http://www.pressesagro.be/base/ Publisher: Les Presses agronomiques de Gembloux, ISSN 1370-6233, eISSN 1780-4507. fr-be http://www.pressesagro.be/picture/cover/issn/small/13706233.jpg http://hdl.handle.net/11006/65 http://hdl.handle.net/11006/66 By Deneufbourg M., Vandenberghe C., Gaule D., Bolly P.Y., Marcoen J.M. / Application of the Sustainable Nitrogen Management Program in two small agricultural watersheds (Arquennes – Belgium) and impact evaluation by monitoring of nitrate fluxes at outlets and by numerical modeling. Four water catchments used by the Walloon Society of Water (SWDE) in the rural village of Arquennes (Province of Hainaut, Belgium) have been contaminated by nitrate (concentrations between 60 and 70 mg NO3-·l-1) for several years. The catchment basins (31 ha and 47 ha) are located exclusively in a cultivated area on loamy soils. Since October 2004, these basins have been used as a pilot area for the environmental evaluation of good agricultural practices as regards nitrogen management (adaptation of amounts of mineral nitrogen fertilizers, farm manure management, soil cover after harvest, etc.) thanks to monitoring by farmers. This approach fits into the general pattern of the Sustainable Nitrogen Management Program (PGDA in French), which implements the European Nitrates Directive as part of Walloon legislation. The second objective of the working scheme is to study and to set up a decision-making tool aimed at preventing the contamination of water by agricultural nitrate around water catchments. Two numerical models (SWAT and FEFLOW®) were used together in order to simulate the passage of water and nitrogen from the soil surface to the water catchments outlets. Calibration and validation of models were based, among other things, on soil and subsoil characterization and on tracer testing in both saturated and unsaturated zones. Moreover crop yield, farming practices, water and nitrate fluxes in water catchments, groundwater levels and nitrate concentration in groundwater were monitored for eight years. The results of simulations show that the application of PGDA in Arquennes watersheds would lead to a decrease in nitrate concentration (to almost 50 mg NO3-·l-1) in water catchments in 2012. This expected improvement in water quality has been visible since 2009 in water catchments, with mean nitrate concentrations of lower than 50 mg NO3-·l-1 at the end of 2012. http://hdl.handle.net/11006/67 By Deneufbourg M., Vandenberghe C., Heens B., Marcoen J.M. / Monitoring of nitrate leaching in open fields by lysimeters: results from an eight year study. Since 2003, nitrate leaching has been monitored in six plots located in a loamy area (Hesbaye, Belgium), mainly dedicated to wheat, sugarbeet and vegetable crops. Open-field lysimeters have been used in order not to impede agricultural operations. Lysimeters are used as follow-up tools to quantify the amounts of nitrate leaching below the root zone. This study aims to evaluate the suitability of PLN (Potentially Leachable Nitrogen – APL in French) defined in the Sustainable Nitrogen Management Program (PGDA in French) as an environmental indicator by relating nitrogen management practices (including fertilization recommendations) to PLN values and groundwater quality. This study demonstrates that lysimeters are efficient in collecting representative amounts of leaching water. Lysimeters show that PLN is identified as being related to the nitrate content in leaching water, which will not be taken up by the next crop. The amount of nitrate leaching below the root zone demonstrates the necessity and the relevance of the organic nitrogen spreading limits defined in the Sustainable Nitrogen Management Program. The lysimeter tool also shows that respect for leaching water quality standards under agricultural plots needs to be considered from an integrated and generalized approach, taking into account complete crop sequences and rotations, including rational fertilization rates and the introduction of catch crops in rotation. Some suitable or unsuitable crop sequences with regard to good groundwater quality are listed. http://hdl.handle.net/11006/68 By De Toffoli M., Oost J.F., Lambert R. / Impact of the destruction of grassland on soil nitrogen residue and the management of nitrogen fertilization. When permanent grassland is destroyed, the mineralization of organic matter accumulated in the soil leads to a substantial enrichment of soil mineral nitrogen for several years after the destruction occurs. Results show that, following the destruction of grassland in early spring, yields of maize silage were high for a period of two years. Furthermore, residual nitrogen in the soil after harvest far exceeded the expected values for the crop. Results from other studies show that the risk of nitrogen loss is high following the destruction of permanent pasture before winter even in colder climates. Reducing the risk of nitrogen loss between two cultures requires not only a more accurate control of fertilization by carrying out soil analyses, but also the application of a generalized ban on grassland destruction before winter and the carrying of appropriate crop sequences to remove nitrogen available in large quantities over as long a period as possible. http://hdl.handle.net/11006/64 By Godden B., Luxen P., Destain J.P. / Efficiency and fate of slurry N applied to permanent grass in Ardenne (Belgium) – Effect of the choice of spreading period. In Haute Ardenne and Pays de Herve, areas devoted to grass, slurry represents the main source of nitrogen; slurry is applied on permanent pasture. This paper aims to compare the nitrogen efficiency of cattle slurry with that of mineral fertilizers and to determine the influence of the choice of spreading period on N use by grasses. Results from two long terms trials and from one in micro plots using stable 15N are presented. Results show that the fertilizers applied (organic and mineral) only affected at a mean level of 25% N absorbed by grassland. The efficiency of spring slurry applications carried out in favorable spreading conditions matched those of mineral N. From our results, it can be concluded that N losses in grasslands are very low and are due to volatilization just after the spreading of slurry. http://hdl.handle.net/11006/69 By Hennart S., Lambert A., Stilmant D. / Impact of cattle stocking rate, under grazing, during autumn on potential nitrogen leaching: reference values established in the south-east of Belgium. Grassland, which accounts for half of the agricultural area in Wallonia, forms the basis of many ecosystemic services: cultural, grass production, regulatory services, etc. Nevertheless, the poor ability of cattle to fix ingested nitrogen leads to significant N rejection during grazing. N is excreted in concentrated form via urine, and thus becomes unevenly distributed within the paddock. This phenomenon increases the risk of N leaching in grazed grasslands, especially if urine deposit occurs later during the grazing season, in the autumn. It is therefore necessary to specify good livestock management practices, with particular reference to the livestock stocking rate to be applied during autumn grazing. This ensures the reconciliation of both animal and environmental performance. With this aim, a study was performed over a five-year period, during the autumn, to test the impact of the livestock stocking rate on the risk of nitrate leaching in grazed grassland, in the Jurassic area of south-east Belgium. A gradient of stocking rate was established, ranging between 150 and 350 BLU grazing days·ha-1. Results underlined a highly significant impact of the "year" factor on potentially leached nitrogen (APL), ranging between 9 (2010) and 23 (2005) kg of N-NO3-·ha-1. The impact of the stocking rate was only marginally significant. Whatever the year or the stocking rate, the recorded APL level never represented a significant risk to water resources, and this was in spite of a relatively high stocking rate at the end of the grazing season. This low impact of the stocking rate could be explained by the type of cattle (beef breed heifers and dry cows) mobilized in order to apply these end-of-season stocking rates. A further explanation could lie in the addition of hay to the cattle's diet in order to achieve the highest stocking rates. Higher level of APL would be expected under grazing with dairy cows. http://hdl.handle.net/11006/70 By Heens B. / Nitrogen fertilization of vegetables. Industrial vegetables occupy 2% of the utilized agricultural area in the Walloon region; of nearly 15,000 ha., 73% is given over to the growing of legumes. Nitrogen inputs are low or zero for legumes. Experiments have shown that an appropriate supply of nitrogen to broad beans and beans contributes to a better start for the crop without increasing soil nitrogen residue after harvest. The mineralization of crop residues is responsible for the increase in soil nitrogen residue. The only way to reduce the Potentially Leachable Nitrogen (PLN: an environmental indicator in Wallonia) in the beginning nitrate leaching period is to employ good management of catch crops. The carrot has a crop cycle similar to sugar beet and has a low level of nitrogen fertilization. PLN is generally not a problem in carrots. Spinach is a nitrogen demanding crop, whose needs are well known as a result of previous experiments. Spinach is harvested during intensive growth and so its leaves sometimes have high soil nitrogen residues. The plant's short crop cycle allows double cropping. After harvesting winter and spring spinach, the mineralization of crop residues contributes to a good start for the next crop. After harvesting autumn spinach, either planting a catch crop classified as a nitrate trap or allowing the regrowth of spinach represent solutions for reducing PLN. http://hdl.handle.net/11006/71 By Abras M., Goffart J.P., Destain J.P. / Prospects for improving the provisional nitrogen fertilization recommendation at field scale in Wallonia using the AzoFert® software. The French software AzoFert® for nitrogen fertilization recommendation is currently under adaptation and validation for soil and climatic conditions in Wallonia by the CRA-W within the INTERREG IV project "SUN" (Sustainable Use of Nitrogen). This adaptation has raised the need for a change of values in the parameter tables and catalogs relating to meadow residues, crop residues, catch crop practices, crops, organic amendments and soil type. Data from 25 trials of increasing nitrogen fertilizer rates conducted by CRA-W between 1996 and 2011 in cereal, potato and vegetable crops located on loam and sandy loam soil were used to validate the AzoFert® software adapted for Wallonia. The difference between nitrogen rates recommended on the one hand by AzoFert® or Azobil® (software currently used in the reference lab for Nitrate [Requasud] at CRA-W) and the optimal dose of nitrogen fertilizer assessed in each trial on the other hand shows that, in most cases, AzoFert® gives a recommendation closer to the optimum than Azobil®. The nitrogen uptake measured in the plants collected in the unfertilized control plot also shows a higher correlation with nitrogen supply from the soil assessed by AzoFert® than for plants assessed by Azobil®. The more accurate estimate of the mineralization of organic sources, probably linked to the dynamic soil nitrogen supply approach integrated into AzoFert®, may explain the gain in the greater accuracy of the AzoFert® recommendation in comparison with that of Azobil®. http://hdl.handle.net/11006/72 By Goffart J.P., Abras M., Ben Abdallah F. / Nitrogen fertilization management of open-field crops. Opportunities for improvement of nitrogen use efficiency based on crop nitrogen status monitoring. The improvement of nitrogen use efficiency in crops is currently an important issue in farming due to current and future economical and environmental constraints. Splitting of N fertilizer application is the most suitable approach for providing an optimal match of N need and supply. The implementation of monitoring methods to assess crop N status is required to define the relevant amounts and periods required for split applications. This paper discusses the available methods of split N fertilizer application and their mode of use and implementation. After a short overview of the concept of crop N status, the main existing methods to estimate nitrogen needs are examined for their accuracy, specificity and sensitivity based on research conducted at CRA-W (Production and Sectors Department, Crop Production Systems Unit) over the last two decades, focusing specifically on the potato crop. The methods and the results described relate to the petiole sap nitrate concentration test assessed via a reflectometer, the measurement of leaf chlorophyll concentration with a handheld chlorophyll meter, leaf chlorophyll fluorescence readings with handheld fluorimeters, and the measurement of crop light reflectance with a handheld radiometer (ground-based remote sensing) or with satellite imagery (spatial remote sensing). Conditions for implementing such methods within decision support systems are briefly described, by focusing on the need to use relative values rather than raw values taken from the readings, and also on the requirement for threshold value definition. The integration of crop nitrogen status values into N fertilization recommendation models is illustrated through a Decision Support System created at CRA-W for the potato crop. http://hdl.handle.net/11006/73 By Vandenberghe C., De Toffoli M., Bachelart F., Imbrecht O., Lambert R., Marcoen J.M. / Control of potentially leachable nitrogen in the soil at the start of the lixiviation period. Establishment of reference values. Based on observations in the field, for ten years, Gembloux Agro-Bio Tech (ULg) and the Catholic University of Louvain set annual benchmarks for nitrate-nitrogen concentrations in the soil at the beginning of the leaching period (referred to as 'PLN' - Potentially Leachable Nitrogen). These values are used as a reference to monitor farmers located in vulnerable zones, with the monitoring being carried out by the Public Service of Wallonia. Soil samples were taken twice a year (October and December) from approximately 250 plots subjected to reasoned nitrogen fertilization. The plots were located within 34 reference farms (constituting the Agricultural Survey Areas). The samples were then analyzed for nitrate-nitrogen content. The results allowed to establish reference values for eight classes of cultivation or meadow. Analysis of the results recorded in 2011, as in previous years, illustrates the importance of "crop" and "year" in establishing reference values. http://hdl.handle.net/11006/74 By De Toffoli M., Decamps C., Lambert R. / Evaluation of intermediate crops to trap nitrogen and produce forage. Experiments on catch crops were carried out over a period of three years in the loamy region of Belgium at the Catholic University of Louvain. The results were used to evaluate the performance of certain species of grass and legume, in pure or mixed culture. The performance of each species was judged according to its ability to take up nitrogen (catch crops), to produce forage of a sufficient quality and to meet certain agronomic criteria for intercropping. The results showed that grasses in pure culture or when mixed with legumes were able to significantly reduce soil nitrogen at the beginning of the drainage period, provided that the proportion of non-legumes constituted at least 50% of the mixture. Biomass produced by most of the tested crops can be harvested as complementary forage, which can be useful in times of shortage. http://hdl.handle.net/11006/75 By Beckers Y. / A balanced diet for bovines: strategies to improve the efficiency of nitrogen use. The main aim of this paper was to present some feeding recommendations, which, when applied on the farm, would increase nitrogen use by bovines and to give information as to how the effects of the nitrogen produced can be reduced. Ruminants have the ability to digest structural carbohydrates and to produce meat and milk proteins for human consumption. At the animal cells level, amino acids are essential for biological functions, mainly involving their maintenance and production. These amino acids are supplied by the intestinal digestion of microbial protein and feed protein that escapes microbial degradation in the rumen. Today, the efficiency of nitrogen utilization is typically low and highly variable in ruminants. Nitrogen excretion by ruminants mainly depends on the level of nitrogen intake and of the animal's productivity. Optimal N utilization may be achieved through an understanding of the key mechanisms involved in the control of N digestion and metabolism. These include the efficiency of N capture in the rumen and the protein degradation according to the type of diet and forage, the control of the rumen microorganisms involved in protein degradation and the proper formulation of the diet, avoiding feeding excess protein in relation to requirements. The dependence on energy supply in transferring feed nitrogen into milk and meat protein is strong both at the rumen and the cell levels of ruminants. The rumen metabolism is identified as the single most important factor contributing to the low level of efficient use of nitrogen in ruminants and partially depends on practical farming operations. http://hdl.handle.net/11006/76 By Dufrasne I., Knapp E., Istasse L., Veselko D., Piraux E., Robaye V., Hornick J.L. / Study on environmental factors influencing the urea content of cow's milk in Wallonia and estimation of nitrogen rejection. In Wallonia (South of Belgium), the urea content of milk produced on farms is assessed by the "Comité du lait". A total of 8,295,337 pieces of data recording the urea content in milk tanks was collected on Walloon farms in 2000 and during the period 2002-2011. These data were analyzed using a linear model. The fixed effects of the agricultural area or vulnerable zone, the month, the year and the interactions between these parameters were included in the model. The levels of fat and protein content in the milk were used as covariates. The average urea content in milk was found to be 255 mg·l-1. Four percent of the observations recorded a urea content of over 350 mg·l-1 and 14% recorded a urea content of over 400 mg·l-1. The models explained 38% and 35% of the variation in milk urea for the agricultural area and the vulnerable area variables, respectively. Within these models, the variables of month, region, year and the month-year interaction were the components that provided the most information. Milk urea content was higher in the summer period – April to October – than during the winter period – November to March – (287 vs 210 mg·l-1). This observation can be explained by the change in the cows' diet. During the summer, most of the cows grazed; ingestion of grass can lead to a nitrogen surplus in the diet. In the so-called "Limoneuse" and "Sablo-limoneuse" agricultural areas, recorded urea content was lower than in "Ardenne" and "Haute-Ardenne" (223 and 220 mg vs 278 and 284 mg·l-1, respectively). This difference can be explained by a greater use of grass in the diet in Ardenne and Haute-Ardenne. In vulnerable areas, urea content was lower (236 vs 273 mg·l-1). Annual nitrogen production calculated using different prediction equations ranged from 82 to 119 kg N per cow depending on the agricultural area. http://hdl.handle.net/11006/77 By Knapp E., Istasse L., Hornick J.L., Dufrasne I. / Improvements after precision dietary management of nitrogen rejection in two commercial dairy farms in Wallonia. Two dairy farms located in Pays de Herve and in Ardennes were followed at regular intervals in order to assess levels of nitrogen rejection. In Farm 1, the cows were divided into two groups: group HP contained high production cows and group BP contained cows with a lower production yield. Each group was offered a specific basal diet. In Farm 2, only one group of cows was assessed. The feed rations on both farms were characterized by a imbalance between the yields allowed by the energy or the nitrogen supplies and by an extremely high OEB balance of 794, 582 and 726 g, respectively, in groups HP and BP and in the Farm 2 group. Dietary changes were proposed in order to balance milk yields and to reduce the hypothesized nitrogen balance. The yield and urea content data from each milk record, along with data regarding nitrogen rejection, were statistically analyzed using a mixed model, which included an autoregressive covariance. The data from records 2, 3, 4 and 5 were then compared to the data from record 1. The advised changes implemented in the feeding management plan maintained milk yields at values similar to the yields observed in record 1 – 36.2, 24.3 and 23.0 l of 4% fat-corrected milk expressed for fixed days in milk produced by groups HP and BP and the Farm 2 group. The changes induced a significant reduction in the milk urea content (220 vs 300 mg·l-1) and a significant reduction in nitrogen rejection, whether expressed in terms of g per day per cow, g·l-1 or kg per year per cow. The cows in the Farm 2 group rejected less nitrogen in absolute terms (217.9 vs 260.1 g per day). However, it is interesting to note that the management approach in Farm 1 was more efficient in terms of nitrogen rejection since the level was on average 9 g·l-1 in comparison with 10 g·l-1 in Farm 2. In conclusion, it appears that, for either farm, whether an intensive or extensive management regime was being employed, the provision of well balanced feed rations led to a reduction in nitrogen rejection. It should, however, be noted that management advice needs to be provided on a farm by farm basis. http://hdl.handle.net/11006/78 By Aurousseau P. / Assessing the impact of streams on eutrophication in the coastal strip: the need to consider concentrations and loads. The approach of using measurements of water quality concentrations has been favored to date because of the current standards for drinking water, which are defined in terms of concentration. For example, the standard for the concentration of nitrate is 50 mg·l-1, although this standard, in fact, derives from a limited quantity of nitrate absorbed by drinking water with a concentration of 20 mg nitrogen per day. The dual assessment of flow and concentration is essential when studying environmental impacts because the intensity of these impacts is mainly linked to the quantity of nutrients reaching a compartment of the environment. This link between nutrient load and environmental impact is particularly established in coastal marine environments exposed to the phenomena of green tides, diatoms or Phaeocystis blooms. At the watershed scale, flow control presents some metrological problems but assessment based on flow has the advantage of providing a better comparison of the overall impact (at the coastal band scale) of several watersheds. At the catchment scale, in order to reduce the outflow, it is important to intervene at the level of the inflow by reducing any excesses in the N and P balance. This approach is illustrated by the example of the eutrophication of coastal marine water in the Eastern English Channel and at the mouth of the North Sea. http://hdl.handle.net/11006/79 By Dorioz J.M. / Mechanisms and control of agricultural diffuse pollution: the case of phosphorus. The movement of phosphorus is primarily a surface phenomenon closely related to surface runoff and erosion. It is a discontinuous process, set in motion during surface runoff events. The potential for surface runoff begins with any process reducing the infiltration rate of the soil surface. The contribution of cultivated fields to surface runoff varies spatially and temporally in relation to their permeability, soil type, land use, and soil cover. The contribution of these fields to P transfer and export varies in the same way but depends also on the P content of the soils, especially at the soil surface. Subsurface flows general carry in much less phosphorus due to its fixation in the subsoil, except in some conditions such as sandy soils, long-term over-fertilization, and agricultural drainage. Some elements of the landscape are considered as buffers because they can filter and thus attenuate the P fluxes transferred in the hydrologic network (grass filter strips which are purposely constructed but also hedgerows and riparian vegetation). Within the network, particulate forms of P may settle may and dissolved forms of P may sorb onto sediment particles or precipitate or be taken up by biota. In addition, major obstacles such as wetlands can store and/or transform some of the phosphorus emitted from upstream fields. Thus a set of interacting processes moves P through the landscape within a "transfer system", which includes emission from sources (mainly soils or sediments) and transport (including transformation and attenuation). This transfer system comprises a highly diverse and complex set of landscape structures arranged in a complex and diverse hydrologic hierarchy and interacting with agricultural practices and management of the hydrologic network. This paper attempts to characterize the key phenomena and structures of the transfer system that determine the flux, storage, transfer and mass balance of phosphorus in agricultural watersheds. Strategies for controlling diffuse phosphorus pollution are also indicated. http://hdl.handle.net/11006/80 By Henriet F., De Proft M. / Impact of crop sequences (including intercropping) on the use of pesticides. Crop sequences and the introduction of catch crops influence the development of agricultural pests (weeds, pests and diseases). This paper gives an overview of the problems that may arise for farmers in practice. Adaptation of crop interventions is often based on the use of plant protection products in the following crop, and these changes serve to solve problems that have been previously generated. Nevertheless, the poorly reasoned introduction of a catch crop can cause unwanted effects in terms of pest management and in relation to the protection of water resources. http://hdl.handle.net/11006/81 By Bodson B., Vandenberghe C. / Sustainable use of nitrogen beyond the single "nitrate" issue. The aim of the sustainable management of nitrogen is to reduce dramatically the risk of nitrogen leaching into groundwater. Regulations and recommendations have resulted in a more judicious use of manure as a mineral fertilizer to benefit both the environment and farmers. Rehabilitating leguminous plants into our rotations and our forage areas needs to become a priority. These plants can partially substitute for imported soya and, at the same time, synthesize the free nitrogen available to plants. Management of intercropping and in particular of catch crops can no longer be limited to the single issue of nitrate in water. Integrated crop protection and risk reduction of greenhouse gas emissions also need to be taken into account and flexibility needs to be incorporated into the implementation of these intercropping rules. http://hdl.handle.net/11006/82 By Vandenberghe C., Destain J.P., Beckers Y., Bodson B., Deneufourg M., De Toffoli M., Dufrasne I., Goffart J.P., Heens B., Henriet F., Lambert R., Abras M., Stilmant D., Marcoen J.M. / Evaluation of the third Action Programme. Recommendations for regulatory and scientific research. In accordance with the Nitrates Directive, the third "Durable Nitrogen Management Plan" (PGDA) will be soon reviewed in Wallonia (Belgium). The second "Nitrate – Water" workshop took place between 28th May and 1st June 2012. The workshop was attended by both Belgian scientists (Université catholique de Louvain - UCL, Walloon Agricultural Research Center CRA-W, Université de Liège - ULg, Gembloux Agro-Bio Tech) and French scientists (National Institute for Agricultural Research - INRA). In the light of the results of experiments presented by scientists at this workshop, modifications to the PGDA are now recommended. These concern organic and mineral nitrogen fertilization for crops and meadows; catch crops; soil nitrate-nitrogen residue limitation in autumn, at the start of the nitrate leaching period; the management of meadow ploughing and a modification of the dairy cow standard for nitrogen production.