Pesticide leaching in Danish groundwater: identification of vulnerable areas

In Denmark the supply of drinking water is based almost solely on groundwater. During the past few decades Danish groundwater monitoring has encountered numerous instances of pollution with pesticides and their metabolites (GEUS 2003a). As a result, some hundreds of abstraction wells out of about 8000 in general water supply have been closed. With this background, there is a particular concern for reducing the leaching of pesticides into the groundwater. In the present study an approach for identification of areas potentially prone to pesticide leaching is described. The potential risk of leaching of pesticides from agricultural areas into groundwater is minimised through a procedure of approval; however, some leaching still occurs (GEUS 2003b). The Danish counties are therefore obliged to identify areas where there is a particular risk of pesticide leaching, and where restrictions in use of pesticides may be introduced to reduce the risk (Miljøstyrelsen 2000). The Geological Survey of Denmark and Greenland (GEUS) and the Danish Institute of Agricultural Sciences (DJF) have carried out a project, focusing on sandy agricultural areas, that attempts to establish the necessary background knowledge for identifying areas particularly prone to pesticide leaching. The project aims to distinguish vulnerable and less vulnerable areas, both locally and nationwide, in a cost-effective way

Simulation of Above-Ground Suppression of Competing Species and Competition Tolerance in Winter Wheat Varieties

Cereal crop species and varieties differ in competitive ability against weeds mainly as influenced by differences in canopy architecture. The FASSET crop model was used to separate the effects of a number of crop traits on the suppressive ability of winter wheat varieties and the ability to tolerate weeds. The model simulated the competition between different varieties of winter wheat and a sown grass mixture for light, water and nitrogen. Crop physiological parameters of eight varieties and one variety mixture were estimated from measurements in a 3-year field experiment. The parameters estimated were thermal time from emergence to flag leaf appearance, thermal time from flag leaf appearance to anthesis, thermal time from anthesis to yellow ripeness, height development rate and final plant height, specific leaf area, leaf area per N uptake, vertical displacement of leaf area, and extinction coefficient for light. Variety differences were found in most of the parameters. The varieties were evaluated in terms of their abilities for suppression and tolerance. A suppression index (SI) was defined as the ratio of grass biomass at start of grain filling in a specific variety divided by the average biomass over all cultivars. A tolerance index (TI) was defined as the slope of a linear regression between crop yield and weed biomass at anthesis. Significant variety differences were observed for SI, but not for TI. The simulation model was able to capture about 75% of the variation in observed SI and about 47% of the variation in TI. The suppression and tolerance indices were highly correlated both for the observed and simulated data. A model sensitivity analysis documented that several crop traits were affecting both SI and TI leading to this correlation. The crop traits that affected the suppression index most in the simulations were early crop development, rapid height growth and specific leaf area. The response of the tolerance index to variation in crop characters was smaller and also related to factors such as the extinction coefficient and leaf area per unit N uptake. The suppressive ability of the winter wheat varieties were found in the simulations to have a smaller inter-annual variability than the ability to tolerate a given weed pressure. The results show that a simulation model may be used in selecting for competitive genotypes by measuring a few key variety traits. This may be done either by direct use of the model or indirectly through the development of simpler indices based on the simulation model. It is further proposed that a simulation model may be an effective tool in including crop competitiveness in the official variety approval since the measurements of the variety dependent input parameters defining competitiveness may be less costly than performing variety trials under a range of weed densities

Nitrogen leaching from conventional versus organic farming systems - a systems modelling approach

Abstract The level of nitrogen leaching from organic compared to conventional farming was evaluated by using a systems modelling approach. Two different methods were used for estimating and evaluating nitrate leaching. A simple function was used in which nitrate leaching is dependent on percolation, soil clay content, average nitrogen input and crop sequence. A nitrogen balance model was used to estimate the long-term potential for nitrate leaching. These methods were applied to models of both current conventional farming systems in Denmark in 1996 and of well-managed organic farming systems. On average, the total estimated nitrogen input to the organic systems was lower (104-216 kg N ha − 1 year − 1 ) than to the conventional farming systems (146 -311 kg N ha ). The N-balances in the organic fields showed a surplus of nitrogen (net input of nitrogen) in to the root zone of 60 -143 kg N ha . In the conventional systems the surplus varied from 25 to 155 kg N ha − 1 year − 1 . The modelled nitrogen leaching from the organic systems varied from 19 to 30 kg N ha − 1 year − 1 on loamy soils to 36 -65 kg N ha − 1 year − 1 on sandy soils. The modelled nitrogen leaching from the organic systems was always lower than from the comparable conventional agricultural systems due to: (I) the lower total input of nitrogen to the organic systems; and (II) the composition of the organic crop rotations including extensive use of catch crops. However, the modelling of nitrogen leaching has many uncertainties, principally due to difficulties in predicting the nitrogen leaching from different types of grass fields. Comparison of the results from two methods: (i) modelling of nitrogen leaching; and (ii) N-balances for the root zones, showed that organic arable crop production and dairy/beef farming on sandy soils are farming systems with a clear potential for lower nitrogen leaching than from the selected conventional systems. It is still uncertain whether the nitrogen leaching is lower or higher from organic arable crop production systems on loamy soil and organic pig production on loamy and sandy soil than from the same conventional systems in Denmark. The results point to the need for future research in the following areas: (i) the ability to build up soil organic nitrogen in organic farming systems and the consequences for both the level of crop production and nitrogen 65-82 66 leaching in the long term; (ii) the effects of catch crops in organic crop rotations; and (iii) a better operational understanding of nitrogen leaching from different types of organically managed grass and grass-clover fields