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A field experiment with maize for silage was conducted to assess the effects of mineral nitrogen (N) fertilizer application rates (0, 50, 100, 150 kg ha⁻¹), slurry application rates (0, 20, 40 m³ ha⁻¹) and the use of an understorey with perennial ryegrass on nitrate (NO₃)-leaching losses. Leachate was collected using ceramic suction cups. Soil mineral N (SMN) was determined to a depth of 90 cm at the end of the growing season. Higher levels of N supply with mineral fertilizer or slurry resulted in higher leaching losses. The grass understorey significantly reduced the losses. The amount of N lost to the groundwater was positively related to SMN at the end of the growing season, with leaching losses representing less than 0·45 of SMN on average. Leaching losses were positively related to the N surplus, which was calculated from the difference between N input (N from fertilizer, slurry and atmospheric deposition) and N output (N removed with maize herbage mass and bound in the understorey biomass in spring). In view of the large variation in weather conditions between the experimental years, it is suggested that for the sandy soils in this experiment N-leaching losses under maize can be estimated satisfactorily from SMN and the calculated N surplus.

A field experiment was conducted from 1998 to 2001 to measure the performance and environmental effects of a maize crop (Zea mais L.) in a continuous production system with and without a grass understorey (Lolium perenne L.), with varied N inputs. The experiment was located on a sandy soil in northern Germany and comprised all combinations of slurry application rate (0, 20, 40 m 3 ha )1 ) and mineral N fertilizer (0, 50, 100, 150 kg N ha )1 ). Understorey treatments included maize with and without perennial ryegrass. Net energy (NEL) yield of maize increased with mineral N application rate but reached a plateau at high rates. Increase in yield of dry matter because of mineral N fertilizer was lower with increased slurry application rate. Neither slurry and mineral N application nor a grass understorey affected NEL concentration of maize, whereas crude protein (CP) concentration increased with increase in application of slurry and mineral N fertilizer. Nitrogen supply by slurry or mineral fertilizer had no effect on the amount of N in the grass understorey after the harvest of maize. The average amount of N bound annually in the understorey was 60 kg N ha )1 . The reduced biomass of the understorey because of enhanced maize competition was compensated for by an increased CP concentration in the grass. The grass understorey affected the NEL yield of maize negatively only at very low levels of N input but increased the N surplus at all levels.

Based on experimental data gathered in a research project on nitrogen fluxes in intensive dairy farming in Northern Germany, an analysis of fossil energy input and energy efficiency in forage production from permanent grassland and maize for silage was conducted. Field experiments comprised different defoliation systems and different rates of mineral N fertilizer and slurry application. Each change from grazing to cutting in grassland systems reduced the energy efficiency. Energy efficiency consistently decreased with increasing rates of mineral N application. In the production of maize for silage, maximum energy efficiency was obtained with an application of 50 kg N ha−1 from slurry only. Net energy yields of maize for silage were much higher than that of grassland when compared at the same level of fossil energy and nitrogen fertilizer input. Considering both nitrate-leaching losses and a necessary minimum quantity of grass herbage in a well-balanced ration, it is suggested that a high proportion of maize for silage in combination with N-unfertilized grass/clover swards used in a mixed cutting/grazing system represents a good trade-off between the leaching of nitrates and energy efficiency.

The aim of this work was to assess the ability of near-infrared reflectance spectroscopy (NIRS) to be a rapid and reliable method for estimating quality variables for forage maize with an extremely wide range of maturity and growth stage, as it occurs, e.g. in experiments dealing with growth analysis. For maximum variability samples for analysis were collected over 4 years from field trials which comprised a wide range of nitrogen (N) fertiliser (0–150 kg N ha −1 ) and slurry application (0, 20 and 40 m 3 ha −1 ) treatments, but one maize variety named Naxos. Phenological variability was obtained by sampling in intervals of 14 days during growth of maize. A total of 6296 samples was collected and 398 samples were selected to calibrate estimated net energy and crude protein contents and validate the equations derived. To increase accuracy separate calibrations were developed for reproductive and vegetative fractions of maize. For both groups NIRS equations were scrutinized by a set of validation samples which were selected from the same sample pool before the samples for calibration were chosen. Predictions of crude protein and net energy contents over a wide range of plant maturity showed satisfactory accuracy. Standard error of prediction was below 0.3 MJ NEL kg DM −1 for energy value and below 123 g kg −1 of dry matter (DM) for crude protein. In the course of 4 years the number of necessary samples to be included in the calibration decreased to between 2.6 and 15% of sample number in the first year and the validity of the equation increased.