覆盖作物及其作用的研究进展

在农作物种植系统中,田间杂草、土壤因素对作物的生长发育、产量和品质的影响一直都是农业领域关注的热点。大量使用化肥和除草剂可以达到作物增产、除草的目的,但其对土壤和环境造成的负面影响,严重制约了农业生产的可持续发展。种植覆盖作物是一种实现农业可持续发展的新策略,可以达到控制杂草、减少氮肥施用、改善土壤质量等目的。本文主要从覆盖作物的起源与发展过程、主要种类和作用及其种植制度等方面,总结了目前覆盖作物的研究进展及其在作物种植中的应用,以期为覆盖作物在我国农业生产中的研究与应用提供理论基础。     

Relay-intercropped forage legumes help to control weeds in organic grain production

In organic grain production, weeds are one of the major limiting factors along with crop nitrogen deficiency. Relay intercropping of forage legume cover crops in an established winter cereal crop might be a viable option but is still not well documented, especially under organic conditions.Four species of forage legumes (Medicago lupulina, Medicago sativa, Trifolium pratense and Trifolium repens) were undersown in six organic wheat fields. The density and aerial dry matter of wheat, relay-intercropped legumes and weeds were monitored during wheat-legume relay intercropping and after wheat harvest until late autumn, before the ploughing of cover crops.Our results showed a large diversity of aerial growth of weeds depending on soil, climate and wheat development. The dynamics of the legume cover crops were highly different between species and cropping periods (during relay intercropping and after wheat harvest). For instance, T. repens was two times less developed than the other species during relay intercropping while obtaining the highest aerial dry matter in late autumn. During the relay intercropping period, forage legume cover crops were only efficient in controlling weed density in comparison with wheat sole crop. The control of the aerial dry matter of weeds at the end of the relay intercropping period was better explained considering both legumes and wheat biomasses instead of legumes alone. In late autumn, 24 weeks after wheat harvest, weed biomass was largely reduced by the cover crops. Weed density and biomass reductions were correlated with cover crop biomass at wheat harvest and in late autumn. The presence of a cover crop also exhibited another positive effect by decreasing the density of spring-germinating annual weeds during the relay intercropping period.     

ROTOR,a tool for generating and evaluating crop rotations for organic farming systems

As with conventional farming, the improvement of organic farming systems requires agronomic planning tools to enhance economic performance. Crop rotation planning plays a crucial role in organic arable farming systems due to the renunciation of mineral nitrogen fertilisers and pesticides. Our objective was to develop a tool for generating and evaluating site-specific and agronomically sustainable crop rotations for organic farming systems in central Europe. The resulting static rule-based model, called ROTOR, consists of two basic steps: (A) A set of annual crop production activities (CPAs) is assembled semi-automatically from single site and crop-specific field operations using a relational data base. The database includes all relevant crops recorded separately with inputs and outputs, machinery and timing. Starting from stubble tillage and ending with the last harvest measure, the CPAs describe the current best cropping practices. Different CPAs are included for each crop according to (i) the type of crop preceding and (ii) the field operations following: whether ploughing or non-inverting tillage, undersowing crops, using catch crops, manuring, straw harvesting, or mechanical weed control. The former allows for the modelling of all possible positions of a crop within a crop rotation and the consequential effects of preceding crops. The CPAs are evaluated using rule-based assessment modules for yield, economic performance, N balance, nitrate leaching, and weed infestation risks. These modules have been developed using data from field experiments, farm trials and surveys, expert knowledge and a soil–crop simulation model. (B) Within the crop generation module, all possible sequences of CPAs are linked to 3–8-year preliminary crop rotations. Agronomically sustainable crop rotations are selected according to exclusion criteria (i.e., thresholds for N balance, weed infestation risks, phytosanitary and chronological restrictions) and ranked, e.g. by economic performance. The model was tested by comparing (i) estimated with observed yields and (ii) generated with existing rotations. These comparisons, based on data obtained from two farm surveys from North Eastern Germany, indicate the validity and usability of the model approach. ROTOR was found to support the complex crop rotation planning in organic farming systems requiring rotations with overlapping undersown main and cover crops. ROTOR is able to reduce the risk of planning failures by offering a quantitative method of optimisation of weed and site-specific N management.     

A survey on actual agricultural practices and their effects on the mineral nitrogen concentration of the soil solution

In intensive integrated crop-livestock farming systems, the surplus of N at the farm scale may be large and reflects on the N balance at the field scale. A study was conducted to assess the N fertilizer efficiency in four private farms in intensively cropped areas of NW Italy, and to monitor the effects of agricultural practices on the mineral N concentration of the soil solution, sampled every 2 weeks for 2 years and considered as an indicator of potential leaching. Two cultivation systems were compared in each farm, one involving continuous maize rotation, the other assuring a continuous soil cover (permanent meadow or winter cereal-maize double cropping system). The fertilization level in the arable crops was high (369–509 kg N ha⁻¹ year⁻¹) compared to the crop removals, and resulted in a low efficiency, as indicated by the four examined efficiency indexes (calculated N surplus, N removal-fertilizer ratio, N apparent recovery, N use efficiency). The soil-water-nitrate concentration showed large temporal variations in the range of 1–150 mg l⁻¹ for five out of the eight cropping situations, while concentrations smaller than 10 mg l⁻¹ were always recorded in the meadows and in one of the four soils (Aeric epiaquept). The fertilizer management that characterized each cropping system affected the soil-mineral-nitrate content in shallow arable soils. The longer soil cover duration in double-cropping systems did not result in a reduction of soil N compared to maize as a single crop, not even in winter (the bare-soil intercropping period in maize-based systems). However, the temporal oscillations of the concentration were buffered by the crop cover duration and by the presence of a shallow water table (1 m deep) in the soil profile. The average nitrate content of the soil could be predicted by the N uptake of the crop, the N removal–fertilizer ratio, the soil pH and sand content, however no simple explanatory relationship was found with the experimental factors. Hence, in farm conditions, in the absence of sufficient data for a deterministic model approach, the target of reducing the risk of leaching should be achieved by maximizing the fertilizer efficiency.     

Effects of organic farming on weed flora composition in a long term perspective

In 1987, the Ekhaga Experimental Farm in Sweden was established on a site that previously had been subjected to conventional farming, and has been managed since then as an organic farm. To study the effects of organic farming on weed population development and crop yields, two different crop rotations were designed, one adapted for animals (six fields) and one without animals (six fields). Each field contained a fixed 1 m² reference plot in which all the weed observations were done each year. During the period 1988–2002, number of weed plants in spring and weed biomass at harvest were recorded in the reference plots. No differences in these two parameters were observed between the crop rotations. Number of weed plants in spring did not differ between annual crops and did not increase over the 15-year period. Neither did weed biomass at harvest nor weed species diversity change over the 15 years. The two crop rotations kept weed pressure at the same level as under the previous conventional farming practice. General field observations suggest that invasion of Cirsium arvense (L.) Scop. is occurring along the field borders. Competitive ability of the crop showed to be important in weed regulation. Peas, a weak competitor, had significantly higher weed biomass at harvest compared with oats and winter wheat. Weather conditions during the period from April to September caused weed occurrence and development through the season to vary between years. To improve weed management in organic farming, advisors and farmers should recognise the importance of individual field and farm analyses to design location-specific, farm-adapted crop rotations.     

以作物残茬为生物篱在裸露农田营建防风带技术的研究

根据农田防护林等生物篱网防治农田风蚀的原理,把作物残茬作为生物篱间隔插入马铃薯裸露农田,形成以残茬为生物篱的农田防护篱网,可以解决北方旱作马铃薯生产基地农田严重风蚀问题,核心技术是利用残茬把连片的裸露农田间隔分成宽7.2m以下的带田,形成留茬带与裸露带间作的农田,不仅使留茬带的风蚀量降低80%以上,其裸露带的风蚀量也降低50%以上,取得防治马铃薯裸露农田的风蚀沙化,保护和提高耕地质量的实效。总结提出在北方旱作区采用麦类/油菜等条播作物留茬与马铃薯等根茎类作物间作轮作营建裸露农田防风篱网的保护性耕作技术。     

Nitrogen use efficiency and fertiliser fate in a long-term experiment with winter cover crops

The use of winter cover crops enhances environmental benefits and, if properly managed, may supply economic and agronomic advantages. Nitrogen retained in the cover crop biomass left over the soil reduces soil N availability, which might enhance the N fertiliser use efficiency of the subsequent cash crop and the risk of depressive yield and pre-emptive competition. The main goal of this study was to determine the cover crop effect on crop yield, N use efficiency and fertiliser recovery in a 2-year study included in a long-term (10 years) maize/cover crop production system. Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.), as cover crops, were compared with a fallow treatment during the maize intercropping period. All treatments were cropped following the same procedure, including 130 kg N ha⁻¹ with ¹⁵N fertiliser. The N rate was reduced from the recommended N rate based on previous results, to enhance the cover crop effect. Crop yield and N uptake, soil N mineral and ¹⁵N fertiliser recovered in plants and the soil were determined at different times. The cover crops behaved differently: the barley covered the ground faster, while the vetch attained a larger coverage and N content before being killed. Maize yield and biomass were not affected by the treatments. Maize N uptake was larger after vetch than after barley, while fallow treatment provided intermediate results. This result can be ascribed to N mineralization of vetch residues, which results in an increased N use efficiency of maize. All treatments showed low soil N availability after the maize harvest; however, barley also reduced the N in the upper layers before maize planting, increasing the risk of pre-emptive competition. In addition to the year-long effect of residue decomposition, there was a cumulative effect on the soil’s capacity to supply N after 7 years of cover cropping, larger for the vetch than for the barley.     

作物种植模式对土壤微生物和农田有害生物的影响

土壤是联系地上和地下生态系统的纽带,土壤微生物在土壤养分循环和作物吸收中起关键作用,被称为土壤质量的指标。土壤微生物通过分解土壤有机物,促进养分循环利用,并调控植物生长发育,随着现代农业种植结构的变化,特别是种植制度的改变,地上植物种类和生长状况常常影响土壤中微生物的群落结构和多样性,调控着作物生长发育,农田有害生物的发生,而影响农作物生产。综述了现代农业中几种主要种植模式,如轮作、连作和覆盖等对土壤微生物群落结构及与农作物有害生物的影响,强调科学合理选择种植模式的重要性,最后,讨论了这些种植模式有待深入研究的一些关键问题。     

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

Current agricultural practice favours winter cover crops, which can not only optimize N management in field crop rotation; but also affect subsequent crops. Three field experiments were carried out in Eastern Slovenia to examine the effects of Italian ryegrass (Lolium multiflorum Lam.), winter rape (Brassica napus ssp.oleifera (Metzg.) Sinsk), subclover (Trifolium subterraneum L.), and crimson clover (Trifolium incarnatum L.) as winter cover crops on the mineral N (N_min) content of soil and on the yield and N content of subsequent maize (Zea mays L.), fertilized with 120 kg N ha⁻¹. Italian ryegrass and winter rape decreased soil N_min contents before winter and in spring more than both clovers. In contrast, clovers accumulated significantly higher amounts of N in organic matter and had lower C/N ratios than winter rape and especially Italian ryegrass. In comparison to the control (bare fallow without cover crop), clovers increased the whole above ground maize dry matter yield, maize grain yield and N contents in whole above ground plants and in grain. The yields and N contents of maize following winter rape were on the same level as the control, while yields and N contents of maize following Italian ryegrass were, in two of the experiments, at the same level as the control. The effects of Italian ryegrass on the maize as subsequent crop in the third experiment were markedly negative. Maize in the control treatment exploited N much more efficiently than in treatments with cover crops. Therefore, cover crop N management should be improved, especially with a view to optimizing the timing of net N mineralization in accordance with the N demands of the subsequent crop.     

Seasonal and crop effects on soil loss and rainfall retention probabilities: An example from the U.S. Southern Piedmont

Soil loss from and rainfall retention on cropland during individual seasons vary from year to year. To quantify this variability for evaluation of soil and water related risks for different seasons and crops, probability distributions of soil loss and rain water retention are needed. In this study, probability distributions of soil loss and rainfall retention rates were computed using rainfall, runoff, and soil loss data from three field watersheds with Cecil-Pacolet soil (Typic Hapludults) in the Southern Piedmont of the United States. Long-term (34-year) rainfall records from a nearby gage were included in the computations. Resulting probability distributions were compared to evaluate risks of soil loss and low rainfall retention for different seasons and crops. Risks due to watershed differences in slope and in terrace and waterway conservation practices were also compared. These comparisons showed that soil loss risks are greater for the summer than for the winter crop season and greater for soybean (Glycine max. L. Merr.) than for corn (Zea mays L.). Considerable soil loss risk reduction was also observed for watersheds with less land slope and with terrace and grassed waterway installation. Risk of low rainfall retention was found to be less for the winter crop season than for the summer season. Rainfall retention risks for the winter crop season appeared to be unaffected by crop and watershed differences. For the summer crop season, however, risk of low rainfall retention was observed to be slightly higher for soybean than for corn and slightly lower for fields with terraces, grassed waterways, and lesser slopes. Soil loss and rainfall retention risks computed in this study can be coupled with economic costs for crop production and conservation planning.     

Early assessment of ecological services provided by forage legumes in relay intercropping

In organic agriculture, weeds and nitrogen deficiency are the main factors that limit crop production. The use of relay-intercropped forage legumes may be a way of providing ecological services such as weed control, increasing N availability in the cropping system thanks to N fixation, reducing N leaching and supplying nitrogen to the following crop. However, these ecological services can vary considerably depending on the growing conditions. The aim of this study was to identify early indicators to assess these two ecological services, thereby giving farmers time to adjust the management of both the cover crop and of the following crop.Nine field experiments were conducted over a period of three years. In each experiment, winter wheat was grown as sole crop or intercropped with one of two species of forage legumes; Trifolium repens L. or Trifolium pratense L. Two levels of fertilization were also tested (0 and 100 kg N ha⁻¹). After the intercropping stage, the cover crop was maintained until the end of winter and then destroyed by plowing before maize was sown. Legume and weed biomass, nitrogen content and accumulation were monitored from legume sowing to cover destruction.Our results showed that a minimum threshold of about 2 t ha⁻¹ biomass in the aboveground parts of the cover crop was needed to decrease weed infestation by 90% in early September and to ensure weed control up to December. The increase in nitrogen in the following maize crop was also correlated with the legume biomass in early September. The gain in nitrogen in maize (the following crop) was correlated with legume biomass in early September, with a minimum gain of 60 kg N ha⁻¹ as soon as legume biomass reached more than 2 t ha⁻¹.Legume biomass in early September thus appears to be a good indicator to predict weed control in December as well as the nitrogen released to the following crop. The indicator can be used by farmers as a management tool for both the cover crop and following cash crop. Early estimation of available nitrogen after the destruction of the forage legume can be used to adjust the supply of nitrogen fertilizer to the following crop.     

Mechanical wounding under field conditions: A potential tool to increase the allelopathic inhibitory effect of cover crops on weeds?

To increase the inhibitory effect of soil-incorporated cover crop residues on germination and early growth of weeds, the allelochemical content of the cover crop at the time of soil incorporation should be maximal. We investigated whether mechanical damaging in spring induced the production of allelochemicals in late-summer sown lucerne, winter rye and winter oilseed rape. Allelopathic activity and biomass of intact cover crop plants were determined throughout spring, and mechanically damaged plants were monitored till 14 days after wounding. Allelopathic activity was determined directly by lettuce seedling bioassays (lucerne and winter rye) or indirectly by glucosinolate quantification (winter oilseed rape). During spring, the allelopathic activity per unit biomass of intact plants showed a gradual decline for winter rye and lucerne, and a steep decline at the onset of flowering for winter oilseed rape. All cover crop species attained the highest allelopathic activity per unit area at the end of the sampling period as the increase in biomass surpassed the decline in allelopathic activity per unit biomass. Although mechanical wounding enhanced the allelopathic activity per unit biomass of all three species, the effect was only minor and often just sufficient to compensate for the loss in biomass resulting from wounding. This study therefore indicates that the best option for maximizing the inhibitory effect is to incorporate residues of intact cover crops as late as possible.     

Strahlungsnutzung durch Bestände ölreicher Körnerfruchtarten — Winterraps, Öllein und Sonnenblume im Vergleich

Radiation use by oil seed crops — a comparison of winter rape, linseed and sunflower For the production of grain crops rich in oil, winter rape, linseed and sunflower are similarly suitable at many arable locations. We wanted to compare the extent to which radiation (PAR) is intercepted and utilized by the individual species for dry matter and yield production. For this purpose, a 2‐year field experiment comprising the factors genotype, N fertilization and soil tillage was conducted. For five phases of crop development, growth rates (CGR, RGR and NAR) and PAR utilization were calculated. At full ripeness, total dry matter, grain, oil and energy yields, the crop‐ and year‐specific PAR supply, its interception and utilization for dry matter production and the resulting energy binding were determined. Due to the different individual vegetation periods, the PAR supply of the crops differed. The crop assimilation areas also differed, with values for winter rape and sunflower higher than those for linseed. The yield productivity of winter rape and sunflower was also higher than that of linseed. N fertilization increased yield to different extents for the different crops. On average, winter rape and sunflower produced the same amounts of dry matter and energy yield. Due to a higher harvest index, sunflower had the highest grain yield, and because the oil concentration in grain was comparatively high sunflower produced the highest oil yield, too. Under cool and wet climate conditions, however, the productivity of sunflower is offset by a relatively high yield risk because of uncertain ripening. The highest PAR utilization by linseed did not compensate for its very short vegetation period in combination with the lowest PAR interception.     

Einfluß von Bodenbearbeitung, Kulturart und Zwischenfruchtanbau auf den Bodenabtrag und den Oberflachenwasserabfluß

The effects of different soil tillage systems, crop rotations and short time cover crops on soil losses and runoff
Soil and water losses were carried out from 1979 to 1986 on a pseudogley-parabrownearth of the farm Ihinger Hof throughout the growth period of green maize and sugar-beet, both planted by plough and rotary hoe. From 1983 to 1986 the effect of short time soil cover crops (October—Dezember) were also studied.
The soil losses under rotary hoe were significantly lower in comparison to plough, but the differences in runoff between the tillage treatments were not significant. Under sugar-beet the erosion caused by rainfall was less than under maize. From the short time soil cover crops, the legume mixtures were found to have the best influence on soil and water conservation, and on the maize growth as well. There was no relationship between runoff or rainfall amount and soil losses. The soil losses correlated strongly to EI₃₀-indices, and this means that the USLE equation of W ischmeier and S mith (1965) can be applied in our experimental Farm in Ihinger Hof.     

Azodyn: a simple model simulating the date of nitrogen deficiency for decision support in wheat fertilization

A dynamic soil–crop model was developed to predict the date on which N deficiency occurs for winter wheat crops in the temperate climate of Northwest Europe. It is based on the daily simulation of soil N supply and crop N requirement for the period during which N-fertilizer is usually applied to wheat crops, the end of winter until flowering. The soil sub-model was derived from the `balance-sheet method' used in France for nitrogen fertilization recommendations. It describes the net mineralization of various sources of organic matter (soil humus, crop residues, organic products). The crop sub-model simulates crop biomass production and its nitrogen content using a radiation use efficiency model and a critical dilution curve for nitrogen content. Both soil and crop sub-models require few parameters and inputs, most of which are readily available on commercial farms, together with daily climatic data. The model tested with various rates and timings of N application in three experiments accurately simulated the date on which nitrogen deficiency began in wheat crops. The interest in using the model for tactical and strategic approaches is discussed.     

Model evaluation of cover crops,application to eleven species for banana cropping systems

Cover crops are increasingly used for weed management. But selecting the most suitable species of cover crop to be associated with a main crop requires long-term trials. We present a model-based method that uses a reduced number of parameters to help select cover crops in the context of banana cover-cropping systems. We developed the SIMBA-CC model to focus on radiation interception. The model was calibrated for 11 cover crop species by measuring their growth in 4 m² plots with three levels of shade (0, 50, and 75%). The SIMBA-CC model served to predict the long term growth potential of the 11 cover crop species in function of the radiation under the banana crop canopy. The model was validated using three species in association with banana plants. We defined three indicators based on outputs of the model to assess the ability of each of the 11 species (i) to compete with weeds and (ii) to be maintained in the long-term under the canopy of the main crop, and (iii) to evaluate competition with the main crop for nitrogen resource. This ex ante evaluation revealed the most promising species to be intercropped with banana. Finally, the SIMBA-CC model was used to define the light interception traits of a virtual cover crop that satisfy the three indicators in the case of intercropping with banana. We showed that to satisfy the three criteria, cover crops with low values of optimal photosynthetically active radiation (PARopti) should have moderate maximal biomass productivity, while crops with higher PARopti values should have a higher maximal productivity. The use of functional traits and modeling appears effective to disentangle the relations between intrinsic traits of cover crops and effect traits that affect the performances of the intercropping system.     

Crop sequence,crop protection and fertility management effects on weed cover in an organic/conventional farm management trial

A survey of 128 plots, in 2008, of a trial where the effects of crop protection can be separated from those of fertility management, generated weed cover data within six crops (winter wheat, winter barley, spring barley, potatoes, cabbages and a grass/clover ley). The effects of the 2008 crop types, of the two preceding crops and of organic and conventional crop protection and fertility management, were assessed using mixed-effects models and constrained ordination. Cover data for 22 weed species and for monocotyledon, dicotyledon, annual, perennial and total weed cover were used. Cover of 15 weed species, and of the five weed groups, was significantly affected by 2008 crops, with cover highest in spring beans and cabbage. Nine and four weed species 2008 cover were significantly related to crops grown in 2007 and 2006 respectively, as were dicotyledon, annual and total weed cover, but not monocotyledon or perennial cover. Cover of 15 species, and the five groups, was significantly higher in plots with organic crop protection, but only eight species and annuals were significantly affected by fertility management. Crop:crop protection produced the most significant interactions with most cover in organically managed plots. Five species, perennials and total weed cover produced significant three-factor models. The greatest weed cover was in organic crop protected but conventionally fertilised spring barley and the least in totally conventional winter barley. Other factors such as crop density and mechanical weeding also affected 2008 weed cover. The ordination indicated that most of the 22 species were strongly associated with crops from all three years. The sequence of crops in the rotation had a profound effect on weed cover. Where three spring-sown, difficult to weed, crops were grown in sequence (spring beans, potatoes and vegetables, spring barley) weed cover increased. However, cover was limited in grass/clover and some cereal plots with different preceding crops. Models predicting weed cover may need to take into account crop sequences within crop rotations, as well as the more usual management inputs.     

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

The advantages and disadvantages of varying mixture proportion of crimson clover (Trifolium incarnatum L.) and Italian ryegrass (Lolium multiflorum Lam.), used as winter cover crops, and cover crop biomass management before maize sowing (Zea mays L.) were studied in a series of field experiments in Eastern Slovenia. Pure stands and mixtures of cover crops on the main plots were split into different cover crop biomass management subplots: whole cover crop biomass ploughed down before maize sowing, aboveground cover crop biomass removed before ploughing and sowing, or aboveground cover crop biomass removed before sowing directly into chemically killed residues.Cover crop and cover crop biomass management affected the N content of the whole aboveground and of grain maize yields, and the differences between actual and critical N concentrations in the whole aboveground maize yield. The whole aboveground and grain maize dry matter yields, and the apparent remaining N in the soil after maize harvesting, showed significant interaction responses to cover crop × management, indicating positive and negative effects. Crimson clover in pure stand provided high, and pure Italian ryegrass provided low maize dry matter yields and N content in the yields in all the observed methods of biomass management. However, within individual management, mixtures containing high proportions of crimson clover sustained maize yields and N contents similar to those produced by pure crimson clover. Considering the expected ecological advantages of the mixtures, the results thereby support their use.     

Integrated crop–livestock systems in the Brazilian subtropics

In the subtropical region of Brazil, integrated crop–livestock systems (ICLSs) are characterized by the annual rotation of pastures and crops in a no-till system where the pasture component is used to produce either meat or milk. These systems focus on integration within the farm rather than between farms, being characterized by alternating cropping and pasturing in the same area. Independent of the crop rotations possible in a subtropical environment, the main integrated farming system found was rotation or succession of summer crops (Glycine max, Zea mays, Phaseolus vulgaris or Oryza sativa) with winter annual grazing grasses (mixed or solely Avena strigosa and Lolium multiflorum) or successive natural pastures.The high variability of crop yield in the Brazilian subtropics (due to climate extremes) as well as associated high costs and low prices has encouraged farmers to integrate livestock into their enterprises as a low-risk diversification option. Long-term experiments have demonstrated the benefits of crop–livestock integration with respect to many aspects of the soil–plant–animal system. There is evidence that such a system is not only a livestock–agriculture combination but also a unique system reaching a new complexity threshold, resulting in emergent properties with novel functionalities, some of which have yet to be investigated. In addition to greater environmental gains with less vulnerability, there are higher yields and more financial gain by the farmer, compared to that in the use of monocultures or non-integrated livestock farming. We conclude that ICLSs in Subtropical Brazil provide the opportunity for intensification with sustainability.     

Consequences of climate change for European agricultural productivity, land use and policy

This paper reviews the knowledge on effects of climate change on agricultural productivity in Europe and the consequences for policy and research. Warming is expected to lead to a northward expansion of suitable cropping areas and a reduction of the growing period of determinate crops (e.g. cereals), but an increase for indeterminate crops (e.g. root crops). Increasing atmospheric CO₂ concentrations will directly enhance plant productivity and also increase resource use efficiencies.

In northern areas climate change may produce positive effects on agriculture through introduction of new crop species and varieties, higher crop production and expansion of suitable areas for crop cultivation. Disadvantages may be an increase in the need for plant protection, the risk of nutrient leaching and the turnover of soil organic matter. In southern areas the disadvantages will predominate. The possible increase in water shortage and extreme weather events may cause lower harvestable yields, higher yield variability and a reduction in suitable areas for traditional crops. These effects may reinforce the current trends of intensification of agriculture in northern and western Europe and extensification in the Mediterranean and southeastern parts of Europe.

Policy will have to support the adaptation of European agriculture to climate change by encouraging the flexibility of land use, crop production, farming systems etc. In doing so, it is necessary to consider the multifunctional role of agriculture, and to strike a variable balance between economic, environmental and social functions in different European regions. Policy will also need to be concerned with agricultural strategies to mitigate climate change through a reduction in emissions of methane and nitrous oxide, an increase in carbon sequestration in agricultural soils and the growing of energy crops to substitute fossil energy use. The policies to support adaptation and mitigation to climate change will need to be linked closely to the development of agri-environmental schemes in the European Union Common Agricultural Policy.

Research will have further to deal with the effect on secondary factors of agricultural production, on the quality of crop and animal production, of changes in frequency of isolated and extreme weather events on agricultural production, and the interaction with the surrounding natural ecosystems. There is also a need to study combined effects of adaptation and mitigation strategies, and include assessments of the consequences on current efforts in agricultural policy to develop a sustainable agriculture that also preserves environmental and social values in the rural society.