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Due to the increased herd size in the Netherlands, there is need to assess the performance of different grazing systems at high stocking densities. The objective of the current experiment was to assess the effect of two extreme grazing systems, kurzrasen (continuous grazing at 3&ndash, 5 cm sward height) and strip-grazing at a high stocking rate, on grass production and quality, grass morphology and sward density, root development and load bearing capacity on peat soil. To this end, a two-year grazing trial with four herds of 15 cows on 2 ha each was conducted. Kurzrasen showed 18% lower herbage dry matter production on average compared to strip-grazing. The yield penalty of using a shorter regrowth period under kurzrasen was limited due to the strong response in grass morphology, resulting in a dense and lamina-rich sward. There was a small decline in root density at 10 cm soil depth, but no evidence of a lower root density at 20 cm soil depth for kurzrasen compared to strip-grazing. Sward density was higher for kurzrasen compared to strip-grazing, which had a positive impact on load bearing capacity. This is an important feature on peat soils, where load bearing capacity is often limited.

Background & aims: Roots are of paramount importance in protecting grassland in numerous ecosystem services e.g. soil organic matter build-up. However, studies that quantified root biomass in grasslands predominantly focused on areas managed less intensively than the management that is common to most North-West European grassland-based farms. To fill this knowledge gap, we compared, root and stubble biomass, the distribution in the soil and root diameter classes of five common European forage grass species grown under intensive management. Methods: On a 3 year old trial comparing yield of five cool season forage grass species at two N fertilization levels (190 kg N ha−1 yr−1 or 300 kg N ha−1 yr−1) we sampled root and stubble biomass until a depth of 90 cm deep. Results: Tall fescue (Festuca arundinacea) displayed the highest root and stubble biomass and had the highest mean root diameters of all studied grass species. The total dry biomass below cutting height (stubble + roots up to a depth of 90 cm below the soil surface) varied between 18 and 19 tonnes ha−1 for tall fescue and 10 and 11 tonnes ha−1 for Festulolium at 190 kg N ha−1 yr−1 and 300 kg N ha−1 yr−1, respectively. Conclusions: Our findings emphasize that in intensively managed grassland, root and stubble biomass under a 3 years old sward can be as high as 19 t DM ha−1. Owing to the high forage and root biomass of tall fescue, this species has a high potential in maintaining several ecosystem services.

Di nitrogen (N) fixation of legume-rhizobia symbiosis represents a relevant N source for agricultural systems and has the potential to reduce the input of synthetic N fertiliser. Legumes in mixture with grass constitutes an important component of cropping systems of crop-livestock farms. In recent years, these mixtures became an interesting alternative in stockless farms as feedstock for biogas production. Clover growing in association with grass receives 80% of its N from symbiotic N2 fixation. Estimations of fixed N have usually considered neither belowground clover N nor clover N transferred to the associated grass. One reason might be that the assessment of belowground N is laborious, since roots have to be recovered from the soil and N derived from rhizodeposition has to be estimated. Rhizodeposition N, composed of particulate and non-particulate compounds, is released into the soil from living roots via exudation and root turnover. Rhizodeposition has been studied by stable isotope 15N enrichment techniques. Likewise, N transfer from clover to grass has been assessed with 15N techniques using both the 15N enrichment and 15N natural abundance method. Fixed N contained in above- and belowground N of clover-grass swards potentially presents a significant N input in both conventional and organic cropping systems. These systems differ in fertilisation and crop protection strategies. The amount and the quality of applied fertilisers result in differences in soil nutrientavailability. Organically cropped soils often have a greater soil microbial biomass both in size and in activity compared to conventionally cropped ones. There is a lack of understanding on how these factors affect the input of symbiotically fixed N and on the fate of legume N remaining in the soil. To examine these relations, a microplot study was conducted in the DOK long-term field experiment, since 33 years of organic vs. conventional cropping with respective fertilisation and plant protection strategies resulted in soils with a gradient in nutrient-availability, soil microbial biomass both in size and in activity, and 15N natural abundance of soil N. Red clover (Trifolium pratense L.) above- and belowground N was quantified in model clover-grass swards. Swards were cultivated in microplots over two consecutive years. Microplots were located in DOK field plots with different fertilisation strategies. In general, the fertilisation increased in the order zero-fertilisation control (NOFERT), organic cropping system with half dose fertilisation (BIOORG1), organic cropping system with regular dose fertilisation (BIOORG2), and conventional cropping system (CONMIN2) with regular dose fertilisation. The organic cropping system at level 1 and 2 was fertilised with farmyard manure (manure and slurry) while the conventional cropping system was supplied by mineral fertiliser exclusively. Red clover rhizodeposition N was determined by 15N multiple-pulse leaf labelling (chapter 1). All roots were carefully removed from the soil. Subsequently, the fate of N derived from rhizodeposition being still present in the soil was investigated at different points of time using a sequential extraction. This procedure allows to extract soluble N and microbial biomass N from the soil. The remaining soil organic matter pools were separated in low and high density occluded particulate organic matter and silicate and quartz mineral-organic associations using a sequential density fractionation. Cropping system related effects from the size and activity of the microbial biomass on the General introduction 4 incorporation of N derived from rhizodeposition in soil pools and soil organic matter pools were assessed (chapter 2). Furthermore, different 15N natural abundance and 15N enrichment procedures were compared to determine the transfer from red clover N to perennial ryegrass (Lolium perenne L.). Subsequently, the 15N natural abundance method was verified with cropping systems under identical environmental and management conditions but differing in 15N natural abundance of the applied N fertilisers. One 15N natural abundance procedure was selected to quantify red clover N and symbiotically fixed red clover N being transferred to perennial ryegrass (chapter 3). Finally, the results from chapter 1 to 3 were scaled up from the microplot level to the field plot level of the DOK experiment. For this, N yields and clover proportions of clover-grass swards of field plots were used. Results were synthesised to present an overall picture on symbiotically fixed N in the plant-soil system of clover-grass swards under different cropping systems (general discussion). Red clover belowground N developed proportional to aboveground N at a ratio of 0.4 to 1 irrespective of the fertilisation strategy and the time of cultivation. However, the ratio N derived from rhizodeposition to root N changed with time. More than 90% of rhizodeposition N was incorporated into soil organic matter pools. Thereof, about 40% was found in silicate mineral-organic associations, 40% to 50% in both occluded particulate organic matter fractions, and the remainder in quartz mineralorganic associations irrespective of the fertilisation strategy related organic matter input. The proportions of grass N transferred from red clover N being estimated by 15N natural abundance procedures were within the range of that being estimated by 15N enrichment based procedures. About 40% of perennial ryegrass N was transferred from red clover in the low N fertilised swards (< 50 kg mineral N ha-1 a-1) NOFERT, BIOORG1 and BIOORG2. This corresponds to more than one third of perennial ryegrass N if related to symbiotically fixed red clover N. Up scaled from the microplot level to the field plot level of the DOK experiment, the sward plant-soil system obtained 300 to more than 400 kg N ha-1 from the symbiotic N2 fixation of clover after two years of cultivation. From that symbiotically fixed clover N, nearly 50% was present in the clover yield, about one third was transferred to grass, nearly 15% was accumulated in soil organic matter pools, 5% remained in the stubble and the root, and less than 1% was found in the both soil pools soluble N and microbial biomass N. Subsequent to the last harvest at the end of the 2nd year, on average 100 kg ha-1 symbiotically fixed clover derived N remained in the stubble and the roots of clover and grass and in the soil pools. Remaining N increased in the order NOFERT, CONMIN2, BIOORG2, and BIOORG1 at a ratio of 0.9 to 0.9 to 1.1 to 1.2 related to the average of the four cropping systems. In conclusion, red clover belowground N could be estimated from aboveground N by a factor of 0.4 irrespective of the fertilisation strategy and the cultivation time. Allocation of red clover rhizodeposition N to the silicate mineral-organic association was the dominant process N derived from rhizodeposition remaining in the soil was exposed. This process proceeded within months, but remained unaffected by the cropping system related microbial size and activity. 15N natural abundance procedures resulted in somewhat less variable estimates of N transfer from red clover to perennial ryegrass than 15N enrichment General introduction 5 procedures. Cropping systems affected the amount of red clover and perennial ryegrass N accumulation, red clover N derived from rhizodeposition, and N transfer to grass, but hardly affected the partitioning of N derived from rhizodeposition to soil pools. The partitioning of red clover N between above- and belowground and the partitioning within soil organic matter pools was not affected by cropping systems in the studied plant-soil system. Up scaled from the microplot to the field plot level of the DOK experiment, about 50% of symbiotically fixed clover N was deposited into the soil (≈15%) or transferred to grass (≈35%) at the end of the 2nd cultivation year. Hence, clover belowground N and N transfer to grass may represent important and considerable N inputs to agricultural systems.

Broad-leaved dock is a common and troublesome grassland weed with a wide geographic distribution. In conventional farming the weed is normally controlled by using a selective herbicide, but in organic farming manual removal is the best option to control this weed. The objective of our work was to develop a robot that can navigate a pasture, detect broad-leaved dock, and remove any weeds found. A prototype robot was constructed that navigates by following a predefined path using centimeter-precision global positioning system (GPS). Broad-leaved dock is detected using a camera and image processing. Once detected, weeds are destroyed by a cutting device. Tests of aspects of the system showed that path following accuracy is adequate but could be improved through tuning of the controller or adoption of a dynamic vehicle model, that the success rate of weed detection is highest when the grass is short and when the broad-leaved dock plants are in rosette form, and that 75% of weeds removed did not grow back. An on-farm field test of the complete system resulted in detection of 124 weeds of 134 encountered (93%), while a weed removal action was performed eight times without a weed being present. Effective weed control is considered to be achieved when the center of the weeder is positioned within 0.1 m of the taproot of the weed—this occurred in 73% of the cases. We conclude that the robot is an effective instrument to detect and control broad-leaved dock under the conditions encountered on a commercial farm. © 2010 Wiley Periodicals, Inc.

Rumex obtusifolius is a common grassland weed that is hard to control in a non-chemical way. The objective of our research was to automate the detection of R. obtusifolius as a step towards fully automated mechanical control of the weed. We have developed a vision-based system that uses textural analysis to detect R. obtusifolius against a grass background. Image sections are classified as grass or weed using 2-D Fourier analysis. We conducted two experiments. In the first (laboratory) experiment, we collected 28 images containing R. obtusifolius and 28 images containing only grass. Between 23 and 25 of 28 images were correctly classified (82-89%) as showing R. obtusifolius; all grass images were correctly classified as such. In the second (field) experiment, a self-propelled platform was used to obtain five sequences of images of R. obtusifolius plants. We used the parameters that gave the best classification results in the first experiment. We found, after changing one of the algorithm's parameters in response to prevailing light conditions, that we were able to detect R. obtusifolius in each image of each sequence. The algorithm scans a ground area of 1.5¿m2 in 30¿ms. We conclude that the algorithm developed is sufficiently fast and robust to eventually serve as a basis for a practical robot to detect and control R. obtusifolius in grassland.

Grassland management has a large influence on the operating cost and environmental impact of dairy farms and requires accurate, detailed, and timely information about the yield and quality of grass. Our objective was to evaluate imaging spectroscopy as a means to obtain accurate, detailed, and rapid measurements of grass yield and quality. The work consisted of three steps. In the first step, a new mobile measurement system comprising several hyperspectral sensors was constructed and calibrated on measurements collected in six field experiments in the Netherlands in 2 yr. A partial least squares regression model was used to fit parameters derived from hyperspectral images to values of DM (dry matter) yield and quality obtained through destructive sampling. Leave-k-out cross validation showed relative errors of prediction of 8 to 22% (167¿477 kg DM ha¿1 absolute) for DM yield, 21% (0.07 absolute) for the fraction of clover in DM, 6 to 12% for nutrient concentration, 15 to 16% for sugar concentration, and 3 to 5% for feeding values. In the second step, the measurement system was used to predict grassland yield and quality on fields from two farms. In the third step, the absence of calibration data for a specific date was simulated with a leave-harvest-out procedure. Predictions of absolute values were strongly biased due to system instability. Prediction of relative values was good, with a mean absolute error of 183 kg ha¿1 for DM yield. The instability of the measurement system requires that duosampling must be used for prediction of absolute values.

Effects of differences in both land use history and levels of nitrogen (N) application on nitrate concentration in the groundwater were studied for permanent pastures located on a single soil series in the Frisian Woodlands in the north of the Netherlands. The study was carried out for three fields: A, B and C. Field A was an old pasture, field B was a reseeded pasture and field C had been previously used for growing silage maize. The models SWAP and ANIMO were used for long-term simulations of the soil organic matter and soil N dynamics. The soil data from fields A, B and C were combined with different N application levels derived from commercial dairy farms on the same soil series for 2000. Soil organic matter and soil organic N were lower in field C than in fields A and B. In field C also the probability of exceeding the environmental threshold for nitrate in groundwater of 50 mg l−1 was lowest, which was ascribed to net immobilization irrespective of the high levels of N applied. However, this probability increased rapidly when the soil properties were similar to those of the old pasture (field A). Simulated levels of N uptake were higher for field A than for fields B and C at all levels of N applied. On old pasture, reducing N application levels can lower the probability of exceeding the environmental threshold for nitrate by up to 20% whilst hardly affecting N uptake.

Em pastagens, a avaliação da eficiência do processo de fertilização com N-uréia é importante em virtude das altas doses utilizadas. Vários trabalhos relatam que a aplicação de uréia associada com cloreto de potássio (KCl) e superfosfato simples (SFS) pode melhorar a sua eficiência. Na recuperação de pastagens degradadas ou em sistemas de exploração intensiva, as quantidades de KCl e SFS empregadas como fertilização corretiva são altas e aplicadas em novembro, no início da estação das águas. O parcelamento do KCl e SFS associado às coberturas nitrogenadas com uréia seria de fácil adoção sem custos adicionais. Com o objetivo de avaliar este manejo, foi desenvolvido um experimento em que se realizou o balanço anual da aplicação de 15N da uréia quando o SFS e, ou, o KCl foram parcelados, associados à aplicação da uréia em cinco coberturas, ou quando ambos foram aplicados de uma só vez, no mês de novembro. A maior produção de forragem ocorreu quando o SFS foi parcelado, seguido pelo parcelamento do KCl, da aplicação única de ambos e, finalmente, do parcelamento dos dois. A recuperação do N-uréia na parte aérea e no sistema solo-pastagem não diferiu com os tratamentos. Entretanto, a recuperação na coroa da planta e no sistema radicular diferiu entre os tratamentos e mostrou-se positivamente correlacionada com a produção de forragem. A recuperação de fertilizante na liteira foi favorecida pelo parcelamento do KCl. Apesar de não ter sido verificado aumento na recuperação total do sistema entre os tratamentos, o parcelamento do KCl e do SFS tem sido indicado por melhorar a recuperação do N-uréia em várias estruturas da planta, refletindo em maior produção da forrageira.In pastures, the evaluation of fertilization efficiency of urea-N is important since it is applied on a massive scale. Several studies report an enhancement of the fertilizer's efficiency by associated applications of urea with potassium chloride (KCl) and ordinary superphosphate (OSP). In the recovery of degraded pastures or in intensive exploration systems, high quantities of KCl and OSP used as corrective fertilization are applied at the november, beginning of the rain season. Split applications of KCl and OSP could easily be associated with urea-N surface application without additional costs. An evaluation of this management was the objective of this experiment. The annual balance of 15N application with urea was obtained in treatmentrs where OSP and/or KCl were split, top-dressed in five applications associated with urea, or when both were applied together in November. Highest forage production was obtained when OSP was split, followed by split KCl, the unique application of both together, and finally both split. The recovery of urea-N in the aerial part and the soil-pasture system remained unaltered by the treatments. However, the recovery of plant crown and root system differed among the treatments and was positively correlated with forage production. Fertilizer-N recovery in the litter was favored by splitting KCl. Even though the total recovery of the system was not improved by the treatments, splitting of KCl and OSP are indicated for an increased recovery of urea-N in numerous plant structures, resulting in a higher forage production.

Em pastagens, a avaliação da eficiência do processo de fertilização com N-uréia é importante em virtude das altas doses utilizadas. Vários trabalhos relatam que a aplicação de uréia associada com cloreto de potássio (KCl) e superfosfato simples (SFS) pode melhorar a sua eficiência. Na recuperação de pastagens degradadas ou em sistemas de exploração intensiva, as quantidades de KCl e SFS empregadas como fertilização corretiva são altas e aplicadas em novembro, no início da estação das águas. O parcelamento do KCl e SFS associado às coberturas nitrogenadas com uréia seria de fácil adoção sem custos adicionais. Com o objetivo de avaliar este manejo, foi desenvolvido um experimento em que se realizou o balanço anual da aplicação de 15N da uréia quando o SFS e, ou, o KCl foram parcelados, associados à aplicação da uréia em cinco coberturas, ou quando ambos foram aplicados de uma só vez, no mês de novembro. A maior produção de forragem ocorreu quando o SFS foi parcelado, seguido pelo parcelamento do KCl, da aplicação única de ambos e, finalmente, do parcelamento dos dois. A recuperação do N-uréia na parte aérea e no sistema solo-pastagem não diferiu com os tratamentos. Entretanto, a recuperação na coroa da planta e no sistema radicular diferiu entre os tratamentos e mostrou-se positivamente correlacionada com a produção de forragem. A recuperação de fertilizante na liteira foi favorecida pelo parcelamento do KCl. Apesar de não ter sido verificado aumento na recuperação total do sistema entre os tratamentos, o parcelamento do KCl e do SFS tem sido indicado por melhorar a recuperação do N-uréia em várias estruturas da planta, refletindo em maior produção da forrageira. In pastures, the evaluation of fertilization efficiency of urea-N is important since it is applied on a massive scale. Several studies report an enhancement of the fertilizer's efficiency by associated applications of urea with potassium chloride (KCl) and ordinary superphosphate (OSP). In the recovery of degraded pastures or in intensive exploration systems, high quantities of KCl and OSP used as corrective fertilization are applied at the november, beginning of the rain season. Split applications of KCl and OSP could easily be associated with urea-N surface application without additional costs. An evaluation of this management was the objective of this experiment. The annual balance of 15N application with urea was obtained in treatmentrs where OSP and/or KCl were split, top-dressed in five applications associated with urea, or when both were applied together in November. Highest forage production was obtained when OSP was split, followed by split KCl, the unique application of both together, and finally both split. The recovery of urea-N in the aerial part and the soil-pasture system remained unaltered by the treatments. However, the recovery of plant crown and root system differed among the treatments and was positively correlated with forage production. Fertilizer-N recovery in the litter was favored by splitting KCl. Even though the total recovery of the system was not improved by the treatments, splitting of KCl and OSP are indicated for an increased recovery of urea-N in numerous plant structures, resulting in a higher forage production.

Effects of differences in both land use history and levels of nitrogen (N) application on nitrate concentration in the groundwater were studied for permanent pastures located on a single soil series in the Frisian Woodlands in the north of the Netherlands. The study was carried out for three fields: A, B and C. Field A was an old pasture, field B was a reseeded pasture and field C had been previously used for growing silage maize. The models SWAP and ANIMO were used for long-term simulations of the soil organic matter and soil N dynamics. The soil data from fields A, B and C were combined with different N application levels derived from commercial dairy farms on the same soil series for 2000. Soil organic matter and soil organic N were lower in field C than in fields A and B. In field C also the probability of exceeding the environmental threshold for nitrate in groundwater of 50 mg l–1 was lowest, which was ascribed to net immobilization irrespective of the high levels of N applied. However, this probability increased rapidly when the soil properties were similar to those of the old pasture (field A). Simulated levels of N uptake were higher for field A than for fields B and C at all levels of N applied. On old pasture, reducing N application levels can lower the probability of exceeding the environmental threshold for nitrate by up to 20% whilst hardly affecting N uptake.

Broad-leaved dock is a common and troublesome grassland weed with a wide geographic distribution. In conventional farming the weed is normally controlled by using a selective herbicide, but in organic farming manual removal is the best option to control this weed. The objective of our work was to develop a robot that can navigate a pasture, detect broad-leaved dock, and remove any weeds found. A prototype robot was constructed that navigates by following a predefined path using centimeter-precision global positioning system (GPS). Broad-leaved dock is detected using a camera and image processing. Once detected, weeds are destroyed by a cutting device. Tests of aspects of the system showed that path following accuracy is adequate but could be improved through tuning of the controller or adoption of a dynamic vehicle model, that the success rate of weed detection is highest when the grass is short and when the broad-leaved dock plants are in rosette form, and that 75% of weeds removed did not grow back. An on-farm field test of the complete system resulted in detection of 124 weeds of 134 encountered (93%), while a weed removal action was performed eight times without a weed being present. Effective weed control is considered to be achieved when the center of the weeder is positioned within 0.1 m of the taproot of the weed—this occurred in 73% of the cases. We conclude that the robot is an effective instrument to detect and control broad-leaved dock under the conditions encountered on a commercial farm. © 2010 Wiley Periodicals, Inc.

Managed grasslands are occasionally ploughed up and reseeded in order to maintain or increase the sward productivity. It has been reported that this renovation of grassland is associated with a flush of soil organic nitrogen (N) mineralization and with a temporary increase in soil mineral N contents. Here, we report on the effects of method and time of grassland renovation on herbage yield, nitrate (NO3 -) leaching and nitrous oxide (N2O) emission. Field experiments were carried out at three sites (two sandy soils and a clay soil) in the Netherlands for three years. Renovation of grassland increased the percentage of Perennial ryegrass from 48–70% up to more than 90%. However, averaged over three years, dry matter yields were higher for the reference (not reseeded) swards (on average 13.6 Mg ha-1 for the highest N application rate) than for the renovated grasslands (12.2–13.1 Mg ha-1 dry matter). Grassland renovation in April did not increase N leaching in comparison to the reference. However, renovation in September increased the risk of leaching, because mineral N contents in the 0–90 cm were in November on average 46–77 kg N ha-1 higher than in the reference. Contents of dissolved organic N (DON) in the soil were not affected by renovation. Renovation increased N2O emissions by a factor of 1.8–3.0 relative to the reference grassland. Emissions of N2O were on average higher after renovation in April (8.2 kg N2O-N ha-1) than in September (5.8 kg N2O-N ha-1). Renovation without ploughing (i.e. only chemically destruction of the sward) resulted in a lower percentage of perennial ryegrass (60–84%) than with ploughing (>90%). Moreover, N2O emissions were higher after renovation without ploughing than with ploughing. Clearly, farmers need better recommendations and tools for determining when grassland renovation has beneficial agronomic effects. Losses of N via leaching and N2O emission after renovation can probably not be avoided, but renovation in spring in stead of autumn in combination with ploughing and proper timing of fertilizer application can minimize N losses.

Rumex obtusifolius is a common grassland weed that is hard to control in a non-chemical way. The objective of our research was to automate the detection of R. obtusifolius as a step towards fully automated mechanical control of the weed. We have developed a vision-based system that uses textural analysis to detect R. obtusifolius against a grass background. Image sections are classified as grass or weed using 2-D Fourier analysis. We conducted two experiments. In the first (laboratory) experiment, we collected 28 images containing R. obtusifolius and 28 images containing only grass. Between 23 and 25 of 28 images were correctly classified (82-89%) as showing R. obtusifolius; all grass images were correctly classified as such. In the second (field) experiment, a self-propelled platform was used to obtain five sequences of images of R. obtusifolius plants. We used the parameters that gave the best classification results in the first experiment. We found, after changing one of the algorithm's parameters in response to prevailing light conditions, that we were able to detect R. obtusifolius in each image of each sequence. The algorithm scans a ground area of 1.5¿m2 in 30¿ms. We conclude that the algorithm developed is sufficiently fast and robust to eventually serve as a basis for a practical robot to detect and control R. obtusifolius in grassland.

The longevity and producing capacity of perennial grasses swards was studied on mineral soils at the LUA Research Institute of Agriculture in long-term experiment during 1974-2010. There were applied lime and mineral fertilizers with different NPK doses (0-400 kg ha-1) protractedly many years. In such way there formed soils with various content of P, K, organic matter content and pHKCl level as well. Research results showed that liming of soils and using of mineral fertilizer changed not only productivity of grass mixtures but also botanical composition. Mineral fertilizer N200P100K300 provided the highest yield of dry matter – 7.32 - 12.0 t ha-1 and optimal botanical composition of a sward during many years. On unlimed soils (pHKCL less then 4.0 in 1997) dry matter yields of grass sward was substantially lower and there was observed disappearance of seeded valuable grasses out of the sward and increase of herbs and non-seeded grasses –Festuca rubra L., Agrostis tenuis Sibth., Taraxacum officinale Wigg. and others. Liming of soils increased dry matter yield in treatments with high doses of N (300-400) fertilizer.

The preference of grazing herbivores to feed on grass regrowth following savanna fires rather than on unburnt grass swards is widely recognised. However, there is little information on which factors govern patterns of resource selection within burnt areas. In this study, we attempted to disentangle the effects of different habitat and grass sward characteristics on the utilisation of post-fire regrowth by nine species of ungulates in a fire-dominated woodland savanna in north Cameroon. We used resource-selection functions based on logistic regression. Overall, the resource-selection functions identified the time elapsed since burning as the most influential parameter in determining probability of use by ungulates, as most species strongly selected swards that were recently burned. This pattern might be related to nutrient levels in the grass sward. In addition, most species selected areas with high grass cover and avoided grass swards with high amounts of dead stem material. This is likely to increase bite mass and, hence, intake rates. The avoidance of high tree cover by some species may suggest selection for open areas with good visibility and, hence, reduced risk of predation. Body mass seemed to have no effect on differential selection of post-fire regrowth, irrespective of feeding style.

Intensively managed grasslands are occasionally chemically killed with herbicide and ploughed in order to grow an arable crop. After this management, large N mineralization rates with large losses to the environment are commonly observed. However, it remains to be determined to what extent the chemical killing contribute to increased N mineralization. In this study the potential nitrogen (N) mineralization from grasslands, that were killed with herbicides but otherwise undisturbed, was investigated in a laboratory experiment with undisturbed soil columns. Subsequently we assessed the predictive value of several laboratory indices for N mineralization after chemically killing of the grass. Mineralization rates varied from 0.5 to 3.0 g N m−2 wk−1. The contents of total N, total C, dissolved organic carbon (DOC) and hot-KCl extractable NH 4 + were best related to N mineralization rates (R2 = 50, 48, 38 and 47%, respectively). In combination with information on the N content of the roots and stubble and the age of grassland at destruction, up to 62% of the variation in N mineralization rates could be explained. Although previous studies suggested that dissolved organic nitrogen (DON) is a good indicator for mineralization rates, this was not the case after chemically killing grass in the current study.