Günter Leithold

Growth, composition, biological N2 fixation and nutrient uptake of a leguminous cover crop mixture and the effect of their removal on field nitrogen balances and nitrate leaching risk

Cover crops (CC) are an important source of nitrogen (N) in organic farming systems. Only few data are available about the effect of management activities (liquid slurry amendments, crop residue management) on growth, nutrient uptake and biological N2 fixation (BNF) of a CC mixture. Furthermore, little information is available about the effect of CC harvesting on nutrient flows, nitrate leaching risk and soil mineral N supply of the succeeding main crop. The objectives of the presented field trials were (1) to measure the impact of organic manuring (straw residues and liquid slurry applications) on growth, composition, and BNF of a CC mixture with legumes and oil radish as components; (2) to determine the effect of CC species composition on nutrient content and uptake (N, P, K, Mg); and (3) to evaluate the effect of CC removal on field N balances and nitrate leaching risk. A CC mixture with legumes and non-legumes was able to compensate for many environmental and cultivation effects by influencing the competitive ability of the partners. For example, an increase of soil N supply due to additions of slurry or removal of cereal straw promoted growth of non-legumes at the expense of the legumes, resulting in N shortage at the end of the growing period, as shown by lower N contents and a wider C/N ratio of the non-legume partner. Low N availability at the beginning of the CC growth enhanced legume growth and/or reduced non-legume growth, resulting in a higher N supply in later periods of CC growth. A high legume percent composition within a CC mixture increases overall N content in the aboveground biomass and the N content of non-legumes within the mixture, and decreases the C/N ratio. Large amounts of nutrients were removed from the field by the harvesting of the CC aboveground biomass, significantly reducing the nitrate leaching risk. However, a reduction of the nitrate leaching risk was found only on fields where the green manure was incorporated in autumn.

The humus balance model (HU-MOD): a simple tool for the assessment of management change impact on soil organic matter levels in arable soils

With this paper we present a simple model for the assessment of management impact in arable farming systems on soil organic matter (SOM) levels. The humus balance model (HU-MOD) is designed for application by farmers and extension workers in practice as a tool for management support. To enable practice applicability, HU-MOD bypasses the need for data on soil parameters and can be run with simple management data. HU-MOD is based on a simplified model on carbon and nitrogen pools and fluxes in the soil–plant system. The model proved to be an applicable simple tool for the comparison of management systems in arable farming with regard to the impact on SOM levels. Even though an absolute quantification of SOM level changes is not possible due to the methodical approach bypassing the need for any data on soil parameters, the model may be used to assess a positive or negative impact of a management system or management period compared to a reference and thus may be used to assess the impact of management changes, or to analyse a specific impact for different management periods on a defined spatial unit.

Development of soil organic matter stocks under different farm types and tillage systems in the Organic Arable Farming Experiment Gladbacherhof

In 1998, the Organic Arable Farming Experiment Gladbacherhof (OAFEG) was started in order to explore the impact of different organic arable production systems (mixed farming, stockless farming with rotational ley, stockless cash crop farming) and of different tillage intensities (conventional plough as a full inversion tillage, two-layer plough, inversion tillage at reduced depth, non-inversion tillage) on sustainability parameters. In this article, we present results on the development of soil organic matter (SOM) levels. Starting with organic mixed farming with approximately 0.7 livestock units (LU) per ha cattle before set-up of the experiment, only the mixed farming system in the experiment was able to maintain SOM levels. The stockless system with ley maintained soil organic carbon (SOC), but lost soil total nitrogen (STN), and the stockless cash crop system had a significant SOM loss in the magnitude of 7.7 t SOM ha−1, or roughly 8.4% of the initial SOM mass. Reducing tillage intensity had no impact on SOM masses, but only on organic matter stratification in soils. We conclude that specialization of organic farms towards stockless arable crop production requires special attention on SOM reproduction to avoid detrimental effects. Further, reduced tillage intensity does not necessarily have a positive effect on SOM.

Soil organic matter balances in organic versus conventional farming—modelling in field experiments and regional upscaling for cropland in Germany

The question of whether organic farming leads to higher soil organic matter (SOM) levels in arable soils compared with conventional farming is an ongoing debate. Building on several studies reported in the literature, we hypothesize that the impact on SOM levels is not an intrinsic characteristic of any farming system but is the result of the actual structure of the farming system, in particular, the composition and management of crop rotations, and the availability and utilization of organic manure. The SOM balances for organic versus conventional farming in Germany are compared by considering data on the structure of organic and conventional farming systems from agricultural census reports and then applying the SOM balance model HU-MOD. Preliminary testing confirmed the applicability of the model using a survey on soil organic carbon (SOC) change and SOM balances in four long-term field experiments in Germany and Switzerland and found that more positive SOM balances coincided with higher SOC levels. We therefore conclude that, where the SOM supply level of organic farming systems is higher than in conventional management, a shift from conventional to organic agriculture would increase SOM levels. Upscaling using agricultural census data in Germany, we found that SOM balances of organic farming were more positive than for conventional farming in the scenarios without consideration of animal manure application, but SOM balances for the two systems were not different where animal manure application rates were assumed to be at the current average rate for all cropped land. However, in fact, animal manure availability and application shows strong regional variations, and it is likely that this would affect the mean cropland SOM balance if it were possible to calculate it based on such spatially disaggregated data. We confirm the applicability of simple SOM balance models to compare the impact of farming systems and cropland structures on SOC levels. More work is needed to develop data inputs at a sufficient spatial and structural resolution to support more detailed evaluation.

Biogas Energy From Agricultural By-Products: Energy Yields and Effects on Organic Farming Systems Compared with Energy Maize Cropping

Organic farming systems produce large amounts of organic residues suitable for biogas production. Two organic farming systems were investigated in field trials. In the dairy production system liquid manure, fodder residues, straw and cover crops were fermented. In the tested stockless farming system clover grass, straw, cover crops and in this case non marketable potatoes were used. The biogas yield potential of the stockless farming system averaged 1,742 cubic meters of methane per hectare and year, respectively 1,015 cubic meters in the tested dairy farm system. The utilisation of crop residues can replace (non-organiv) maize cropping on more than 27% of the farmland without using extra land in the stockless farming system. In the investigated dairy system, these residues correspond to approximately 16% of the farmland used for maize cropping. The energy yields and additional positive effects (higher dry matter yields of non-legume maincrops, lower nitrogen losses and a reduction of trace gas emissions) can promote the use of crop residues for digestion and the implementation of biogas plants in organically managed farms. There are some technical and economical problems regarding the implementation of the recommended systems, but the solution of these problems seems to be very profitable.

Das Anbauverfahren Weite Reihe für Winterweizen im ökologischen Landbau: Möglichkeiten zur Verbesserung der Backqualität unter stickstofflimitierten Bedingungen The cultivation method wide row spacing for winter wheat in organic farming: its possibilities to improve the baking quality in nitrogen-limiting conditions

Die Erzeugung von Winterweizen mit hoher Backqualität ist im ökologischen Landbau eine besondere Herausforderung. Die übliche Anbauweise mit Reihenabständen von ca. 12 cm führt häufig nicht zu dem gewünschten Erfolg. Berichtet wird über Ergebnisse von Feldversuchen auf vier Praxisstandorten in Deutschland. Es galt, unter Berücksichtigung verschiedener Standortbedingungen ein verbessertes und praxistaugliches Verfahren zu entwickeln, mit dessen Hilfe ohne wesentliche Ertragseinbußen mit größerer Sicherheit eine bessere Backqualität erzielt werden kann. Die Ergebnisse zeigen die Möglichkeit, Winterweizen erfolgreich mit Reihenabständen von 50 cm anzubauen. Allerdings sind insbesondere in ertragreichen Jahren Mindererträge bis zu ca. 10% nicht ausgeschlossen. Die gemessenen indirekten Indikatoren der Backqualität Rohproteingehalt, Feuchtklebergehalt und Sedimentationswert nach Zeleny wurden durch die Ausdehnung der Reihenweite signifikant verbessert. Die Aussaat legumer Untersaaten im zeitigen Frühjahr in die Reihenzwischenräume dient zur Abminderung der Erosionsdisposition und zur Verbesserung des Vorfruchtwertes. Das Mulchen der Aufwüchse in den Reihenzwischenräumen mit Hilfe eines speziell entwickelten Reihenmulchgerätes verhindert Konkurrenzbeziehungen zwischen Hauptfrucht und Untersaat ausreichend. The production of high baking-quality winter wheat in organic farming is a particular challenge. The usual cultivating procedure, involving row distances of c. 12 cm, does not normally lead to the desired results. This report concerns the conclusions of field trials from four German farm locations. Under consideration of different site conditions an improved and applicable technique should be developed, with whose help a better baking-quality could almost certainly be achieved. This should be attained without significant yield losses. The findings indicate the possibility of cultivating winter wheat with row distances of 50 cm. Although, especially in high-yield years, a possible yield deficit of up to 10% must be taken into account. The measured indirect indicators of baking quality crude-protein content, wet-gluten content and Zeleny-sedimentation value were significantly improved by the widening of distances between rows. The sowing of legume undersown crops, in early spring, into the spaces between rows leads to a reduction of water-erosion disposition and an enhancement of preceding crop value. The mulching of growth in the spaces between rows with the help of a specially developed row mulching machine sufficiently prevents competition between main crop and cover crop.