Accumulation of biologically fixed nitrogen by legumes cultivated as cover crops in Switzerland

Aims Biological nitrogen fixation by legumes is expected to play a greater role in future cropping systems. Our study evaluated 19 legume species grown as cover crops in Swiss agroecosystems. Methods Two field experiments were set up to monitor the biomass production and nitrogen content of 19 legumes and two non-legumes. The proportion of nitrogen derived from atmospheric N2 (%Ndfa) was assessed using the 15N natural abundance method. In parallel, a pot experiment was set up to determine the species-specific B values necessary to apply this method. Results Some species produced an important amount of biomass in 3 months, up to 6.86 t/ha for Vicia faba. Five species, Lathyrus sativus, Pisum sativum, Vicia sativa, Vicia villosa, and V. faba, acquired more than 100 kg/ha of N through biological fixation. Important amounts of nitrogen were also derived from the soil. %Ndfa values showed high variability between and within species, ranging from 0 % to almost 100 %. Conclusions Some legumes showed high N accumulation even in a short growing period, and could play an important role in fixing renewable nitrogen in crop rotation

Performance of eleven winter wheat varieties in a long term experiment on mineral nitrogen and organic fertilisation

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

Long and short term changes in crop yield and soil properties induced by the reduction of soil tillage in a long term experiment in Switzerland

To address the influence of soil tillage reduction on crop yield and soil properties, an experiment was set up in 1969 in the western part of Switzerland. A conventional tillage treatment with plough was compared to a minimum tillage treatment and a deep non inversion tillage treatment, converted to no till in 2007. Evolution of crop yield through time was investigated, as well as the soil properties in 2013. Mean soil properties and their stratification with depth were assessed. The results showed that, after 44 years, globally, all tillage treatments allowed to maintain similar yields in the long term. However, during the same time, soil properties have changed deeply. Soil organic carbon has decreased compared to the initial situation, in all treatments except in the minimum tillage. This treatment also allowed to reach high clay to carbon ratio in the upper layer, suggesting good soil structural quality compared to the other treatments. In contrast, this did not result in significant differences in carbon stocks between tillage treatments, probably due to low carbon inputs in all treatments. In addition, a strong stratification pattern with depth was observed for most of the nutrients in the minimum tillage treatment, while the situation was more homogeneous in the plough treatment. The adoption of no till also modified soil properties and lead to clear stratification patterns after only six years. These results showed that crop yield could globally be maintained in reduced tillage systems, while insuring high soil fertility and structural quality. The important decrease in the number of tillage interventions and intensity of disturbance induced an improvement of soil properties. Reduced tillage practices could thus be advantageously adopted to insure crop production together with soil fertility improvement in rather short time period

Spatial variability of potassium in agricultural soils of the canton of Fribourg, Switzerland

Potassium (K) is a crucial element for plant nutrition and its availability and spatial distribution in agricultural soils is influenced by many agro-environmental factors. In Switzerland, a soil monitoring network (FRIBO) was established in 1987 with 250 sites distributed over the whole of the canton of Fribourg (representing 4% of the surface area of Switzerland), whose territory is shared between the Swiss Midlands and the Western Alp foothills. In this study area, diverse geological deposits (sandstone, marlstone, silts and calcareous rocks), soil types (Cambisols, Gleysols, Rendzinas, Luvisols and Fluvisols) and land uses (cropland, permanent grassland and mountain pasture) are present, making the network interesting for assessing the relative contribution of environmental variables and land use management on soil properties. The aims of the present study were to (i) characterize the soil K status in the Fribourg canton according to four different extraction methods; (ii) analyse the spatial variability of soil K in relation to land use, soil type, soil parent material and topography; (iii) evaluate the spatial predictability of K at the canton level; and (iv) analyse the implications for K fertilization management. The overall amount of soil total K averaged 13.6 g.kg-1 with significant variations across the sites (5.1-22.1 g.kg-1). The spatial distribution of total K was particularly influenced by soil parent materials, as suggested by a significant global spatial autocorrelation measure (Moran’s I10km = 0.43) and significant differences observed among soil types and soil parent materials. On the other hand, available mean K forms were significantly different among land uses, with the highest mean values of available K encountered in permanent grasslands, from 46.3 mg.kg-1 (water extraction) to 198 mg.kg-1 (acetate ammonium + EDTA extraction). All K forms showed similar spatial regional patterns for all spatial interpolation methods, with areas dominated by permanent grassland and crops presenting higher values. However, these trends were less pronounced for the available K forms due to the prevalence of on-farm management practices for these K forms and their high temporal variability. This hypothesis was supported by spatial clustering of low and/or high K fertility status that could be related to local particular farming practices. Grasslands require particular attention with regard to overall high K fertility status

Spatial variability of soil phosphorus in the Fribourg canton, Switzerland

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 P crops management. In Switzerland, the FRIBO network was launched in 1987 and comprises of 250 sites covering a wide diversity of soils and three different land uses (croplands, grasslands and mountain pastures) across the Fribourg canton. A spatial investigation of the different P forms 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 to 81.3 mg.kg-1 according to the indicator used), whereas total P was more abundant in permanent grasslands (1186.2 mg.kg-1), followed by mountain pastures (1039.0 mg.kg-1) and croplands (935.0 mg.kg-1). A full characterization of the soil P status provides necessary data on P distribution related to soil properties and land use, and should help to develop more accurate estimation procedures and fertilization strategies in a near future; ii) Environmental variables derived from digital elevation model (DEM) only explained a small part of the spatial variation of the different P forms (20 to 25%). Thus, the geostatistic analyses revealed that land use play a major role in soil P distribution. However, this pattern was less visible for total P than for available P. Future studies should include more data points as well as additional variables such as parent material and soil type to accurately estimate the role of soil parameters on the distribution of P-related forms

Influence of root and leaf traits on the uptake of nutrients in cover crops

Aims: Cover crops play an important role in soil fertility as they can accumulate large amounts of nutrients. This study aimed at understanding the nutrient uptake capacity of a wide range of cover crops and at assessing the relevance of acquisition strategies. Methods: A field experiment was conducted to characterize 20 species in terms of leaf and root traits. Plant traits were related to nutrient concentration and shoot biomass production with a redundancy analysis. Acquisition strategies were identified using a cluster analysis. Results: Root systems varied greatly among cover crop species. Five nutrient acquisition strategies were delineated. Significant amounts of nutrients (about 120 kg ha−1 of nitrogen, 30 kg ha−1 of phosphorus and 190 kg ha−1 of potassium) were accumulated by the species in a short period. Nutrient acquisition strategies related to high accumulations of nutrients consisted in either high shoot biomass and root mass and dense tissues, or high nutrient concentrations and root length densities. Species with high root length densities showed lower C/N ratios. Conclusions: The same amounts of nutrients were accumulated by groups with different acquisition strategies. However, their nutrient concentrations offer different perspectives in terms of nutrient release for the subsequent crop and nutrient cycling improvement

Long-Term Effects of Organic Amendments on Soil Organic Matter Quantity and Quality in Conventional Cropping Systems in Switzerland

Increasing soil organic carbon (SOC) in agroecosystems is a promising solution to simultaneously address climate change mitigation, adaptation, and food security. Yet, the best management practices that could achieve these goals remain to be identified. Here, we analyze the long-term effects of application of green manure, cereal straw, farmyard manure, and cattle slurry on SOC in a 37 year long field experiment in Switzerland. The treatment effects were compared against control conditions that received only optimal mineral fertilization. More specifically, this study aimed at evaluating the effect of organic amendments on SOC accumulation and distribution in different soil particle-size fractions by means of a set of indicators about organic matter quality (biological reactivity, humification index) and microbial activity (extracellular enzyme activities). In the absence of organic matter input, application of mineral fertilizers alone resulted in the lowest SOC content and the highest humification index of the bulk soil organic matter. Among the organic amendments, cereal straw, farmyard manure, and cattle slurry promoted a higher SOC content and a lower humification index due to an increase of SOC in the clay-size fraction. The annual C accrual reached 4.4‰ per year over 37 years with farmyard manure. The higher biological reactivity measured for the green manure and cereal straw amendments was associated with higher soil enzymatic activities, while C retention coefficients decreased by at least 2.5 times compared to animal-derived amendments. The low availability of nutrients in green manure and straw amendments as suggested by the high phosphatase and N-acetylglucosaminidase activities may indicate a reduction in C retention of organic matter inputs due to nutrient microbial mining with plant-derived amendments

Critical plant and soil phosphorus for wheat, maize, and rapeseed after 44 years of P fertilization

Phosphorus (P) crop fertilization requires optimal management to avoid the waste of a non-renewable resource and water pollution, but current methods for assessing soil phyto-available P and plant P requirements are not sufficiently precise to meet this goal. The objectives of the present study were to (1) evaluate the effect of long-term P fertilization on the grain yield of winter wheat, maize, and rapeseed, (2) validate or establish models of critical shoot P concentration (P-C) based on relationships of shoot P concentration with either shoot biomass or shoot nitrogen (N) concentration, and (3) assess both plant-based and soil-based diagnostic tools for managing P fertilization. A long-term field experiment with contrasted P fertilizer treatments, established in 1971 by Agroscope in Changins (Switzerland), was used to measure the shoot biomass and P concentration of winter wheat in 2011, maize in 2012, and rapeseed in 2014 weekly during the growing period and the grain yield at harvest. Soil available P in the 0-0.20m soil layer was assessed by three chemical extractions: ammonium acetate EDTA (P-AAE), sodium bicarbonate (P-NaHCO3), and CO2-saturated water (P-CO2). Long-term P fertilization increased soil available P extracted by P-CO2 (+24%), P-AAE (+200%), and P-NaHCO3 (+155%), shoot growth and grain yield by 8.4% and 26.2% for winter wheat and rapeseed respectively but had no effect on maize. The relationships between P-C and shoot biomass or N concentration were described respectively by allometric and linear models (R-2>0.85, n=21, 28 and 32 for winter wheat, maize and rapeseed respectively; slope P values for linear models <0.05). The P-C-shoot N concentration model (slope: 0.083, intercept: 0.88) for winter wheat confirmed results from previous studies and can be used for calculating the P nutrition index. For the three soil available P indicators, threshold values needed to achieve 95% of the maximum yield for the three crops were less than those currently used in the official fertilization guidelines in Switzerland. Our results obtained after 44years of contrasted P fertilization confirm the relationship between P-C and shoot N concentration for grain crops and the need to revise P fertilizer recommendations based on currently used soil P tests

Soil and plant phosphorus status and crop yields after 40 years of mineral P fertilization

National audiencePhosphorus (P) fertilizers are an essential input for economically sustainable crop production but they may represent a significant problem for water quality if managed incorrectly. Appropriate evaluation of soil P availability is a prerequisite for ensuring the productivity and long-term sustainable management of agroecosystems. A long-term trial at Agroscope-Changins in Switzerland has been conducted in a clay Gleyic Cambisol (FAO classification system) for 40 years to analyze the effect of P fertilization (0 to 60 kg P ha-1 yr-1) on soil and plant P status, and crop yields. Soil analyses (0-20 and 20-50 cm depth) included total, organic, inorganic and available-P assessed by a process-based approach and different chemical extractions. Shoot biomass and plant P concentration of wheat in 2011 and corn in 2012 were measured approximately weekly during the growing season (7 sampling dates) and the P nutrition index [PNI: 100 × (Pmeasured/PC)] was determined using a critical P concentration (PC) based on whole plant shoot biomass [PC = α × (DM)β]. After 40 years of cultivation, cumulative P (applied minus exported P) ranged from -567 to +1554 kg P ha-1, respectively for 0 and 60 kg P ha-1 yr-1. As a consequence, P-fertilization significantly affected, except organic P, all other measured soil P parameters for the 0-20 cm soil layer. Thus, the total P ranged from 0.78 to 1.14 g P (kg soil)-1 while the concentration of phosphate ions in soil solution varied from 0.06 to 0.75 mg P l-1, respectively for 0 and 60 kg P ha-1 yr-1. Phosphorus fertilization also significantly increased wheat and corn grain P concentration but did not affect grain yield. The PNI ranged at harvest from 97 to 166 % for wheat and 98 to 128 % for corn, showing that P was not crop-limiting even after 40 years of cultivation without P fertilization. This study highlights the interest of plant-based diagnostic methods alongside soil analyses for the optimization of P fertilization practices for croplands in Switzerland

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