Different methods have been proposed for in situ root-length density (RLD) measurement. One widely employed is the time-consuming sampling of soil cores or monoliths (MO). The profile wall (PW) method is a less precise, but faster and less laborious alternative. However, depth-differentiated functions to convert PW RLD estimates to MO RLD measurements have not yet been reported. In this study, we perform a regression analysis to relate PW results to MO results and determine whether calibration is possible for distinct crop groups (grasses, brassicas and legumes) consisting of pure and mixed stands, and whether soil depth affects this calibration. The methods were applied over two years to all crop groups and their absolute and cumulative RLD were compared using a linear (LR) and multiple linear (MLR) regression. PW RLD was found to highly underestimate MO RLD in absolute values and in highly rooted areas. However, a close agreement between both methods was found for cumulative root-length (RL) when applying MLR, highlighting the influence of soil depth. The level of agreement between methods varied strongly with depth. Therefore, the application of PW as the main RLD estimation method can provide reliable estimates of cumulative root distribution traits of cover crops.

Background and aims: The bicinchoninic acid (BCA) method was not yet applied on soil extracts of extracellular polymeric substances (EPS) to quantify polysaccharides, although this might be possible by introducing a cleavage step to produce monosaccharides. A pre-extraction with CaCl₂ to remove interfering substances is usually performed before extracting EPS. The main objective of this study was to optimize the BCA assay for total carbohydrates quantification by applying a hydrolysis step to the EPS extracts, while also testing carbohydrate contents of CaCl₂ pre-extracts. Methods: Total carbohydrates were quantified with BCA in EPS extracts of three soils, after hydrolysis with H₂SO₄, using two acid concentrations (0.75 and 1.0 M), three hydrolysis temperatures (100, 120 and 130 °C), and five hydrolysis times (10, 30, 50, 70, and 90 min). EPS were extracted with the cation exchange resin (CER) method adapted to soils. Two versions of pre-extraction with CaCl₂ were tested twice consecutively. Results: More carbohydrates were measured after hydrolysis with 0.75 M H₂SO₄ at below 100 °C and after 10 min for all soils. Decreasing values were seen after longer reaction times and higher temperatures. CaCl₂ extracted no or negligible amounts of carbohydrates from the soil. Conclusion: The pre-extraction step can be done without in most cases. The BCA assay is free of toxicity and easily performed, while also tolerant to interferences from most compounds in EPS extracts. These characteristics highlight the potential of this method for a rapid quantification of carbohydrates in studies of extractable polymers in several areas of soil biogeochemistry.

Drought events are becoming more severe and recurrent over Europe. Changes in temperature and rain patterns can affect soil nutrient mobility and availability, modulating the biomass and activity of soil microbial communities. Here, we investigated the effects of drought on extracellular polymeric substances (EPS) and microbial biomass carbon (MBC) and nitrogen (MBN) in differently managed cropping systems. An on-field drought simulation experiment using rain-out shelters was conducted as part of a long-term field experiment cultivated with winter wheat, comparing cropping systems with contrasting fertilization strategies and crop protection measures: A biodynamic system and a mixed conventional system with no pesticide application, and a purely minerally fertilized conventional system, with conventional pesticide use. The implemented drought lasted for three months, starting at plant tillering stage and ending at ripening stage. No watering was performed on the drought treatment during that period. Soils were sampled at stem elongation, flowering, and ripening. EPS-carbohydrates and EPS-proteins significantly increased by approximately 20% due to induced drought but remained roughly constant from stem elongation to ripening under drought. Mean EPS-carbohydrates to EPS-proteins ratio was 1.9. MBC and MBN remained largely unaffected by drought. The ratio of both EPS fractions to microbial biomass was lowest in the biodynamic system and highest in the minerally fertilized conventional system, indicating that rhizodeposits and mucilage were predominantly diverted into microbial biomass, rather than into microbial EPS. This might be an important reason for the higher soil fertility of the biodynamic system.

Background: An on-vineyard approach was used to investigate the effects of biodynamic (BD) preparations on microbial functional diversity and extracellular polymeric substances (EPS) in four vineyards on different bedrocks under organic management. Methods: Soil organic carbon (SOC), total N, microbial biomass carbon (MBC), multi-substrate-induced respiration (MSIR), with 17 substrates and H₂O, EPS, and glomalin-related soil protein (GRSP) were measured in soils taken from vineyards without (BD -) and with (BD +) biodynamic preparations. Results: All parameters showed a significant vineyard effect due to specific soil types, and all, except GRSP and the GRSP/EPS-prot, showed an effect of BD preparations. BD + resulted in significant increases in MBC, MBC/SOC, EPS-carbohydrates and respiratory response for most vineyards but a significant decrease in the qCO₂ values. The significant increases in mean SOC, Total N, CO₂C, and the ratios EPS-carb/EPS-prot with BD +, as well as decreases in mean EPS-proteins and the ratios EPS-carb/MBC and EPS-prot/MBC were not reflected by significant differences between the individual vineyards. GRSP was negatively related to the microbial respiratory response of all substrates added. Conclusions: The significant effects of vineyard are closely connected to soil pH and texture. The significant increases in BD +, visible in MBC, MBC/SOC and EPS-carbohydrates, and the latter positive correlation with the respiratory response demonstrates an improvement of soil chemical and biological properties for most vineyards. Lower ratios of EPS-carb/MBC, EPS-prot/MBC and amounts of EPS-protein indicate that soil microorganisms diverted less substrate to the formation of EPS and more to the production of microbial biomass. GRSP and GRSP/EPS-prot did not show any explainable pattern. Future investigations on soil structure might be of benefit for studies on the effect of BD preparations in vineyards. Graphical

Aims: Increasing droughts affect crop yield and health. Plants can respond to drought by adapting their root biomass, root morphology, and quality and quantity of rhizodeposition to improve water and nutrient uptake. Besides droughts, agricultural management influences roots and rhizodeposition; however, it is not well studied how agricultural management can affect the response of roots and rhizodeposition to drought. Methods: A semi-continuous ¹³ CO ₂ isotope labelling experiment was performed in a long-term field experiment comparing biodynamic, mixed conventional, and mineral conventional cropping systems. Rainout shelters were installed to induce drought. Root, net rhizodeposition, and the rhizosphere microbiome were determined at ripening of wheat. Results: Drought enhanced the total root carbon mainly through the increase of fine roots. Fine root carbon under drought was primarily enhanced in the mixed conventional and biodynamic cropping system, both receiving farmyard manure, whereas no increase was measured in the mineral fertilized conventional system. Net rhizodeposition carbon was enhanced in all cropping systems under drought, particularly in the first 0.25 m. While some plant-growth-promoting genera such as Streptomyces and Rhizophagus showed relative increases under drought, other plant growth-promoting genera often involved in nitrogen fixation such as Rhodoferax and Mesorhizobium were decreased. Conclusion: This field trial suggests that drought increases total belowground carbon input via fine root and net rhizodeposition carbon inputs. Since fine root carbon increased under drought in cropping systems with farmyard manure, adding manure under future drought periods could be advantageous to increase soil carbon inputs and improve nutrient foraging.

Coupled effects of drought and cropping system on the transfer of wheat rhizodeposits to soil microbial biomass (MB), extracellular polymeric substances (EPS), and particulate organic matter (POM) were investigated down to 75 cm. Wheat plants were labelled with 13CO2 and 15N urea on the DOK trial in Switzerland. Drought was induced by rainout shelters on microplots of the BIODYN (biodynamic with farmyard manure (FYM) fertilization), CONFYM (conventional, mineral and FYM fertilization), and CONMIN (conventional, solely mineral fertilization) cropping systems. Drought generally reduced N uptake by wheat plants and transfer of rhizodeposition N into soil but increased N transfer to roots in the systems receiving FYM. All MB indices were highest in the BIODYN system. Drought increased rhizodeposition-derived (RD) microbial biomass carbon (MBCRD) down to 75 cm compared with the rainfed control, whereas MB nitrogen (MBNRD) was only increased at 0-25 cm depth. Drought increased the EPSCRD content at 0-25 cm and that of EPSNRD down to 75 cm. The content of EPS-carbohydrate contents was approximately 8 times higher in the rhizosphere than in the bulk soil, that of EPS-protein and EPSCSD were 4 times higher, whereas that of EPSNSD were roughly doubled. Drought increased the POMCRD contents down to 50 cm and those of POMNRD only to 25 cm. Drought also increased the (soil organic matter) SOM-derived POMCSD contents down to 75 cm and those of POMNSD again only to 25 cm depth. Drought increased total CdfR by roughly 50% and decreased total NdfR by approximately 50%. However, the absolute contribution of the defined fraction MB, EPS, and POM to CdfR but particularly to NdfR was significantly increased in all cases by drought. CdfR and NdfR are both related to the amount of roots by cannot be simply estimated from the root biomass.