No abstract

Biochar (BC) application as a soil amendment has aroused much interest and was found to considerably improve soil nutrient status and crop yields on poor, tropical soils. However, information on the effect of BC on temperate soils is still insufficient, with effects expected to differ from tropical soils. We investigated the effects of BC on soil nutrient dynamics, crop yield, and quality in a greenhouse pot experiment. We compared three agricultural soils (Planosol, Cambisol, Chernozem), and BCs of three different feedstocks (wheat straw [WS], mixed woodchips [WC], vineyard pruning [VP]) slowly pyrolyzed at 525°C, of which the latter was also pyrolyzed at 400°C. The BCs were applied at two rates (1% and 3%, which would correspond to 30 and 90 t ha–1 in the field). Three crops, namely mustard (Sinapis alba L.), barley (Hordeum vulgare L.), and red clover (Trifolium pretense L.) were grown successively within one year. The investigated soil properties included pH, electrical conductivity (EC), cation‐exchange capacity (CEC), calcium‐acetate‐lactate (CAL)–extractable P (PCAL) and K (KCAL), C, N, and nitrogen‐supplying potential (NSP). The results show a pH increase in all soils. The CEC increased only on the Planosol. The C : N ratio increased at 3% application rate. Despite improving the soil nutrient status partly, yields of the first crop (mustard) and to a lesser extent of the second crop (barley) were significantly depressed through BC application (by up to 68%); the yield of clover as third crop was not affected. Only the BC from WS maintained yields in the range of the control and even increased barley yield by 6%. The initial yield reduction was accompanied by notable decreases (Cu, Fe, Mn, Zn) and increases (Mo) in micronutrient concentrations of plant tissues while nitrogen concentrations were hardly affected. The results of the pot experiment show that despite additional mineral fertilization, short‐term growth inhibition may occur when applying BC without further treatment to temperate soils.

H, C, and O stable isotope ratios and the elemental profile of 267 olive oils and 314 surface waters collected from 8 European sites are presented and discussed. The aim of the study was to investigate if olive oils produced in areas with different climatic and geological characteristics could be discriminated on the basis of isotopic and elemental data. The stable isotope ratios of H, C, and O of olive oils and the ratios of H and O of the relevant surface waters correlated to the climatic (mainly temperature) and geographical (mainly latitude and distance from the coast) characteristics of the provenance sites. It was possible to characterize the geological origin of the olive oils by using the content of 14 elements (Mg, K, Ca, V, Mn, Zn, Rb, Sr, Cs, La, Ce, Sm, Eu, U). By combining the 3 isotopic ratios with the 14 elements and applying a multivariate discriminant analysis, a good discrimination between olive oils from 8 European sites was achieved, with 95% of the samples correctly classified into the production site.

Summary This study investigates (i) the effect of biochar amendments on soil microbial communities in temperate agricultural soils, (ii) the involvement of microorganisms (MOs) in degradation of biochar and (iii) techniques to quantify degradation of biochar in short‐term experiments. The study involved an incubation experiment and a pot experiment with two arable soils (a sandy acidic Planosol and a calcareous loamy Chernozem) amended with 13C‐depleted biochar from wheat husk and willow plants. Phospholipid fatty acids (PLFAs), 13C‐PLFA, CO2, 13C‐CO2, soil organic carbon (Corg) and 13C‐Corg were monitored for 100 days. Effects of biochar application on the soil microorganisms (MOs) were generally minor. In the incubation experiment, microbial biomass was elevated by wheat husk biochar, especially in the Planosol. The increase in PLFAs was attributed to Gram‐negative bacteria and actinomycetes. Fungi and Gram‐positive bacteria were less affected. In the pot experiment, MOs did not respond to the addition of willow biochar. The effects of biochar were mainly attributed to an increase in the pH of the Planosol. Additionally, MOs were probably less responsive to inorganic fertilizer in biochar‐amended soil. In the incubation, only the actinomycetal PLFA 10Me18:0 incorporated biochar C, while in the pot experiment, Gram‐negative bacterial PLFAs (16:1ω7c, 16:1ω5c, 18:1ω7c) and Me16:0 & i17:1ω8 and i17:0 indicated degradation of biochar after 5 weeks. Uptake of around 20% biochar C in these PLFAs was monitored, which accounts for 2% biochar C in the total microbial biomass. From the PLFA data the mean residence time of biochar carbon was estimated in time‐scales of centuries to millennia. The CO2 concentration decreased after biochar addition until its production was masked by root respiration. The use of 13C‐CO2 labelling to estimate degradation was complicated by the interference with an initial negative priming effect and the dissolution/precipitation of carbonate. In conclusion, soil MOs were not particularly affected by addition of biochar, and the effects recorded were mainly attributed to changing environmental conditions after biochar addition. Nonetheless, uptake of 13C label into microbial PLFAs was successfully used to estimate microbial degradation of biochar in short‐term experiments.

The benefits of biochar (BC) application to fertile, non-acidic soils in temperate climate regions might not always be as evident as for highly weathered tropical soils. The aim of our study was to investigate the effects of BC on soil characteristics, nutrient uptake and crop yield in field experiments on two temperate soils (Cambisol and Chernozem) in Austria. Maize and wheat (Cambisol), and barley and sunflower (Chernozem) were grown in successive vegetation periods following different BC application rates (0, 24 and 72 t ha-1 at the start of the experiment), supplemented with identical mineral N supply in 33 m² plots. BC treatments showed varying impacts on nutrient uptake of the investigated crops. The first growing season in the Chernozem region was affected by a prolonged drought period, which resulted in positive effects of BC on soil water-holding capacity (WHC) and barley crop yield (+ 10%) for the 72 t ha-1 BC + N treatment compared to a control with identical nutrient supply but without BC. However, maize and wheat grain yield decreased by 46 and 70%, respectively, after the highest BC application rate (72 t ha-1) in an additional treatment without supplementary N-fertilisation. Still, even with high BC application rates we did not observe any adverse effects on crop yield and nutrient uptake, as long as the soil was supplied with sufficient N according to local agricultural practice.