Dynamics of phosphorus fractions in the rhizosphere of common bean (Phaseolus vulgaris L.) and durum wheat (Triticum turgidum durum L.) grown in monocropping and intercropping systems

The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosphere of durum wheat (Triticum turgidum durum L.) and common bean (Phaseolus vulgaris L.) grown in monocropping and intercropping systems with nitrate supply. Wheat and common bean were grown either alone or in association in a cropping device with a thin (1 mm) soil layer sandwiched between large root mats. Wheat intercropped with common bean exhibited a 33% increase in shoot biomass and a 22% increased root biomass, without significantly affecting common bean growth. After 12 days of culture, rhizosphere pH decreased by 1.66 and 1.13 units in monocropping system of common bean and intercropping system, respectively. Wheat increased intercropped common bean proton release by 36% compared with monocropped beans. Common bean and wheat exhibited different behaviors in rhizosphere P dynamics. Monocropped wheat decreased Resin-P, NaHCO₃-P and NaOH-P in its rhizosphere by 24, 96 and 10%, respectively. However, NaHCO₃-P and NaOH-P were increased by 61 and 10% in the rhizosphere of intercropping. Almost all values about P fraction in intercropping system were between those in monocropped common bean and monocropped wheat. Through taping different P fraction, different plants species possibly can alleviate competition for phosphorus in intercropping system.     

Maize grain concentrations and above-ground shoot acquisition of micronutrients as affected by intercropping with turnip, faba bean, chickpea, and soybean

Most research on micronutrients in maize has focused on maize grown as a monocrop. The aim of this study was to determine the effects of intercropping on the concentrations of micronutrients in maize grain and their acquisition via the shoot. We conducted field experiments to investigate the effects of intercropping with turnip (Brassica campestris L.), faba bean (Vicia faba L.), chickpea (Cicer arietinum L.), and soybean (Glycine max L.) on the iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) concentrations in the grain and their acquisition via the above-ground shoots of maize (Zea mays L.). Compared with monocropped maize grain, the grain of maize intercropped with legumes showed lower concentrations of Fe, Mn, Cu, and Zn and lower values of their corresponding harvest indexes. The micronutrient concentrations and harvest indexes in grain of maize intercropped with turnip were the same as those in monocropped maize grain. Intercropping stimulated the above-ground maize shoot acquisition of Fe, Mn, Cu and Zn, when averaged over different phosphorus (P) application rates. To our knowledge, this is the first report on the effects of intercropping on micronutrient concentrations in maize grain and on micronutrients acquisition via maize shoots (straw+grain). The maize grain Fe and Cu concentrations, but not Mn and Zn concentrations, were negatively correlated with maize grain yields. The concentrations of Fe, Mn, Cu, and Zn in maize grain were positively correlated with their corresponding harvest indexes. The decreased Fe, Mn, Cu, and Zn concentrations in grain of maize intercropped with legumes were attributed to reduced translocation of Fe, Mn, Cu, and Zn from vegetative tissues to grains. This may also be related to the delayed senescence of maize plants intercropped with legumes. We conclude that turnip/maize intercropping is beneficial to obtain high maize grain yield without decreased concentrations of Fe, Mn, Cu, and Zn in the grain. Further research is required to clarify the mechanisms underlying the changes in micronutrient concentrations in grain of intercropped maize.     

Nitrogen Fixation of Faba Bean (Vicia faba L.) Interacting with a Non-legume in Two Contrasting Intercropping Systems

A field experiment was carried out to quantify biological nitrogen fixation (BNF) using the ¹⁵N isotope natural abundance method in maize (Zea mays L.)/faba bean (Vicia faba L.) and wheat (Triticum aestivum L.)/faba bean intercropping systems. Faba bean was yielding more in the maize/faba bean intercropping, but not in the wheat/faba bean intercropping. Biomass, grain yield and N acquisition of faba bean were significantly increased when intercropped with maize, and decreased significantly with wheat, irrespective of N-fertilizer application, indicating that the legume could gain or lose productivity in an intercropping situation. There was yield advantage of maize/faba bean intercropping, but no in wheat/faba bean intercropping. The grain yield of the faba bean intercropped with maize was greater than that of faba bean monoculture due to increases of the stems per plant and the pods per stem of faba bean. N fertilization inhibited N fixation of faba bean in maize/faba bean and wheat/faba bean intercropping and faba bean monoculture. The responses of different cropping systems to N-fertilizer application, however, were not identical, with competitive intercropping (wheat/faba bean) being more sensitive than facilitative intercropping (maize/faba bean). Intercropping increased the percentage of N derived from air (%Ndfa) of the wheat/faba bean system, but not that of the maize/faba bean system when no N fertilizer was applied. When receiving 120 kg N/ha, however, intercropping did not significantly increase %Ndfa either in the wheat/faba bean system or in the maize/faba bean system in comparison with faba bean in monoculture. The amount of shoot N derived from air (Ndfa), however, increased significantly when intercropped with maize, irrespective of N-fertilizer application. Ndfa decreased when intercropped with wheat, albeit not significantly at 120 kg N/ha. Ndfa was correlated more closely with dry matter yield, grain yield and competitive ratio, than with %Ndfa. This indicates that that total dry matter yield (sink strength), not %Ndfa, was more critical for the legume to increase Ndfa. The results suggested that N fixation could be improved by yield maximization in an intercropping system.     

Effects of rhizobial inoculation, cropping systems and growth stages on endophytic bacterial community of soybean roots

Interspecific interactions and soil nitrogen supply levels affect intercropping productivity. We hypothesized that interspecific competition can be alleviated by increasing N application rate and yield advantage can be obtained in competitive systems. A field experiment was conducted in Wuwei, Gansu province in 2007 and 2008 to study intercropping of faba bean/maize, wheat/maize, barley/maize and the corresponding monocultures of faba bean (Vicia faba L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and maize (Zea mays L.) with N application rates of 0, 75, 150, 225 and 300 kg N ha^?1. Total land equivalent ratios (TLER) were 1.22 for faba bean/maize, 1.16 for wheat/maize, and 1.13 for barley/maize intercropping over the 2-year study period. Maize was overyielding when intercropped with faba bean, but underyielding when intercropped with wheat or barley according to partial land equivalent ratios (PLER) based on grain yields of individual crops in intercropping and sole cropping. There was an interspecific facilitation between intercropped faba bean and maize, and interspecific competition between maize and either wheat or barley. The underyielding of maize was higher when intercropped with barley than with wheat. Fertilizer N alleviated competitive interactions in intercrops with adequate fertilizer N at 225 kg ha^?1. Yield advantage of intercropping can be acquired with adequate nitrogen supply, even in an intensive competitive system such as barley/maize intercropping. This is important when using intercropping to develop intensive farming systems with high inputs and high outputs.     

Intercropping green manure crops—effects on rooting patterns

Greater productivity under intercropping has been attributed to the complementary use of environmental resources. However, the rooting pattern of component species under intercropping, which is an important morphological feature considering the complementary uptake of nutrients, has been studied only rarely under field conditions because of inherent technical difficulties. We examined rooting patterns of three green manure species, both sole cropped and intercropped, using a newly developed multi-color staining technique. Species were chosen from different functional groups: sorghum (Sorghum bicolor (L.) Moench.), a C4 grass; crotalaria (Crotalaria juncea L.), a legume; and sunflower (Helianthus annuus L.), a C3 dicot. We also investigated these species’ aboveground biomass and N uptake. Sorghum distributed roots deeper under intercropping than under sole cropping; it was the most important contributor to increased biomass under intercropping. Crotalaria had a deep rooting system under both sole cropping and intercropping. Sunflower, with a shallow rooting system, was suppressed extremely under intercropping, possibly because of water deficiency in late in the season. The rooting patterns of green manure species examined using multi-color staining were related closely to the aboveground performance of these species under intercropping.     

Using competitive and facilitative interactions in intercropping systems enhances crop productivity and nutrient-use efficiency

This paper reviews recent research on the processes involved in the yield advantage in wheat (Triticum aestivum L.)/maize (Zea mays L.), wheat/soybean [Glycine max (L.) Merr.], faba bean (Vicia faba L.)/maize, peanut (Arachis hypogaea L.)/maize and water convolvulus (Ipomoea aquatica Forsk.)/maize intercropping. In wheat/maize and wheat/soybean intercropping systems, a significant yield increase of intercropped wheat over sole wheat was observed, which resulted from positive effects of the border row and inner rows of intercropped wheat. The border row effect was due to interspecific competition for nutrients as wheat had a higher competitive ability than either maize or soybean had. There was also compensatory growth, or a recovery process, of subordinate species such as maize and soybean, offsetting the impairment of early growth of the subordinate species. Finally, both dominant and subordinate species in intercropping obtain higher yields than that in corresponding sole wheat, maize or soybean. We summarized these processes as the `competition-recovery production principle'. We observed interspecific facilitation, where maize improves iron nutrition in intercropped peanut, faba bean enhances nitrogen and phosphorus uptake by intercropped maize, and chickpea facilitates P uptake by associated wheat from phytate-P. Furthermore, intercropping reduced the nitrate content in the soil profile as intercropping uses soil nutrients more efficiently than sole cropping.     

Weed Dynamics during Transition to Conservation Agriculture in Western Kenya Maize Production

Weed competition is a significant problem in maize (Zea mays, L.) production in Sub-Saharan Africa. Better understanding of weed management and costs in maize intercropped with beans (Phaseolus vulgaris, L.) during transition to conservation agricultural systems is needed. Changes in weed population and maize growth were assessed for a period of three years at Bungoma where crops are grown twice per year and at Trans-Nzoia where crops are grown once per year. Treatments included three tillage practices: minimum (MT), no-till (NT) and conventional (CT) applied to three cropping systems: continuous maize/bean intercropping (TYPICAL), maize/bean intercropping with relayed mucuna after bean harvest (RELAY) and maize, bean and mucuna planted in a strip intercropping arrangement (STRIP). Herbicides were used in NT, shallow hand hoeing and herbicides were used in MT and deep hoeing with no herbicides were used in CT. Weed and maize performance in the maize phase of each cropping system were assessed at both locations and costs of weed control were estimated at Manor House only. Weed density of grass and forb species declined significantly under MT and NT at Manor House and of grass species only at Mabanga. The greatest declines of more than 50% were observed as early as within one year of the transition to MT and NT in STRIP and TYPICAL cropping systems at Manor House. Transitioning to conservation based systems resulted in a decline of four out of five most dominant weed species. At the same time, no negative impact of MT or NT on maize growth was observed. Corresponding costs of weed management were reduced by $148.40 ha^-1 in MT and $149.60 ha^-1 in NT compared with CT. In conclusion, farmers can benefit from effective and less expensive weed management alternatives early in the process of transitioning to reduced tillage operations.     

Effect of peanut mixed cropping with gramineous species on micronutrient concentrations and iron chlorosis of peanut plants grown in a calcareous soil

To gain a better understanding of the mechanisms of improvement of iron nutrition of peanut (Arachis hypogaea L.) intercropped with maize (Zea mays L.) in calcareous soil, both greenhouse and field experiments were conducted to investigate the rhizosphere (phytosiderophores) effects from maize, barley, oats and wheat with different phytosiderophores release rates on iron nutrition and other micronutrients in calcareous soil. Six cropping treatments were examined in a greenhouse experiment: peanut grown separately in monoculture, normal peanut/maize intercropping (two genotypes: Danyu13, Zhongdan12), peanut/barley intercropping, peanut/oats intercropping, and peanut/wheat intercropping. Additionally, we investigated in a field experiment the same five cropping systems as the greenhouse experiment (maize/peanut intercropping not including Zhongdan12). Our results show that the chlorophyll and active Fe concentrations in the young leaves of the peanut in the intercropping system with different gramineous species were much higher than those of the peanut in monoculture. In greenhouse conditions, the Fe concentration in the shoots of peanut plants grown in the intercropping systems of two maize genotypes separately were 1.40–1.44, 1.47–1.64 and 1.15–1.42 times higher respectively than those of peanut plants grown in monocropping at 55, 60 and 70 days. In particular, the Fe concentration in shoots of peanut plants grown in the intercropping systems of barley, oats and wheat were not only higher than those in monocropping but also higher than those in peanut intercropped cropping with maize. In the field, the concentration of Fe in shoot of intercropped peanut plants in rows 1–3 from gramineous species were significantly higher than in monocropping at the flowering stage. Simultaneously with iron nutrition variation in peanut, Zn and Cu concentrations of intercropped grown peanut increased significantly compared to those in monocropping in the greenhouse experiment, and different intercropping treatments generally increased the Zn and Cu content in the shoot of peanut in the field. Systemic mechanisms may be involved in adaptation to nutrient stresses at the whole plant level. The study suggests that a reasonable intercropping system of nutrient efficient species should be considered to prevent or mitigate iron and zinc deficiency of plants in agricultural practice.     

Crop nitrogen use and soil mineral nitrogen accumulation under different crop combinations and patterns of strip intercropping in northwest China

Increasing crop nitrogen use efficiency while also simultaneously decreasing nitrogen accumulation in the soil would be key steps in controlling nitrogen pollution from agricultural systems. Long-term field experiments were started in 2003 to study the effects of intercropping on crop N use and soil mineral N accumulation in wheat (Triticum aestivum L. cv 2014)/maize (Zea mays L. cv Shendan16), wheat/faba bean (Vicia faba L. cv Lincan No. 5) and maize/faba bean intercropping and monocropping systems. Monocropping was compared with two types of strip intercropping: continuous intercropping (two crops intercropped continuously on the same strips of land every year) and rotational intercropping (two crops grown adjacently and rotated to the other crop??s strip every year). Maize/faba bean intercropping had greater crop N uptake than did wheat/faba bean or wheat/maize. Wheat/maize accumulated more mineral N in the top 140 cm of the soil profile during the co-growth stage from maize emergence to maturity of wheat or faba bean. Continuously intercropped maize substantially decreased soil mineral N accumulation under wheat and faba bean rows (60?C100 cm soil depth) at maize harvest. Soil mineral N accumulation under wheat rows increased with rotational intercropping with faba bean. Rotational intercropping may potentially alleviate the adverse effects of wheat on N use by other crops and increase the nitrogen harvest index of wheat, maize and faba bean. Intercropping using species with different maturity dates may be more effective in increasing crop N use efficiency and decreasing soil mineral N accumulation.     

间作对植株生长及养分吸收和根际环境的影响

通过盆栽实验研究了线辣椒和玉米间作对其植株生长、矿质养分吸收、根际环境以及铁载体分泌的影响,以探索间作促进铁、磷等养分吸收利用的可能生理机制.结果表明:(1)与单作相比,间作线辣椒地上部干重降低23.0%,根系干重增加44.2%,玉米地上部和根系的干重分别增加8.7%和22.9%;间作线辣椒根冠比和根系活力分别显著提高86.4%和29.8%;间作线辣椒、玉米叶绿素含量分别显著提高12.6%和7.8%.(2)与单作相比,间作线辣椒的铁、锌、锰含量分别增加1.50倍、1.39倍和1.34%,而间作玉米则无显著变化;间作线辣椒和玉米的钙含量都显著低于相应单作,氮含量没有显著变化,但磷、钾含量显著增加.(3)间作线辣椒和玉米的根际土、非根际土的酸性磷酸酶活性及根系酸性磷酸酶活性都显著高于相应单作,而其根际土和非根际土的pH值无显著变化;间作玉米根系的铁载体分泌比单作减少32.8%,间作线辣椒根系的铁还原酶活性是单作的1.10倍.研究发现,线辣椒/玉米间作能通过影响根际生物学特征和化学过程提高植株的铁、锌、磷和钾养分水平,缓解养分胁迫,是一种很有推广价值的种植模式.     

Root distribution and interactions between intercropped species

Even though ecologists and agronomists have considered the spatial root distribution of plants to be important for interspecific interactions in natural and agricultural ecosystems, few experimental studies have quantified patterns of root distribution dynamics and their impacts on interspecific interactions. A field experiment was conducted to investigate the relationship between root distribution and interspecific interactions between intercropped plants. Roots were sampled twice by auger and twice by the monolith method in wheat (Triticum aestivum L.)/maize (Zea mays L.) and faba bean (Vicia faba L.)/maize intercropping and in sole wheat, maize, and faba bean up to 100 cm depth in the soil profile. The results showed that the roots of intercropped wheat spread under maize plants, and had much greater root length density (RLD) at all soil depths than sole wheat. The roots of maize intercropped with wheat were limited laterally, but had a greater RLD than sole-cropped maize. The RLD of maize intercropped with faba bean at different soil depths was influenced by intercropping to a smaller extent compared to maize intercropped with wheat. Faba bean had a relatively shallow root distribution, and the roots of intercropped maize spread underneath them. The results support the hypotheses that the overyielding of species showing benefit in the asymmetric interspecific facilitation results from greater lateral deployment of roots and increased RLD, and that compatibility of the spatial root distribution of intercropped species contributes to symmetric interspecific facilitation in the faba bean/maize intercropping. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Winter grass cover crop effects on nematodes and yields of double cropped soybean

Rye (Secale cereale L.), wheat (Triticum aestivum L.), and annual ryegrass (Lolium multiflorum Lam.) are commonly double cropped with soybean (Glycine max L.). Recent greenhouse studies have shown variability in plant-parasitic nematode response to cool season grass species and cultivars. However, subsequent soybean performance was not affected by previous annual ryegrass cultivar in the green-house. The objective of this research was to determine whether winter cover crop species or cultivars affected nematode populations and subsequent performance of soybean in teh field. Four cultivars of annual ryegrass, wheat, and rye, and a fallow control were seeded on a Suffolk sandy loam (fine-loamy, siliceous, thermic Typic Hapuldult) soil in each of three years. Nematode-susceptible soybeans were seeded following forage removal. Soil samples for nematode counts were taken immediately before soybean harvest each year. In another experiment, one cultivar each of annual ryegrass, wheat, and rye, and a fallow control were followed by three soybean cultivars selected for differing nematode susceptibility. Grass cultivars did not affect nematode populations under succedding soybean. The only nematodes affected by grass species in either experiment were Pratylenchus spp., Heterodera glycines Ichinohe, and Tylenchorhynchus claytoni (Kofoid and White) Chitwood. Nematode population means were usually low following ryegrass and high following the fallow control. High soybean yields followed the fallow control, and low soybean yields followed annual ryegrass.     

Studies on the improvement in iron nutrition of peanut by intercropping with maize on a calcareous soil

Both rhizobox and field experiments were conducted to investigate nutritional interactions between peanut and maize in intercropping systems for Fe acquistion. Field observations indicated that Fe deficiency chlorosis symptoms in peanut grown in monoculture were more severe and widespread compared to those of peanuts intercropped with maize. This indicated a marked improvement in the iron nutrition of peanut intercropped with maize in the field and was further studied. In experiments with rhizoboxes, roots of maize and peanut were either allowed to interact with each other or prevented from making contact by inserting a solid plate between the root systems of the two species. A field experiment for four cropping treatments were examined: peanut grown separately in monoculture, normal peanut/maize intercropping, peanut/maize intercropping with solid plates between the root systems of the two crop species and peanut/maize intercropping with 30 μm nylon nets between the root systems. The results show that the chlorophyll and HCl-extractable Fe concentrations in young leaves of peanut in the intercropping system with unrestricted interactions of the roots of both plant species were much higher than those of peanut in monoculture. In the nylon mesh treatment, the beneficial effects of the maize extended to row 3. The improvement of Fe nutrition in the intercropping system got reduced but not diminished completely in the treatment with nylon net. It is suggested that the improvement in the Fe nutrition of peanut intercropped with maize was mainly caused by rhizosphere interactions between peanut and maize. This revised version was published online in June 2006 with corrections to the Cover Date.     

Forage production, N uptake, N2 fixation, and N recovery of berseem clover grown in pure stand and in mixture with annual ryegrass under different managements

In Mediterranean countries, forage grasses and legumes are commonly grown in mixture because of their ability to increase herbage yield and quality compared with monocrop systems. However, the benefits of intercropping over a monocrop system are not always realized because the efficiency of a grass–legume mixture is strongly affected by agronomic factors. The present study evaluated productivity, N₂ fixation, N transfer, and N recovery of berseem clover (Trifolium alexandrinum) grown in pure stand and in mixture with annual ryegrass (Lolium multiflorum) under high or low defoliation frequencies and varying plant arrangements (sowing in the same row or in alternating rows). On average, the berseem–ryegrass mixtures resulted in a greater yield and N yield than the monocrops. When mixed together, ryegrass was more efficient than berseem at absorbing soil N, increasing the reliance of berseem on N₂ fixation. Both defoliation management and plant arrangement affected forage yield and the quality of the mixture, modifying the proportion of the two components, the N content of the forage, and the symbiotic N₂ fixation of the legume. Reducing the proximity between plants of the two species may benefit the weaker component of the mixture. No apparent transfer of fixed N from berseem to ryegrass was detected.     

The Dynamic Process of Interspecific Interactions of Competitive Nitrogen Capture between Intercropped Wheat (Triticum aestivum L.) and Faba Bean (Vicia faba L.)

Wheat (Triticum aestivum L.)/faba bean (Vicia faba L.) intercropping shows significant overyielding and high nitrogen (N)-use efficiency, but the dynamics of plant interactions have rarely been estimated. The objective of the present study was to investigate the temporal dynamics of competitive N acquisition between intercropped wheat and faba bean with the logistic model. Wheat and faba bean were grown together or alone with limited N supply in pots. Data of shoot and root biomass and N content measured from 14 samplings were fitted to logistic models to determine instantaneous rates of growth and N uptake. The superiority of instantaneous biomass production and N uptake shifted from faba bean to wheat with their growth. Moreover, the shift of superiority on N uptake occurred 7–12 days earlier than that of biomass production. Interspecific competition stimulated intercropped wheat to have a much earlier and stronger superiority on instantaneous N uptake compared with isolated wheat. The modeling methodology characterized the temporal dynamics of biomass production and N uptake of intercropped wheat and faba bean in different planting systems, which helps to understand the underlying process of plant interaction for intercropping plants.     

Can R*s Predict Invasion in Semi-arid Grasslands?

We estimated R*s and tested the applicability of R* theory on nonindigenous plant invasions in semi-arid rangeland. R* is the concentration of a resource that a species requires to survive in a habitat. R* theory predicts that a species with a lower R* for the most limiting resource will competitively displace a species with a higher R* under equilibrium conditions. In a greenhouse, annual sunflower (Helianthus annuus L.), bluebunch wheatgrass (Agropyron spicatum Pursh), and spotted knapweed (Centaurea maculosa Lam.) were grown in monoculture and 2- and 3-species mixtures for three growth periods in an attempt to reduce soil NO₃-N concentrations below each species’ R*. At the end of each growth period, aboveground biomass by species and soil plant available nitrogen were sampled. Decreasing biomass coupled with decreasing soil plant available nitrogen was used to quantify R*s for the three species. R*s for annual sunflower, bluebunch wheatgrass, and spotted knapweed were estimated to be 0.6±0.16 ppm NO₃⁻, less than 0.05 ppm NO₃⁻, and 0.6±0.13 ppm NO₃⁻, respectively. Estimated R*s did not predict the outcome of competition among species. To successfully predict plant community dynamics on semi-arid rangeland with and without the presence of a nonindigenous invasive species, a more comprehensive model that includes mechanisms in addition to competition may have to be considered. We speculate that R* theory may prove most useful for predicting the outcome of competition within functional groups.     

Changes in soil phosphorus fractions following sole cropped and intercropped maize and faba bean grown on calcareous soil

Aims

This study aimed to investigate the effects of coexistence with faba bean, a phosphorus (P)-efficient crop, on soil-accumulated P use by a maize/faba bean intercropping system on dynamic changes in soil P pool.

Methods

Maize and faba bean were grown in P-accumulated soil as either sole cropping or intercropping. After one year (Stage I) or four years (Stage II) of no P application, soil samples were collected respectively and analyzed for soil P pools using sequential fractionation. Aboveground biomass and P content were annually measured from 2013 to 2016 to assess the annual P balance.

Results

The intercropped maize/faba bean system showed a P-uptake advantage, with a Land Equivalent Ratio (LER) ranging from 1.2 to 1.5. The average shoot P content over the four years in intercropped maize and faba bean was significantly greater than that of the corresponding sole crops by 29% and 30%, respectively. Over the three-year P depletion period, the three cropping systems primarily depleted the 1 M HCl-P_i fraction, followed by sole maize, which depleted the NaOH-P_i and concentrated HCl-P_o fractions. Sole faba bean depleted the alkali-soluble P_o fraction (extracted by NaHCO₃ and NaOH), and the intercropped maize/faba bean system depleted the conc. HCl-P_o fraction, which was similar to the effect of sole maize.

Conclusions

Both sole crops and intercrops mainly depleted 1 M HCl-P_i, but differed in P_o depletion. Sole maize and maize/faba bean intercropping depleted the sparingly labile P_o fraction, while sole faba bean depleted the labile and moderately labile P_o fractions.

     

小麦蚕豆间作对蚕豆根际微生物群落功能多样性的影响及其与蚕豆枯萎病发生的关系

通过田间小区试验,研究了小麦与蚕豆间作对蚕豆枯萎病发生和根际微生物代谢功能多样性的影响。结果表明,小麦与蚕豆间作使蚕豆枯萎病的发病率和病情指数分别比单作显著降低20%和30.4%。与单作处理相比,间作显著增加了蚕豆和小麦根际微生物对31种碳源的平均利用率（AWCD）,其中间作蚕豆的AWCD值最高,比单作增加82.7%,单作蚕豆最低。间作蚕豆和间作小麦根际微生物的Shannon多样性指数与丰富度指数均显著高于单作,间作使蚕豆和小麦的丰富度指数分别增加29.2%和30.3%。根际微生物对六类碳源的利用强度百分比以糖类、羧酸类和氨基酸最高,分别为41.96%,19.80%和18.13%。主成分分析表明,小麦与蚕豆间作改变了根际微生物的群落组成;相关分析表明,糖类、羧酸类和氨基酸类碳源是区分单间作处理差异的主要碳源,其中氨基酸类碳源是最敏感的碳源。小麦与蚕豆间作增加了根际微生物活性,提高了Shannon多样性指数和丰富度指数,改变了微生物群落功能多样性,是抑制蚕豆枯萎病的有效措施。该研究为阐明根际微生物功能多样性变化在间作体系病害控制中的作用与机制奠定了理论基础。     

Nitrogen Fertilization Effects on Productivity and Nitrogen Loss in Three Grass-Based Perennial Bioenergy Cropping Systems

Nitrogen (N) fertilization can greatly improve plant productivity but needs to be carefully managed to avoid harmful environmental impacts. Nutrient management guidelines aimed at reducing harmful forms of N loss such as nitrous oxide (N₂O) emissions and nitrate (NO₃^-) leaching have been tailored for many cropping systems. The developing bioenergy industry is likely to make use of novel cropping systems, such as polycultures of perennial species, for which we have limited nutrient management experience. We studied how a switchgrass (Panicum virgatum) monoculture, a 5-species native grass mixture and an 18-species restored prairie responded to annual fertilizer applications of 56 kg N ha^-1 in a field-scale agronomic trial in south-central Wisconsin over a 2-year period. We observed greater fertilizer-induced N₂O emissions and sub-rooting zone NO₃^- concentrations in the switchgrass monoculture than in either polyculture. Fertilization increased aboveground net primary productivity in the polycultures, but not in the switchgrass monoculture. Switchgrass was generally more productive, while the two polycultures did not differ from each other in productivity or N loss. Our results highlight differences between polycultures and a switchgrass monoculture in responding to N fertilization.     

Seasonal N uptake and N2fixation by common and adzuki bean at various spacings

The adzuki bean (Vigna angularis (Wild.) Ohwi and Ohashi) and common bean (Phaseolus vulgaris L.) have a high physiological demand for N. A 2-year field study was conducted to investigate the seasonal change of available soil N and symbiotic N₂ fixation usage. The beans were seeded at two densities, 22.2 plants m^–2 with a row spacing of 0.3 m and 11.1 plants m^–2 with a row spacing of 0.6 m. The amount of fixed N₂ in the shoot was calculated using the ¹⁵N natural abundance method. The common bean demonstrated low N₂ fixation and the ability to accumulate high levels of soil N. Soil nitrate under the common bean was continually absorbed. The adzuki bean, on the other hand, had a remarkable peak of N accumulation in the early reproductive stage. This was mainly due to N₂ fixation, though the soil nitrate level was high. Narrowing the plant row spacing increased the dry matter yield of both species, but the origin of the increased N differed between the species. For the first 77 DAP in 1999 (73 DAP in 2000) the N increase for both beans was due to both soil and atmospheric N₂. At harvest, though, the increase of N in common bean was mainly due to soil N, while that in adzuki bean was mainly due to atmospheric N₂. It can be concluded that the low symbiotic N₂ fixation ability of common bean was due to its high soil N uptake ability and constant N accumulation, which enabled an efficient soil N absorption. Adzuki bean absorbed N mainly for a short period and depended more on symbiotically fixed N₂ and, in contrast to common bean, left a high level of NO₃-N remaining in the soil after cropping.