2449 Enhancing ecosystem services of current cropping systems is a priority for sustaining crop and livestock production, developing biofuel industries, and maintaining or improving soil and environmental quality. Integrating CCs with existing cropping systems has the potential to enhance ecosystem services such as: (i) food, feed, fi ber, and fuel production, (ii) C and other nutrient and water cycling, and (iii) soil, water, and air quality improvement. Th is is particularly important with increased concerns about the following challenges to agriculture: high production costs, environmental degradation, food security, and climate change. According to the Soil Science Society of America Glossary of Terms, CCs are defi ned as a “close-growing crop that provides soil protection, seeding protection, and soil improvement between periods of normal crop production, or between trees in orchards and vines in vineyards. When plowed under and incorporated into the soil, CCs may be referred to as green manure crops” (SSSA, 2008). While the use of CCs is not a new concept, the implications of their re-emerging importance and impacts on ecosystem services such as crop and livestock production and soil and environmental quality deserve further discussion. Historically, CCs have been used to meet a few specifi c needs (i.e., soil conservation, N2 fi xation, and weed and pest management), but now CC management questions increasingly revolve around the potential multi-functionality of CCs including soil C sequestration, mitigation of greenhouse gas emissions, benefi ts to “soil health,” feed for livestock, biofuel production, farm economics, and others. Th ere are many studies on CCs assessing soil and crop production, but few have attempted to discuss or integrate all the multiple ecosystem services that CCs provide (Dabney et al., 2001; Snapp et al., 2005). Th us, a summarization of the existing knowledge about potential multiple CC benefi ts is needed for a broader understanding of CC impacts on soil and agricultural production and identifi cation of knowledge gaps that deserve further research. Th is summarization will help answer the following question: Can CCs provide multiple ecosystem services to address the current challenges in soil and environmental quality, crop and livestock production, biofuel production, among others? review & interpretation

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Cover Crops and Ecosystem Services: Insights from Studies in Temperate Soils

Allelopathy is a naturally occurring ecological phenomenon of interference among organisms that may be employed for managing weeds, insect pests and diseases in field crops. In field crops, allelopathy can be used following rotation, using cover crops, mulching and plant extracts for natural pest management. Application of allelopathic plant extracts can effectively control weeds and insect pests. However, mixtures of allelopathic water extracts are more effective than the application of single-plant extract in this regard. Combined application of allelopathic extract and reduced herbicide dose (up to half the standard dose) give as much weed control as the standard herbicide dose in several field crops. Lower doses of herbicides may help to reduce the development of herbicide resistance in weed ecotypes. Allelopathy thus offers an attractive environmentally friendly alternative to pesticides in agricultural pest management. In this review, application of allelopathy for natural pest management, particularly in small-farm intensive agricultural systems, is discussed.

The role of allelopathy in agricultural pest management.

Cover crops play an increasingly important role in improving soil quality, reducing agricultural inputs and improving environmental sustainability. The main objectives of this critical global review and systematic analysis were to assess cover crop practices in the context of their impacts on nitrogen leaching, net greenhouse gas balances (NGHGB) and crop productivity. Only studies that investigated the impacts of cover crops and measured one or a combination of nitrogen leaching, soil organic carbon (SOC), nitrous oxide (N2 O), grain yield and nitrogen in grain of primary crop, and had a control treatment were included in the analysis. Long-term studies were uncommon, with most data coming from studies lasting 2-3 years. The literature search resulted in 106 studies carried out at 372 sites and covering different countries, climatic zones and management. Our analysis demonstrates that cover crops significantly (p   0.05) effects on direct N2 O emissions. Cover crops could mitigate the NGHGB by 2.06 ± 2.10 Mg CO2 -eq ha-1  year-1 . One of the potential disadvantages of cover crops identified was the reduction in grain yield of the primary crop by ≈4%, compared to the control treatment. This drawback could be avoided by selecting mixed cover crops with a range of legumes and non-legumes, which increased the yield by ≈13%. These advantages of cover crops justify their widespread adoption. However, management practices in relation to cover crops will need to be adapted to specific soil, management and regional climatic conditions.

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A critical review of the impacts of cover crops on nitrogen leaching, net greenhouse gas balance and crop productivity.

Replacing bare fallow with cover crops in a maize cropping system: Yield, N uptake and fertiliser fate

Cover crop crucifer-legume mixtures provide effective nitrate catch crop and nitrogen green manure ecosystem services

Effects of cover crops on soil mineral nitrogen and on the yield and nitrogen content of maize

Winter cover crop: the effects of grass–clover mixture proportion and biomass management on maize and the apparent residual N in the soil

To investigate the environmental advantages of using grass-clover binary mixtures over pure stands as winter cover crops, a serial of five field experiments (each designed as randomized complete blocks with four replicates) was carried out in eastern Slovenia. Trifolium incarnatum L. and Lolium multiflorum Lam. were sown in late summer as pure stands and binary mixtures. Pooled data calculated from all the experiments revealed that the soil mineral N in spring and accumulation of N by plants decreased with decreasing proportion of T. incarnatum in the binary mixtures, while the C:N ratio of cover crop organic matter increased. C accumulation was the highest when the seeding ratio of the binary mixture of T. incarnatum and L. multiflorum was 50:50. In the C and N environmentally sustainable management efficiency coefficients, three important traits of winter cover crops for environmental protection were given equal importance (low soil mineral N content in spring, high C accumulation in plants, and high N accumulation in plants). The coefficient was higher for binary mixtures of T. incarnatum and L. multiflorum than for pure stands of these crops, proving the complex environmental advantages of binary mixtures over pure stands.

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Environmental advantages of binary mixtures of Trifolium incarnatum and Lolium multiflorum over individual pure stands

The effects of cutting frequencies at equal fertiliser rates on bio-diverse permanent grassland: Soil organic C and apparent N budget

Climatic changes have led to extreme weather events, with longer dry periods affecting forage production in mesic grasslands. The effects of grassland management and years with periods of low precipitation on herbage dry matter (DM) yield were studied in two-long term grassland experiments with different cutting and fertilization regimes for the period 2000–2012. In both experiments, the annual herbage DM yields had high correlations with the amount of precipitation. The correlation was stronger in frequent cuttings regimes. The management type and the year significantly affected the herbage DM yield in both experiments. There was also a significant management × year interaction. On average, over the whole observation period, the herbage DM yield of equally fertilized treatments in experiment I was higher in treatments with two cuts per season than in treatments with more cuts. Furthermore, longer periods of low precipitation exerted fewer effects on the DM yield of the two cuts treatments compared to higher cutting frequencies. However, the increase in herbage productivity in years following seasons with low precipitation was higher in the treatments with higher cutting frequencies than in those with two cuts per season. When the treatment, cut four times per year, received a higher amount of fertilizer than the treatment, cut twice per year (experiment II), the long-term average annual herbage DM yield was higher and the yield was less decreased by longer periods of low precipitation than the two cuts per year treatment. Despite the fact that the effects of different treatments were proved in both experiments, the differences in the DM yields among the treatments in low precipitation years were not high enough to recommend best-management practices for forage production on mesic grasslands in areas subject to increasing periods of low precipitation.

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Anastazija Gselman

Papers

Effects of cover crops on soil mineral nitrogen and on the yield and nitrogen content of maize

Winter cover crop: the effects of grass–clover mixture proportion and biomass management on maize and the apparent residual N in the soil

Environmental advantages of binary mixtures of Trifolium incarnatum and Lolium multiflorum over individual pure stands

The effects of cutting frequencies at equal fertiliser rates on bio-diverse permanent grassland: Soil organic C and apparent N budget

Effects of low precipitation periods on the herbage yield of mesic semi-natural grasslands under different cutting regimes.