Diedrich Steffens

Plant growth improvement mediated by nitrate capture in co-composted biochar

Soil amendment with pyrogenic carbon (biochar) is discussed as strategy to improve soil fertility to enable economic plus environmental benefits. In temperate soils, however, the use of pure biochar mostly has moderately-negative to -positive yield effects. Here we demonstrate that co-composting considerably promoted biochars’ positive effects, largely by nitrate (nutrient) capture and delivery. In a full-factorial growth study with Chenopodium quinoa, biomass yield increased up to 305% in a sandy-poor soil amended with 2% (w/w) co-composted biochar (BCcomp). Conversely, addition of 2% (w/w) untreated biochar (BCpure) decreased the biomass to 60% of the control. Growth-promoting (BCcomp) as well as growth-reducing (BCpure) effects were more pronounced at lower nutrient-supply levels. Electro-ultra filtration and sequential biochar-particle washing revealed that co-composted biochar was nutrient-enriched, particularly with the anions nitrate and phosphate. The captured nitrate in BCcomp was (1) only partly detectable with standard methods, (2) largely protected against leaching, (3) partly plant-available, and (4) did not stimulate N2O emissions. We hypothesize that surface ageing plus non-conventional ion-water bonding in micro- and nano-pores promoted nitrate capture in biochar particles. Amending (N-rich) bio-waste with biochar may enhance its agronomic value and reduce nutrient losses from bio-wastes and agricultural soils.

Potassium uptake of rye-grass (Lolium perenne) and red clover (Trifolium pratense) as related to root parameters

SummaryRye-grass (Lolium perenne) is known to be a strong competitor to red clover (Trifolium pratense) for soil K+ under conditions of low K availability in the soil. The objective of this study was to clarify whether this competitive behaviour of the two species can be explained by root morphology. Total K+ uptake ofL. perenne andT. pratense was studied under field conditions in relation to root fresh weight, root density, root cation exchange capacity, root surface and root length. The soil was an Alfisol, Udalf. All root parameters, when calculated per unit soil surface (M2), were higher inL. perenne than inT. pratense. In addition,L. perenne had longer root hairs and a denser root hair system thanT. pratense. The greatest difference in root morphology between species was root length, withL. perenne roots averaging 4–6 times longer than those ofT. pratense.Significant correlations were found between the total K+ uptake and all root parameters examined, with highest correlationsforroot fresh weight (r,0.92***T. pratense; 0.94***L. perenne) and root length (r, 0.91***T. pratense;r, 0.93***L. perenne). Potassium uptake per unit root fresh weight, root surface and root length were all significantly higher forT. pratense than for L. perenne. Differences in the rate of K+ uptake between species were particularly high when expressed per unit root length. Because of its greater root length and surface area,L. perenne can take up more soil K+ thanT. pratense, particularly where there is a low K− supply in the soil. Under such conditionsL. perenne will be a particularly strong competitor toT. pratense.

Kinetics of carbon mineralization of biochars compared with wheat straw in three soils.

Application of biochars to soils may stabilize soil organic matter and sequester carbon (C). The objectives of our research were to study in vitro C mineralization kinetics of various biochars in comparison with wheat straw in three soils and to study their contribution to C stabilization. Three soils (Oxisol, Alfisol topsoil, and Alfisol subsoil) were incubated at 25°C with wheat straw, charcoal, hydrothermal carbonization coal (HTC), low-temperature conversion coal (LTC), and a control (natural organic matter). Carbon mineralization was analyzed by alkali absorption of CO released at regular intervals over 365 d. Soil samples taken after 5 and 365 d of incubation were analyzed for soluble organic C and inorganic N. Chemical characterization of biochars and straw for C and N bonds was performed with Fourier transformation spectroscopy and with the N fractionation method, respectively. The LTC treatment contained more N in the heterocyclic-bound N fraction as compared with the biochars and straw. Charcoal was highly carbonized when compared with the HTC and LTC. The results show higher C mineralization and a lower half-life of straw-C compared with biochars. Among biochars, HTC showed some C mineralization when compared with charcoal and LTC over 365 d. Carbon mineralization rates were different in the three soils. The half-life of charcoal-C was higher in the Oxisol than in the Alfisol topsoil and subsoil, possibly due to high Fe-oxides in the Oxisol. The LTC-C had a higher half-life, possibly due to N unavailability. We conclude that biochar stabilization can be influenced by soil type.

Use of reflectance measurements for the early detection of N, P, Mg, and Fe deficiencies in Zea mays L.

Mineral deficiencies can seriously reduce crop yield and economic returns to farmers. Reflectance measurements may provide inexpensive and fast estimates of the mineral status of plants. This study was conducted to examine specific changes of leaf reflectance due to nutrient deficiencies. During the 1998 and 1999 growing seasons leaf scans of N-, P-, Mg-, and Fe-deficient corn plants were performed with a digital LEICA S1 PRO camera under controlled light conditions. Leaf scans were evaluated with the L*a*b*-color system. This is a three-dimensional system with parameter a* describing the green/red percentage and parameter b* the blue/yellow percentage of a color. L* represents the lightness of a color. The a* and b* parameters provided good prediction of N, P, Mg, and Fe status of the plants in the wavelength ranges of 380—390 nm, 430—780 nm, 516—780 nm, 516—IR, and 540—600 nm because reflectance changed specifically due to the nutrient deficiency. Analyses of water-soluble and propanol-soluble pigments showed no significant changes in absorbance during latent deficiency. The results indicate that reflectance measurements may provide a powerful tool for the specific detection of latent nutrient deficiencies in corn plants. Reflexionsmessungen zur fruhzeitigen Erkennung von N-, P-, Mg- und Fe-Mangel bei Zea mays L. Mangel an Pflanzennahrstoffen vermindert vielfach den Ertrag und fuhrt zu wirtschaftlichen Einbusen fur den Landwirt. Zur Vermeidung von Ertragsverlusten ist eine spezifische und fruhzeitige Erkennung von Mangelsituationen erforderlich. Reflexionsmessungen konnten eine kostengunstige und schnelle Moglichkeit fur die Bestimmung der Nahrstoffversorgung von Pflanzen sein. Zur Vermeidung von Ertragsverlusten ist allerdings eine sichere und fruhzeitige Erkennung von Mangelsituationen erforderlich. Die vorliegende Studie diente der Untersuchung spezifischer Reflexionsanderungen bei Pflanzen, ausgelost durch einen Nahrstoffmangel. In den Jahren 1998 und 1999 wurden Blatt-Scans von Maispflanzen mit N-, P-, Mg- und Fe-Mangel mit einer digitalen LEICA-S1-PRO-Kamera unter kontrollierten Lichtbedingungen durchgefuhrt. Die Scans wurden im L*a*b*-Farbraum ausgewertet. Es handelt sich um ein dreidimensionales System, wobei der Parameter a* den Grun/Rot-Anteil und der Parameter b* den Blau/Gelb-Anteil einer Farbe beschreibt. L* reprasentiert die Helligkeit einer Farbe. Anhand der a*- und b*-Werte konnten die untersuchten Nahrstoffmangel eindeutig in den Wellenlangenbereichen 380—390 nm, 430—780 nm, 516—780 nm, 516—IR und 540—600 nm identifiziert werden, da sich die Reflexion nahrstoffspezifisch anderte. Die Analyse der wasser- und propanolloslichen Pigmente zeigte jedoch keine signifikanten Unterschiede in der Absorption wahrend eines leichten Nahrstoffmangels im Vergleich zur Kontrolle. Die Ergebnisse der Reflexionsmessungen stellen eine gute Grundlage fur die Fruherkennung von Ernahrungsstorungen dar.

PHYTOTOXIC SUBSTANCES IN SOILS

Plant species are continuously exposed to their ambient soil environment during their life cycle. Sometimes the presence, application and/or formation of certain substances in soils increase to the extent that they become phytotoxic – the property of a substance at a specified concentration that restricts or constrains plant growth. Phytotoxic substances have long been accumulating in the terrestrial ecosystem including soils. Phytotoxicity in soils can be grouped into five broad categories: (1) pesticide toxicity, (2) metal and metalloid toxicity, (3) soil acidity and aluminum and manganese toxicity, (4) soil flooding and manganese and iron toxicity, and (5) soluble salt and sodium toxicity.

Extractability of 15N-labeled corn-shoot tissue in a sandy and a clay soil by 0.01 MCaCl2 method in laboratory incubation experiments

Management of N fertilization depends not only on the mineral N measured at the beginning of the growing season but also on the status of the low-molecular-weight organic-N fraction. Our study was conducted to analyze how much of the 15N applied in labeled cornshoot tissue would be recovered in 0.01 M CaCl2-extractable 15N fractions and wheter a decrease in the CaCl2-extractable 15N fraction quantitatively followed the trend in net mineralization of the 15N applied in corn-shoot tissue during an incubation period. The effects of adding 15N-labeled young corn-shoot tissue to a sandy soil and a clay soil were investigated for 46 days in an aerobic incubation experiment at 25°C. The application of 80 mg N kg-1 soil in the form of labeled corn-shoot tissue (24.62 mg 15N kg-1 soil) resulted in a significant initial increase, followed by a decrease the labeled organic-N fraction in comparison with the untreated soils during the incubation. The labeled organic-N fraction was significantly higher in the sandy soil than in the clay soil until the 4th day of incubation. The decrease in labeled organic N in the sandy soil resulted in a subsequent increase in 15NOinf3sup-during the incubation. Ammonification of applied plant N resulted in a significant increase in the 1 M HCl-extractable non-exchangeable 15NHinf4sup+fraction in the clay soik, owing to the vermiculite content. The 15N recovery was analyzed by the 0.01 M CaCl2 extraction method; at the beginning of the incubation experiment, recovery was 37.0% in the sandy soil and 36.7% in the clay soil. After 46 days of incubation, recovery increased to 47.2 and 43.8% in the sandy and clay soils, respectively. Net mineralization of the 15N applied in corn-shoot tissue determined after the 46-day incubation was 6.60 mg 15N kg-1 soil (=34.9% of the applied organic 15N) and 4.37 mg 15N kg-1 soil (=23.1% of the applied organic 15N) in the sandy and the clay soils, respectively. The decrease in the labeled organic-N fraction extracted by 0.01 M CaCl2 over the whole incubation period was 3.14 and 2.33 mg 15N kg-1 soil in the sandy and clay soil, respectively. These results indicate that net mineralization of 15N was not consistent with the decrease in the labeled organic-N fraction. This may have been due to the inability of 0.01 M CaCl2 to extract or desorb all of the applied organic 15N that was mineralized during the incubation period.

Effect of various types of thermochemical processing of sewage sludges on phosphorus speciation, solubility, and fertilization performance

Sewage sludge has one of the highest phosphorus (P) recovery potentials of all waste materials. Therefore, P-recycling from sewage sludge could contribute to closing the P-cycle. Recently, various thermal processes for P-recovery have been developed, but there is still a demand for information on the effect of different process parameters (e.g. additives and temperature) on P-speciation and especially on the fertilization performance. In the present study, two common methods (low-temperature conversion at 400-500°C and thermochemical treatment at 950°C) were investigated and combined to produce highly bioavailable P-fertilizers from two different types of sewage sludge based on chemical phosphorus precipitation (Chem-P) and enhanced biological phosphorus removal (Bio-P). The results of P-fractionation, X-ray diffraction analysis, and pot experiments with maize showed that Bio-P sludges attain high P-plant-availability after treatment at low temperatures (400°C). In contrast, Chem-P sludges can adequately be treated at higher temperatures under reductive conditions with sodium additives to form highly bioavailable calcium-sodium-phosphate. Additionally, also highly heavy-metal contaminated sludges can be thermochemically treated at high temperatures to achieve the legal requirements for fertilizers.

VARIATION IN PHOSPHORUS EFFICIENCY AMONG BRASSICA CULTIVARS II: CHANGES IN ROOT MORPHOLOGY AND CARBOXYLATE EXUDATION

Increased phosphorus (P) efficiency is needed to sustain agriculture productivity on soils with low available P. Significant differences were found among Brassica cultivars for growth, P utilization, and remobilization under P deficiency (see our companion paper, Aziz et al., 2011a). To identify the possible mechanisms of P acquisition from low soluble P compounds, four cultivars (‘Rainbow’, ‘CON-1’, ‘Dunkeld’, and ‘Peela Raya’) were selected to ascertain the relationship of their differential P acquisition and growth with their root length in soil and with organic acid release pattern in solution culture experiments. For this purpose their growth and P acquisition from phosphate rock (PR) was compared with calcium di-hydrogen phosphate (Ca-P) when adding uniform dose of 100 mg P kg−1 soil separately from the two sources. Biomass accumulation, root length, root fineness, plant P uptake and ash alkalinity was significantly (P < 0.01) different in plants of all the four cultivars when supplied with PR or Ca-P in soil. Minimum biomass produced by ‘Peela Raya’ grown with either P source was followed by ‘CON-1’, ‘Dunkeld’, and ‘Rainbow’ in ascending order. Shoot dry matter production had a significant positive correlation with root dry matter production (r = 0.85, P < 0.01), root length (r = 0.59, P < 0.05) and root P uptake (r = 0.95, P < 0.01). Cultivars varied significantly for organic acid secretion in solution culture experiment. Higher quantities of secreted citric acid, malic acid and tartaric acid in solution culture experiment were measured for ‘Rainbow’ and ‘Dunkeld’ cultivars. Efficient performance of these two cultivars for growth and P uptake was associated with their longer roots and more secretion of organic acids especially citric acid.

Importance of EUF-extractable organic C for soil N mineralization and for N management of sugar beet

The quality of sugar beet (Beta vulgaris) is mainly influenced by N nutrition. Nitrogen mineralization is not only influenced by the amount of organic soil N, but also by organic soil C. The objective of our investigations was to determine the importance of organic C extracted by means of EUF for N mineralization and for N fertilizer recommendation of sugar beet. The importance of EUF-extractable organic C was investigated at 21 different sugar beet sites which were fertilized with 0 (=control treatment), 40, 80, 120, 160, and 200 kg N/ha. The experimental sites were located in southern Germany and in Austria.

Effect of Different Soil Phosphate Sources on the Active Bacterial Microbiota Is Greater in the Rhizosphere than in the Endorhiza of Barley (Hordeum vulgare L.)

Phosphate is a macronutrient and often the limiting growing factor of many ecosystems. The aim of this work was to assess the effect of various phosphate sources on the active bacterial microbiota of barley rhizosphere and endorhiza. Barley was grown on poor soil supplemented with either Ca(H2PO4)2 (CaP), Gafsa rock phosphate (Gafsa), sodium hexaphytate (NaHex), or not amended (P0). RNA was extracted and cDNA synthesized via reverse transcription from both rhizosphere and endorhiza of barley roots; the obtained 16S rRNA cDNA was sequenced by Ion Torrent and analyzed with QIIME and co-occurrence network analysis. Phosphatase activity was measured in the rhizosphere. The phosphate source significantly affected alpha- and beta-diversities of the active microbiota, especially in the rhizosphere. CaP enriched the relative abundance of a broad range of taxa, while NaHex and Gafsa specifically enriched one dominant Massilia-related OTU. Co-occurrence network analysis showed that the most abundant OTUs were affected by phosphate source and, at the same time, were low connected to other OTUs (thus they were relatively “independent” from other bacteria); this indicates a successful adaptation to the specific abiotic conditions. In the rhizosphere, the phosphatase activities were correlated to several OTUs. Moreover, the phosphodiesterase/alk. phosphomonoesterase ratio was highly correlated to the dominance index of the microbiota and to the relative abundance of the dominant Massilia OTU. This study shows the differential response of the rhizosphere- and endorhiza bacterial microbiota of barley to various phosphate sources in soil, thus providing insights onto this largely unknown aspect of the soil microbiome ecology and plant-microbe interactions.