The effects of mineral fertilizers and organic amendments on soil properties, carbon (C) sequestration, and crop yields are studied in a 37‐year field experiment, Phosphorus–Potassium‐balanced design, in Switzerland. Treatments included a control (mineral fertilization) without nitrogen (N) fertilizers (Min‐N0) and with optimal N (Min‐Nopt) and 5 organic amendments (green manure [Gm], cereal straw [Str], fresh cattle manure in 2 doses 35 and 70 t ha−1 [Ma35 and Ma70] and cattle slurry [Slu]) all receiving the same optimal N fertilization as Min‐Nopt. All mineral and organic treatments received optimum P–K fertilization. Nitrogen fertilization (Min‐Nopt vs. Min‐N0) increased soil organic C, microbial activity, and microporosity but decreased pH, magnesium, and macroporosity. All organic treatments with optimal mineral N resulted in higher soil organic C content compared with Min‐Nopt, however, these effects were significant only for the highest dose of manure. The organic amendments supplied 25% to 80% additional C input to the soil compared with Min‐Nopt, and their amendment‐C retention coefficients ranged from 1.6% (Gm) to 13.6% (Ma70). Chemical, physical, and biological soil properties were not or slightly significantly different among organic treatments. Nevertheless, soils fertilized with farmyard manure produced generally higher grain yield (up to 7.3%) compared with Min‐Nopt whereas the opposite effect was noted for Gm (−2.2%) and Str (−5.2%) treatments due to their negative effect on N availability. In conclusion, Gm and Str treatments were as effectives as Ma35 and Slu treatments to prevent soil degradation but required higher chemical fertilizer to maintain crop yield.

Phosphorus (P) is the second essential nutrient for plant growth but can become an ecological and economical concern in case of over-fertilization. Soil P dynamic is influenced by many parameters like soil physical-chemical properties and farming practices. A better understanding of the factors controlling its distribution is required to achieve best management of P in cropping systems. In Switzerland, the FRIBO network was launched in 1987 and consists of 250 sites covering a wide diversity of soils (Cambisols, Gleysols, Rendzinas, Lithosols, Luvisols, Fluvisols) and three different land uses (cropland, grassland and mountain pasture) across the Fribourg canton. A spatial investigation of the different P forms (total, organic and available) for the FRIBO network led to the following main conclusions:(i) The P status in agricultural soils was significantly different among the three land uses encountered, with the highest mean values of available P found in croplands, from 2.12 (CO 2 saturated water extraction) to 81.3 mg.kg −1 (acetate ammonium + EDTA extraction); whereas total P was more abundant in permanent grasslands (1186 mg.kg −1 ), followed by mountain pastures (1039 mg.kg −1 ) and croplands (935 mg.kg −1). This full characterization of the soil P status provides important data on P distribution related to soil properties and land use.(ii) Environmental variables such as altitude, slope, wetness index or plan curvature, derived from the digital elevation model (DEM) only explained a small part of the spatial variation of the different P forms (20 to 25%). Thus, the geostatistical analyses revealed that land use plays a significant role in soil P distribution. Improved predictions of the spatial distribution of P-related forms at landscape scales are needed and would require additional data points and variables such as parent material, soil types and terrain attributes.

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There is an increasing awareness about the need for improving nitrogen use efficiency in crop 24 production in order to meet economic and ecological standards. The present work provides 25 insight into the varietal factors of wheat that determine nitrogen use in the plant. The 26 performance of eleven winter wheat varieties in terms of grain yield and nitrogen uptake and 27 use efficiency was tested within the framework of a 40-year long term field experiment of 28 organic enrichment and mineral nitrogen fertilisation treatments. Globally, organic 29 enrichment had a beneficial effect on the yield and grain nitrogen concentration and showed a 30 strong interaction with the amount of applied mineral nitrogen fertiliser. Manure application 31 generally had positive effects on varietal performances mainly due to indirect long term 32 effects on the soil properties. Varieties showed a broad range of responses to the treatments of 33 the long term experiment, revealing significant genotype x environment interactions. 34 Nevertheless, the varieties which performed well at high input levels were also the best at low 35 input levels, suggesting that the genotype x environment interactions were not strong enough 36 to inverse the performance ranking. Similarly, the varietal traits associated with high yielding 37 or grain nitrogen concentration in high input conditions were the same as those identified 38 under low input conditions. To conclude, these results suggest that the selection of wheat for 39 nitrogen efficiency is possible under any nitrogen fertilisation regime. However, to be adapted 40 to low input or organic agriculture, varieties also need traits other than nutrient use efficiency, 41 for example, disease resistance, resilience to abiotic stresses and competitiveness against 42 weeds. 43