François Papy

Effects of tillage on runoff directions: consequences on runoff contributing area within agricultural catchments

Abstract In areas of intensive agriculture, e.g. ‘Pays de Caux’ in France, which was the study area, field observations have shown that runoff directions were modified by agricultural activities. In order to account for factors responsible for modifications of the runoff direction (roughness, tillage direction and agricultural patterns, e.g. dead furrow or dirt tracks), we constructed a discriminant function based on field observations. This function enables us to decide whether flow direction for slopes of up to 15% was imposed by slope direction or tillage direction. It can be applied to any location, provided there are known roughness, known slope intensity, known aspect and known tillage azimuth. In order to examine the effects of these agricultural activities at the catchment scale, we compared two models by analysing the same hydrological variables: the area contributing to runoff and the flow network. The first model (Topo) was built according to the runoff direction derived from a Digital Elevation Model (DEM). The second model (Tillage) was constructed by combining information from the DEM, and information from rules based on field observations or resulting from statistical analysis. For 23 basic catchments, the result of the comparison between the two models (Topo and Tillage) showed that a major part of the catchments and the drainage network was affected by modifications related to the introduction of man-made agricultural factors. For example, for 20 of 23 catchments, the runoff flows over more than 50% of the surface of such areas were produced along the direction imposed by tillage. The introduction of tillage effect brings about modifications of both the shape and size of catchments.

Rill erosion as a function of the characteristics of cultivated catchments in the north of France

Summary This study analyses variations in rill erosion as a function of the morphological, pedological and land use characteristics of cultivated catchments. 20 elementary catchments in Northern France, from 3.7 to 100 ha, were studied during the winter of 1988/89. The between-catchment differences in total and talweg rill volumes (m 3 ) and rates (m 3 /ha) were very large, and could not be explained by the variations in rainfall. The size of runoff contributing area, defined by combining soil susceptibility to crusting and certain land use characteristics, was found to be the main factor accounting for variations in erosion. Other factors, such as the soil sand content, talweg incisable length, catchment compacity index and proportion of upslope contributing areas were also correlated with total and talweg rill volumes, but slope characteristics were not. Cropping systems greatly affected the catchment susceptibility to rill erosion through their influence on runoff generation, runoff concentration and soil susceptibility to scouring.

Modelling ephemeral gully erosion in small cultivated catchments

Abstract This paper describes a new erosion model to predict the location and volume of ephemeral gullies within the main runoff collector network of agricultural catchments. This model, using an expert-based approach, combines field experiment results and knowledge about erosion processes and agricultural practices. It takes into account slope gradient, parameters reducing runoff flow velocity or increasing soil resistance (land use, plant cover percentage, roughness and soil surface crusting stage), the hydrological structure of catchments and the runoff volume. The model is used to calculate the soil sensitivity to ephemeral gully erosion at any point in four small cultivated catchments. Results show that it is possible to predict gully erosion from simple information that can easily be recorded by farmers. However, our model tends to overestimate the erosion level in some cases. Furthermore, the quality of the results varies strongly according to the catchment and to the rainfall event used. To increase the quality of the results, it will be necessary to improve our knowledge database from experimental results and to use a calibration procedure.

Work organization simulation as a basis for farm management advice (equipment and manpower, levels against climatic variability)

Abstract The product and the farm costs in arable farming systems are dependent on the interannual climatic variability. In the present context of agricultural price stagnation, the increase of worker productivity is one of the first priorities in this kind of system. Previous studies revealed that in the arable farming systems studied, equipment and manpower levels are settled by the amount of autumn work. So the authors try to give prominence to available margins retarding climatic risks during this peak period. The method presented is based on a simulation of the running of autumn work. The simulator employs structural data such as a cropping plan, equipment and manpower combination, and a general organization model which includes decision rules. In fact, it appears as a work calendar which gives, under the same climatic conditions, the same cultivation operations and the same work dates as the farmers ones. The computerized setting has been achieved on a compatible microcomputer and written in C language. After validation from work dates truly observed on the farm, the simulation operated over fifteen different climatic years and so allows the analysis of the system in non-observable situations. An illustration of the models possibilities is given from an example.

Unexpected N and K nutrition diagnosis in oil palm smallholdings using references of high-yielding industrial plantations

The rising demand for vegetable oil is inducing an expansion of oil palm cultivation in the tropics. In southern Cameroon oil palm smallholdings have been growing fast since the mid-1990s. Now, industrial plantations and smallholdings exist side by side. The current technical advice given to smallholders originates from agroindustrial practices. However, industrial plantations were created by planting on previous forest cover with no food intercrops, whereas for smallholdings food crops are a common previous cover and an intercrop during the juvenile phase. Technical advice used for industrial plantations may therefore not apply to smallholdings. Huge yield differences are observed in oil palm smallholdings, ranging from 2 to 14 t·ha−1 of fresh fruit bunches, while in industrial plantations yields average 14–16 t·ha−1. As no agronomic evaluation to date had explained those variations, we carried out a regional agronomic diagnosis of N and K nutrition on smallholder plots planted with selected oil palms. To prepare leaf samples and determine mineral contents, we used the same standardised method and the same laboratory as the regional industrial plantations. We compared smallholder leaf N and K contents with reference models of critical mineral contents, previously built with data from the high-yielding industrial plantations. Statistical links were also established between nutritional status and practices. Our results showed two groups of oil palm plantations: a group with N deficiencies ranging between 80 and 90% of the reference and K deficiencies ranging from 45 to 90% of the reference, and another group with satisfactory N and K status. The N deficiency was statistically linked to food cropping as the previous cover or as an intercrop, whilst K deficiency was qualitatively linked to an absence of K fertilisation. N deficiency is a specificity of oil palm smallholdings that had never been encountered in African industrial plantations. To conclude, the current technical advice given to smallholders is not well adapted.

Global agronomy, a new field of research. A review

The global impact of agriculture has recently become a major research topic, stressed by the rapid growth of the world population. Agriculture management is indeed influencing the quality of water, air, soil, and biodiversity at the global scale. The main agricultural challenges have already been reviewed, but these reviews did not discuss in detail the adaptations of agricultural techniques to global issues and the research challenges for agronomy. Here, we propose a research planning for global agronomy including the following advices. Agronomists should update their research objects, methods, and tools to address global issues. Yield trends and variations among various regions should be analyzed to understand the sources of these variations. Crop model simulations should be upscaled to estimate potential yields and to assess the effect of climate change and resource scarcity at the global scale. Advanced methods should analyze output uncertainty of complex models used at a global scale. Indeed various global models are actually used, but these models are too complex and the output uncertainty is difficult to analyze. The meta-analysis of published data is a promising approach for addressing global issues, though meta-analysis must be applied carefully with appropriate techniques. Finally, global datasets on the performance and environmental impact of cropping systems should be developed to allow agronomists to identify promising cropping systems.

Tapping panel diagnosis, an innovative on-farm decision support system for rubber tree tapping

Latex is a key product for many tropical countries, of which 80% is produced by smallholders. Latex is produced by the rubber tree (Hevea brasiliensis). Given the 7-year immature unproductive period, establishing a rubber plantation requires considerable investment by smallholders, emphasizing the need for sustainable management. The difficulty of performing an agronomic diagnosis of a tree crop is to obtain an accurate picture of current and past cultivation practices, to be able to assess their impacts on the agro-ecosystem as well as on sustainability. Smallholders do not usually keep records of latex yield or of their technical practices, making it impossible to perform a diagnosis based on productivity. As latex harvesting involves tapping the bark, which leaves scars on the trunk, we hypothesised that these morphological traces would be good indicators of current and past practices and would thus enable a diagnosis based on the economic lifespan of plantation. To this end, we formalised a tapping panel diagnosis that involved reproducing the scars on tapping panel diagrams, and analysing them using two indicators: the amount of virgin bark consumed and the number of tapping years that remained. We validated this tapping panel diagnosis in a sample of 25 smallholder plantations in Cameroon, where we characterised eight tapping management systems reflecting different levels of tapping intensity. The assessment of the respective share of each tapping practice on virgin bark consumption revealed major effects of tapping frequency and of shaving thickness. We showed that the tapping panel diagnosis used as a decision support tool can increase remaining tapping years by 33% to 355%. To conclude, the tapping panel diagnosis formalised here for the first time will be a useful support for the participatory development of innovating tapping management schemes involving both technicians and smallholders.