Jörg Rühlmann

Effect of mineral and organic fertilization on crop yield, nitrogen uptake, carbon and nitrogen balances, as well as soil organic carbon content and dynamics: results from 20 European long-term field experiments of the twenty-first century

Assembled results from 20 European long-term experiments (LTE), mainly from the first decade of the twenty-first century, are presented. The included LTEs from 17 sites are the responsibility of institutional members of the International Working Group of Long-term Experiments in the IUSS. Between the sites, average annual temperatures differ between 8.1 and 15.3°C, annual precipitation between 450 and 1400 mm, and soil clay contents between 3 and 31%. On average of 350 yield comparisons, combined mineral and organic fertilization resulted in a 6% yield benefit compared with mineral fertilization alone; in the case of winter wheat, the smallest effect was 3%, the largest effect, seen with potatoes, was 9%. All unfertilized treatments are depleted in soil organic carbon (SOC), varying between 0.36 and 2.06% SOC. The differences in SOC in unfertilized plots compared with the respective plots with combined mineral (NPK) and organic (10 t ha−1 farmyard manure) fertilization range between 0.11 and 0.72%, with an average of 0.3% (corresponding to ∼15 t ha−1). Consequently, the use of arable soils for carbon sequestration is limited and of low relevance and merely depleted soils can temporarily accumulate carbon up to their optimum C content.

Effects of organic amendments on soil carbon content and microbial biomass – results of the long-term box plot experiment in Grossbeeren

The Box Plot Experiment in Grossbeeren was set up in 1972 to investigate diverse fertilization strategies within an irrigated vegetable crop rotation system for three different soils. Here we report on the long-term effects of applying different organic amendments and mineral N fertilizer levels to soils on the content of: (1) microbially decomposable carbon (Cdec); and (2) microbial biomass carbon (Cmic). We determined the Cdec content of soils that were covered with a vegetable crop rotation, and established that the differences between treatments with and without organic amendments corresponded very well to those found under arable crop rotations. Under the given experimental conditions, leaving the crop residues on the field generated an optimum level of soil organic matter content. When we compared the Cdec content of the soils after applying different organic amendments as based on the C input, we found them to be similar. 10 t ha − 1 yr − 1 farmyard manure (FYM) has been reported to be sufficient to generate an optimum level of organic matter in arable soils. Here we show that this effect can also be transferable to other organic amendments if the C input is used as the reference base. Regarding Cmic content, we obtained a linear relationship for the differences of Cdec between treated plots which were influenced by different C input and the controls. This relationship did not differ with soil type. Therefore, we assumed that Cdec may be regarded as a permanently present substrate for the nutrition of microorganisms regardless of soil type.

Humus und Klimaänderung - Ergebnisse aus 15 langjährigen Dauerfeldversuchen

Zusammenfassung Die Quantifizierung des Einflusses von Klimaänderungen auf den Humusgehalt des Bodens ist von großer wirtschaftlicher und wissenschaftlicher Bedeutung. Eine Möglichkeit dieser Quantifizierung besteht in der Auswertung von Dauerfeldversuchen mit der kontinuierlichen Bestimmung des Kohlenstoff- und Stickstoffgehaltes von Böden über einen Zeitraum von mehreren Jahrzehnten unter Wahrung des Ceteris-Paribus-Prinzips. Für die vorliegende Arbeit wurden die Ergebnisse von insgesamt 15 Dauerfeldversuchen an zehn verschiedenen Standorten mit rund 150 unterschiedlichen Düngungsvarianten ausgewertet. Die Versuchsdauer lag mit einer Ausnahme zwischen 40 und 110 Jahren. Die Corg-Daten konnten nahezu lückenlos über einen Zeitraum von jeweils 20 Jahren einbezogen werden. Die Nt-Gehalte wurden in sechs Versuchen berücksichtigt. Die Ergebnisse zeigen, dass bei allen Prüfgliedern mit kombinierter organisch-mineralischer Düngung in der Größenordnung, wie sie der “guten fachlichen Praxis“ oder auch der Humusbilanzmethode entspricht, keine Verringerung der Corg-Gehalte eingetreten ist. In einigen Fällen waren signifikante Erhöhungen zu verzeichnen. In 11 von 15 Versuchen war auch ohne Düngung oder mit ausschließlicher Mineraldüngung keine Reduzierung und somit keine klimabedingte Verringerung der Humusgehalte im Untersuchungszeitraum nachweisbar. Stattdessen wurde in einigen Fällen eine signifikante Erhöhung gefunden. Auch bei den Nt-Gehalten war in keinem Fall eine signifikante Verringerung festzustellen. Umfangreiche Großzahlanalysen und Dauerfeldversuchsauswertungen anderer Autoren bestätigen uneingeschränkt die Ergebnisse.

The Box Plot Experiment in Grossbeeren after six rotations: Effect of fertilization on crop yield

Abstract The Box Plot Experiment in Grossbeeren was set up in 1972 to investigate the efficiency of diverse fertilization strategies within an irrigated vegetable crop rotation system for three soil types (silty sand, sandy loam, and clayey silt). Here we report on the long-term effects on plant yield after subjecting soils to different fertilization strategies using various organic amendments and amounts of mineral N fertilizer. We estimated that the nitrogen quantity necessary to produce 95% of the plant dry matter yield potential differed between 205, 235, and 350 kg N ha−1 year−1 for clayey silt, sandy loam and silty sand respectively. This mean long-term yield potential was estimated to be about 11.5 tons plant dry matter per hectare per year for both in our experiment with an irrigated vegetable crop rotation as well as in another experiment with an irrigated arable crop rotation in Thyrow, 15 km south of Grossbeeren. Thus, yield potential for a region appears to be highly independent of differences in soil properties and crop rotation when water and nutrient supply were optimal.

Gross N transfer rates in field soils measured by 15N-pool dilution

Abstract A micro-plot 15N-tracer experiment was established in three different soils of a long-term soil fertility field experiment. The nutrient-poor loam sand has been subjected to various treatments over the years and this has resulted in different organic C (0.35% – 0.86%), microbial biomass (38.3 – 100.0 µg C mic g−1 soil), clay and fine silt contents. Using the 15N-pool dilution technique, we assessed gross N-transfer rates in the field. Gross N mineralization rates varied strongly among the three plots and ranged between 0.4 and 4.2 µg N g−1 soil d−1. Gross nitrification rates were estimated to be between 0 and 2.1 µg N g−1 soil d−1. No correlation between gross N mineralization rates and the organic matter content of the soils was established. However, gross nitrate consumption rates increased with increasing soil C content. The 15N-pool dilution technique was successfully used to measure gross N transfer rates directly in the field.

Kalkulation der Rhizo-C-Deposition in gemüsebaulich genutzten Böden eines Dauerversuches am Standort Großbeeren

A carbon dynamics model was used to calculate the mean annual rhizo-C deposition (CRCD) of a vegetable crop rotation in a long-term experiment with soils having different textures in relation to manure application. It was observed that CRCD increased when i) the soil texture became coarser and ii) also with manure application. This may be becaused of the differences in biological activity of the different soils. Relationship of CRCD to microbial soil parameters was tested by determining the specific respiration activity. A close positive correlation between these two parameters was indicated and also the higher the substrate supply to the microbial biomass the lower their substrate utilization efficiency.

Einfluss langjährig differenzierter düngungsmassnahmen auf die schwefel- und stickstoffversorgung von sommergerste in berlin-dahlem (D) und tartu (Est)

In den IOSDV-Dauerfeldversuchen Berlin-Dahlem und Tartu wurden Schwefel- und Stickstoffgehalte in Boden und Sommergerste-Blättern bestimmt. Im Boden fanden sich an beiden Standorten in den organisch-mineralisch gedüngten Prüfgliedern die höchsten N- und S-Gehalte, aber auch die niedrigsten N/S-Verhältnisse. Am Standort Berlin ergab die Messung des N-Gehaltes in den Pflanzen die höchsten Werte in den Proben aus den Parzellen mit organischer Düngung; am Standort Tartu dagegen lagen in den Proben aus den Prüfgliedern mit mineralischer Düngung die Werte am höchsten. Die S-Gehalte in den Pflanzenproben vom Standort Berlin waren in den Prüfgliedern mit organischer Düngung höher als in den Prüfgliedern mit mineralischer Düngung. Am Standort Tartu ergab sich dagegen keine Differenzierung der S-Gehalte in den Pflanzenproben. In the IOSDV long-term field experiments at Berlin-Dahlem and Tartu the nitrogen and sulphur content of soil and spring barley leaves were determined. In the soil from both investigated sites the highest N- and S- contents as well as the smallest N/S ratios were found in samples from plots with a combination of organic manuring and mineral fertilization. In barley leaf samples from Berlin the highest nitrogen contents were measured in plants from organic manured field plots; in Tartu highest nitrogen contents were found in minerally fertilized plots. The sulphur contents in plant samples from Berlin were higher in plots with organic manuring than in plots with mineral fertilization. In contrast, no precise distinction was found in plant samples from Tartu.

Microbially-mediated gross N transfer rates in field soils in relation to physico-chemical transfer processes

Abstract Measurements of gross N transfer in soils have as yet not distinguished between biological or physico-chemical processes. Here, we present a new approach that allows microbially-mediated gross N transfer rates to be estimated in undisturbed soils without adding 15N. It is based on the assumption that in undisturbed soil, the soil microbial growth rate is equal to its death rate. To assess the contribution of biological versus physico-chemical N transfer processes, we combined the new approach with the 15N-pool dilution technique. The relationship between both processes varied with soil C and fine particle contents. Nearly equal rates were observed within the carbon-poor soil (0.35% Corg, low fine particle content), whereas up to 2.5 times higher physico-chemical than biological N transfer rates were measured within the carbon-enriched soil (0.86% Corg, higher fine particle content). Furthermore, microbially-mediated gross N transfer rates increased three-fold after N fertilization compared to the unfertilized control.

Zeitreihenanalyse der Temperaturdynamik eines Sandbodens

Die Stundenwerte der Temperatur eines Sandbodens wurden schichtweise bis zur Tiefe von 1 m mit Hilfe der Zeitreihenanalyse untersucht. Es wurden die Verzogerung des Tagesganges der Bodentemperatur gegenuber der der Lufttemperatur und die Dampfung der taglichen Amplitude der Lufttemperatur in Abhangigkeit von der Bodentiefe berechnet. Die Verzogerung des Temperaturverlaufs in Abhangigkeit von der Bodentiefe wurde durch die Krosskorrelation zwischen einzelnen Temperaturmesreihen bestimmt. Diese Abhangigkeit war linear: je 10 cm Bodenschicht wurde eine Verzogerung der Temperaturausbreitung um ca. 2 Stunden berechnet. Die Dampfung der Amplitude des Tagesganges der Temperatur wurde als Zusammenhang zwischen den “saisonalen”; Komponenten des Tagesganges der Temperatur bei “additiver Census‐1‐Decomposition”; und der Bodentiefe bestimmt. Diese Abhangigkeit war exponentiell. Ein Pflanzenbestand wirkte als ein zusatzlicher Puffer sowohl auf die Dampfung als auch auf die Verzogerung. Die ermittelten Parameter ermogl...