Cover cropping is currently increasing in vineyards as it provides solutions to some of the problems encountered in vine growing. However, its development is still hampered in Mediterranean regions ...because of fears of severe competition for water. Recent studies have shown that soil resources other than water may also be restrictive, and particularly nitrogen. Over a three-year period, the effect of introducing a cover crop was studied with respect to the temporal and spatial changes to nitrogen dynamics in a Mediterranean vineyard. The experiment compared the impact of three different types of soil cover management on nitrogen dynamics, and particularly on soil nitrogen mineralization which is the principal source of inorganic nitrogen in situations with no application of N fertilizers which are frequent in viticulture.
This experiment provided evidence that the presence of an intercrop significantly reduced nitrogen accumulation in aerial parts of grapevine during the year due to competition for soil resources. This reduction varied markedly between years and treatments, and was more pronounced during dry years. The competition for nitrogen was direct as intercrop deprived grapevine of soil nitrogen beneath the inter-row and caused grapevine uptake to be higher beneath the row. In deep soils, a grapevine can adapt its root system in order to access deeper water resources, but it then partially abandons the mineralization zone containing most inorganic nitrogen. Competition for nitrogen was less marked with a temporary cover crop than with a permanent one, because of the shorter period of uptake with the former and the time needed for an annual cover crop to develop its root system each year. Intercrop also competed indirectly for nitrogen with grapevine as it took up soil water and made inorganic nitrogen less mobile and accessible to grapevine. Intercrop markedly decreased soil nitrogen mineralization. Although it did not significantly affect organic matter characteristics or soil temperature, it clearly modified the water regime. Indeed, under either temporary or perennial cover crops, the upper soil layers dried more rapidly than when there was only evaporation from bare soil. Consequently, nitrogen mineralization decreased faster with intercropped treatments and halted prematurely during the summer.
The earliness of the reduction in nitrogen accumulation in intercropped vineyards also suggested that a lower level of nitrogen transfer to perennial reserves was involved. Indeed, grass cover grows and competes for nitrogen during the autumn which is a favourable period for nitrogen accumulation in wood reserves. Although better water infiltration was observed in the presence of a cover crop (notably in the autumn), the favourable conditions for nitrogen mineralization were propitious for grass cover growth and uptake. Consequently, intercrop reduced grapevine growth of the year but also the potential growth for the next year by decreasing grapevine nitrogen perennial reserves.
The use of cover cropping is currently increasing in vineyards but its development remains hampered in Mediterranean regions because of the possibility of severe competition for resources. However, ...recent studies on intercropping in vineyards have shown that in some situations, water stress may not be greater than that prevailing in bare soil vineyards. Over a 4-year period, we studied the effects of introducing a cover crop in terms of temporal and spatial (i.e. row vs. inter-row) changes to the water regime of a Mediterranean vineyard. The experiments compared the water dynamics prevailing under three different treatments: a perennial cover crop, annual cover crop or the use of chemical weed control.
A compensatory growth of the grapevine root system was revealed, thus partly prevented direct competition for resources between it and the intercrop. The rooting of a permanent cover crop was deeper than that of an annual crop, with a higher root density. Consequently, the soil compartment dried by the cover crop was larger and the grapevine was forced to explore deeper soil layers. In the presence of a cover crop on the inter-row, the grapevine also concentrated its root system below the row and dried out this soil compartment more intensively. Overall, associating grapevine with a cover crop led to a spatial distinction of soil zones exploited by the two species. The present study provides evidence that this spatial shift mainly resulted from a temporal shift in the dynamics of resource uptake by the associated species. Indeed, cover crops began to take up water before grapevine budbreak and had almost completely dried out the soil compartment they explored before grapevine water uptake became significant. This led the grapevine to modify its rooting and explore other soil zones. This phenomenon is possible in deep soils and limits competition for water between the grapevine and cover crop. Such competition is also reduced because of better soil water replenishment during the winter in the presence of a cover crop. Nevertheless, our experiments showed that this additional water mainly benefited the intercrop and did not totally compensate for transpiration by the grass cover.
In conclusion, this work shows how cover cropping can spatially and temporally modify the water regime of a vineyard, and how grapevine can partially adapt to limit water competition under certain conditions. These findings provide a clearer understanding of the water dynamics prevailing in such a system, and an opportunity to model these dynamics.
Service crops are crops grown to provide services to other cash crops, rather than for production purposes, with the ultimate aim of improving the environmental and production performances of ...cropping systems. Service crops can be intercropped with cash crops to facilitate interactions between crops and to optimize the use of the cropping season. Many terms exist to describe these practices, which highlights their diversity. However, this diversity of terms may be a source of confusion. Here, we present an overview of the current uses of intercropped service plants in temperate cropping systems, with the main services they provide and their management. (1) First, we show that a limited range of service crop species, mostly from the Fabaceae family, have been studied to date. This finding suggests that the diversity of species and cultivar resources that can be used as service crops has been poorly explored in the literature. In contrast, the combinations of service and cash crops tested appear wider. We address this diversity by defining synchronous intercropping, living mulch and relay intercropping. (2) Then, we show that intercropped service crops can efficiently reduce weed biomass and pest attacks and improve nitrogen cycling, thereby increasing soil fertility and improving crop nutrition. The intensity of these services is positively associated with service crop biomass, but excessive service crop biomass increases the risk of competition with cash crops. (3) The balance between the services and disservices provided can primarily be interpreted in terms of biomass production of coexisting crops. The resulting effect of service crops on cash crop yield is variable and reflects the integration of the effects of the various individual services, together with possible disservices. (4) The diversity in management methods makes it possible to manage this trade-off and to adapt the system to different conditions with a few tested species.
•Organic nitrogen fertilization disturbed intercropped forage legume establishment.•Organic nitrogen fertilization decreased nitrogen accumulation in forage legume.•Organic nitrogen fertilization had ...no effect on weed control by forage legume.•Forage legume sensitivity to organic fertilizer impact on provided services depended on species.
Nitrogen (N) deficiency and weed infestation are main factors limiting yield and yield stability in organic wheat. Organic fertilizers may be used to improve crop performance but off-farm input costs tend to limit profitability. Instead, forage legumes may be inserted into the crop rotation to improve the N balance and to control weed infestation. In opposition to simultaneous cropping, relay intercropping of legumes in organic winter wheat limits resource competition for the legume cover crop, without decreasing the performance of the associated wheat.
The aim of this study is to evaluate the effect of spring organic fertilization on the performance of intercropped legumes and wheat, and on services provided by the legume cover.
Two species of forage legumes (Trifolium pratense L. and Trifolium repens L.) were undersown in winter wheat (Triticum aestivum L. cv Lona) in five organic fields during two consecutive crop seasons. Organic fertilizer was composed of feather meal and applied on wheat at legume sowing. The cover crop was maintained after the wheat harvest and destroyed just before sowing maize.
Spring organic nitrogen fertilization increased wheat biomass (+35%), nitrogen (+49%), grain yield (+40%) and protein content (+7%) whatever the intercropping treatment. At wheat harvest, red clover biomass was significantly higher than white clover one (1.4 vs. 0.7tha−1). Nitrogen fertilization decreased forage legume above-ground biomass at wheat harvest, at approximately 0.5tha−1 whatever the specie. No significant difference in forage legume biomass production was observed at cover killing. Nitrogen accumulation in legume above-ground tissues was significantly higher for white clover than for red clover. Both red and white clover species significantly decreased weed infestation at this date. Nitrogen fertilization significantly increased weed biomass whatever the intercropping treatment and decreased nitrogen accumulation in both clover species (−12%).
We demonstrated that nitrogen fertilization increased yield of wheat intercropped with forage legume while the performance of legumes was decreased. Legume growth was modified by spring fertilization whatever the species.
The use of the perennial grain intermediate wheatgrass (Thinopyrum intermedium (Host) Barkworth & D.R. Dewey) may have the potential to sustain soil health and fertility through the development of an ...extensive root system. However, references are scarce to demonstrate its potential influence in a context of a limited perennial grain growth phase, integrated into annual grain crops succession. This study aims at determining how early a perennial crop rooting system differs from that of an annual crop through root development and root traits and microbial indicators. Our results indicate that the two-year-old intermediate wheatgrass promotes a denser and deeper rooting system with proportionally more root biomass and length deeper in the soil profile. From the first growing season, the perennial grain demonstrated a suite of root traits typical of a more resource-conservative strategy, and more belowground-oriented resource allocation. Soil fungal biomass indicators were enhanced. Arbuscular mycorrhizal fungi (AMF) indicators were notably found to be improved at 1 m depth during the second growing season. This study provides evidence that grain-based agriculture can benefit from the potential of deeper and long-lived root systems of intermediate wheatgrass to manage soils. The periodic use of a short-term perennial phase in the crop rotation has the potential to improve soil functioning in the long term.
In the Mediterranean area, the introduction of cover crops in vineyards is hampered by the risk of severe competition for water. Belowground interactions are still not very clear in this ...perennial-herbaceous association. This work was aimed at characterizing the development of the root systems of associated crops and the soil water dynamics. It also investigated whether water competition could be the cause of vine vigour and yield reductions. Experiments were conducted in a 4-year-old association (vine – tall fescue) and in a weed controlled vineyard. Water transfers in the soil were estimated on the basis of the soil water potential and soil hydrodynamic properties. The vine root system was concentrated in the soil under the row, whereas the intercrop highly colonized a soil compartment under the inter-row to a depth of approximately 1 m. Despite this spatial complementarity in root distribution, intercropping reduced the amount of soil water available for the vine crop. The low soil water content reduced soil water conductivity thereby limiting water transfers, despite a significant gradient in the soil water potential. This conductivity did not differ significantly between treatments but the intercrop enhanced the infiltration of winter rainwater, probably by limiting surface runoff. There was temporal complementarity in this association since the period of intense water uptake by the intercrop occurred earlier than noted for the vine under bare soil conditions. Nevertheless, the competition for water was limited by better refilling of the soil water profile during winter in the intercropped treatment. The intercrop clearly interacted with the vine and decreased its vegetative vigor. Since predawn leaf water potential and stomatal conductance did not differ among treatments, mechanism(s) other than competition for water (e.g. nutrient competition, allelopathy) may be responsible.
•We propose to assess ecological services provided by forage legume from early biomass.•Legume biomass of 2tha−1 in early September ensured weed control of about 90%.•Legume biomass of 2tha−1 in ...early September are needed to ensure N gain of at least 50kgha−1.•Cover crop biomass indicator may be used by farmers as a decision support tool for management.
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 100kgNha−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 2tha−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 60kgNha−1 as soon as legume biomass reached more than 2tha−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.
•Intercropping systems promote complementarity between plants, legumes in particular and facilitation processes in soil.•Complementarity/facilitation processes lead to better exploitation of soil ...resources.•Plant production is positively correlated with soil microbial abundance and diversity.•Increased attention should be paid to innovative perennial systems with intercropping for facilitative root interactions.
Intercropping is a powerful way to promote a more diversified plant community in the field, thereby enabling complementary and facilitative relationships. In these systems, legumes are a key functional group, and are highly valued for the agroecological services they provide. This review identifies the different complementarity and facilitation processes in soils in intercropped legume/cereal systems and the key role of soil microorganisms in these processes.
The intercropped legumes/cereal systems reduce inter-specific competition by enhancing complementarity/facilitation processes thereby improving the exploitation of resources, which is, in turn, reflected in the increase in plant production corresponding to greater efficiency of the agroecosystem as a whole.
Plant production, including above- and belowground biomass, is positively correlated with microbial abundance and diversity. This microbial life is assumed to play a significant role in the availability and transfer of soil nutrients to plants as well as in plant health and soil fertility. Although we are currently unable to identify a reliable and exhaustive pattern of plant-microbe interactions, perhaps simply because no universal relationship exists between plants and microorganisms, reliable scenarios reveal strong trends and define the conditions required for successful intercropping systems and microbial interactions.
Given our incomplete knowledge of facilitation processes and belowground interactions, intercropping systems must learn from and apply the experience gained in successful experiments. Intercropping dynamics play a critical role in explaining the establishment of facilitative root interactions and finally suggest perennial plant associations may be more effective than annual ones.
► Cover cropping impacts grapevine water and nitrogen status along crop cycle. ► Grapevine N Nutrition Index gives a new indicator to evaluate nitrogen status. ► Nitrogen stress is highly dependent ...on water constraints in such agroecosystems. ► Perennial reserves play a role by buffering soil offer/crop demand variations. ► Water/N stress are uncoupled as soil layers providing these resources are different.
Cover cropping is developing in vineyards as it may induce numerous ecosystem services. However, soil cover also competes with grapevine for soil resources. This work aimed at evaluating both the period and intensity of the resulting water and nitrogen stress experienced by grapevine by comparing treatments with bare soil, permanent and non-permanent soil cover. The adopted stress indices were the Fraction of Transpirable Soil Water (FTSW) and the Nitrogen Nutrition Index (NNI).
Cover cropping improved winter soil water refilling, but the grass transpiration during spring later led to similar water stress of grapevine among treatments. In dry years, summer water stress was not higher with non-permanent cover than with bare soil. The building of a critical nitrogen content curve for grapevine enabled to diagnose an early nitrogen stress, from budbreak to flowering, in cover cropped treatments. NNI dropped then in dry years, particularly in cover cropped treatments.
The early growth limitation of grapevine observed in cover cropped treatments was the consequence of mild early nitrogen stress, which suggests that perennial nitrogen reserves were reduced because of an earlier competition with cover crop. After grapevine flowering, water appeared to be the most limiting factor for both grapevine growth and nitrogen availability.
In water limited environment, nitrogen stress is highly dependant on water constraints. However, this work reveals the partial uncoupling of the dynamics of water and nitrogen stress during the grapevine cycle in water-limited cropping systems, which highlights the relevance of a co-ordinated management of water and nitrogen.
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