The spatial root distribution of plant species is generally altered by infra- and interspecific competition. The assessment of species specific root distribution in intercrops was limited so far because of the difficulties to identify roots on a species level. We investigated horizontal and vertical root distribution of eight winter faba bean genotypes (Vicia faba L.) and one winter wheat cultivar (Triticum aestivum L.) grown in sole stands and in 50/50 substitutive row intercrops. Root samples were taken within and between rows with a root auger down to 60 cm soil depth in May 2015 and May 2016 at a field site in central Germany. We used Fourier transform infrared (FTIR) spectroscopy for root species identification. Vertical root distribution was described by the equation y = 1 -beta(d) according to Gale and Grigal (1987). Horizontal root distribution did not differ between bean and wheat and between sole stands and intercrops averaged across the eight bean genotypes: Bean and wheat root biomass was on average 65% lower between rows than within rows in sole stands and in intercrops. Both species proliferated into the soil space between the rows and into the intercropping partner's row to a similar extent. Bean developed 36% of its root biomass in 0-10 cm soil depth, while wheat had 51%. Bean and wheat had shallower roots within their own row in intercrops (beta(b)(ean) = 0.933 ; beta(wheat)=0.858) compared to their own row in sole stands (beta(b)(ean)= 0.945; beta(wheat)= 0.902). In the intercrops both species occupied deeper soil layers within their partner's row (beta(b)(ean)= 0.947; beta(wheat) = 0.960) compared to their own row ( beta(b)(ean)= 0.933; beta(wheat) = 0.858). This change in vertical root distribution was more pronounced for wheat than for bean. Bean genotypes grown in sole stands did not differ in their horizontal and vertical root distribution. However, there were significant differences between bean genotypes within wheat rows in the intercrops: bean genotype Vf6 had the largest horizontal spread but the most shallow root growth within the wheat row, while Vf5 showed the lowest horizontal spread and the highest root fractions in deep soil layers within the wheat row. The alteration of the vertical root distribution of both species in intercrops, compared to the sole crops, could lead to a better resource utilization and an intercrop advantage.

Background and aimsLegume-cereal mixtures are often characterized by higher biomass and grain yields compared to their sole crop equivalents due to complementary resource use. Little is known about the contribution of the root system to this overyielding potential and the related cultivar differences. This study investigated pure stands and mixtures of eight winter faba bean (Vicia faba L.) genotypes and one winter wheat cultivar (Triticum aestivum L., cv. Genius) with regard to their intra- and interspecific variation of shoot and root biomass and overyielding potential at full flowering of the bean.MethodsShoot biomass of 1m(2) was harvested and roots were sampled with a root auger down to 0.6m soil depth in two sampling years. Fourier transform infrared (FTIR) spectroscopy was successfully used to determine species specific root biomasses in mixtures. Statistics were performed using linear mixed effects models.ResultsMixtures of winter faba bean and winter wheat overyielded more below- than aboveground. Bean genotypes grown in mixtures with wheat differed significantly in their root biomass, root:shoot ratio and overyielding potential but not in their shoot biomass.ConclusionsGenotype differences in root biomass and overyielding indicate breeding potential of winter faba bean cultivars for mixed cropping.

Biochar application in combination with slurry might be an option to increase aggregate formation and organic carbon (OC) sequestration in agricultural soil. However, to assess the value of these management options for improving soil structure more precisely, naturally occurring effects of changing moisture on soil aggregation and feedbacks on organic matter (OM) decomposition need to be addressed. Therefore, we aimed to quantify the effects of biochar or slurry application on the amount of OC associated with macro‐aggregates and OM decomposition under different moisture conditions. Four silty loam sites in Germany were sampled, and the soil macro‐aggregates were crushed. We added biochar (53–250 μm) and slurry individually and in combination at two rates before incubating the samples under changing moisture conditions for 60 days. As well as monitoring CO2 fluxes, samples were analyzed for microbial biomass carbon, macro‐aggregate yields and macro‐aggregate‐associated OC. Biochar application decreased macro‐aggregate yields by 50–70%. However, the macro‐aggregate‐associated OC of treatments with biochar was similar to or greater than in treatments without, indicating biochar incorporation into these fractions. This was especially pronounced for biochar treatments with large volumes of slurry. Thus, slurry seems to promote the formation of biochar–mineral interactions. Drying and rewetting decreased macro‐aggregate yields and associated OC, being most pronounced for samples with biochar and slurry. In contrast to slurry, biochar typically did not increase macro‐aggregate formation. However, the combination with slurry could further enhance the suitability of biochar for carbon sequestration, although this might be less pronounced in soils experiencing frequent drying‐wetting cycles.

The differentiation of roots of agricultural species is desired for a deeper understanding of the belowground root interaction which helps to understand the complex interaction in intercropping and crop-weed systems. The roots can be reliably differentiated via Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR). In two replicated greenhouse experiments, six pea cultivars, five oat cultivars as well as seven maize cultivars and five barnyard grass proveniences (n = 10 plants/cultivar or provenience) were grown under controlled conditions. One root of each plant was harvested and five different root segments of each root were separated, dried and measured with FTIR-ATR spectroscopy. The results showed that, firstly, the root spectra of single pea and single oat cultivars as well as single maize and single barnyard grass cultivars/proveniences separated species-specific in cluster analyses. In the majority of cases the species separation was correct, but in a few cases, the spectra of the root tips had to be omitted to ensure the precise separation between the species. Therefore, species differentiation is possible regardless of the cultivar or provenience. Consequently, all tested cultivars of pea and oat spectra were analyzed together and separated within a cluster analysis according to their affiliated species. The same result was found in a cluster analysis with maize and barnyard grass spectra. Secondly, a cluster analysis with all species (pea, oat, maize and barnyard grass) was performed. The species split up species-specific and formed a dicotyledonous pea cluster and a monocotyledonous cluster subdivided in oat, maize and barnyard grass subclusters. Thirdly, cultivar or provenience differentiations within one species were possible in one of the two replicated experiments. But these separations were less resilient.

The field experiments were conducted in 2008, 2009 and 2010 on a Gleyic Cambisol near Goettingen, Lower Saxony, Germany. A crop sequence of summer barley, winter cover crops (intercropped oat and sunflower) and summer faba bean was examined under organic farming conditions. Emphasis was given to the studying of arable weeds in faba beans. However, enhancing symbiotic nitrogen fixation of summer faba beans by accumulation of soil-nitrogen by winter cover crops was a second objective in these experiments. The faba bean field plots had been cultivated with three different tillage systems: 1. zero tillage, sowing with cross-slottechnique, 2. conservation tillage (wing share cultivator, rotary harrow) sowing with cross-slot-technique and 3. conventional tillage with mouldboard plough followed by rotary harrow, sowing with precision monoseeder. In plots with zero tillage preceding cover crops were left as mulch on the soil surface. Cover crops accumulated adequate nitrogen amounts and following faba beans reacted with significant increase (up to 10%) in symbiotic nitrogen fixation. Maximum of arable weed biomass was observed in zero tillage-plots at the end of May or early in June. The abundance of the predominant weed wild mustard (Sinapis arvensis) increased with tillage intensity, whereas the abundance of creeping thistle (Cirsium arvense) increased in 2010 with decreasing tillage intensity. Average grain yield of faba beans was low with only 3.0 and 2.4 t ha-1 in 2009 and 2010, respectively.

Verfahren reduzierter Bodenbearbeitung bis hin zur Direktsaat gewinnen im Okologischen Landbau zunehmend an Bedeutung. Grunde hierfur sind die damit verbundenen positiven Effekte auf das Bodengefuge (Erosionsschutz) und auf den Treibstoff- und Arbeitsaufwand. Im Rahmen des Projektes wurden von drei Konsortialpartnern Feldversuche zur reduzierten Bodenbearbeitung von Kornerleguminosen (Ackerbohne, Kornererbse, Sojabohne, Schmalblattrige Lupine) auf Versuchs- und Praxisstandorten des Okologischen Landbaus in NRW, NS und SN durchgefuhrt. Schwerpunkte der Untersuchungen waren die Nahrstoffversorgung und die Unkrautregulierung. Geringe Nmin Gehalte im Boden zur Aussaat und nachfolgend geringe Mineralisation fuhrten zu hohen NdfA-Werten (80%) von Ackerbohnen. Zwischenfruchtanbau vor Korner-leguminosen fuhrte zu einer temporaren N-Immobilisierung, nicht jedoch zu hoheren NdfA-Werten. Reduzierte Bodenbearbeitung fuhrte im Vergleich zu Pflugbearbeitung wider Erwarten nicht zu hoheren NdfA-Werten. Vermutet wird ein geringerer Gasaustausch mit der Atmosphare als Folge hoherer Dichtlagerung und eines geringeren Anteils Luft fuhrender Poren nach reduzierter Bodenbearbeitung, insbesondere nach Direktsaat. Ein ertragssteigernder Effekt einer Dungung mit Schwefel wurde unabhangig von der Verabreichungs-form (elementar oder sulfatisch) bei Smin Gehalten im Boden von > 25 kg ha-1 weder bei Ackerbohnen noch bei Sojabohnen festgestellt. Eine kombinierte Dungung von Rohphosphat (Apatit) mit elementarem Schwefel fuhrte auf einem sauren Auenlehm (P-Versorgungsstufe B-C) weder zu Mehrertragen noch zu P-Mehraufnahmen von Acker- und Sojabohnen. Einige Kornerleguminosenarten, insbesondere Ackerbohnen, z.T. auch Kornererbsen, sind fur Verfahren der reduzierten Bodenbearbeitung, bedingt geeignet. Bei Problemen mit perennierenden Unkrautern, z.B. Ackerkratzdistel, ist der Verzicht auf Pflugbearbeitung jedoch nicht zu empfehlen. Reduzierte Bodenbearbeitung erhoht in der Regel deutlich das Anbaurisiko von konkurrenzschwachen Kornerleguminosenarten wie Sojabohne und Schmalblattriger Lupine. Betriebe, die dennoch auf wendende Bodenbearbeitung zu diesen Kornerleguminosenarten verzichten wollen, mussen die unkrautregulierende Wirkung des Pfluges durch umfassende ackerbauliche Masnahmen (zum Beispiel Anbau von Sorten mit hoher Konkurrenzkraft) und intensive mechanische Unkrautkontrolle kompensieren.

Im Zuge der Greening-Anforderungen der neuen Gesetzgebung der Europaischen Kommission wird der Anbau von Zwischenfruchten, einschlieslich Winterzwischenfruchten, an Bedeutung gewinnen. Es wird ein Ansatz vorgelegt, Winterzwischenfruchte zu bewerten. Aus den vielfaltigen okonomischen und okologischen Leistungen werden drei Messgrosen ausgewahlt und bewertet: (1) Stickstoffkonservierung uber Winter, (2) Methanerzeugung und (3) Wirkung auf den Ertrag des nachfolgenden Maises. Die Bewertung erfolgt anhand einfacher Teilindizes, die mathematisch so konstruiert sind, dass sie mit zunehmender Leistung der Zwischenfruchte groser werden. Abschliesend werden die drei Teilindizes durch Addition zu einem Index der relativen (IrA) zusammengefuhrt. 33 Winterzwischenfrucht-Varianten wurden in zweijahrigen Feldversuchen angebaut und die Teilidindizes berechnet. Die gunstigsten IrA-Werte erzielten Mischsaaten, das (bestehend aus Zottelwicke, Welschem Weidelgras und Inkarnatklee) und der (bestehend aus Winterroggen und Zottelwicke). Die Wintergetreidearten schnitten vergleichsweise schlecht ab. Auf der Grundlage von IrA kam den groskornigen Leguminosen, Winterackerbohnen und Wintererbsen, die geringste Anbauwurdigkeit zu. IrA ermoglicht eine Schwachstellenanalyse. So wurde fur die Winterackerbohnen bereits ein neues Anbausystem vorgestellt, das den grosten Nachteil dieser Feldfrucht, die fehlende Nmin-Absenkung uber Winter, ausgleichen kann. Die Teilindizes konnen gewichtet und damit an die Standortgegebenheiten angepasst werden. Erweiterungsmoglichkeiten von IrA waren zum Beispiel: Teilindizes fur Silierfahigkeit, Wasserbedarf und Wurzelbildung (Humuswirkung). Auch soziookonomisch ausgerichtete Teilindizes sind denkbar. Ein Teilindex ergibt sich jetzt aus der Abweichung der Leistung einer Winterzwischenfrucht vom Mittel der Leistungen aller untersuchten Winterzwischenfruchte. Es erscheint moglich, anstelle des Mittels aller gepruften Winterzwischenfruchte auch feste Zielwerte zu verwenden. Evaluation of winter cover crops preceding maize for biogas utilization In the wake of the greening requirements that are part of the new legal framework of the European Commission, the cultivation of cover crops, including winter cover crops, will gain importance. An approach is submitted to evaluate winter cover crops. From the manifold economic and ecological services of winter cover crops, three parameters are selected and evaluated: (1) nitrogen conservation during the winter, (2) methane production, and (3) preceding crop effects on maize. The evaluation is carried out using simple sub-indices mathematically designed in such a way that they are greater the better the performance of the winter cover crop is. Finally, the three sub-indices are added together to obtain the Index of relative cultivation advantage (IrA). 33 winter cover crop variants were grown in two-year field trials and the sub-indices calculated. The most favorable IrA values attained mixed stands like the Landsberger Gemenge (hairy vetch + Italian ryegrass + crimson clover) and Wickroggen (rye + hairy vetch). Winter cereals performed comparatively poorly. Based on the IrA, the large-grained legumes, winter faba beans and winter peas, had the lowest cultivation potential. IrA can be used for a weak point analysis. Thus, for the winter faba beans, a novel cropping system was already presented which is able to compensate for this field crop’s biggest disadvantage, namely its poor nitrogen uptake during the winter months. The sub-indices can be weighted and thus adapted to specific local conditions. Expansion options for IrA could be for example sub-indices for ensilability, water requirement and root growth (humus effect). Furthermore, socioeconomically-oriented sub-indices are conceivable. An individual sub-index now results from the deviation of a specific performance of a winter cover crop from the mean performance of all tested winter cover crops. It seems possible to use fixed target values instead of the mean performance of all tested winter cover crops. Evaluation des cultures derobees d’hiver precedant le mais pour l‘utilisation du biogaz Suite aux exigences formulees en matiere de greening dans le cadre de la nouvelle legislation de la Commission Europeenne, la mise en place des cultures derobees d’hiver revetira une importance croissante. Une approche sera presentee pour l‘evaluation des cultures derobees d’hiver. Partant des nombreuses prestations economiques et ecologiques, on selectionne et l’on evalue trois parametres : (1) le potentiel de conservation de l’azote durant l’hiver, (2) la production de methane et (3) l’effet exerce sur la recolte du mais qui suit. L’evaluation s’effectue a l’aide de simples sous-indices mathematiquement etablis, de telle sorte que la grandeur des cultures derobees augmente en fonction de la croissance des performances. Finalement, on additionne les trois sous-indices pour obtenir un index de l’avantage relatif (IrA) pour l’implantation des cultures derobees d’hiver. 33 varietes de cultures derobees d’hiver ont ete implantees pendant deux ans en procedant a des essais en champ et l’on a calcule les sous-indices. Les valeurs IrA les plus favorables ont ete realisees pour des melanges tels que le Landsberger Gemenge (vesce velue + ray grass + trefle incarnat) et la vesce melangee au seigle (seigle d’hiver + vesce velue). Les varietes de cereales hivernales n’ont pas donne par comparaison de resultats satisfaisants. Sur la base de l’IrA, la culture des legumineuses a gros grains, celle des vicia faba et des pois d’hiver ne presentent qu’un interet tres minime. L’IrA permet de faire l’analyse des points faibles. Ainsi un nouveau systeme de mise en culture des vicia faba a deja ete presente qui est capable de compenser, le plus grand desavantage de cette culture, c’est-a-dire la faible reduction d’azote mineral pendant les mois d’hiver. Les sous-indices peuvent etre ponderes et ainsi adaptes aux conditions locales. Les options d’extension de l’IrA seraient par exemple : les sous-indices pour ce qui concerne l’ensilage, les besoins en eau, et la croissance de racines (effet humus). De plus, des sous-indices d’orientation socio-economique sont imaginables. Un sous-indice resulte a present de la deviation de la performance specifique d’une culture derobee hivernale par rapport a la moyenne des performances de toutes ces cultures derobees hivernales testees. Il est probable qu’au lieu des performances moyennes de toutes les cultures derobees hivernales, des valeurs cibles fixes peuvent aussi etre utilisees.

Root discrimination of species is a pre-condition for studying belowground competition processes between crop and weed species. In this experiment, we tested Fourier transform mid-infrared (FT MIR)-attenuated total reflection (ATR) spectroscopy to discriminate roots of closely related crop and weed species grown in the greenhouse: maize/barnyard grass, barley/wild oat, wheat/blackgrass (Poaceae), and sugar beet/common lambsquarters (Chenopodiaceae). Fresh (moist) and dried root segments as well as ground roots were analyzed by FT MIR-ATR spectroscopy. Root absorption spectra showed species specific peak distribution and peak height. A clear separation according to species was not possible with fresh root segments. Dried root segments (including root basis, middle section, and root tip) of maize/barnyard grass and sugar beet/common lambsquarters formed completely separated species clusters. Wheat and blackgrass separated in species specific clusters when root tips were removed from cluster analysis. A clear separation of dried root segments according to species was not possible in the case of barley and wild oat. Cluster analyses of ground roots revealed a 100% separation of all tested crop and weed species combinations. Spectra grouped in Poaceae and Chenopodiaceae clusters. Within the Poaceae cluster, C3 and C4 species differed significantly in heterogeneity. Thus, root spectra reflected the degree of kinship. To quantify species proportion in root mixtures, a two- and a three-species model for species quantification in root mixtures of maize, barnyard grass, and wild oat was calculated. The models showed low standard errors of prediction (RMSEP) and high residual predictive deviation values in an external test set validation. Hence, FT MIR-ATR spectroscopy seems to be a promising tool for root research even between closely related plant species.

In the wake of the "greening" requirements that are part of the new legal framework of the European Commission, the cultivation of cover crops, including winter cover crops, will gain importance. An approach is submitted to evaluate winter cover crops. From the manifold economic and ecological services of winter cover crops, three parameters are selected and evaluated: (1) nitrogen conservation during the winter, (2) methane production, and (3) preceding crop effects on maize. The evaluation is carried out using simple sub-indices mathematically designed in such a way that they are greater the better the performance of the winter cover crop is. Finally, the three sub-indices are added together to obtain the "Index of relative cultivation advantage" (IrA).33 winter cover crop variants were grown in two-year field trials and the sub-indices calculated. The most favorable IrA values attained mixed stands like the "Landsberger Gemenge" (hairy vetch + Italian ryegrass + crimson clover) and "Wickroggen" (rye + hairy vetch). Winter cereals performed comparatively poorly. Based on the IrA, the large-grained legumes, winter faba beans and winter peas, had the lowest cultivation potential.IrA can be used for a weak point analysis. Thus, for the winter faba beans, a novel cropping system was already presented which is able to compensate for this field crop's biggest disadvantage, namely its poor nitrogen uptake during the winter months.The sub-indices can be weighted and thus adapted to specific local conditions. Expansion options for IrA could be for example sub-indices for ensilability, water requirement and root growth (humus effect). Furthermore, socioeconomically-oriented sub-indices are conceivable. An individual sub-index now results from the deviation of a specific performance of a winter cover crop from the mean performance of all tested winter cover crops. It seems possible to use fixed target values instead of the mean performance of all tested winter cover crops.

The objectives of the study were to quantify the effects of 40 years of conventional tillage (CT) and reduced tillage (RT, maximum tillage depth of 8 cm) on C and N dynamics in the surface (0–5 cm) and subsurface (5–25, 25–40 cm) soils of a silty Luvisol in a long-term trial at Garte Süd, Germany (temperate climate). Stocks of C and N and contents of microbial biomass C and N were significantly higher in the surface soil of the RT treatment than in the CT treatment. However, over the entire profile (0–40 cm), C and N stocks did not differ significantly. Cumulative net N mineralization (determined in a laboratory incubation at 13.7°C and 60% water holding capacity) was significantly higher in the surface soil of RT (58.6 mg kg−1) than that of CT (26.7 mg kg−1), whereas in the subsurface soil depths, cumulative N mineralization was higher in the CT treatment. By contrast, gross N mineralization rates did not generally differ significantly between the treatments. Overall, different tillage intensities affected C and N dynamics only slightly in the entire profile because increases in C and N stocks and N mineralization rates in the surface soil of RT were counterbalanced at greater depths.

Cultivation of maize is more demanding in organic than conventional farming. However, an increasing interest in this cultivation is noticeable. Weed regrowth is a key problem in organic maize cultivation. Therefore, an agronomy subproject of the main project ‘Breeding of maize cultivars for Organic Farming' aims at identifying a combination of maize genotype and undersown crop, which is highly effective in terms of weed suppression and maize grain yield.

Crop and weed species often compete for the same resources. To analyse below-ground competitive processes, crop and weed roots have to be distinguished from one another. Up to now, a reliable and easy method for plant root discrimination does not exist. In a recent study, Fourier transform infrared (FTIR) spectroscopy with an attenuated total reflection (ATR) device was successfully applied in root discrimination of distantly related plant species (pea/oat). In this experiment, we wanted to test the potential of FTIR-ATR spectroscopy to discriminate roots of closely related crop/weed-combinations. In a greenhouse experiment, two crop and associated weed species were cultivated: Maize/barnyard grass (Zea mays/Echinochloa crus-galli) and sugar beet/common lambsquarters (Beta vulgaris/Chenopodium album). To allow inter- and intra-specific competition, plants were grown sole and in crop/weed-combinations. Six weeks after sowing, root biomass was harvested and rinsed with water to remove soil particles. The absorbance patterns of fresh and dry rootlets were recorded by FTIRATR spectroscopy. Spectra of fresh rootlets within one plant family showed similar peak distribution, while dry rootles differ in peak location and height. Cluster analyses grouped the absorbance patterns of the dry crop and weed roots according to their similarity and revealed a complete root discrimination of crop and weed species.

In a long-term tillage experiment comparing mouldboard plough and rotary harrow since 1967, litterbags with green maize residues and wheat straw were buried, recovered from soil and analysed for biochemical degradation indices. Our objective was to investigate whether lignin units and neutral and amino sugars give information on microbial degradation after burial periods of 6 and 12months at two different depths (0–5 and 15–20cm). Tillage and burial depth had no effects on the content and composition of lignin. In contrast, the extended burial period resulted in higher acid/aldehyde ratios of vanillyl units, due to increasing microbial oxidation, and in higher ratios of cinnamyl/vanillyl units, due to the higher resistance of vanillyl units against microbial degradation. The contents of mannose, bacterial muramic acid, and fungal glucosamine were significantly higher in the plough than in the harrow treatment, due to a higher microbial colonisation. For the same reason, the extended burial period led to significant increases in the contents of mannose, glucosamine, muramic acid, and galactosamine as well as in the GM/AX ((galactose+mannose)/(arabinose+xylose)) ratio. The decline in the fungal C/bacterial C ratio indicated that bacterial colonisation of litter followed fungal colonisation with delay. A greater burial depth led to a lower microbial colonisation and consequently had contrasting effects to those of a longer burial period. Treatment effects on maize residues and wheat straw were generally similar, despite the strong differences in composition. The combination of litterbags and biochemical degradation indices gave further evidence that lower tillage intensity reduces microbial turnover and decomposition activity.

A litterbag experiment was carried out in a tillage trial near Gottingen, Germany, comparing the long-term effects of mouldboard plough and rotary harrow on organic matter dynamics. The aim was to investigate the C loss and N balances in litterbags filled with N-poor, lignin-rich wheat straw and N-rich, lignin-poor maize residues, simulating the properties of green manures. The litterbags were buried at 0-5 and 15-20 cm depth and one fourth of them were removed after 3, 6, 9, and 12 months, respectively. The C loss rates, corrected for soil input into the litterbags, were significantly affected by tillage and bury depth and showed significant litter material x bury depth interactions. These were caused by generally higher C loss rates in the plough treatment, especially at 15-20 cm depth, and in the litterbags with maize residues. More soil was transferred to the litterbags in the plough treatment than in the rotary harrow treatment and more soil was found in the litterbags at 0-5 cm than at 15-20 cm depth. A smaller amount of stable aggregates in the surrounding soil is the most plausible explanation for this higher soil input. Nearly 40% of maize residue C was lost in the first three months from November to February, followed by a further exponentially decreasing loss of 40% over the next 9 months. Almost no wheat straw C was lost in the first three months, followed by a nearly linear loss of 60% over the next 9 months. The N balance showed strong N losses in the litterbags with maize residues for all exposure periods. In contrast, the N balance was always positive for wheat straw. The N balances, corrected for soil input, revealed significant bury depth effects and exposure period x bury depth interactions, but no significant tillage effects. (C) 2011 Elsevier Masson SAS. All rights reserved.

Differences in the mechanisms of storage and decomposition of organic matter (OM) between minimum tillage (MT) and conventional tillage (CT) are generally attributed to differences in the physical impact through tillage, but less is known about the effects of residue location. We conducted an incubation experiment at a water content of 60% of the maximum water-holding capacity and 15°C with soils from CT (0–25 cm tillage depth) and MT fields (0–5 cm tillage depth) with 15N-labeled maize straw incorporated to different depths (CT simulations: 0–15 cm; MT simulations: 0–5 cm) for 28 d in order to determine the effects of the tillage simulation on (1) mineralization of recently added residues, (2) the dynamics of macroaggregate formation and physical protection of OM, and (3) the partitioning of maize-derived C and N within soil OM fractions. The MT simulations showed lower relative C losses, and the amount of maize-C mineralized after 28 d of incubation was slightly but significantly lower in the MT simulations with maize added (MTmaize) than in the respective CT (CTmaize) simulations. The formation of new water-stable macroaggregates occurred during the phase of the highest microbial activity, with a maximum peak 8 d after the start of incubation. The newly formed macroaggregates were an important location for the short-term stabilization of C and N with a higher importance for MTmaize than for CTmaize simulations. In conclusion, our results suggest that a higher amount of OM in MT surface soils compared with CT surface soils may not only result from decreased macroaggregate destruction under reduced tillage but also from a higher efficiency of C retention due to a more concentrated residue input.

The study of sustainable land use is complex and long-term experiments are required for a better understanding of the processes of carbon stabilization. Objectives were (i) to describe for four long-term experiments the effects of fertilization and soil management on crop yields and the dynamics of soil organic carbon (SOC) and total N, and (ii) to discuss the usefulness of models for a better understanding of the underlying processes. Data of soil organic carbon and total N of four long-term experiments in Germany and China which studied the effect of fertilization (Bad Lauchstädt, Darmstadt) and tillage (Göttingen, Quzhou) were evaluated and soil organic carbon fractionation was carried out. The Rothamsted Carbon Model was used for a description and prediction of soil organic carbon dynamics as affected by fertilization and tillage in Bad Lauchstädt and Quzhou. The type of fertilizer added at common rates — either mineral N or farmyard manure — affected the crop yields only slightly, with slightly lower yields after manure application compared with mineral N fertilization. For both fertilization trials, manure applications at common rates had beneficial effects on soil organic carbon stocks in the labile pool (turnover time estimated as <10 years) and to a greater extent in the intermediate pool (turnover time estimated to be in the range of 10 to 100 years). A comparison of the effects of conventional tillage, reduced tillage and no-tillage carried out in Göttingen and Quzhou indicated only small differences in crop yields. Reduced tillage in Göttingen resulted in an increased C storage in the surface soil and C was mainly located in the mineral-associated organic matter fraction and in water-stable macro-aggregates (>0.25 mm). For Quzhou, no-tillage and conventional tillage had similar effects on total C stocks, with a greater spatial variability in soil organic carbon stocks in the no-tillage plots. Modeling required site-specific calibrations for the stock of inert organic matter for each of the sites, indicating that not all carbon stabilization processes are included in the model and that application of a model to a new site may also need site-specific adjustments before it can be used for predictions. After site-specific calibration, however, model predictions for the remaining treatments were generally accurate for the fertilization and tillage trials, which emphasizes the importance of temperature, moisture, soil cover and clay content on the decomposition dynamics of soil organic carbon and the significance of amounts and quality of carbon inputs in the soil for maintaining or increasing soil organic carbon stocks in arable soils.