Browsing by Subject "Nutrient cycling"

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Hidden miners – the roles of cover crops and soil microorganisms in phosphorus cycling through agroecosystems
(2019) Hallama, Moritz; Pekrun, Carola; Lambers, Hans; Kandeler, Ellen
Background Phosphorus (P) is a limiting nutrient in many agroecosystems and costly fertilizer inputs can cause negative environmental impacts. Cover crops constitute a promising management option for sustainable intensification of agriculture. However, their interactions with the soil microbial community, which is a key driver of P cycling, and their effects on the following crop, have not yet been systematically assessed. Scope We conducted a meta-analysis of published field studies on cover crops and P cycling, focusing on plant-microbe interactions. Conclusions We describe several distinct, simultaneous mechanisms of P benefits for the main crop. Decomposition dynamics, governed by P concentration, are critical for the transfer of P from cover crop residues to the main crop. Cover crops may enhance the soil microbial community by providing a legacy of increased mycorrhizal abundance, microbial biomass P, and phosphatase activity. Cover crops are generally most effective in systems low in available P, and may access ‘unavailable’ P pools. However, their effects on P availability are difficult to detect by standard soil P tests, except for increases after the use of Lupinus sp. Agricultural management (i.e. cover crop species selection, tillage, fertilization) can improve cover crop effects. In summary, cover cropping has the potential to tighten nutrient cycling in agricultural systems under different conditions, increasing crop P nutrition and yield.
Microbial drivers of plant richness and productivity in a grassland restoration experiment along a gradient of land‐use intensity
(2022) Abrahão, Anna; Marhan, Sven; Boeddinghaus, Runa S.; Nawaz, Ali; Wubet, Tesfaye; Hölzel, Norbert; Klaus, Valentin H.; Kleinebecker, Till; Freitag, Martin; Hamer, Ute; Oliveira, Rafael S.; Lambers, Hans; Kandeler, Ellen
Plant–soil feedbacks (PSFs) underlying grassland plant richness and productivity are typically coupled with nutrient availability; however, we lack understanding of how restoration measures to increase plant diversity might affect PSFs. We examined the roles of sward disturbance, seed addition and land‐use intensity (LUI) on PSFs. We conducted a disturbance and seed addition experiment in 10 grasslands along a LUI gradient and characterized plant biomass and richness, soil microbial biomass, community composition and enzyme activities. Greater plant biomass at high LUI was related to a decrease in the fungal to bacterial ratios, indicating highly productive grasslands to be dominated by bacteria. Lower enzyme activity per microbial biomass at high plant species richness indicated a slower carbon (C) cycling. The relative abundance of fungal saprotrophs decreased, while pathogens increased with LUI and disturbance. Both fungal guilds were negatively associated with plant richness, indicating the mechanisms underlying PSFs depended on LUI. We show that LUI and disturbance affect fungal functional composition, which may feedback on plant species richness by impeding the establishment of pathogen‐sensitive species. Therefore, we highlight the need to integrate LUI including its effects on PSFs when planning for practices that aim to optimize plant diversity and productivity.
Towards a sustainable nutrient management in organic farming : closing the nutrient gap with recycled fertilizers from urban waste
(2022) Reimer, Marie; Möller, Kurt
Nutrient scarcity is one of the main challenges in arable organic farming. Yet, little is known about the current supply and need of nutrients on organic farms and even less about the nutrient sources utilized by organic farmers. However, most stakeholders within the organic sector agree that additional nutrients, preferably from recycled sources, such as urban waste materials, are needed. In this thesis, the current need and use of nutrients (N, P, K, Mg, S) in the organic farming systems was investigated by performing a meta-analysis of previous studies and two farm gate nutrient budget studies across Europe. Further, the effect of recycled fertilizers from urban waste, such as compost from household and green waste, human urine and sewage sludge on crop yield, nutrient balances, soil fertility, and risk of contamination with potentially toxic elements (PTEs) were examined. To this end, three long-term field trials using different recycled fertilizers were investigated and combined with results of a simulation using the soil-plant-atmosphere model DAISY. The results of this thesis show that the organic cropping system within Europe operates under nutrient limited conditions, which limits the yield potential and can cause soil nutrient depletion, especially of P. Farms that relied to a high extend (>60%) on biological nitrogen fixation for their N supply were particularly prone to the risk of soil P and K depletion. Further, 17% of external N inputs derived from the conventional livestock system, which is often considered contentious. Omitting these would further increase the nutrient gap. Therefore, changes to the contemporary practice are needed to ensure sustainability in the organic nutrient management. First, a better distribution of nutrients within the organic sector is needed. In particular, to avoid nutrient surpluses in one farm type (e.g., livestock or vegetable farms), while other farm types (e.g., arable farms) experience nutrient deficits. Further, due to N losses during processing the nutrient composition of organic fertilizers does not match the crops’ nutrient offtake. Digestates from biogas plant show the closest resemblance. However, to avoid nutrient imbalances an adequate use of external inputs that is tailored to the specific farm’s nutrient demands and reliance on biological N fixation is necessary. Increased awareness of tools like nutrient budgeting among farmers and advisors could facilitate achieving a more balanced nutrient management. Still, additional nutrients are needed to close the current nutrient gap and to substitute animal manures from conventional origin. Recycled fertilizers from urban waste represent a suitable nutrient source to this end. Sewage sludge and human urine performed similarly to cattle slurry with N recovery rates of about 0.5 – 0.6 and household waste compost had similar values to straw-rich animal manures with recovery rate of about 0.3. Nitrogen losses after field application ranged between 34-55% of the applied N amount, with nitrate leaching being the main loss pathway. Total N losses were slightly smaller for compost and cattle manure and were accompanied by a higher soil N accumulation of about 25% of applied N. Similar to the accumulation of soil N, compost also resulted in the highest soil C sequestration. Using cattle manures and sewage sludge showed a smaller effect, while cattle slurry did not cause a soil C increase. Most concerns related to the use of recycled fertilizers derive from the risk of contaminants, such as potentially toxic elements (PTEs). Compost and sewage sludge fertilization can lead to a higher amount of PTEs in the soil. However, significant changes in crop PTE uptake were rare due to low PTE bioavailability. The risk to human health and soil environment associated with PTEs through recycled fertilizer application is therefore neglectable. Urban waste can also be refined by incineration or precipitation processes to ensure less contamination, yet this results in nutrient (e.g., N) and organic matter loss. An argument can therefore be made for the use of raw materials if they lie within the contamination threshold values. In conclusion, the organic nutrient management in Europe requires more external nutrient inputs. Recycled fertilizers from urban wastes are an adequate source in terms of yield effect and soil fertility to close the nutrient gap and to substitute animal manures from conventional origin. However, the infrastructure and availability of recycled fertilizers need to be improved and suitable policy making is needed to fulfil the whole potential of these nutrient sources by for example permitting fertilizers derived from human excreta or the strategical placement of biogas plants which recycle urban wastes.