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In the 1960s, the agricultural “Green Revolution” brough new technologies and heavy mechanisation to the fields. These technologies brought rapid answers to increase the crop yields and improve food security. Among these technologies we found pesticide and plastic mulch applications. Since then the scientific community and the general public became worried of the long term consequences of these short term solutions. Indeed plastic mulch and pesticides leave debris which accumulate in the soil and are potentially harmful to divers organisms. With this PhD thesis we try to encompass the threat posed by plastic mulch and pesticide residues in agriculture. The research was organised in seven different chapters described below.Chapter 1: In introduction we presented the diverse benefices of pesticide and plastic use in agriculture. The many services they provide explained why they are use abundantly worldwide. However both plastic and pesticides have the potential to accumulate in the soil. We narrowed down the focus to plastic mulch as it is used abundantly worldwide and is recognize as an important source of plastic debris. We presented three different plastic types: Low density Polyethylene (LDPE), Pro-oxidant Additive Containing (PAC) and biodegradable (BIO) mulches. Finally, we presented the threats posed by plastic and pesticide residues and the need for more research. We elaborated six main questions that are addressed in the following five research chapters.Chapter 2: The objective of this field assessment was to measure plastic and pesticide residues in agricultural soils and their effects on the soil microbiome. For this, we sampled soil from 18 parcels from 6 vegetable farms in Southeast Spain. The farms were under either organic or conventional management, where plastic mulch had been used for > 25 years. We measured the macro and micro light density plastic debris content, the pesticide residue levels, and a range of physiochemical properties. We also carrie

Long-term soil organic matter (SOM) and nutrient dynamics following different crop residue management were studied in two field experiments in Austria: in Marchfeld since 1982 and in Alpenvorland since 1986. The turnover of SOM was modeled with the CCB (CANDY carbon balance) model. SOM parameters such as soil organic carbon (SOC), active C (KMnO4), total nitrogen (Nt), and the N-mineralization potential increased significantly following crop residue incorporation. C/N ratios, however, did not differ significantly. Plant-available potassium (K) increased by 40% (Alpenvorland) and 50% (Marchfeld), magnesium (Mg) only in Marchfeld (+ 9.7%), and no effect was evident for phosphorus at either site. Our results showed a strong agreement between measured and simulated SOC values. SOC can be maintained in the long term with the incorporation of crop residues, but it will decrease with annual removal.

Near infrared (NIR) spectroscopy was used to predict the soil organic carbon (SOC) contents at local scale in eleven target sites. For that, eight spectral libraries of different sizes (ranging from 3482 to 36 samples) were used to construct national, provincial and local scale models. Inaccurate predictions were obtained except when the largest national library was used to construct the model. We also obtained SOC predictions once the models were adapted to target sites characteristics. For the models' adaptation, we used a two-step approach consisting on spiking (as first step) and extra-weighting (as second step). The effect of spiking was small in larger-sized models and high in smaller-sized models, whereas the effect of extra-weighting was small in smaller-sized models and large in larger-sized models. The very high accuracy obtained after models' adaptation (R2>0.95; RPIQ>5.48), regardless of the size of the spectral library, suggests that large spectral libraries are not needed for local scale SOC assessment. These results have important implications regarding the way that NIR spectroscopy can result highly effective for land management and how users can focus and organize the analytical efforts.