Soil organic carbon (SOC) is an important and manageable property of soils that impacts on multiple ecosystem services through its effect on soil processes such as nitrogen (N) cycling and soil physical properties. There is considerable interest in increasing SOC concentration in agro-ecosystems worldwide. In some agro-ecosystems, increased SOC has been found to enhance the provision of ecosystem services such as the provision of food. However, increased SOC may increase the environmental footprint of some agro-ecosystems, for example by increasing nitrous oxide emissions. Given this uncertainty, progress is needed in quantifying the impact of increased SOC concentration on agro-ecosystems. Increased SOC concentration affects both N cycling and soil physical properties (i.e., water holding capacity). Thus, the aim of this study was to quantify the contribution, both positive and negative, of increased SOC concentration on ecosystem services provided by wheat agro-ecosystems. We used the Agricultural Production Systems sIMulator (APSIM) to represent the effect of increased SOC concentration on N cycling and soil physical properties, and used model outputs as proxies for multiple ecosystem services from wheat production agro-ecosystems at seven locations around the world. Under increased SOC, we found that N cycling had a larger effect on a range of ecosystem services (food provision, filtering of N, and nitrous oxide regulation) than soil physical properties. We predicted that food provision in these agro-ecosystems could be significantly increased by increased SOC concentration when N supply is limiting. Conversely, we predicted no significant benefit to food production from increasing SOC when soil N supply (from fertiliser and soil N stocks) is not limiting. The effect of increasing SOC on N cycling also led to significantly higher nitrous oxide emissions, although the relative increase was small. We also found that N losses via deep drainage were minimally affected by increased SOC in the dryland agro-ecosystems studied, but increased in the irrigated agro-ecosystem. Therefore, we show that under increased SOC concentration, N cycling contributes both positively and negatively to ecosystem services depending on supply, while the effects on soil physical properties are negligible.

Decoupling productivity and environmental pollution growth is a key objective of modern agricultural systems. The use of diverse (multispecies) pastures may contribute to this objective. Increasing the species diversity of intensively managed pastures can potentially increase annual herbage growth and N use efficiency. Here, we review the literature on simple (predominantly perennial ryegrass and white clover mixes) and diverse temperate pastures (those with three or more sown species) that address the soil–plant–animal interrelationships relevant to N leaching losses from intensive grazing systems. An analysis of trial results suggests that annual herbage yields from diverse mixtures are greater than those from simple mixtures. The review also suggests that greater species diversity in pastures can increase sward N uptake, attributable to complementarity of species through differentiation in rooting depths and seasonal plant growth activity. The presence of specific species in the sward was more relevant to herbage production and N dynamics than the number of species present in the sward, emphasizing the role of well‐adapted plant functional types. The inclusion of forbs (e.g., chicory and plantain) in pastures is also shown to aid in reducing the N load of urine patches, thereby reducing the risk of N leaching from grazed pastures. To achieve the objective of increasing productivity and reducing N leaching, research questions remain around the role of species diversity on other aspects of the production system and N cycle, such as soil type and species adaptation, plant N uptake, and management of diverse pastures for successful on‐farm implementation. Decoupling productivity and environmental pollution growth is critical to modern agriculture. The use of diverse (multispecies) pasture swards may contribute to this objective. Annual herbage yields from diverse mixtures are greater than those from simple mixtures. Greater species diversity in pastures can increase plant N uptake. The inclusion of forbs aid in reducing the N load of urine patches, which reduces the risk of N leaching.

We conducted a study of N resources in a loamy sand soil in the shortgrass steppe of northeastern Colorado, on a site dominated by both shrubs and grasses. Our objective was to determine whether the soil N resources were more evenly distributed with depth than is typical for this environment, thereby helping to explain the coexistence of the two plant life forms. We measured total soil C and N, potential net N mineralization, and in situ available inorganic N (using ion exchange resin bags) through the soil profile to a depth of 150 cm. All three measures confirmed that available N was greatest in the surface soil layers (0–10 cm) and decreased substantially with depth. A supplemental watering treatment was imposed on the soil during the spring of 1996 to examine N‐leaching potential. The water addition increased soil water content and available NO−3 to a depth of 60 cm, indicating that NO−3 leaching might occur on this soil type under favorable conditions. To confirm this assertion, we used two simple models to examine the impact of increased soil moisture on in situ mineralization and solute transport processes. The results indicated that NO−3 leaching could better account for the observed patterns in available N. This process, by contributing to a more even distribution of resources through a coarse‐textured soil profile, could be important for improving the competitive status of shrubs in an otherwise grass‐dominated ecosystem.

The performance of three white clover cultivars (Huia, Tahora and Prop) was monitored in summerdry hill country at the Whatawhata Research Centre for 9 years. The cultivars were oversown into three steep north-aspect paddocks in autumn 1990. White clover abundance was measured every spring using line transects, and stolon fragments were sampled to determine the contribution of the cultivars to overall populations by allozyme electrophoresis on three occasions (1991, 1993, and 1994). White clover abundance declined from ~50% in the first year to ~4% in 1999. There were no significant differences in abundance between the three cultivar treatments after year 2. There were significant differences in the contribution of the cultivars to white clover populations after 5 years as follows: Huia 27%, Tahora 33% and Prop 56%. The implications of these results for introducing new white clover genotypes into summer-dry hill country are discussed. Keywords: 'Grasslands Huia', 'Grasslands Tahora', hill country, long-term, 'Prop', summerdry, white clover