Hans-Werner Olfs

Effect of microbial nitrogen immobilization during the growth period on the availability of nitrogen fertilizer for winter cereals

Abstract Pot and field experiments were conducted to determine microbial immobilization of N fertilizer during growth periods of winter wheat and winter barley. In a pot experiment with winter wheat, Ca(15NO3)2 was applied at tillering [Zadoks growth stage (GS) 25)], stem elongation (GS 31) and ear emergence (GS 49). Rates of 100 mg N pot–1, 200 mg N pot–1 or 300 mg N pot–1 were applied at each N application date. At crop maturity, 15N-labelled fertilizer N immobilization was highest at the highest N rate (3×300 mg N pot–1). For each N-rate treatment about 50% of the total immobilized fertilizer N was immobilized from the first N dressing, and 30% and 20% of the total 15N immobilized was derived from the second and third applications, respectively. In field trials with winter wheat (three sites) and winter barley (one site) N was applied at the same growth stages as for the pot trial. N was also applied to fallow plots, but only at GS 25. N which was not recovered (neither in crops nor in soil mineral N pools) was considered to represent net immobilized N. A clear effect of N rate (51–255 kg N ha–1) on net N immobilization was not found. The highest net N immobilization was found for the period between GS 25 (March) and GS 31 (late April) which amounted to 54–97% of the total net N immobilized at harvest (July/August). At GS 31, non-recovered N was found to be of similar magnitude for cropped and fallow plots, indicating that C from roots did not affect net N immobilization. Microbial biomass N (Nmic) was determined for cropped plots at GS 31. Although Nmic tended to be higher in fertilized than in unfertilized plots, fertilizer-induced increases in Nmic and net N immobilization were poorly correlated. It can be concluded that microbial immobilization of fertilizer N is particularly high after the first N application when crop growth and N uptake are low.

Effect of increasing rates of 15N-labelled fertilizer on recovery of fertilizer N in plant and soil N pools in a pot experiment with winter wheat

The effect of increasing rates of 15N-labelled Ca(NO3)2 (N0 = no N application, N300 = 300 mg N/pot; N600 = 600 mg N/pot;  N900 = 900 mg N/pot) on recovery of fertilizer N in winter wheat plants and soil (total soil N, soil microbial biomass N [Nmic], extractable organic N [Norg]) and on N mineralization (NMsoil) was investigated at milk-ripe growth stage in a pot experiment. The N rates were equally split at tillering, stem elongation and ear emergence.  Fertilizer N recovered in crops increased with increasing N rates (N300: 223.5 mg N/pot [74.5% of applied fertilizer N], N600: 445.6 mg N/pot [74.3%], N900: 722.1 mg N/pot [80.2%]). NMsoil slightly increased from N0 (43.8 mg N/pot) to N900 (75.6 mg N/pot) indicating that N application enhanced availability of soil-derived N for the plants. However, in fertilized treatments NMsoil is balanced by immobilization and losses (non-recovered fertilizer N). Therefore the effective soil N mineralization is indicated by apparent net N mineralization (ANNM = NMsoil — fertilizer N immobilization — lost fertilizer N). Fertilizer N immobilization in soil increased from N300 (38.7 mg N/pot) to N600 (60.7 mg N/pot) and N900 (65.5 mg N/pot). Lost fertilizer N increased from N300 (14.8 mg N/pot) to N600 (56.7 mg N/pot) and N900 (62.1 mg N/pot). As a consequence negative ANNM values were calculated at N600 and N900. Due to the small differences between N600 and N900 fertilizer N immobilization and lost fertilizer N did not increase linearly with increasing N rates, i.e. both processes were limited by factors other than N rate. Only 5.6—7.4% of the immobilized fertilizer N was recovered in Norg and 5.4—9.3% in Nmic soil pools. It is assumed that most of the immobilized fertilizer N was in non-extractable organic N forms. Nmic and Norg were weak indicators for the extent of fertilizer N immobilization. Einfluss steigender 15N-Dungermengen auf die Wiederfindung von Dungerstickstoff in Winterweizenpflanzen und N-Fraktionen des Bodens im Gefasversuch In einem Gefasversuch wurde der Einfluss steigender Mengen von 15N-markiertem Ca(NO3)2 (N0 = ungedungt, N300 = 300 mg N/Gefas, N600 = 600 mg N/Gefas, N900 = 900 mg N/Gefas) auf die Wiederfindung dieses 15N-markierten Dungerstickstoffs in Winterweizenpflanzen und N-Fraktionen des Bodens (gesamter N im Boden, mikrobieller Biomasse N [Nmic], extrahierbarer organischer N [Norg]) sowie auf die N-Mineralisation aus dem Bodenvorrat (NMsoil) untersucht. Die Dungung wurde zu gleichen Teilen zur Bestockung, zum Schossen und zum Ahrenschieben appliziert. Der Versuch wurde zur Milchreife geerntet.  Die Wiederfindung des Dungerstickstoffs nahm mit steigender N-Dungung zu (N300: 223,5 mg N/Gefas [74,5% des Dunger-N], N600: 445,6 mg N/Gefas [74,3%], N900: 722,1 mg N/Gefas [80,2%]). Auch NMsoil nahm durch die N-Dungung zu (75,6 mg N/Gefas fur N900 gegenuber 43,8 mg N/Gefas fur N0). In gedungten Prufgliedern wird NMsoil durch Immobilisation und Verluste von Dunger-N ausgeglichen. Die den Pflanzen effektiv zur Verfugung stehende N-Mineralisation wird daher durch die apparente Netto-N-Mineralisation (ANNM = NMsoil — Dunger-N-Immobilisation — Dunger-N-Verluste) beschrieben. Fur N600 und N900 wurden negative ANNM-Werte errechnet. Die Dunger-N-Immobilisation nahm zwischen N300 (38,7 mg N/Gefas) uber N600 (60,7 mg N/Gefas) bis N900 (65,5 mg N/Gefas) zu und die Dunger-N-Verluste stiegen von N300 (14,8 mg N/Gefas) uber N600 (56,7 mg N/Gefas) bis N900 (62,1 mg N/Gefas). Die geringen Unterschiede zwischen N600 und N900 zeigen an, dass weder die Immobilisation noch Verluste von Dunger-N stetig linear mit steigender N-Dungung zunahmen und andere Faktoren als die N-Dungermenge limitierend waren. Nur 5,6—7,4% des immobilisierten Dunger-N konnten als Norg und 5,4—9,3% im Nmic gefunden werden. Der Rest des immobilisierten Dunger-N lag in nicht-extrahierbaren organischen N-Fraktionen vor. Nur anhand von Nmic oder Norg konnte daher nicht auf die Hohe der Dunger-N-Immobilisation geschlossen werden.

Characterization of soil nitrogen and nitrogen uptake by grass following a two-year fallow of potted soils receiving mineral and organic sources of nitrogen

Abstract Nitrogen turnover in fertilized soils with or without a supply of decomposable organic matter and the time-dependent remineralization of immobilized nitrogen were studied in a 3-year pot experiment. In three treatments, 15 N-labelled fertilizer was used. After 2yr of fallow the soils were planted with ryegrass and N uptake was measured. Soil samples were taken during the fallow and the following period of plant growth and contents of mineral nitrogen (N min ) and readily extractable organic N compounds (N org ) were determined. Changes in the Nn min content during the 2-yr fallow became differentiated according to (1) the amount of applied mineral N and (2) the C-to-N ratio that was established. Even 2 yr after C incorporation N was immobilized in some treatments. Changes of N org values during the first 4 weeks of the fallow depended primarily on the amount of added carbon. In the 3rd experimental yr differentiation of N contents were smaller and the amount of added nitrogen had a pronounced effect. Increase or decrease of the N org contents were not related to a reverse change in the N min content. Total N uptake was significantly related to N min content in the soil at the end of the fallow, i.e. prior to sowing ( r 2 = 0.98 ∗∗ ). The relationship was less close between N org and N uptake during the following growth period ( r 2 = 0.48 ∗ –0.56 ∗ ). The results of the 15 N treatments proved that application of fertilizer N enhanced N uptake from the native soil pool. Production of stabilized N compounds seemed to depend on the amount of microbial usable carbon, the C-to-N ratio of the added substrate and the number of turnover cycles.

Assessing crop performance in maize field trials using a vegetation index

Abstract New agronomic systems need scientific proof before being adapted by farmers. To increase the informative value of field trials, expensive samplings throughout the cropping season are required. In a series of trials where different application techniques and rates of liquid manure in maize were tested, a handheld sensor metering the red edge inflection point (REIP) was compared to conventional biomass sampling at different growth stages and in different environments. In a repeatedly measured trial during the 2014, 2015, and 2016 growing seasons, the coefficients of determination between REIP and biomass / nitrogen uptake (Nupt) ascended from 4 leaves stage to 8 leaves stage, followed by a decent towards tasseling. In a series of trials in 2014, and 2015, the mean coefficients of determination at 8 leaves stage were 0.65, and 0.67 for biomass and Nupt, respectively. The predictability of biomass or Nupt by REIP however, is limited to similar conditions (e.g. variety). In this study, REIP values of e.g. ~721, represent Nupt values from ~8 kg ha-1 to ~38 kg ha-1. Consequently, the handheld sensor derived REIP used in this series of experiments can show growth differences between treatments, but referential samples are necessary to assess growth parameters.

Slurry injection with nitrification inhibitor in maize: Plant phosphorus, zinc, and manganese status

ABSTRACT Slurry injection below the maize (Zea mays L.) row may substitute a mineral nitrogen (N) phosphorus (P) starter fertilizer (MSF) and thus reduce nutrient surpluses in regions with intensive livestock husbandry. We investigated the plant P, zinc (Zn), and manganese (Mn) status compared to the current farm practice. In 2014 and 2015 field trials were conducted to evaluate plant nutrient status at different growth stages. Besides an unfertilized control, two slurry injection treatments (±nitrification inhibitor (NI)) were compared to slurry broadcast application plus MSF. In both experiments NI addition significantly increased nutrient concentrations during early growth (6-leaf 2015: +33% P, +25% Zn, +39% Mn). Under P deficiency due to cold weather conditions broadcast application showed higher P uptake until 6-leaf (36–58%), while it was lower at 8- (32%) and 10-leaf (19%) stage compared to slurry injection (+NI). Zn availability was enhanced for slurry injection (+NI) during early growth and Zn and Mn uptakes were higher at harvest. Slurry injection decreased P balances by 10–14 kg P ha−1, while Zn and Mn balances were excessive independent of treatments. Slurry injection (+NI) can substitute a MSF without affecting early growth and enhances the Zn and Mn status. This new fertilizing strategy enables farmers to reduce P surpluses.

Eco-innovations in the German fertilizer supply Chain : Impact on the carbon footprint of fertilizers

The aim of this paper is to analyse to what extent the existing eco-innovations in the German fertilizer domain might reduce the fertilizer carbon footprint without compromising on crop productivity. The continuously growing demand for agricultural products will require a further increase in agricultural production mostly achieved with additional external inputs (fossil energy, pesticides, irrigation water and fertilizers). Fertilizer in general and nitrogen fertilizers in particular are major factors for yield increases in crop production. On the other hand, emissions of greenhouse gases play a dominant role in the debate on the environmental burden of fertilizers. Typical mineral fertilizers were compared with so-called stabilized nitrogen fertilizers and secondary raw material fertilizers in this study. Additionally, an effect of the combination of irrigation with fertilization (i.e. fertigation) was investigated. With an adopted life cycle assessment approach focusing on CO2 and N2O emission, the carbon footprints of the different fertilizer options were considered. The calculations showed that especially the use of stabilized nitrogen fertilizer reduced the fertilization-related carbon footprint up to 13%. However, because of higher costs or incomplete supply chain relationships, adoption of these innovations is expected to be rather limited in the near future. Fertilizers made from secondary raw materials resulted in similar carbon footprints as mineral ones, but they can help to close nutrient cycles and use by-products of other production processes.