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Soil health is a critical aspect of sustainable agriculture, with soil organic matter (SOM) serving as a key indicator. In arable fields, growing cover crops has been advocated as a prime practice to promote SOM accumulation. However, the effectiveness of cover crops to promote SOM accumulation can vary widely. Furthermore, accurate quantification of SOM at field scale is severely constrained by the labour intensity and destructive nature of traditional methods, which limits the ability to quantify and monitor cover crop impacts on SOM. We tested whether cover crop mixtures promote SOM accumulation more than cover crop monocultures in a 6-year field experiment with arable crop rotation on sandy soil. We found that the cover crops radish and oat-radish mixture significantly increased SOM levels compared to the fallow treatment. Next, on soil sampled in year 4, we explored the use of proximal (VIS-NIR, MIR) and remote sensing using Unmanned Aerial Vehicles (UAVs) to upscale SOM from wet lab-based point samples to the whole field and map its SOM status. Thereto, we used Random Forest (RF), Support Vector Regression (SVR), and Partial Least Squares (PLS) models and found that the best fitting model depended on the type of spectral sensor. With proximal sensing (MIR) the best SOM prediction was achieved using SVR (R2= 0.84, RMSE= 1.55 g/kg SOM). For UAV imagery with hyperspectral camera the best model was RF (R2 = 0.69, RMSE= 2.19 g/kg SOM) and enabled digital mapping of SOM distribution across the field. The accuracy of MIR enabled identifying radish cover crop treatments as having on average higher SOM levels compared to the fallow. However, infield spatial SOM variation can override cover crop effects on SOM levels. Therefore, UAV time series are required to remotely quantify cover crop impacts on SOM changes. Overall, our results show potential for combining proximal and UAV-based sensing SOM as a tool for more efficient and accurate spatiotemporal monitoring of SOM

Recycling of organic resources into agriculture has the potential to greatly increase nutrient use efficiency and improve soil carbon balance, but improper management can have adverse effects on the environment. Agriculture therefore faces large challenges to increase yields while decreasing these emissions to the environment. In this paper, we review (i) the availability and composition of organic resources, (ii) their agronomic value and risk of emissions, (iii) potential measures to reduce their emissions, and (iv) future challenges to support farmers and policy makers. The total amount of organic resource applied to soil amounted on average 41 kg nitrogen per ha agricultural land, 9 kg phosphorus per ha, and 456 kg carbon per ha in EU-27 + UK in 2017. Solid pig and cattle manures and cattle slurry are the most used organic resources. The availability of new organic resources from food processing, sewage sludge, municipal bio-wastes, and upcoming manure treatment techniques as fertilizer or soil conditioner is expected to strongly increase over the coming decade. Insight is needed into the composition of organic resources, the plant-availability of nutrients, the degradability of organic matter and the presence of contaminants. Measurement techniques become available to characterize soils, manures, crops, and emissions to the environment. However, the interpretation, and integration of data, and recommendations to farmers and policymakers using large amounts of data is expected to become more and more challenging. Many measures are available to improve nutrient and carbon management and to reduce emissions, including proper application, technological measures and structural changes in agriculture. For many measures, there is a risk of trade-offs that could lead to pollution swapping at different scales. We should focus on finding synergies between measures and no-regret management choices to develop effective mitigation strategies. The main future challenge for m

Agricultural soils are at risk of nitrogen (N) leaching especially during the fallow period in autumn and winter. Cover crops are grown to capture soil mineral N that otherwise would leach to the groundwater. They can serve as green manure providing mineral N to the cash crop in spring. We investigated whether mixing species of cover crops can enhance N capture and therefore reduce N leaching more effectively than pure stands in autumn without increasing the risk of N leaching in spring. We hypothesised that mixed species with complementary traits will capture more N and accumulate more biomass. It was also expected that residues from cover crops with higher biomass and lower C:N ratio would mineralise faster and subsequently increase N leaching in spring. In a 4-year field experiment, cover crops were grown between August and February in a rotation with different cash crops. We used eight cover crop treatments, including three pure stands: radish (Raphanus sativus), vetch (Vicia sativa) and oats (Avena strigosa), all possible 2- and 3-species mixtures and a fallow (no cover crop). Treatment effects on leaching losses were estimated by analysing N concentrations in samples of leached pore water below the rooting zone and by modelling the volume of water leached per plot. Most N leaching occurred in autumn and winter while the amount of N leached in spring was negligible due to the lower precipitation. N leaching in autumn correlated negatively with cover crop biomass, N uptake and root length density. Radish and oats were the most productive species and dominated mixtures. Compared to the fallow, radish and mixtures that con- tained radish reduced N leaching by 49–73% and were characterized by quick soil cover, high N uptake and low to moderate C:N ratio. Subsequently, residues from radish and mixtures containing radish mineralized quickly, resulting in an increase in soil mineral N in spring by 70–

Vergisting van plantaardige reststromen kan bijdragen aan hernieuwbare energieproductie en ook emissies uit gewasresten en organische reststromen voorkomen. In tegenstelling tot digestaten gebaseerd op dierlijk mest, is er nog weinig onderzoek gedaan naar effecten van digestaat gebaseerd op plantaardige reststromen. In deze studie zijn de effecten van plantaardig digestaat op lachgas, ammoniak en CO2-emissies, bodemvruchtbaarheid en gewasopbrengst onderzocht door middel van literatuuronderzoek en een lab-incubatie- en potexperiment. In de experimenten zijn plantaardige digestaten uit gewasresten, suikerbietenpulp en bietenblad vergeleken met reguliere meststoffen (kunstmest, runderdrijfmest, co-vergiste runderdrijfmest en compost). De emissies van de plantaardige digestaten zijn vergelijkbaar met runderdrijfmest en ook de gewasopbrengst en N-opname is vergelijkbaar en hoger dan bij toediening van compost. Uit deze studie blijkt dat er geen reden is om aan te nemen dat plantaardige digestaten hoge emissierisico’s of een negatief effect op bodemvruchtbaarheid en gewasopbrengst met zich mee zouden brengen.---Anaerobic digestion of plant-based residues can contribute to renewable energy production and prevent emissions from crop residues and organic waste. In contrary to digestates derived from animal manure, only limited research is available on the effects of digestate from plant-based residues. In this study the effects of plant based digestate on nitrous oxide, ammonia and CO2 emissions, soil fertility and crop yields were investigated, using literature research and an incubation and pot experiment. In the experiments plant based digestates from crop residues, sugar beet residues and sugar beet leaves were compared with regula rfertilizers (mineral fertilizer, cattle slurry, co-digested cattle slurry and compost). The emissions of the plant based digestates were comparable to cattle slurry. Also crop yield and N uptake were comparable to cattle slurry and higher com

De Provinciale Staten in Gelderland hebben de ambitie vastgesteld om in 2030 de uitstoot van broeikasgassen in Gelderland 55% lager te laten zijn dan in 1990. Ook koolstofvastlegging in bodem en vegetatie moet hier aan bijdragen. In deze studie is de potentie voor CO2-vastlegging in Gelderse landbouwbodems in kaart gebracht. Het gaat dan om potentie voor verschillende maatregelen en ook waar (regio en grondsoort) deze potentie hebben. Meer blijvend grasland en het toepassen van extra vaste mest hebben de hoogste potentie voor Gelderland, gevolgd door mais in grasland met strokenfrees en het zaaien van een vanggewas/groenbemester na de oogst.

Cover crops incorporated in an agricultural rotation can improve ecosystem services such as nutrient cycling and carbon sequestration in soil. Cover crop mixtures, through complementarity, can have a greater effect on these ecosystem services as well as being an effective tool to improve plant biodiversity. The aim of this thesis is to mechanistically understand how cover crop mixtures can provide synergistic benefits in terms of carbon (C) and nitrogen (N) cycling. In a meta-analysis of litter decomposition studies across the world I showed that on average, mass loss of mixed litters is equal to the weighted average of the mass loss of the constituent single litters. Any interactive effects (positive or negative) between litter species are contextual, and cannot be predicted based on litter traits. In a greenhouse study synergistic effects of mixing cover crop residues on mineralisation rates and N2O emissions were also not found. Residue of the single cover crops did have divergent effects on N mineralisation and N2O emissions, highlighting that cover crop residue quality is important when considering timing of cover crop incorporation and main crop planting. In a field experiment I found that, during cover crop growth, cover crop mixtures perform equally well as the best performing monocrop in reducing nitrogen leaching. Fertilising cover crops in order to kick-start growth does not increase biomass nor N recovery. Thus fertilisation is not necessary and increases the risk of N leaching just after fertilisation. After 4 years of including cover crop (mixtures) in an agricultural rotation on a sandy soil, none of the single cover crops and 2 out of 4 cover crop mixtures increased the soil organic matter content. None of the single cover crops had any effect on the stable or labile carbon pool in the soil. This thesis shows that mixtures of cover crops perform as well as the highest performing single cover crops in terms of N cycling, and mixtures can increase C se

This database belongs to a meta analysis on litter mixture decomposition. Published data was included when the research on litter mixture decomposition used litterbags and two species mixtures. Litter quality, environment and experimental design are recorded as well as mass loss in percentage