Growing vetches (Vicia villosa Roth) in irrigated cotton systems: inputs of fixed N, N fertiliser savings and cotton productivity

We compared symbiotic N₂ fixation by winter forage legumes (clovers, medics and vetches) using the ¹⁵N natural abundance technique in three experiments. Vetches (Vicia spp.) were the most productive legumes, and woollypod vetch fixed (shoot+root) up to 265 kg N ha^–1 (mean 227 kg N ha^–1) during a 4–5 months period over winter and early spring. Balansa and Berseem clovers, and Gama medic were highly productive in the first experiment, but fixed significantly less N than woollypod vetch in the second experiment. A 6-year study (1997–2003) compared cotton (Gossypium hirsutum L.) systems with and without vetch, or with faba beans (Vicia faba L.) to assess the effects of these crops on cotton production. Woollypod vetch was grown either between annual cotton crops, or between wheat (Triticum aestivumL.) and cotton crops. Vetch added 230 kg N ha^–1 (174 kg fixed N ha^–1) to the soil when incorporated as a green manure. Faba bean shoot residues and nodulated roots contributed 108 kg fixed N ha^–1 to the soil, following the removal of 80 kg N ha^–1 in the harvested seed (meaned over three crops). Lablab (Lablab purpureus L. – summer-growing and irrigated) added 277 kg N ha^–1 (244 kg fixed N ha^–1) before incorporation as a green manure in the first year of the experiment. The economic optimum N fertiliser rate for each cropping system was determined every second year when all systems were sown to cotton. Cotton following cotton required 105 kg fertiliser N ha^–1, but only 40 kg N ha^–1 when vetch was grown between each cotton crop. Cotton following wheat required 83 kg fertiliser N ha^–1 but no N fertiliser was needed when vetch was grown after wheat (the highest yielding system). Cotton following faba beans also required no N fertiliser. The vetch-based systems became more N fertile over the course of the experiment and produced greater lint yields than the comparative non-legume systems, and required less N fertiliser. While no cash flow was derived from growing vetch, economic benefits accrued from enhanced cotton yields, reduced N fertiliser requirements and improved soil fertility. These findings help explain the rotational benefits of vetches observed in other regions of the world.     

Estimation of residual N effect of faba bean and pea on two succeeding cereals using15N methodology

A field experiment was conducted using¹⁵N methodology to study the effect of cultivation of faba bean (Vicia faba L.), pea (Pisum sativum L.) and barley (Hordeum vulgare L.) on the N status of soil and their residual N effect on two succeeding cereals (sorghum (Sorghum vulgare) followed by barley). Faba bean, pea and barley took up 29.6, 34.5 and 53.0 kg N ha^–1 from the soil, but returned to soil through roots only 11.3, 10.8 and 5.7 kg N ha^–1, respectively. Hence, removal of faba bean, pea and barley straw resulted in a N-balance of about –18, –24, and –47 kg ha^–1 respectively. A soil nitrogen conserving effect was observed following the cultivation of faba bean and pea compared to barley which was of the order of 23 and 18 kg N ha^–1, respectively. Cultivation of legumes resulted in a significantly higher A_N value of the soil compared to barley. However, the A_N of the soil following fallow was significantly higher than following legumes, implying that the cultivation of the legumes had depleted the soil less than barley but had not added to the soil N compared to the fallow. The beneficial effect of legume cropping also was reflected in the N yield and dry matter production of the succeeding crops. Cultivation of legumes led to a greater exploitation of soil N by the succeeding crops. Hence, appreciable yield increases observed in the succeeding crops following legumes compared to cereal were due to a N-conserving effect, carry-over of N from the legume residue and to greater uptake of soil N by the succeeding crops when previously cropped to legumes.     

Effect of nitrogen fertilization and cropping system of the reference crop on estimation of N2 fixation by vetch using15N methodology

This study was conducted to examine the effects of varying N rates and cropping systems (mixedversus pure stand) on the suitability of oats (Avena sativa L.) for estimating N₂ fixed in sequentially harvested vetch (Vicia sativa L.) over two growing seasons (1984–85 and 1985–86). The N rates were, 20 and 100 kg N ha^–1 in 1984–85 and 15 and 60 kg N ha^–1 in 1985–86. In the 1984–85 season, vetch at maturity derived 76 and 63% N from fixation at the high and low N rates respectively. The corresponding values for the second season were 66 and 42%. Except in the 1985–86 season when some significantly higher values of % N₂ fixed were estimated by using the reference crop grown at the higher (A-value approach) than at the lower N rate (isotope-dilution approach), both approaches resulted in similar measurements of N₂ fixed. In the 1984–85 season, similar values of N₂ fixed were obtained using either the pure or mixed stand oats reference crops. Although in the 1985–86 season, the mixed reference crop occasionally estimated lower % N₂ fixed than pure oats, total N₂ fixed estimates were always similar (P<0.05). Thus, in general, N fertilization and cropping system of the reference crop did not significantly influence estimates of N₂ fixation.     

Measurements of nitrogen fixation in fababean at different N fertilizer rates using the 15N isotope dilution and ‘A-value’ methods

The ¹⁵N isotope dilution and A-value methods were used to measure biological nitrogen (N₂) fixation in field grown fababean (Vicia faba L.), over a 2-year period. Four N rates, 20, 100, 200 and 400 kg N ha^–1 were examined. The two isotope methods gave similar values of % N derived from the atmosphere (%Ndfa). With 20 kg N ha^–1, %Ndfa in fababean was about 85% in both years. Increasing the N rate to 100 kg N ha^–1 decreased N₂ fixation slightly to 75%. Further reductions in N₂ fixed to 60 and 43% occurred where 200 and 400 kg N ha^–1 were applied, respectively. Thus even higher rates of N than normally applied in farming practice could not completely suppress N₂ fixation in fababean.We also devised one equation for both the isotope dilution and A-value approaches, thereby (i) avoiding the need for different calculations for the ¹⁵N isotope methods, and (ii) showing once again that the isotope dilution and A-value methods are mathematically and conceptually identical.     

Sustainable agriculture in the semi-arid tropics through biological nitrogen fixation in grain legumes

Sustainable agriculture relies greatly on renewable resources like biologically fixed nitrogen. Biological nitrogen fixation plays an important role in maintaining soil fertility. However, as BNF is dependent upon physical, environmental, nutritional and biological factors, mere inclusion of any N₂-fixing plant system does not guarantee increased contributions to the soil N pool. In the SAT where plant stover is also removed to feed animals, most legumes might be expected to deplete soil N. Yet beneficial legume effects in terms of increased yields in succeeding cereal crops have been reported. Such benefits are partly due to N contribution from legumes through BNF and soil N saving effect. In addition, other non-N rotational benefits, for example, improved nutrient availability, improved soil structure, reduced pests and diseases, hormonal effects are also responsible. In this paper we have reviewed the research on the contribution of grain legumes in cropping systems and the factors affecting BNF. Based on the information available, we have suggested ways for exploiting BNF for developing sustainable agriculture in the semi-arid tropics (SAT). A holistic approach involving host-plant, bacteria, environment and proper management practices including need based inoculation for enhancing BNF in the cropping systems in the SAT is suggested.     

Quantifying below-ground nitrogen of legumes

Quantifying below-ground nitrogen (N) of legumes is fundamental to understanding their effects on soil mineral N fertility and on the N economies of following or companion crops in legume-based rotations. Methodologies based on ¹⁵N shoot-labelling with subsequent measurement of ¹⁵N in recovered plant parts (shoots and roots) and in the root-zone soil have proved promising. We report four glasshouse experiments with objectives to develop appropriate protocols for in situ ¹⁵N labelling of the four legumes, fababean (Vicia faba), chickpea (Cicer arietinum), mungbean (Vigna radiata) and pigeonpea (Cajanus cajan). Treatments included ¹⁵N-urea concentration (0.1–2.0% w/w), feeding technique (leaf-flap and petiole), leaflet/petiole position (top and bottom of shoot) and frequency of feeding (one and two occasions). ¹⁵N-labelling via the leaf-flap was best for fababean, mungbean and pigeonpea, whilst petiole feeding was best for chickpea, in all cases at the lower-stem nodes 3 or 4 using 0.2 mL volumes of 0.5% urea (98 atom% ¹⁵N excess). Fed leaflets and petioles were removed within 2 weeks of labelling. Uneven ¹⁵N enrichment of the nodulated roots because of effects of the less-enriched nodules meant that root derived N in soil would be overestimated if recovered roots were more heavily nodulated than unrecovered roots. One possible solution would be to assume crown nodulation of the plants. Thus, recovered roots would be nodulated; root-derived N remaining in soil may be without nodules. The ratios of nodulated root to unnodulated root enrichments could then be used as an adjustment in the calculations, i.e. in the case of fababean and chickpea, by dividing calculated root-derived N in soil by 1.12 (fababean) and 1.56 (chickpea).     

Comparative Characteristics of Carbohydrate Binding by Lectins from Broad Bean,Pea, Common Vetch,and Lentil Seeds

Lectins from the seeds of broad bean (Vicia faba L.), pea (Pisum sativum L.), common vetch (V. sativa L.), and lentil (Lens culinaris Medik.) were isolated and purified by affinity chromatography. The hemagglutinating activity of lectins was most effectively inhibited by methyl--D-mannopyranoside, trehalose, and D-mannose. Other carbohydrate haptens, such as methyl--D-glucopyranoside, maltose, and alginic and D-glucuronic acids were less effective. Two lectins obtained from different lentil cultivars, unlike other lectins, had a relatively high affinity for melecitose, N-acetyl-D-glucosamine, L-sorbose, and sucrose. Furthermore, these lectins interacted with soluble starch. All the lectins examined had similar, but not identical, carbohydrate-binding properties. Because of their similar D-mannose/D-glucose specificity, these lectins interacted with lipopolysaccharides and exopolysaccharides of Rhizobium leguminosarum bv. viciae, root nodule bacteria that infect broad-bean, pea, common-vetch, and lentil plants with the formation of nitrogen-fixing symbiosis. However, owing to individual distinctions of carbohydrate-binding properties, these lectins showed a higher affinity for the polysaccharides of those microsymbionts within the R. leguminosarum bv. viciae species that were better specialized towards one or the other host plant from the cross inoculation group of legumes.     

Biological nitrogen fixation: An efficient source of nitrogen for sustainable agricultural production?

A fundamental shift has taken place in agricultural research and world food production. In the past, the principal driving force was to increase the yield potential of food crops and to maximize productivity. Today, the drive for productivity is increasingly combined with a desire for sustainability. For farming systems to remain productive, and to be sustainable in the long-term, it will be necessary to replenish the reserves of nutrients which are removed or lost from the soil. In the case of nitrogen (N), inputs into agricultural systems may be in the form of N-fertilizer, or be derived from atmospheric N₂ via biological N₂ fixation (BNF).Although BNF has long been a component of many farming systems throughout the world, its importance as a primary source of N for agriculture has diminished in recent decades as increasing amounts of fertilizer-N are used for the production of food and cash crops. However, international emphasis on environmentally sustainable development with the use of renewable resources is likely to focus attention on the potential role of BNF in supplying N for agriculture. This paper documents inputs of N via symbiotic N₂ fixation measured in experimental plots and in farmers' fields in tropical and temperate regions. It considers contributions of fixed N from legumes (crop, pasture, green manures and trees), Casuarina, and Azolla, and compares the relative utilization of N derived from these sources with fertilizer N.     

The15N methodology in estimating N2 fixation by vetch and pea grown in pure stand or in mixtures with oat

Cereal-legume mixtures are frequently the best management decision for forage production instead of growing crops in pure stands. Nitrogen fertilization of cereal-legume mixtures is questionable since combined nitrogen could depress N₂ fixation by legumes. The objectives of this study were (1) to examine the effect of N fertilization on N₂ fixation by vetch and field peas in pure and in mixed stands with oats, and (2) to examine if there is any transfer of N from legumes to associated cereals. The field experiment was conducted for two growing seasons. The treatments were pure stands of vetch, pea and oats, and the mixtures of the two legumes with oats at the seeding ratios 90:10 and 75:25, fertilized with labelled¹⁵N at the rates of 15 and 90 kg N ha⁻¹. Nitrogen fertilization of 90 kg N ha⁻¹ suppressed N₂ fixation in both legumes grown in pure and in mixed stands. Crops grown in mixtures in many instances had lower atom %¹⁵N excess. Whether this was due to high N₂ fixation in the case of legume and transfer in the case of oat or the differences were due to practical problems of the¹⁵N technique is not clearly shown by the results, so based on the literature the aspect is discussed as well as the precautions which should be considered in using the¹⁵N technique in such studies.     

Quantifying below-ground nitrogen of legumes. 2. A comparison of 15N and non isotopic methods

Accurate information on below-ground nitrogen (N) of legumes is necessary for quantifying legume effects on soil N pools and on the N economies of crops following legumes in rotation systems. We report a series of glasshouse pot experiments to determine below-ground N (BGN) of the four legumes, fababean (Vicia faba), chickpea (Cicer arietinum), mungbean (Vigna radiata) and pigeonpea (Cajanus cajan) using both ¹⁵N shoot-labelling and ¹⁵N-labelled soil isotope-dilution methods, a mass N balance approach and the physical recovery of nodulated roots. Data from the ¹⁵N shoot-labelling experiment were manipulated in different ways in an attempt to counter errors associated with uneven ¹⁵N enrichment of roots and nodules. Values for BGN as percent of total plant N based on the physical recovery of nodulated roots ranged from 4 to 15%. With ¹⁵N shoot-labelling, a total of 8.11 mg ¹⁵N was supplied to each pot (six plants) as 0.5% ¹⁵N urea using either leaf-flap (fababean, mungbean and pigeonpea), petiole (chickpea) or leaf-tip (wheat) feeding. Calculations based on measurement of ¹⁵N enrichments of harvested plant parts and root-zone soil suggested that BGN represented 39% of total plant N for fababean, 53% for chickpea, 20% for mungbean and 47% for pigeonpea. The value for wheat was 60%. Adjustment for uneven nodulation patterns on the roots and nodule ¹⁵N depletion, resulting in different ¹⁵N enrichments between nodulated and unnodulated roots, reduced the fababean value to 37% and chickpea to 42%. Values using the other methods were generally in the same range, viz. 15–57% (simple ¹⁵N balance), 11–52% (soil ¹⁵N dilution) and 30–52% (mass N balance). We conclude that physical recovery of roots was the most inaccurate method for estimating BGN. Average values for BGN as percent of total plant N using all isotopic and mass N balance methods were 30% for fababean, 48% for chickpea, 28% for mungbean, and 43% for pigeonpea.¹⁵N shoot-labelling may be the best method for quantifying BGN of field-grown plants. The methodology is simple, apparently accurate provided care is taken in obtaining representative nodulated root samples and, unlike the soil ¹⁵N dilution method, does not require pre-treatment of the soil with ¹⁵N enriched material.     

The analysis of core and symbiotic genes of rhizobia nodulating Vicia from different continents reveals their common phylogenetic origin and suggests the distribution of Rhizobium leguminosarum strains together with Vicia seeds

In this work, we analysed the core and symbiotic genes of rhizobial strains isolated from Vicia sativa in three soils from the Northwest of Spain, and compared them with other Vicia endosymbionts isolated in other geographical locations. The analysis of rrs, recA and atpD genes and 16S–23S rRNA intergenic spacer showed that the Spanish strains nodulating V. sativa are phylogenetically close to those isolated from V. sativa and V. faba in different European, American and Asian countries forming a group related to Rhizobium leguminosarum. The analysis of the nodC gene of strains nodulating V. sativa and V. faba in different continents showed they belong to a phylogenetically compact group indicating that these legumes are restrictive hosts. The results of the nodC gene analysis allow the delineation of the biovar viciae showing a common phylogenetic origin of V. sativa and V. faba endosymbionts in several continents. Since these two legume species are indigenous from Europe, our results suggest a world distribution of strains from R. leguminosarum together with the V. sativa and V. faba seeds and a close coevolution among chromosome, symbiotic genes and legume host in this Rhizobium–Vicia symbiosis.     

Effects of crop rotation and fertilization on catalase activity in a soil of the southeastern United States

Summary Catalase activity of a loamy sand under a 3-year crop rotation in the southeastern U.S.A. was monitored. Corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] were the summer crops in the rotation. Winter wheat (Triticum aestivum L.) was planted after corn, and soybean was followed by a winter fallow period. Cotton was followed by a mixture of common vetch (Vicia sativa L.) and crimson clover (Trifolium incarnatum Gibelli & Belli) which was eventually plow-incorporated as a green manure. Highest mean catalase activities were recorded in soil under the wheat, soybean, and winter legume crops; lowest activities were found in soil bearing corn and cotton, and during the winter fallow period. The fertilization regime influenced soil catalase activity independently of the crop. Soil deficient in any of the major elements showed low enzyme activity. Highest activity was found in soil fertilized with P and K, and with N supplied by a winter legume crop. Addition of supplementary mineral nitrogen to this regime reduced catalase activity. Elimination of the winter legume crop from an otherwise complete fertilization regime resulted in a drastic reduction in enzyme activity. In soil receiving a complete fertilization regime there was a close correlation between soil catalase and xylanase activities. A similar correlation between these two enzymes was not found in soil receiving incomplete fertilization.     

The origins of cultivation of Cicer arietinum L. and Vicia faba L.: early finds from Tell el-Kerkh, north-west Syria, late 10th millennium b.p.

Cicer arietinum L. (chickpea) and Vicia faba L. (faba bean, broad bean or horse bean) were found in late 10th millennium b.p. levels at Tell el-Kerkh, in north-west Syria. They are the earliest well preserved archaeobotanical finds of these two species. Over a hundred C. arietinum specimens were recovered which showed a wide morphological diversity varying from C. arietinum ssp. reticulatum to the more rounded shape as seen in cultivated varieties. For Vicia faba, 29 complete and 119 half seeds, as well as many fragments were recovered. Tell el-Kerkh is one of the few early PPNB Near Eastern sites situated in the Mediterranean zone which could have been the habitat of the unknown wild progenitor of the faba bean. The wild progenitor of chickpea, C. a. reticulatum, is found in a limited area of southeast Turkey, at a considerable distance from Tell el-Kerkh. These finds suggest that the use and domestication of these pulses is perhaps earlier than was previously supposed.     

Economic impact of future biological nitrogen fixation technologies on United States agriculture

The economic impact of some future biological nitrogen fixation (BNF) technologies are estimated using AGSIM, an economietric model of United States agriculture. Five separate scenarios were modeled: (1) legumes fix more nitrogen (N₂) with no yield increase, (2) legumes fix more N₂ with an increase in yields of 10%, (3) N fertilization requirements on all crops are reduced 50% with no yield changes, (4) total elimination of N fertilization, and (5) total elimination of N fertilization and non-legume yields decrease 10%. Results indicate that BNF technologies have a high value to society. Increasing the efficiency of legumes to fix N₂ may have an annual US benefit of $1,067 million while decreasing N fertilization by 1,547 thousand metric tons. Total elimination of N fertilization of the major crops has an annual US benefit of $4,484 million.     

Enzymatic synthesis of (R)-cyanohydrins by a novel (R)-oxynitrilase from Vicia sativa L.

The defatted seed meal of common vetch (Vicia sativa L.) served as a source of (R)-oxynitrilase which catalyzed the enantioselective addition of HCN to aromatic, heteroaromatic, fluoro-substituted aromatic aldehydes to produce the corresponding enantiomeric pure cyanohydrins in yields of 52–100% and 88–99% ee at 12°C under micro-aqueous medium (diisopropyl ether) without addition of buffer solution.     

Genetic specificity of nitrogen nutrition in leguminous plants

Summary Mineral nitrogen did not increase grain yield and seed protein levels ofVicia faba L. andLupinus luteus L. in field trials and pot experiments. Fixed N₂ was substituted by mineral nitrogen in these cases because of inhibition of N₂ fixation by mineral nitrogen. Contrary to these results mineral nitrogen increased grain yields and seed protein amounts ofLupinus albus L.,Pisum sativum L., andGlycine max. (L.) Merr. The nitrogen effect was caused at an early stage by saving energy due to inhibition of N₂ fixation (measurement of gas exchange by means of IRGA). In case of the N application after flowering grain, yields and seed protein levels increased because the mineral N was an additional nitrogen source for plants. At this stage the plants had ceased fixing atmospheric nitrogen. The high sink activity of growing fruits induced a lack of assimilates in nodules (determined by means of¹⁴CO₂ application). The N effect was therefore the consequence of the lower assimilate pool for supplying root nodules in these plants in comparison withVicia faba L. andLupinus luteus L. Hence it follows that response to mineral nitrogen can be a criterion for discovering more effective Rhizobium-host combinations.     

Measurements of genetic variability for symbiotic dinitrogen fixation in fieldgrwon fababean (Vicia faba L.) using a low level15N-tracer technique

Before starting a breeding program aimed at improving the nitrogen nutrition ofVicia faba, the authors tried an alternative technique to the acetylene reduction assay, to measure some genetic variability in the plant material. The quantity of dinitrogen fixed by several cultivars ofVicia faba was estimated using a low enrichment¹⁵N tracer method and high precision¹⁵N mass spectrometry. The fababeans were cultivated for two years in two different soils. The percentage of fixed dinitrogen in the seed varied between genotypes from 40 to 83% of the total nitrogen and was positively correlated with the total seed nitrogen (r=0.64 to 0.86). A highly significant positive correlation was also found between the total seed nitrogen and the quantity of fixed dinitrogen in the seed (r=0.95 to 0.99). The technique used to measure dinitrogen fixation proved to be useful and reliable enough to discriminate between various genotypes, grown over a period of two years in two different soils. However, several non-fixing control plants showed significant differences in their¹⁵N enrichment and the problem of choosing a good reference plant was raised and discussed.     

Differences in accumulation of soluble α-galactosides during seed maturation of several <Emphasis Type="Italic">Vicia</Emphasis> species

Composition and levels of soluble α-galactosides: raffinose family oligosaccharides (RFOs) and galactosyl cyclitols (Gal-C) in developing seeds were measured by high resolution gas chromatography (HRGC) method. The studies were performed on maturing seeds of several wild and cultivated Vicia species: Vicia angustifolia L. (common vetch), Vicia cracca L. (bird vetch), Vicia grandiflora Scop. (large yellow vetch), Vicia hirsuta (L.) S.F.Gray (tiny vetch), Vicia sativa L. (garden vetch, spring-growing cultivar Kwarta), and Vicia villosa Roth (winter vetch). In all Vicia species similar patterns in the accumulation of RFOs were observed. Galactinol — the donor of galactosyl moieties in α-galactosides biosynthesis was present in the middle stage of seed development, before appearing measurable levels of RFOs. Accumulation of RFOs started parallel with seed desiccation process. At first accumulation of the raffinose, then few days later stachyose and finally verbascose was noticed. In the final stage of seed maturation the verbascose was the main soluble α-galactoside (up to 3% of dry weight, V. sativa). Besides the RFOs seeds of three Vicia species (V. cracca, V. hirsuta, and V. villosa) accumulated d-pinitol and its α-galactosides (Gal-C). Mono-galactosylpinitols (similar to raffinose) appeared in these species 2–4 days after galactinol, di-galactosyl pinitol A (common name: ciceritol) and di-galactosyl myo-inositol were present several days later than raffinose, and accumulation of tri-galactosyl pinitol A (TGPA) began after accumulation of stachyose. Matured seeds of V. hirsuta contained much more RFOs than Gal-C, opposite to seeds of V. villosa, and V. cracca where concentration of Gal-C was 4–8-fold higher than RFOs. In V. cracca seeds RFOs were almost replaced by Gal-C. In seeds of V. cracca and V. villosa the level of d-pinitol was significantly higher, than the level of myo-inositol. Contents of both cyclitols declined rapidly at the beginning of seed desiccation, when accumulation of RFOs and Gal-C quickly increased. We suggest that α-galactosides of d-pinitol can substitute raffinose family oligosaccharides and play similar role during seed maturation and storage.     

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.     

Dual inoculation withRhizobium sp. andGlomus fasciculatum enhances nodulation,yield and nitrogen fixation in chickpea (Cicer arietinum Linn.)

Summary Seed inoculation with Rhizobium and soil inoculation withGlomus fasciculatum increased nodulation, nitrogen and phosphorus concentration in plants and yield of chickpea (Cicer arietinum) var. BG 212 in pots containing unsterilized soil especially with 50kgP₂O₅ ha⁻¹ in the form of superphosphate. Inoculation with Rhizobium orG. fasciculatum separately or in combination significantly increased the N₂ fixed in straw and grain than uninoculated controls as determined by¹⁵N atom percent excess of plants grown in soil amended with labelled ammonium sulphate (¹⁵NH₄)₂SO₄) at the rate of 20kg N ha⁻¹. These increases were most pronounced when P was applied at 50kgP₂O₅ ha⁻¹.