Organic matter returns to soils must be higher under organic compared to conventional farming

The aim of this paper is to discuss the demand of fresh organic matter (FOM) supply to maintain soil organic matter (SOM) levels and productivity of arable soils under organic management. The basic question is whether the different frame conditions in organic vs. conventional farming result in a different and system‐specific FOM demand. If this is the case, it would follow that the farming system has to be considered in the calculation of SOM balances. SOM balances are the most common decision support tools in organic matter management. A conversion to organic farming in practice usually leads to an increase of SOM levels as well as soil microbial activity over time. The system‐specific driver of this effect is the indispensable extension of the share of (perennial) legumes in crop rotations at the expense of non‐legumes such as cereals, row crops, and maize. Extended legume cropping is essential for N supply in crop rotations as the import of N fertilizer in total is limited by organic farming regulations and mineral N fertilizer may not be used at all. Based on this characteristic of organic management, we argue that the demand of FOM supply to soils must be higher than in conventional crop production. The most relevant factors are (1) the non‐existence of mineral N fertilizer as an external N source that supports the maintenance of SOM by decreasing the demand for SOM‐N, (2) benefits of increasing SOM stocks and turnover for soil productivity under organic management, and, (3) increased mass‐losses of FOM and easily degradable SOM compartments due to higher microbial activity in soils. These effects have to be quantified and must be considered in SOM balances in order to avoid misleading assessments and erroneous decisions.     

Fingerprinting the sources of suspended sediment delivery to a large municipal drinking water reservoir: Falls Lake, Neuse River, North Carolina, USA

Purpose

We employ a geochemical-fingerprinting approach to estimate the source of suspended sediments collected from tributaries entering Falls Lake, a 50-km² drinking water reservoir on the Neuse River, North Carolina, USA. Many of the major tributaries to the lake are on North Carolina’s 303(d) list for impaired streams, and in 2008, the lake was added to that list because of high values of turbidity, likely sourced from tributary streams.

Materials and methods

Suspended sediments were collected from four streams with a time-integrated sampler during high-flow events. In addition, composite sediment samples representing potential sources were collected from stream banks, forests, pastures, construction sites, dirt and paved roads, and road cuts within tributary basins. Radiocarbon dating and magnetic susceptibility measurements were used to determine the origin of stream bank alluvial deposits. Sediment samples were analyzed for the concentrations of 55 elements and two radionuclides in order to identify tracers capable of distinguishing between potential sediment sources. The relative sediment source contributions were determined by applying a Monte Carlo simulation that parameterized the geochemical tracer data in a mixing model.

Results and discussion

Radiocarbon and magnetic susceptibility measurements confirmed the presence of “legacy” sediment in the Ellerbe and New Light Creek valley bottoms. Mixing model results demonstrate that stream bank erosion is the largest contributor to the suspended sediment load in New Light Creek (62%), Ellerbe Creek (58%), and Little Lick Creek (33%), and is the second largest contributor in Lick Creek (27%) behind construction sites (43%).

Conclusions

We find that stream bank erosion is the largest nonpoint source contributor to the suspended sediment load in three of the four catchments and is therefore a significant source of turbidity in Falls Lake. The presence of legacy sediment appears to coincide with increased contributions from stream bank erosion in Ellerbe and New Light creeks. Active construction sites and timber harvesting were also significant sources of suspended sediment. Water quality mitigation efforts need to consider nonpoint-source contributions from stream bank erosion of valley bottom sediments aggraded after European settlement.     

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.     

Investigations on Heat Tolerance of Spring Wheat Varieties of Different Origin Under Growth Chamber Conditions

Winter wheat has replaced spring wheat to a large extent under the climatic conditions of Western and Central Europe. But spring wheat genotypes are still important under the warm climate in large parts of Africa and Central America, since spring wheat needs no vernalization. To reach optimal yield, genotypes must be well adapted to heat stress. In this study 11 spring wheat varieties of Egypt, Sudan, CIMMYT and Germany were exposed to high temperatures at ear emergence and beginning of anthesis. There were reductions in kernel yield and kernel number of the main ear for all genotypes, but the differences in reduction were remarkable. The German variety 'Naxos' was best adapted. Some varieties showed an increased number of florets per spikelet under heat treatment, but this does not prohibit a reduction in kernel number per spikelet.