Sward degradation is a serious threat to the functioning of agricultural grassland and the provision of ecosystem services. Renovation measures are frequently applied to restore degraded swards. The success is highly variable, and substantial trade‐offs can be related to the process of renovation. This paper starts with a general classification of renovation measures and then investigates the processes that are directly related to renovation and lead to a change in botanical composition and affect soil functions and C and N fluxes. These processes are strongly interrelated and dependent on site, climate, and management condition as well as on the timescale. The more an existing and degraded sward is deliberately disturbed prior to a renovation measure, for example, by ploughing, the stronger will be the change in sward composition, and the stronger will be the potential yield and quality advantage. However, the risk of a release of soil organic C and N emissions to the environment will also increase. These emissions will usually decrease in time, but so will the positive effects on sward composition. This demonstrates that the renovation of swards is normally the second best solution and a proper and well‐adapted grassland utilization and management should be adopted to avoid degradation in the first place.

After 3 years of different crop rotations in an organic farming experiment on a sandy soil in northwest Germany, spring triticale was cultivated on all plots in the fourth year to investigate residual effects on yield, nitrogen (N) leaching and nutrient status in the soil. Previous crop rotations differed in the way N was supplied, either by farmyard manure (FYM, 100 and 200 kg N ha⁻¹ year⁻¹) or by arable legumes like grass-red clover and field beans, or as a control with no N. Other crops in the rotations were maize, winter triticale and spring barley. Additional plots had a 3-year grass-clover ley, that was ploughed-in for spring triticale in the fourth year. Yields of spring triticale were moderate and largest for ploughed-in grassland leys and grass-red clover and plots that had previously received farmyard manure. The former crop rotation, including grassland break-up, had a significant effect on most yield and environmental parameters like residual soil mineral nitrogen (SMN) and N leaching and on the level of available K in the soil. The single crop harvested in the year before spring triticale had a significant effect on yield parameters of spring triticale, less so on SMN and N leaching in the fourth year and no effect on available nutrients (P, K, Mg) and pH in the soil. We conclude that the effects of arable legumes were rather short lived while ploughing of 3-year grassland leys had a profound influence on mineralization processes and subsequently on yield and N losses.

Information on the environmental impact of maize production is actually inconsistent. Indeed some experiments report good nitrogen (N) efficiencies and small residual N. Other experiments show large leaching losses, while in practice maize production is often coupled with an intensive production and large N surpluses. Here, we present data from a 4-year experiment with silage maize on a sandy soil of high mineralization potential. The experimental set-up included three N input forms, mineral, cattle and pig slurry and four rates of total N, of 0, 80, 160 and 240 kg N ha⁻¹ year⁻¹ and the use of suction cups. Results show that dry matter and N yields for N0–N240 were relatively high and consistent (158–192 kg N ha⁻¹). Further findings show large residual soil mineral nitrogen, of 138–237 kg N ha⁻¹, and high nitrate concentrations in leaching water during winter, of 39–73 mg NO₃–N L⁻¹, corresponding to leaching losses of 86–152 kg N ha⁻¹. Response to N input was small with apparent N recoveries of 14–22% for manures and mineral fertilizers. We conclude that caution is needed when maize production is extended to fields with an apparently high potential for mineralization and that use as grassland would be a better alternative with regard to N leaching losses.

In future, grass swards need to be adapted to climate change and interactions of management and site are becoming more important. The persistence of Lolium perenne on peatland or during dry periods is limited and alternative forage species are required. We tested the performance of a modern variety of Festuca arundinacea and Phleum pratense as an alternative to Lolium perenne on clay, peat, and sandy soils. Each of these grasses was sown as main species in mixture with Poa pratensis and Trifolium repens and the mixtures were subjected to different frequencies of defoliation. Differences in yield proportions in the third year were significantly influenced by main species, site and their interaction. Remaining mass proportions of main species after three years were smallest on peat; on all sites Festuca arundinacea showed the highest persistence and largest yield, followed by Lolium perenne. Mass proportions of Phleum pratense were small on peat soils and Phleum had been replaced there by Holcus lanatus, and by Lolium perenne and Poa pratensis on the clay and sandy soils. We conclude that the choice of grass species in mixtures is a management tool to control stability and productivity of grass swards under specific site conditions.

In alley cropping, woody perennials are combined with agricultural crops or grassland in order to benefit from favourable interactions between trees and crops. Trees influence growth and senescence processes in grassland as well as plant chemical composition and plant water use. In a field experiment with grassland and alley‐cropped willow coppices, we analysed the impact of distance and position relative to the tree line on grassland herbage biomass, proportion of dead herbage and herbage quality in two successive growth periods of two experimental years. The experimental years were chosen so that growth periods among years showed a similar rainfall pattern. Relative ET (evapotranspiration) as defined by actual divided by potential evapotranspiration reflected the severity of water shortage with a moderately dry (relative ET ~ 0.5) first growth period with increasing dryness in the second growth period of each year. We determined bulk stomatal conductivity of the grass shoot by measuring δ¹³C (carbon) signatures. Stomatal conductivities were higher close to the trees in drier periods (i.e. more negative δ¹³C values). Herbage biomass decreased with decreasing relative ET, but showed no systematic influence of the tree line. We found that vegetation composition changed with distance to the tree line. The proportion of dead herbage was equal at all distances from the tree line under very dry conditions, but smaller close to the trees under moderately dry conditions. Herbage quality, as approximated by crude protein and ADF concentrations in live biomass, was higher closer to the tree line. We conclude that the tree line does not adversely affect grassland productivity under drought and improves the plant water status as reflected by the δ¹³C signature.