SSS9.7

Introduction The agroecosystems at the southern slope of Mt. Kilimanjaro have been an important resource for the provision of ecosystem services, in particular food production. However, their potential is increasingly threatened by a rapid change in agricultural land use and its future sustainability remains uncertain. Various efforts to achieve sustainable management of agroecosystems have not been successful and therefore there is a risk of land degradation and poverty. This problem is attributed to a lack of knowledge about the actual causes and extent of the problem among local farmers, extension officers and researchers, thus limiting decision options on the selection of appropriate adaptation measures. 

Goals Therefore, we conducted a study to determine how changes in traditional farming systems affect soil quality within the agroecosystem at the southern slopes of Mt. Kilimanjaro. 

Material and Methods We measured C, N, P, soil texture, bulk density and the cation exchange capacity (CEC) in 24 plots across major agro-ecological zones (mainly related to elevation) and in two farming systems (maize and agroforestry).

Results We found that sand content increased, clay content and bulk density decreased with increasing elevation. C content was slightly lower in maize compared to agroforestry (-0.88%), but not N and P. C and N contents increased in the upper compared to the lower elevation zones (3.8% and 0.3%, respectively), while P decreased by 19 mg/kg. The content of cations from CEC showed a heterogeneous picture. The largest difference was the decrease of Ca and Mg in the upper elevation zone (-1191 mg/kg and -458 mg/kg, respectively).

Conclusions Soils in the agroecosystems of Mt. Kilimanjaro differ in their properties which implies that crop yield and quality could be higher on some plots than others. Therefore, the vulnerability to food insecurity and efforts required to improve soil quality could vary locally. The use of soil quality indicators would benefit both farmers and extension officers as a decision-making tool to identify suitable locations for crops, achieve precise use of production inputs and manipulate crop calendars.

How to cite: Kimaro, J., Treydte, A., Huwe, B., and Bogner, C.: Soil quality indicators across different agro-ecological zones of Mt. Kilimanjaro, Tanzania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9423, https://doi.org/10.5194/egusphere-egu21-9423, 2021.

Dehydrogenase activity (DHA) has been widely used as a good indicator to assess the oxidative status in soils. The common method determination relies on the reduction of an artificial electron receptor by the soil microorganisms, namely, a soluble tetrazolium salt that acquires a red color in its reduced form (formazan), being this way easily measured by colorimetry, after extraction by a proper solvent. This activity is very sensitive to all the factors that can reach the upper layer of soils, especially temperature and moisture, and its use has become very useful to determine the degree of xenobiotics toxicity or the goodness, or not, of agricultural procedures and management. To establish an appropriate methodology for the measurement and monitoring of this activity, in our work we evaluate the most relevant aspects that must be taken into account so that the determination of this activity is as consistent as possible.

Incubation time and pre-incubation: The incubation time appears as the main source of trouble in the interpretation of results. Most of the time, an incubation time of 24 hours is used, but some authors recommend shorter incubation periods to make the measurements at an initial rate and that way use a linear function. For this reason, some authors advise shorter periods of incubation after having a pre-incubation time with glucose or yeast extract. This way the reducing potential of the soil will be better represented.

Soil moisture:  For the DHA results of a certain area to be comparable, the degree of soil humidity has to be necessarily standardized since any change in soil moisture will lead to changes in DHA. Dry soils give figures of DHA close to zero. Precise readings of DHA can only be obtained minimizing the moisture interactions. A pre-incubation of 10 days with the soil hydrated with 50% of the water holding capacity, not only ensures equal moisture for all the samples but also serves to reactivate the soil microorganism population. After that, samples should be immediately incubated with the electron receptor and analyzed.

Formazan extraction: Special physicochemical properties of soils can lead to better or worse extraction of formazan. Some authors advise carrying out a simple trial to establish the degree of extraction of the formazan according to the slope of a linear function between the added formazan and that extracted.

Optimal TTC concentration: Some toxicity of TTC has been raised recently. Although the concentration of the substrate must be sufficient to saturate all the enzymatic capacity, it is advisable not to add an excess of TTC. The quantity and quality of organic matter may be behind the degree of severity of the toxic effect of TTC.

How to cite: Campos, J. A., Moreno, C., Villena, J., Peco, J. D., García-Noguero, E. M., and Moreno, M. M.: Methodological approaches to evaluate dehydrogenase activity as a good indicator of soil functionality., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15751, https://doi.org/10.5194/egusphere-egu21-15751, 2021.

Soil organic carbon (SOC) content is the major indicator used for soil quality evaluation because provides several ecosystem functions. However, SOC content does not allow to understand the soil potential to deliver the key ecosystem functions because most of soil processes are linked to soil biota. This research aimed to demonstrate the importance of soil indicators related to the SOC cycle rather than SOC content for soil quality evaluation. To reach this goal, three farms characterized by diverse soil types (Fluvisol and Cambisol) were selected in the Po plain of Emilia-Romagna Region, Italy. Moreover, different agricultural practices were performed: three-year-old pear trees using conventional management for Maccanti farm (MAC), 10-year pear orchard with integrated management for Zani (ZAN) and 10-year peach orchard with organic management for Biondi (BIO). MAC is located in ancient reclamation area, where Fluvisols are enriched of peat and organic matter. In each farm, soil samples from 0–15 (hereafter called topsoil) and 15–30 cm (hereafter called subsoil) depth were collected and analysed for the contents of SOC, labile organic carbon (Clab), fulvic acids, humic acids, humin and microbial biomass–C (Cmic), and for microbial respiration (Resp). In order to evaluate the soil processes related to C cycle, the humification rate (HR), metabolic quotient (qMET) and microbial quotient (qMIC) were calculated. MAC soil showed the highest SOC content without differences between topsoil and subsoil, due to ancient reclamation and agricultural management. BIO and ZAN showed similar SOC contents and it was higher in the topsoil than in subsoil due to grassy turf. Compared to BIO and ZAN, MAC soil showed a higher amount of Clab, and SOC was composed by a lower percentage of stable organic carbon (humin). Despite the higher Clab concentration, which is an easily available C source for microbes, no differences of Resp were observed among the sites, and MAC showed the lowest Cmic content. These data would indicate the presence in MAC of stress conditions which do not allow the growth of microbial biomass. The occurrence of stress conditions is clearly showed by the lowest qMET indicating how the conventional agricultural practices in peaty Fluvisol negatively affect the carbon use efficiency of microbial biomass. As a consequence, these stress conditions do not allow the C stabilization as suggested by the lowest qMIC. Further, the low C stabilization processes are highlighted by the highest HR. Conversely, despite the lowest content of Clab, BIO soil showed the lowest qMET and the highest qMIC suggesting how organic managements tend to improve the soil quality. Hence, the present study highlighted the importance of indicators linked to soil microbiome for soil quality evaluation in order to preserve its ecosystem functions. Indeed, organic carbon rich soils as those of MAC would indicate high quality soils but, because of the highly impacting practices, they showed stress conditions when the indicators linked to soil microbiome are taken in account. Therefore, if these indicators are not considered for soil quality evaluation, several fields used for agricultural purposes could become degraded.

How to cite: De Feudis, M., Falsone, G., Salani, G. M., Mistri, E., Brombin, V., Bianchini, G., and Vittori Antisari, L.: Carbon cycle related indicators better describe soil quality compared to total organic carbon content, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2013, https://doi.org/10.5194/egusphere-egu21-2013, 2021.

Reviews and meta-analyses generally support the perception that organic farming systems are more environmentally friendly than conventional farming systems. Organic agriculture results in more soil organic matter and higher microbiological activity, thus, providing better water holding capabilities, decreased both runoff and concentration of nitrate in soil, leading to fewer risks of nitrate leaching loss from the soil to water bodies. However, environmental quality parameters can differ between organic plant and animal production farms, moreover, they can be higher calculated per unit product.

We used the ARMOSA process-based crop model (Valkama et al., 2020) to evaluate contribution of plant and animal organic farming to soil organic carbon (SOC) sequestration and N leaching loss reduction compare to conventional systems in South Savo (Finland). Since organic systems often produce about 30% less yields compared to conventional systems, we calculated SOC changes per total gross energy in harvested yields. For model inputs we used daily meteorological data, statistical annual crop yields, statistical data for sales of nitrogen fertilizers in the region during the last 20 years (1999-2018). Five-year crop rotations were simulated on loamy sand soil (C 3.5 %, C/N ratio 17, pH 6.2). On plant production farms, rotations consisted of cereals (with addition of pea in organic), oilseed rape and grass. Conventional crops were fertilized with mineral fertilizer, and residues were removed (PC-R) or retained (PC+R). Organic crops were fertilized with green manure only (PO_g+R) or also with commercial organic fertilizer (PO_f+R). On animal production farms, conventional (AC-R) and organic (AO-R) rotations consisted of 2 years of cereals and 3 years of grass, sown with clover in organic system. Conventional animal system was fertilized with mineral fertilizer and slurry, while organic system with slurry only, and residues were removed in both systems.

Simulations showed that both conventional plant production systems (PC-R and PC+R) led to SOC decline of 650 kg ha^-1yr^-1 at 0-30 cm soil depth. Organic systems showed either less SOC decline (120 kg ha^-1yr^-1) as in PO_g+R, or slight SOC increase (55 kg ha^-1yr^-1) as in PO_f+R. In contrast, organic animal production system did not differ from conventional system in terms of SOC change, showing a slight decreasing trend of about 150 kg ha^-1yr^-1. Estimates of SOC per gross energy in harvested yields showed the highest value (1.3 kg GJ^-1) for organic plant production fertilized with commercial organic fertilizer (PO_f+R), while the lowest value (-18 and -13 kg GJ^-1) for conventional plant production systems (PC-R and PC+R, respectively). In contrast, the estimates did not differ much between organic (-2.2 kg GJ^-1) and conventional (-1.8 kg GJ^-1) animal production systems. Simulated N leaching loss varied between 6 and 9 kg ha^-1 yr^-1 for all systems, except for organic plant rotation with green manure (PO_g+R), which N leaching loss was only 3 kg ha^-1 yr^-1. 

The modelling results suggest that organic plant production farms can be more environmentally friendly per unit area as well as per unit product compared to conventional farms, while organic animal production farms seem to cause similar environmental impact as conventional farms.

How to cite: Valkama, E. and Acutis, M.: Is organic farming environmentally more friendly?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2389, https://doi.org/10.5194/egusphere-egu21-2389, 2021.

Regenerative agriculture (RA) is gaining increasing recognition as a plausible solution to restore degraded agroecosystems. In Mediterranean drylands, RA has been limitedly adopted by farmers due to its initial state of development and lack of empirical evidence on its impacts. To support its large-scale adoption, we carried out a participatory monitoring and evaluation project in the high steppe plateau of Southeast Spain, involving local farmers applying RA in their almond farms. To assess the effect of RA, we studied 9 farms and selected in each farm one field with regenerative management and one nearby field with conventional management based on frequent tillage (CT). We clustered fields under regenerative management based on the different RA practices being applied and distinguished 4 types of RA treatments: 1) reduced tillage with green manure (GM), 2) reduced tillage with organic amendments (OA), 3) reduced tillage with green manure and organic amendments (GM&OA), and 4) no tillage with permanent natural covers and organic amendments (NT&OA). We used physical (bulk density and aggregate stability), chemical (pH, salinity, total N, P, K, available P, and exchangeable cations) and biological (SOC, POC, PON, microbial activity)  soil propertoes and the nutritional status of almond trees (leaf N, P and K) to evaluate the impacts of RA compared to CT. We found that GM treatment improved physical soil properties, presenting regenerative fields higher soil aggregate stability. Our results showed that OA improved most soil chemical and biological soil properties, however physical properties remained similar. RA treatments combining ground covers and organic amendments (GM&OA and NT&OA) exhibited greater overall soil quality restoration than individual practices, improving physical, chemical and biological soil properties. NT&OA stood out for presenting the highest soil quality improvements. All RA treatments maintained similar crop nutritional status compared to CT. We conclude that RA has strong potential to restore the physical, chemical and biological quality of soils of woody agroecosystems in Mediterranean drylands without compromising their nutritional status, thereby enhancing their resilience to climate change and long term sustainability.

How to cite: Luján Soto, R., Martínez-Mena, M., Cuéllar Padilla, M., and de Vente, J.: Restoring woody agroecosystems in Mediterranean drylands through regenerative agriculture, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5009, https://doi.org/10.5194/egusphere-egu21-5009, 2021.

The aim of this study was to investigate the influence of mineral fertilizer, different composts and combinations of compost/fertilizer as soil amendments on a loamy silt Cambisol after a 27-year field trial. Four different composts were used: urban organic waste (OWC), green waste (GC), farmyard manure (MC) and sewage sludge compost (SSC). In addition to plant growth, (physico-)chemical and microbiological changes in soil properties following amendment were analysed: total organic carbon (TOC) and nitrogen (N), soil pH, water holding capacity (WHC), basal respiration (BR), microbial biomass (C_mic) and microbial community composition. Fertilization promoted plant growth, when SSC or GC in addition with mineral fertilizer were applied compared to control. Concerning the (physico-) chemical properties only minor differences among the treatments were found. Phosphorus concentrations were three times higher in plots receiving SSC and SSC + N  than control or mineral N fertilizer alone and magnesium concentrations in plots treated with SSC were lower compared to soils treated with GC and MC, respectively. The bacterial community exceeded the fungal one in terms of both richness and diversity. Further, bacterial richness, diversity and community composition differed significantly among the treatments, whereas differences in fungal richness, diversity and composition seemed negligible. Our conclusion is that composts produced from various source materials serve as a valuable source for plant nutrients and can partially substitute mineral fertilizers, modulate soil microbial community and increase fertility. This way, they contribute to the mitigation of climate change.

How to cite: Kurzemann, F., Plieger, U., Probst, M., Spiegel, H., Sandén, T., Ros, M., and Insam, H.: Long-term effect of organic amendments, mineral fertilizers and combinations thereof,  on plant yield, soil physic-chemical and microbiological properties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8182, https://doi.org/10.5194/egusphere-egu21-8182, 2021.

Soil carbon (C), now more than ever, attracts the interest of the scientific community for its importance in combating climate change and achieving food security. As a result, its key role in agricultural soil fertility and in anthropogenic greenhouse gas emissions mitigation is high on international agendas. A key issue regarding the linkage between food security and carbon storage concerns the mineralization or the stability of soil organic matter (SOM). Rock-Eval^® analysis was used to examine the thermal stability of SOM and these results were presented in details at the EGU General Assembly in 2020 (EGU2020-11229). Several indicators are used to further appreciate the quantity and quality of SOM: particle size fractionation (POM-C), determination of permanganate oxidizable carbon (POX-C) and carbon mineralization kinetics (Min-C). The results of both approaches are crossed and presented here. Soils were sampled from two soil layers (0-10 et 10-30 cm) in agricultural plots representative organic inputs practices in local agricultural systems (No input, +Millet residues, +Manure and +Organic wastes). Total soil organic carbon (SOC) concentrations ranged from 1.8 to 18.5 g C.kg^-1 soil (mean ± standard deviation: 5.6 ± 0.4 g C.kg^-1 soil) in the surface layer (0-10 cm) and from 1.5 to 11.3 g C.kg^-1 soil (mean ± standard deviation: 3.3 ± 0.2 g C.kg^-1 soil) in 10-30 cm deep layer. The soil organic matter in these Arenosols while positively affected by organic inputs is dominated by thermally labile forms. The POM-C fractions represent respectively 45 % and 24 % of the COS in the 0-10 cm and 10-30 cm soil layers respectively. Permanganate oxidizable carbon (POX-C) and mineralizable C (Min-C) averaged 254 ± 14 mg C.kg^-1 soil and 10.7 ± 1.2 mg C-CO₂ kg^-1 soil in the 0-10 cm layer. Our results show that in different situations, the labile pools POM-C, POX-C and Min-C are linked to the active thermal pools A1 (highly labile pool), A2 (labile pool), A3 (resistant pool) and even A4 (refractory pool). The A3 and A4 pools, which are known to be relatively stable in more clayey soils, are in fact quickly mineralized in the sandy soils of this region. This intense mineralization of SOM promotes the recycling of nutrients which is excellent for productivity of these agrosystems, but not for mitigation of climate change in the long term.

keywords: Sahel ; Arenosols ; Thermal stability ; Biogeochemical stability ; Rock-Eval analysis, POM-C ; POX-C ; Min-C.

How to cite: Malou, O. P., Chevallier, T., Sebag, D., Moulin, P., Badiane Ndour, N. Y., Rakotondrazafy, N., Thiam, A., and Chapuis-Lardy, L.: Is the thermal stability of soil organic matter related to its biogeochemical stability in cultivated Arenosols of the groundnut basin of Senegal?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12211, https://doi.org/10.5194/egusphere-egu21-12211, 2021.

The concept of closed ecological cycles has a high priority in organic farming. As the larvae of the black soldier fly are able to utilize organic residues and convert them into high-quality protein and fat, the larvae could play a role in recycling local organic residues into feed for fish, poultry and pigs and partially replace imported protein feeds. In this work, a wide range of residues was tested as feed components for black soldier fly larvae.

Total C and S of feed substrates and larvae were determined by CNS analyzer. Crude protein/N_tot was analyzed by the Kjeldahl method; crude fat after acid digestion. For the analysis of P_tot and other elements the samples were digested by dry ashing, dissolved in dilute HCl and measured by ICP-OES.

The yield of larval dry matter ranged from 0.10 to 0.23 kg per kg feed dry matter (DM). The highest larval DM was obtained with substrates of bread residues and wheat bran and of distiller's grain solubles (DDGS) and pasta residues. The lowest larval DM and the lowest yield of larval protein were obtained when feeding with substrates containing beet pulp or potatoes.

Crude protein contents of the larvae ranged from 33% to 52% DM, the maximum values almost equalling soybean extraction meal, but still below fish meal. High crude protein contents in the feed did not always correlate with high larval contents. The yield of larval protein was 0.105 kg per kg feed DM at maximum, with a substrate containing rapeseed extraction meal and pasta residues. Substrates of brewer's grains and pasta residues and of DDGS and pasta residues yielded 0.101 kg kg^-1 and 0.98 kg kg^-1, respectively.

Larval crude fat contents ranged between 18% and 38% DM. Of the feed substrates with high DM and protein yields, only that of rapeseed extraction meal and pasta residues achieved a crude protein/crude fat ratio >2.

Phosphorus contents of the larvae were 6.9 - 11.5 g kg^-1 DM, sulfur contents 3.3 - 6.1 g kg^-1. Highest P and S contents were found in larvae fattened on substrates with particularly high P and S contents, such as of corn steep liquor and wheat bran, or of rapeseed extraction meal with maize or pasta residues.

Calcium was enriched in the larvae. With the exception of larvae from Ca-rich feed substrates such as rapeseed extraction meal or beet pulp, which had Ca contents of 20 and 30 g kg^-1 DM, respectively, the Ca contents of the larvae were in the range of soybean extraction meal, 3.4 to 10.5 g kg^-1 DM.

Cu contents ranged from 5.7 to 13.9 mg kg^-1 DM, with the exception of larvae fed with brewer's grains, which had 24.7 mg kg^-1 Cu.

The results show that crude protein and crude fat content of the larvae vary greatly with different feed substrates. In addition to these quality characteristics, the substrate also influences the contents of other nutrients such as P, Ca, Cu, etc. This knowledge can be used specifically in different applications of the larvae in feed production.

How to cite: Erhart, E., Bonell, M., Sager, M., Hissek, K., Haas, D., and Hartl, W.: Recycling of organic residues by black soldier fly larvae - influence of substrate on larval composition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1606, https://doi.org/10.5194/egusphere-egu21-1606, 2021.

Monoculture croplands are commonly associated with deleterious environmental effects due to high fertilization rates. Agroforestry (alternate alleys of trees and crops or alley cropping) has the potential to mitigate the negative environmental effects from agriculture. Understanding the soil-N cycling aids in assessing how the soil function of nutrient cycling is impacted when monoculture system is converted into agroforestry. Currently, there is no systematic comparison in soil-N cycling rates between monoculture and agroforestry croplands in Western Europe. Our study aimed to investigate gross rates of soil-N cycling between agroforestry and monoculture croplands. We measured gross rates of soil-N cycling, using 15N isotopic pool dilution in May-June 2017, at three sites in Germany (Wendhausen, Dornburg, and Forst with Vertic Cambisol, Calcaric Phaeozem, Gleyic Cambisol soils, respectively); each site has paired monoculture and agroforestry systems (established in 2008, 2007, and 2010 at the respective sites). In each management system at each site, we had four replicate plots; for agroforestry system, we conducted measurements in the tree row and within the crop row at 1 m, 4 m, and 7 m from the tree row. The crop management practices in agroforestry crop row and monoculture were the same at each site.

For gross rates of ammonium cycling, differences were observed between agroforestry tree row, crop row and monoculture at the site with Vertic Cambisol soil. Higher gross N mineralization rates were observed in monoculture than agroforestry tree row whilst agroforestry tree row exhibited higher gross NH₄⁺ immobilization rates than agroforestry crop row (P < 0.02). This was correlated to higher soil C/N ratio and higher water-filled pore space in the tree row. Tree rows also tend to have higher microbial biomass at all sites. Gross rates of nitrate cycling were higher in the tree row than in the crop row and monoculture at the site with Calcaric Phaeozem soil. This showed a similar pattern with the gene abundance of ammonium oxidizing archeae (AOA), supporting a niche differentiation of AOA by utilizing ammonium mineralized from soil organic matter rather than from fertilizer source. At the site with Vertic Cambisol soil, dissimilatory nitrate reduction to ammonium was very high in the tree row. These changes in soil-N cycling and AOA gene abundance in the tree rows suggest that trees in sites with older agroforestry systems had enhanced the cycling of N in the soil.

How to cite: Bischel, X., Corre, M. D., Schmidt, M., and Veldkamp, E.: Soil-N cycling in temperate alley cropping agroforestry and monoculture croplands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10463, https://doi.org/10.5194/egusphere-egu21-10463, 2021.

For stockless organic farms an adequate nutrient supply is in many ways a challenge. In order to assess the nutrient management of Austrian organic stockless farms, farm gate-balances for nitrogen, potassium and phosphorus of 15 organic stockless farms located in Austria’s main arable production areas were calculated. Two of the farms were located in Wald- und Mühlviertel (Northern Upper and Lower Austria), two in the Carinthian Basin (Carinthia), two in the Pre-alpine Region (Southern Upper and Lower Austria), two in the South-Eastern Lowlands (Eastern Styria and Burgenland), four in the Marchfeld region (Eastern Lower Austria) and three in the Weinviertel (North-Eastern Lower Austria). The farms were managed according to organic farming guidelines for at least five years at the time of assessment. Nutrient balances were calculated over a period of five years, subtracting all farm outputs (nutrients in sold products) from all farm inputs (seeds and fertilizers, biological N fixation). Yields were assessed in questionnaires from the farmers, nutrient contents were taken from standardized tables.

Nitrogen balances (n = 14 farms) were -14.6 kg N ha^-1 yr^-1 on average, ranging from -61 to +34 kg N ha^-1 yr^-1. Nitrogen balances were strongly negative for one farm, slightly negative for 10 farms, even for one farm and slightly positive for 2 farms. Phosphorus balances (n = 15 farms) were -8.3 kg P ha^-1 yr^-1 on average, ranging from -23 to -3 kg P ha^-1 yr^-1. Phosphorus balances were strongly negative for one farm, slightly negative for 12 farms and even for 2 farms. Potassium balances (n = 15 farms) were -15.6 kg K ha^-1 yr^-1 on average, ranging from -31 to -8 kg K ha^-1 yr^-1. Potassium balances were slightly negative for 5 farms and even for 10 farms.

Plant available potassium contents (K_CAL) on the farm fields ranged from 74 to 378 mg K kg^-1. Two farms were moderately supplied (class B of the Austrian classification scheme), 10 farms were optimally supplied (class C) and 3 farms were over-supplied (class E). Plant available phosphorus contents (P_CAL) on the farm fields ranged from 21 to 102 mg P kg^-1. Two farms were classified as undersupplied (class A), 5 farms were moderately supplied (class B) and 8 farms were optimally supplied (class C).

Potassium availability and potassium balances on the farms were not correlated (r = 0.192, P = 0.899), phosphorus availability and phosphorus balances neither (r = -0.210, P = 0.881). Potassium and phosphorus availability were not significantly correlated to the duration of organic farming as well.

Stockless organic farms in Austria are very diverse, concerning their production conditions and nutrient management. The results indicate no adverse short-term effects on soil fertility for most of the farms. In the long term though, nutrient management should be improved to secure yields and to ensure the sustainability on organically managed cash crop farms. Meaningful options are e.g. farm partnerships with fodder-manure exchange and the use of recycled fertilizers like struvite. This, however, requires an adjustment of organic farming guidelines.

How to cite: Friedel, J. K., Leonhard, A., and Schöpf, C.: Nutrient balances and nutrient availability of organic cash crop farms in Austria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11456, https://doi.org/10.5194/egusphere-egu21-11456, 2021.

Sustainable agriculture should be based on management practices that improve resource usage efficiency and minimize harmful impacts on the environment while maintaining and stabilizing crop production. Both tillage and irrigation can have a great influence on hydrological processes within agroecosystems. However, it remains difficult to directly assess the effect of practices on water fluxes which has been mainly indirectly quantified by complex numerical modelling methods in the past. Therefore, the objective of the study was to use a space for time concept and measure oxygen and hydrogen isotopes (δ¹⁸O, δ²H) in the pore water of soil profiles as well as moisture contents for quantifying the soil water balance and fluxes. Covering all combinations, soil profiles and isotope analysis was performed for 16 sites planted with winter wheat and managed with different tillage (conventional tillage (CT), reduced tillage (RT), minimal tillage (MT), and no-tillage (NT)) and irrigation systems (hose reel boom irrigation with nozzles (BI), sprinkler irrigation (SI), drip irrigation (DI) and no irrigation (NI)). The results indicated that the more intense the tillage, the lower the water content. Among the irrigation systems, DI had the highest average water content. Tracing the minimum in the isotopic composition of the pores water within the depth profiles showed a deeper percolation of water in the CT fields, which indicates higher water flow velocity. Considering both water content and differences in water flow velocities resulted in water fluxes ranging from 90 to 151 mm yr^-1. The losses due to evapotranspiration varied between 57 and 80%. The resulting evapotranspiration within tillage and irrigation variants decreased in the order RT>CT≈MT>NT, and SI>BI>DI>NI. Thus, the method revealed that the lower water content in CT fields is a consequence of deeper water infiltration. Moreover, irrigation water contributed mostly to evapotranspiration, and drip irrigation showed the lowest evapotranspiration losses among irrigation systems. This study demonstrated that water stable isotopes can be used as indicators and are a promising method to quantify water fluxes in agricultural fields with great potential for evaluating management practices.

How to cite: Canet-Marti, A., Morales-Santos, A., Nolz, R., Langergraber, G., and Stumpp, C.: Hydrological processes and water flux quantification in agricultural fields under different tillage and irrigation systems using water stable isotopes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11039, https://doi.org/10.5194/egusphere-egu21-11039, 2021.

How to cite: Thiessen Martens, J., Schneider, K., Zvomuya, F., and Entz, M.: Efficacy of struvite as a phosphorus source for alfalfa in organic cropping systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8078, https://doi.org/10.5194/egusphere-egu21-8078, 2021.

Considering that pesticides have been used in Europe for over 70 years, a system for monitoring pesticide residues in EU soils and their effects on soil health is long overdue. In an attempt to address this problem, we tested 340 EU agricultural topsoil samples for multiple pesticide residues. These samples originated from 4 representative EU case study sites (CSS), which covered 3 countries and four of the main EU crops: vegetable and orange production in Spain (S-V and S-O, respectively), grape production in Portugal (P-G), and potato production in the Netherlands (N-P). Soil samples were collected between 2015 and 2018 after harvest or before the start of the growing season, depending on the CSS. Conventional and organic farming results were compared in S-V, S-O and N-P. Soils from conventional farms presented mostly mixtures of pesticide residues, with a maximum of 16 residues/sample. Soils from organic farms had significantly fewer residues, with a maximum of 5 residues/sample. The residues with the highest frequency of detection and the highest content in soil were herbicides: glyphosate and its main metabolite AMPA (P-G, N-P, S-O), and pendimethalin (S-V). Total residue content in soil reached values of 0.8 mg kg-1 for S-V, 2 mg kg-1 for S-O and N-P, and 12 mg kg-1 for P-G. Organic soils presented 70-90% lower residue concentrations than the corresponding conventional soils. There is a severe knowledge gap concerning the effects of the accumulated and complex mixtures of pesticide residues found in soil on soil biota and soil health. Safety benchmarks should be defined and introduced into (soil) legislation as soon as possible. Soil remediation techniques should be developed to keep the levels of pesticide residues below such benchmarks. Furthermore, the process of transitioning to organic farming should take into consideration the residue mixtures and their residence time in soil.  

How to cite: Silva, V., Geissen, V., Lwanga, E. H., Beriot, N., Oostindie, K., Bin, Z., Pyne, E., Busink, S., Zomer, P., Mol, H., and Ritsema, C. J.:   Cocktails of pesticide residues in conventional and organic farming systems in Europe – legacy of the past and turning point for the future, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-816, https://doi.org/10.5194/egusphere-egu21-816, 2021.