalte im Herbst nur gering. Die im Frühherbst bestellten Weizenbestände erzielen bei geringeren Korn-RP-Gehalten deutlich höhere Korn-Erträge und N-Aufnahmen als die im Spätherbst gesäten

Vergleichende Analyse der Mykotoxinproblematik im konventionellen und ökologischen Getreidebau

Contamination of grain with Mycotoxins by Fusarium spp, Aspergillus spp. and Peni¬cillium spp. is a serious problem in conventional and organic cereal production. Based on a literature survey of in total 183 German and international papers (original articles, review articles, conference abstracts and contributions to textbooks) the following agronomical factors were judged to be of major importance for a possible contamina¬tion of cereals with mycotoxins: growing conditions, choice of variety, pre crop, soil tillage intensity, use of fungicides, weed control, intensity of fertilisation and storing conditions. Due to the fact that conventional compared to organic farming in general shows narrower crop rotations with a higher number of risky pre crops as well as a higher nitrogen fertilisation in combination with the use of growth regulators and a less intensive soil tillage, the authors judge the risk of a potential contamination of cereals with mycotoxins in Germany to be lower in organic than in conventional farming

Impact of organic agriculture on diversity and abundance of farmland birds in an arable landscape with hedges

A comparative study of breeding bird communities of organically and conventionally cultivated arable fields was carried out in northern Germany in 2005. The research was conducted on 40 pairs of fields (conventional/organic), which were selected with regard to similar field sizes and comparable boundary structures (particularly presence of hedges). Bird communities were solely dominated by the skylark Alauda arvensis L., which was the only frequent species on the tested pairs of fields. Diversity of farmland birds (number of species, Shannon-Index) was not affected by type of management. However, the abundance of skylarks (territories/10 ha) was significantly higher in organic than in conventional fields. As the study will be continued, the one-year findings will be verified with respect to changes of crops in rotations