Improved N transfer by growing catch crops – a challenge

Diese Literaturübersicht in Kombination mit unveröffentlichten Daten zeigt verschiedene Verlustursachen von Stickstoff (N) aus ackerbaulich genutzten Böden auf und diskutiert, inwieweit der Anbau von Zwischenfrüchten helfen kann, N-Verluste aus dem System Boden-Pflanze zu vermindern. Der Pool an Nitratstickstoff im Boden im Herbst kann als Ausgangspunkt für verschiedene Verlustpfade von N (gasförmige Verluste, Auswaschung) aus dem System Boden-Pflanze angesehen werden. Eine Verkleinerung des Bodennitratpools verringert die Verlust­risiken und die damit verbundene Belastung der Umwelt. Der Input zum Nitratpool kann durch eine optimierte N-Düngung der Vorfrucht und eine damit einhergehende Reduzierung der N-Überschüsse vermindert werden. Zudem kann eine reduzierte Bodenbearbeitung einer verstärkten N-Freisetzung nach der Ernte der Vorfrucht entgegenwirken. Zwischenfrüchte und teilweise auch Hauptfrüchte können bereits vor Winter erhebliche N-Mengen in ihrer Biomasse akkumulieren und somit vor einer Verlagerung in tiefere Bodenschichten bewahren. Voraussetzung für eine nachhaltige Verbesserung der N-Ausnutzung ist jedoch, dass der aus den Residuen der Zwischenfrucht freiwerdende Stickstoff von der/den nachfolgenden Hauptfrucht/-früchten für ihre Ertragsbildung genutzt wird; andernfalls wird das Problem nur um ein Jahr verschoben. Da Umfang und Zeitpunkt der N-Mineralisation unter anderem von der N-Menge im Zwischenfruchtbestand, dem C:N-Verhältnis der Residuen, Einarbeitungstermin der Residuen und der nachfolgenden Witterung abhängt, ist eine präzise Voraussage des N-Transfers in die Folgefrucht schwierig. Darüber hinaus muss bei der Wahl der geeigneten Zwischenfrucht (-mischungen) darauf geachtet werden, dass keine Schad­erreger vermehrt werden, die auch die Nach­früchte infizieren können.Based on the literature amended by some unpublished data and data compilations from the literature, this review identifies the mechanisms of nitrogen (N) losses from arable land and explores the potential of growing catch crops to mitigate N loss risks from the soil-plant system. The nitrate pool in the soil can be regarded as starting point of most of the N losses via gaseous losses and/or leaching from the soil-plant system. Depleting this pool, especially in autumn, lowers the risk of losses and related impairments of the environment. The input into the nitrate pool can be reduced by adjusting the N fertilization to the N demand of the preceding crop, thus decreasing the N surplus. Less intensive soil tillage after the harvest of the preceding crop may lessen N release from the soil organic matter and the crop residues. On the other hand, cover or catch crops and, to a lesser extent, main crops can take up considerable N amounts in autumn and prevent it from being lost. However, in order to reduce N fertilization of the subsequent crop due to an improved N transfer, the big challenge is to harmonize the N demand of the subsequent main crop and the N release from the catch crop residues. Since the latter depends on several factors like accumulated N amount, C:N ratio of the residues, incorporation date and weather conditions, it can hardly be estimated. Another crucial point is the choice of a suitable cover crop because it should not propagate pests or diseases of the main crops

Multiscale Change-Point Inference

We introduce a new estimator SMUCE (simultaneous multiscale change-point estimator) for the change-point problem in exponential family regression. An unknown step function is estimated by minimizing the number of change-points over the acceptance region of a multiscale test at a level \alpha. The probability of overestimating the true number of change-points K is controlled by the asymptotic null distribution of the multiscale test statistic. Further, we derive exponential bounds for the probability of underestimating K. By balancing these quantities, \alpha will be chosen such that the probability of correctly estimating K is maximized. All results are even non-asymptotic for the normal case. Based on the aforementioned bounds, we construct asymptotically honest confidence sets for the unknown step function and its change-points. At the same time, we obtain exponential bounds for estimating the change-point locations which for example yield the minimax rate O(1/n) up to a log term. Finally, SMUCE asymptotically achieves the optimal detection rate of vanishing signals. We illustrate how dynamic programming techniques can be employed for efficient computation of estimators and confidence regions. The performance of the proposed multiscale approach is illustrated by simulations and in two cutting-edge applications from genetic engineering and photoemission spectroscopy

Yield trend of winter wheat with varying N fertilization

Dauerversuche können helfen, langfristige Entwicklungen zu identifizieren und zu quantifizieren. In einem Stickstoff-(N)-Steigerungsversuch, der seit 1974 auf dem Versuchsgut Hohenschulen im Östlichen Hügelland Schleswig-Holsteins durchgeführt wird, wurde Winterweizen zu den 3 Terminen Vegetationsbeginn, Schossbeginn EC 30 und Ährenschieben EC 50/51 mit jeweils 0, 40, 80 und 120 kg N ha–1 in allen Kombinationen gedüngt (4*4*4 = 64 N-Varianten, 0–360 kg N ha–1), um ex post das jahresspezifische N-Optimum abschätzen zu können. Die Sorte Diplomat wurde als Standardsorte durchgehend von Versuchsbeginn bis 2002 angebaut, während als zweite, jeweils neuere Sorte Kanzler (1983–1991), Orestis (1992–1995), Ritmo (1996–2004) und Tommi (ab 2005) geprüft wurden. Aus den jahres- und sortenspezifischen Ertragsfunktionen (basierend auf einem quadratischen Ansatz mit der N-Gesamtmenge) wurden der Ertrag in der ungedüngten Variante, die optimale N-Düngung und der entsprechende optimale Ertrag abgeleitet. Daraufhin wurde durch lineare Regression geprüft, ob Ertrags­trends vorlagen. Der Ertrag in der ungedüngten Kontrolle veränderte sich im Zeitablauf nicht signifikant. Dem­gegenüber stieg der Ertrag bei optimaler N-Düngung bei allen Sorten um 0,63 dt ha–1 a–1, allerdings auf unterschiedlichem absoluten Niveau, signifikant während der Versuchsdauer an, wobei sich jedoch die Höhe der optimalen N-Düngung nicht veränderte. Mit steigenden Erträgen sank die Rohproteinkonzentration. Ein statistisch absicherbarer Zusammenhang zwischen der jahresspezifisch optimalen N-Düngermenge und dem entsprechenden Ertragsniveau konnte nicht beobachtet werden. Als mögliche Ursachen für die steigenden Erträge bei opti­maler N-Düngung werden Veränderungen der Produk­tionstechnik, der Jahrestemperatur oder der CO2-Konzentration der Atmosphäre diskutiert.    Long-term field experiments allow identifying and quantifying trends. A field trial was set up in 1974 at the Hohenschulen Experimental Farm in Schleswig-Holstein (Northern Germany) to test different nitrogen (N) treatments in wheat. N fertilization varied in timing and total amount. 0, 40, 80 or 120 kg N ha–1 were applied each at the beginning of spring growth, at stem elongation (GS 30) and at ear emergence (GS 50/51) in any possible combination resulting in 64 (4*4*4) N treatments ranging from 0 to 320 kg N ha–1. The cultivar Diplomat was grown from the trial set up until 2002, whereas Kanzler (1983–1991), Orestis (1992–1995), Ritmo (1996–2004) und Tommi (since 2005) were parallelly tested as newer genotypes. Yield in the unfertilized control, optimal N amount and the respective grain yield were estimated from the year and genotype specific N response curves (quadratic polynomial function based on the total N amount). Linear regression was used to test for trends in these coefficients. Grain yield without N fertilization showed no trend. However, yield of the optimal fertilized treatment increased by 0.063 t ha–1 a–1. Yield trend was similar in all varieties, but at different levels indicating genetic improvements. In contrast, the optimal N amount was not affected. Grain protein concentration correlated negatively with the yield level, whereas only a poor relationship between optimal N amount and the respective yield occurred. As causes for the trend in the optimal yield changes in crop management, average mean temperature or CO2 concentration in the atmosphere are discussed.   &nbsp

N-Umsatz und Spurengasemissionen typischer Biomassefruchtfolgen zur Biogaserzeugung in Norddeutschland

Im Rahmen des Verbundprojektes Biogas-Expert an der CAU-Kiel wurden an zwei Standorten Schleswig-Holsteins veschiedene Fruchtfolgen zur Bereitstellung von Biogassubstraten unter Verwendung von Biogasgüllen als N-Dünger durchgeführt. Maismonokultur wies die höchsten Trockenmasseerträge auf, wobei keine signifikanten Unterschiede in den Erträgen zwischen Biogasgärresten, organischen N-Düngern und mineralischen Düngern ermittelt wurden. Während in Bezug auf die N-Düngeform bei N2O- und Nitratauswaschungsverlusten kein Einfluss der N-Form auf die Höhe der Verluste festgestellt wurde, war die Düngung mit Biogasgüllen mit signifikant erhöhten NH3-Verlusten verknüpft. Eine abschließende Bewertung der Produktionssysteme ist erst durch Analyse der experimentellen Ergebnisse mit einem Systemmodell möglich

Efficient N management using winter oilseed rape. A review

During the last decades the acreage of winter oilseed rape has been increased considerably in Europe. Rapeseed can take up a large amount of nitrogen before winter (> 100 kg N/ha) and thus prevent nitrate leaching and pollution. Winter wheat is often grown subsequently, using oilseed rape as a favorable preceding crop. However, under wheat large nitrogen losses via leaching are frequently observed in humid climates during winter, mainly due to high amounts of soil mineral N available in fall and the small N uptake in fall of wheat as a subsequent crop. The low N offtake by the seeds results in a lower N-use efficiency and increases the N surpluses (>90 kg N/ha) compared with winter wheat (c. 40 kg N/ha). In addition, a large soil N pool increases the risk of N2O emission, with its impact on climate change. In our review we discuss several options to increase nitrogen-use efficiency in oilseed rape-based cropping systems ranging from optimizing N fertilization practices to options arising from adopted tillage practices and crop rotation. N application in fall normally increases dry matter accumulation and N uptake before winter. However, because of its limited yield effects in most situations, fall N supply also boosts N surpluses. N fertilization in spring exceeding the need of the crop for optimal seed yield increases the risk of N leaching and decreases the farmer’s net revenue. Considering the amount of N taken up by the canopy before the first spring application improves the determination of the optimal spring N supply. Measuring canopy N in fall gave the best results. At the cropping system level, time and intensity of soil tillage after the harvest of oilseed rape has concurrent goals of controlling volunteer rape, and achieving a successful establishment of the following crop, but avoiding an increased N mineralization. Changing the crop rotation by growing catch crops which prevent N from leaching is very effective in reducing N losses from the system by > 40%. However, the economic losses from growing a usually less profitable spring crop probably limit the acceptance by farmers. Despite the problems addressed above, looking at the whole cropping system, oilseed rape is indispensable because of its beneficial effects on yield levels and nitrogen-use efficiency of following cereals, especially wheat, because alternative crops are often not realistic alternatives

Effect of Sowing Method and N Application on Seed Yield and N Use Efficiency of Winter Oilseed Rape

In northern Europe, replacing winter barley with winter wheat as the preceding crop for winter oilseed rape (Brassica napus L.; WOSR) often results in a delayed WOSR sowing and poor autumn growth. Based on data from a field experiment running in 2009/2010, 2010/2011, and 2012/2013, this study aims (i) to investigate how a delayed sowing method affects seed yield, N offtake with the seeds, and apparent N use efficiency (NUE) of WOSR; (ii) to test the ability of autumn and spring N fertilization to compensate for the negative effects of a delayed sowing method; and (iii) to estimate the minimum autumnal growth for optimal seed yield. In order to create sufficiently differentiated canopies, a combination of four sowing methods (first week of August until the third week of September) and four autumn N treatments (0, 30, 60, and 90 kg·N·ha−1) was established. Each of these 16 different canopies was fertilized with 5 N amounts (0/0, 40/40, 80/80, 120/120, 140/140 kg·N·ha−1) in spring in order to estimate separate N response curves. Above-ground N accumulation in autumn and seed yield and N offtake by the seeds were determined. Plant establishment after mid-September significantly decreased seed yield. Autumn N fertilization of at least 30 kg·N·ha−1 increased seed yield and N offtake by the seeds without any significant interaction with sowing method and spring N supply. However, the pathway(s) remain(s) unclear. Spring N fertilization up to 130 kg·N·ha−1 (estimated by a Linear-Plateau N response curve) increased seed yield. NUE decreased with increasing N supply, where WOSR used autumn N to a lesser extent than spring N. An above-ground N uptake of at least 10–15 kg·N·ha−1 at the end of autumn growth was required to achieve high seed yields. From an environmental point of view, optimal autumn growth should be attained by choosing an adequate sowing method, not by applying additional N in autumn

Evaluating Bioenergy Cropping Systems towards Productivity and Resource Use Efficiencies: An Analysis Based on Field Experiments and Simulation Modelling

Silage maize (Zea mays L.) is the dominating energy crop for biogas production due to its high biomass yield potential, but alternatives are currently being discussed to avoid environmental problems arising from maize grown continuously. This study evaluates the productivity and resource use efficiency of different bioenergy crops and cropping systems using experimental and simulation modelling derived data. The field experiment consisted of two years, two sites differing in soil texture and soil water availability, different cropping systems and increasing nitrogen (N) supply. Continuous (two years) perennial ryegrass and two crop rotations including winter cover crops (double cropping system) and combining C4 and C3 crops were compared with continuous maize (maize–maize). The productivity of the crops and cropping systems in terms of dry matter (DM) yield was analyzed with respect to the fraction of light interception and light use efficiency (LUE). In addition, water use and water use efficiency (WUE), N uptake, and N use efficiency (NUE) were quantified. DM yield of the double cropping system was similar to that of continuous maize, due to a prolonged leaf area duration, compensating for the intrinsic lower LUE of C3 crops. Perennial ryegrass was less productive than the other crops/cropping systems. Nitrogen uptake and consequently N demand of perennial ryegrass and the C3 crops of the crop rotations were higher than for maize–maize. Groundwater recharge was mainly site-dependent, but was at both sites higher for maize than for the crop rotations or the perennial ryegrass system. Our results indicate that, in terms of biomass productivity, optimized rotations are feasible alternatives to maize–maize, but trade-offs exist in terms of water and N use efficiency

The legacy effect of synthetic N fertiliser

Cumulative crop recovery of synthetic fertiliser nitrogen (N) over several cropping seasons (legacy effect) generally receives limited attention. The increment in crop N uptake after the first-season uptake from fertiliser can be expressed as a fraction (∆RE) of the annual N application rate. This study aims to quantify ∆RE using data from nine long-term experiments (LTEs). As such, ∆RE is the difference between first season (RE1st) and long-term (RELT) recovery of synthetic fertiliser N. In this study, RE1st was assessed either by the 15N isotope method or by a zero-N subplot freshly superimposed on a long-term fertilised LTE treatment plot. RELT was calculated by comparing N uptake in the total aboveground crop biomass between a long-term fertilised and long-term control (zero-N) treatment. Using a mixed linear effect model, the effects of climate, crop type, experiment duration, average N rate, and soil clay content on ∆RE were evaluated. Because the experimental setup required for the calculation of ∆RE is relatively rare, only nine suitable LTEs were found. Across these nine LTEs in Europe and North America, the mean ∆RE was 24.4% (±12.0%, 95% CI) of annual N application, with higher values for winter wheat than for maize. This result shows that fertiliser-N retained in the soil and stubble may contribute substantially to crop N uptake in subsequent years. Our results suggest that an initial recovery of 43.8% (±11%, 95% CI) of N application may increase to around 66.0% (±15%, 95% CI) on average over time. Furthermore, we found that ∆RE was not clearly related to long-term changes in topsoil total N stock. Our findings show that the—often used—first-year recovery of synthetic fertiliser N application does not express the full effect of fertiliser application on crop nutrition. The fertiliser contribution to soil N supply should be accounted for when exploring future scenarios on N cycling, including crop N requirements and N balance schemes. Highlights: Nine long-term cereal experiments in Europe and USA were analysed for long-term crop N recovery of synthetic N fertiliser. On average, and with application rates between 34 and 269 kg N/ha, crop N recovery increased from 43.8% in the first season to 66.0% in the long term. Delta recovery was larger for winter wheat than maize. Observed increases in crop N uptake were not explained by proportionate increases in topsoil total N stock