The relationship between competitive ability and yield stability in an old and a modern winter wheat cultivar

This study was conducted to determine if there were differences in competitive ability and yield stability on the growth of an old landrace of winter wheat (Triticum aestivum), Pinglang 40 (PL40), and a modern cultivar, Changwu135, (CW135), which differed in time of cultivar release, height, shoot and root biomass. A second aim was to investigate whether there is a relationship between competitive ability and yield stability. One pot and two field experiments were conducted to monitor changes in the competitive ability and yield stability of an old and a modern winter wheat cultivar grown in monoculture and mixtures using a de Wit replacement series. The pot study was conducted at two soil moisture levels: (a) well watered (WW), soil maintained at 85% field capacity, and (b) moderate drought (MD), soil maintained at 55% field capacity. The field experiments were conducted in 2 years that were drier than the average. In the second field experiment 40 mm of irrigation was applied to half of the plots at jointing, booting and anthesis. The results were similar in the pot and field experiments. In the mixture, the old cultivar PL40 had a greater relative yield with a larger number of spikes per plant when compared with those of the modern cultivar CW135. The dry matter per stem of CW135 tended to decrease with the increasing proportion of PL40, indicating a lower competitive ability of the modern cultivar than that of the old cultivar. The superior competition of PL40 was primarily due to the higher plant height, larger leaf area index, greater tillering capacity and larger root system. Our results showed that the modern cultivar CW135 produced a higher grain yield, yield components (except spike number), water use efficiency (WUE_g) and harvest index under both water regimes in monoculture. However, the reduction in grain yield of CW135 when subjected to water-limited conditions was less than that of PL40 in the pot and field experiments. The greater grain yield of the CW135 was associated with a higher harvest index, thousand-kernel-weight and a lower root:shoot ratio. Water consumption over the entire growing period was significantly lower in CW135 under all soil moisture conditions, and the main difference in water consumption between the two cultivars was observed before anthesis. Post-anthesis accumulation of dry matter was greater in CW135 under water-limited conditions, but there was no difference between cultivars when water was adequate. The dry matter remobilization and contribution to grain yield of CW135 was lower than that of PL40. The results of the present study demonstrated that the higher competitive ability in the old landrace led to an increased sensitivity to environmentally-induced stress. As a result, there was a greater loss in grain yield by the old cultivar when the water supply was unfavorable. In addition, the differences in the life history strategy between the old and modern cultivars imply that reducing competitive ability in the modern cultivar has led to increased yield of the crop population and greater yield stability.     

Responses of various crop species and cultivars to fertilizer application

Summary Crop response to fertilizer application depends not only on the level of available plant nutrients in the soil but is also related to crop physiology and morphology. For a well balanced nutrition the rate of nutrient supply to the roots must correspond with the rate of nutrient required for growth. Species or cultivars with a high growth rate generally respond more favourably to fertilizer application than those with low growth rates. An analogous relationship holds for the biomass produced per unit soil surface. Thus modern rice and wheat cultivars tolerate a more dense spacing than older ones. Due to the dense stand the yield and particularly the grain yield of the modern varieties may be several times higher than those of older cultivars, and therefore also the nutrient requirement, especially the demand for N and P, is higher for the modern cultivars.Modern cereal cultivars are characterized by a high crop index which means that after flowering a high proportion of grain filling material must be produced by photosynthesis. Assimilation and translocation of photosynthates are favoured by K⁺. Thus in particular modern cultivars require a high K⁺ content for optimum grain filling.Nutrient exploitation of soils by plant roots depends on root morphology and root physiology. Grasses generally have much longer roots than dicots. Thus the rate of K⁺ and phosphate uptake per unit root length is lower for grasses than for dicots. It is for this reason that dicots respond earlier to a K⁺ and phosphate dressing than grasses.Species living symbiotically with Rhizobium may depress the rhizosphere pH considerably and thus promote the dissolution of phosphate rock.     

Donald’s Ideotype and Growth Redundancy: A Pot Experimental Test Using an Old and a Modern Spring Wheat Cultivar

Human selection for high crop yield under water-limited conditions should have led modern cereal cultivars to invest less in root biomass, be it unconsciously. To test this hypothesis we conducted a pot experiment with two spring wheat cultivars, one old and one modern, both widely grown in the semi-arid regions of China. Using the replacement series method introduced by de Wit, we showed that the older landrace (Monkhead) was significantly more competitive than the more-modern cultivar (92-46). However, when grown in pure stand, old Monkhead had grown root biomass 3.5 times modern 92-46, whereas modern 92-46 gained a 20% higher grain yield. We also found modern 92-46 significantly increased root biomass per plant and root allocation (i.e., root biomass/total individual biomass) as its frequency in mixtures decreased, whereas old Monkhead did not respond in a similar way. This result suggests that the roots of modern cultivars may have gained an ability to recognize neighboring root systems and show more plastic self-restraining response to intra-cultivar competition.     

Photosynthetic Characteristics of Non-Leaf Organs of Winter Wheat Cultivars Differing in Ear Type and their Relationship with Grain Mass Per Ear

Chlorophyll content, photosystem 2 functioning (F_v/F_m, F_v/F₀), activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, and net photosynthetic rates (P _N) of flag leaf blade, sheath, peduncle, and ear organs were assessed in large-ear type (Pin 7) and small-ear type (ND93) wheat cultivars. Some differences were found in photosynthetic properties between different green plant parts, the values of all studied parameters in ear parts being higher in Pin7 than in ND93. Furthermore, ear surface areas and ear P _N in 26 wheat genotypes measured at anthesis showed highly significant positive correlation with grain mass per ear. Hence a greater capability of ear photosynthesis may result in a greater grain yield in large-ear type cultivars.     

Use ofAzospirillum brasilense as biofertilizer in intensive wheat cropping

Summary Three field experiments were conducted on ten cultivars of winterwheat and four cultivars of springwheat to estimate the growth promoting effect ofAzospirillum brasilense under varying nitrogen doses. Independent of cultivar selection or nitrogen dose a highly significant yield increase could be observed in winterwheat: strains S631 and SpBr14 increased the average grain yield with 9.14% and 14.82% respectively. When the yield components were studied a coinciding increase in ear density could be demonstrated of resp. 10.57% and 13.55%. Less significant results were obtained with springwheat although in one experiment strain SpBr14 significantly increased grain yield. As with winterwheat tillering of the plant was markedly affected by inoculation with both strains. In a companion greenhouse experiment it was found that inoculation with Azospirillum can cause a decrease in the root mass of wheatplants except when strain SpBr14 is used. Therefore it is suggested that the presence of a higher tillering together with an undisturbed nutrient uptake capacity can result in yield increases after inoculation withAzospirillum brasilense.     

源库关系改变对小麦灌浆期植株光合速率及~(14)C同化物运转分配的影响

选用千粒重大小不同的小麦品种,研究了去除顶端两个小穗对两类品种（大粒品种和小粒品种）千粒重、穗粒数、穗粒重、籽粒平均灌浆速率、单穗平均增重速率、植株光合速率及１４Ｃ同化物运转分配的影响。试验结果表明,去除顶端两个小穗后,两类品种的千粒重提高,穗粒数降低或基本不受影响,但降低比例明显低于去除小穗数的比例。籽粒平均灌浆速率和单穗平均增重速率（分别表征籽粒库容活性和穗粒库容活性）相应提高。结果,两类品种的穗粒重表现为补偿性增长。两类品种比较,小粒品种的增长幅度大于大粒品种。穗粒库容活性增强使得小粒品种灌浆中后期的植株光合速率提高,使两类品种分配到籽粒中的１４Ｃ同化物比例增加。从而表明,无论是植株光合速率还是同化物的运转分配皆受穗粒库容活性的调控,调控方式和幅度因品种类型而不同。但提高其穗粒重的着眼点都应当是提高穗粒库容活性。     

Phosphorus (P) efficiencies and mycorrhizal responsiveness of old and modern wheat cultivars

A pot experiment was carried out in a growth chamber to investigate P efficiencies and mycorrhizal responsiveness of modern (Krichauff and Excalibur) and old (Khapstein, Bobin, Comeback and Purple Straw) wheat cultivars (Triticum aestivum). The arbuscular mycorrhizal fungus (AMF) used in this study was Glomus intraradices. The growth medium was a soil/sand mixture with NaHCO₃-extractable P of 9.4 mg P kg^–1 and no extra P was added. Plant P efficiencies (uptake, utilisation and agronomic) were found to differ significantly between cultivars, but no general trends of changes with the year of release of the cultivar were found. AMF colonisation was found to decrease plant growth under our experimental conditions with low light intensity. Mycorrhizal responsiveness (MR) was measured in terms of the improvement in plant P nutrition (shoot P concentrations). MR was found to be generally lower in modern cultivars than in old cultivars, indicating that modern breeding programs may have reduced the responsiveness of modern wheat cultivars to arbuscular mycorrhizal fungi. MR was also found to decrease in general with increased plant P utilisation efficiency.     

Differential responses to K deficiency among soybean cultivars

The seed yield per unit of potassium applied differed for five soybean cultivars which were grown to maturity under different K regimes in a glasshouse. Whereas Dodds was the most responsive cultivar to moderate increases in K supply, the cultivar Bragg was the most efficient in its ability to produce seed with low levels of available K; Lee and Forest were the least efficient cultivars while Bossier and Dodds were of intermediate efficiency. The basis for the efficiency of cv. Bragg was that the growth of its tops, as indicated by mature stem weights and its roots, were less affected by reduced K supply than those of other cultivars. This enabled it to produce more pods under K-deficient regimes, resulting in a greater seed yield per plant. The percentage reduction in oil/protein ratios in the seed of the five cultivars under moderate K deficiency correlated closely with reductions in seed yield. However, changes in this ratio were poorly related to the K percentages in the seed. All cultivars experienced an impairment of plant senescence under K deficiency as evidenced by a reduction in leaf abcission and a delay in pod maturity. The existence of genetic diversity in K-use efficiency means that breeding programmes could utilize K-efficient germplasm in developing new cultivars for soils not naturally high in potassium.     

Wheat Responses to Arbuscular Mycorrhizal Fungi in a Highly Calcareous Soil Differ from those of Clover, and Change with Plant Development and P supply

We evaluated the roles of arbuscular mycorrhizal (AM) fungi in growth and phosphorus (P) nutrition of wheat (Triticum aestivum L.) in a highly calcareous soil and compared the responses of wheat with those of clover (Trifolium subterraneum L). In the first experiment wheat (cv. Brookton) was harvested at 6 wk. Colonisation by four AM fungi was low (<20%). Clover was harvested at 8 wk. Colonisation varied with different fungi, with the highest value (52%) obtained with Glomus intraradices. Although suffering from P deficiency, non-mycorrhizal (NM) wheat grew relatively well with no added P (P0) and application of P at 100 mg kg⁻¹ (P100) increased the dry weight (DW). Shoot P concentrations increased with P application and there were positive effects of all AM fungi at P100. In contrast, NM clover grew very poorly at P0 and did not respond to P application. Clover responded positively to all AM fungi at both P levels, associated with increases in P uptake. In the second experiment colonisation by a single AM fungus (G. intraradices) of two wheat cultivars (Brookton and Krichauff) was well established at 6 wk (~50% in P0 plants) and continued to increase up to maturity (~70%), but decreased greatly at both harvests as P supply was increased (up to 150 mg P kg⁻¹: P150). Addition of P significantly increased plant growth, grain yield and P uptake irrespective of cultivar and harvest time, and the optimum soil P for grain yield was P100. In both cultivars, a growth depression in AM plants occurred at 6 wk at all P levels, but disappeared at 19 wk with added P. At P0, AM plants also produced lower grain yield (weight) per plant, but with higher P, AM plants produced higher grain yields than NM plants. There was a significant positive effect of AM on grain P concentration at P0, but not at other P levels. Brookton was somewhat more P efficient than Krichauff, and the latter responded more to AM fungi. This study showed that responses of wheat to AM inoculation and P supply were quite different from those of clover, and changed during development. Results are discussed in relation to the underlying soil properties.     

A comparative screening of hybrid,modern varieties and local rice cultivar for brown leaf spot disease susceptibility and yield performance

Five rice cultivars, one hybrid (WR96), three modern (BR16, BR26, and BRRI Dhan27) and one local (Pari) were screened for reaction to brown leaf spot disease caused by Cochliobolus miyabeanus and performance of yield-related characters. The severity of brown leaf spot varied with growth stages of rice plant as well as different cultivars tested under field condition. Low disease severity was observed at maximum tillering stage compared to moderate to high at dough stage, with hybrid cultivar WR96 showing highest disease, while local cultivar Pari had the lowest. Brown spot disease severity in different cultivars under induced epiphytic condition also followed the similar trend. The results also revealed that most of the yield-contributing characters examined showed wide variations among the cultivars. Modern cultivar BR16 produced the highest panicle length, number of grain per panicle and grain yield per hectare. At the same time as local cultivar Pari generated the lowest number of tiller per plant, panicle length, grain number per panicle and grain yield per hectare. Moreover, hybrid cultivar WR96 produced the highest percentage of spotted grain per panicle and seed yielding C. miyabeanus, and also the lower percentage of seed germination, while the reverse was observed in local cultivar Pari. These findings may allow producers and breeders to select rice cultivar, resistant or tolerant to brown leaf spot disease and to avoid significant reductions in grain yields.     

小麦不同品种光合速率和14 C同化物分配对源库比改变的影响

 选用千粒重大小不同的小麦品种,研究了去除顶端两个小穗对两类品种(大粒品种和小粒品种)穗部性状、籽粒平均灌浆速率、单穗平均增重速率、植株光合速率及14C同化物运输分配的影响。试验结果表明,去除顶端两个小穗后,两类品种的籽粒平均灌浆速率和单穗平均增重速率(分别表征籽粒库容活性和穗粒库容活性)相应提高,穗粒重表现为补偿性增长。两类品种比较,小粒品种的增长幅度大于大粒品种。穗粒库容活性增强使得小粒品种灌浆中后期的植株光合速率提高,使两类品种分配到籽粒中的14C同化物比例增加。从而表明,无论是植株光合速率还是同化物的运转分配皆受库容活性的调控,调控方式和幅度因品种类型而不同。     

小麦不同品种光合速率和~(14)C同化物分配对源库比改变的响应

选用千粒重大小不同的小麦品种,研究了去除顶端两个小穗对两类品种（大粒品种和小粒品种）穗部性状、籽粒平均灌浆速率、单穗平均增重速率、植株光合速率及１４Ｃ同化物运输分配的影响。试验结果表明,去除顶端两个小穗后,两类品种的籽粒平均灌浆速率和单穗平均增重速率（分别表征籽粒库容活性和穗粒库容活性）相应提高,穗粒重表现为补偿性增长。两类品种比较,小粒品种的增长幅度大于大粒品种。穗粒库容活性增强使得小粒品种灌浆中后期的植株光合速率提高,使两类品种分配到籽粒中的１４Ｃ同化物比例增加。从而表明,无论是植株光合速率还是同化物的运转分配皆受库容活性的调控,调控方式和幅度因品种类型而不同。     

Comparative response of wheat and oilseed rape to nitrogen supply: absorption and utilisation efficiency of radiation and nitrogen during the reproductive stages determining yield

We investigated the response of spring wheat and oilseed rape to nitrogen (N) supply, focusing on the critical period for grain number definition and grain filling. Crops were grown in containers under a shelter and treated with five combinations of applied N. Wheat and oilseed rape produced comparable amounts of biomass and yield when corrected for the costs of biomass synthesis (SC). From the responses of biomass and yield to late N applications and the apparent contribution of mobilised biomass to yield, it seems that the yield of oilseed rape was more source-limited during grain filling than that of wheat, particularly at the medium and high N levels. Both species recovered equal amounts of N from the total available N in the soil and had similar N use efficiencies, expressed as yield per unit of N absorbed. However, oilseed rape had higher efficiency to convert absorbed N in biomass, but lower harvest index of N than wheat. Oilseed rape had similar or lower root biomass than wheat, depending on N level, but higher root length per unit soil volume and specific root length. The specific uptake rate of N per unit root dry weight during the critical period for grain number determination was higher in oilseed rape than in wheat. In wheat, N limitation affected growth through a similar or lower reduction in radiation use efficiency corrected for synthesis costs (RUE_SC) than in the cumulative amount of intercepted photosynthetically active radiation (IPARc). In oilseed rape, lower growth due to N shortage was associated more with RUE_SC than IPARc, during flowering while during grain filling both components contributed similarly to decreased growth. RUE_SC and the concentration of N in leaves and inflorescence (LIN%) decreased from flowering to maturity and were curvilinearly related. Oilseed rape tended to have higher RUE_SC than wheat at high N supply during the critical period for grain number determination, and generally lower during grain filling. The reasons for these differences and possibilities to increase yield potential are discussed in terms of the photosynthetic efficiency of the different organs and changes in source–sink ratio during reproductive stages. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phosphorus requirements of the wheat plant in various stages of its life cycle

Summary In pot experiments root growth and P uptake were found to precede shoot growth. The high rate of P uptake in the early stages of the life cycle is not an expression of luxury consumption but reflects a high P requirement in plants. Plants cultivated in nutrient solutions with different P concentrations during various stages of development showed that a high P supply (1 ppm) between Feekes stages 6 and 9 (30 days) caused a higher grain yield than the same P concentration between Feekes stages 11 and 17 (30 days). The early applied P caused a high number of fertile ears per area, a high number of grains per ear, and a high P pool in vegetative parts. The latter could be mobilized during the grain-filling period. Therefore, for high grain yields soil and fertilizers have to meet the high P requirement (about 20 g P/m root · day) in an early stage of plant growth. During the grain filling period the P supply can be much lower.     

土壤水分对两个冬小麦品种产量和竞争能力的影响

研究了黄土塬区两个旱作冬小麦品种(长武135和平凉40,前者是后者的换代品种)在不同土壤水分条件下竞争能力和产量形成的关系。研究设2种土壤水分条件(土壤含水量为田间最大持水量的75%～80%和40%～45%),采用生态替代法设计了同一播种密度的6个播种比例组合的盆栽试验。低水分单播条件下,长武135具有较高的产量(长武135为27.59g/pot,平凉40为24.91g/pot),而混播条件下平凉40在产量和相对产量上较长武135品种具有明显的竞争优势。高水分条件下,平凉40产量随播种比例的减小下降较快(长武135产量曲线斜率35.468,平凉40为36.237)。平凉40低水分单播时花后干物质积累量较少(长武135为0.67g/pot,平凉40为0.55g/pot),而混播时较多(长武135各比例均值0.58g/pot,平凉40为0.71g/pot),导致了平凉40品种单播时产量较低和混播时产量较高。平凉40地下生物量显著大于长武135(高水分条件下,长武135为10.03g/pot、平凉40为11.51g/pot;低水分条件下二者分别为8.41g/pot和10.69g/pot),且耗水量大(高水分条件下平凉40多耗水2.72kg/pot,低水分条件下多耗0.98kg/pot),而耗水量/地下生物量的比值平凉40低于长武135,从而平凉40品种单位根量消耗的水分低于长武135。总之,在两个生长属性接近的冬小麦品种中,老品种以较大的根系生物量赢得了较高的竞争能力,消耗了较多的水分,而新品种虽然根系生物量较低,耗水量较少,但籽粒产量却较高。亦即,小麦新品种籽粒产量的提高是与根系的减少和对水资源竞争能力的下降相伴随的。     

Landrace of japonica rice,Akamai exhibits enhanced root growth and efficient leaf phosphorus remobilization in response to limited phosphorus availability

Aims

Phosphorus (P) acquisition through extensive root growth and P allocation to different plant organs through efficient remobilization are important for acclimation of crop plants to P-limited environments. This study elucidated changes in rice root growth and leaf P-remobilization and their influence on grain yield under P deficiency.

Methods

Two pot experiments were conducted with (P100) and without (P0) inorganic P supply using two Japanese rice cultivars: Akamai (Yamagata) and Koshihikari. Multiple harvests were made until the panicle initiation stage. Root and shoot growth response, P acquisition, and temporal leaf P-remobilization efficiency were measured. A separate experiment ascertained the final yield and grain P status.

Results

The Akamai rice cultivar showed enhanced root growth and more acquired soil P. The Akamai root dry weight was 66% greater than that of Koshihikari under P0. Confronting P deficiency, Akamai remobilized some P from its lower mature leaves to upper younger leaves starting from early growth. The remobilized P fraction increased to 72% at panicle initiation under P0. Under P0, Akamai exhibited two-fold higher leaf P-remobilization efficiency than under P100.

Conclusions

Enhanced root growth that facilitates acquisition of more soil P through better soil exploration coupled with efficient leaf P remobilization from the early growth stage improves adaptation of Akamai rice cultivar to P-limited environments. Nevertheless, P-starvation responses did not facilitate higher grain yields in P-limited conditions.

     

Some aspects of wheat cultivar response to applied phosphate

Summary Two experiments are described in which a comparison was made of differences in phosphorus contents, dry matter production and root growth between a semi-dwarf wheat (Israel M68) and a standard height cultivar (Olympic). In the first experiment, using soil as a support medium, Olympic had higher root dry weight and root to shoot ratios, but lower root and shoot phosphorus contents, than Israel M68. In the second experiment, using solution culture technique, Olympic had higher root dry weights and root to shoot ratios, but there was no cultivar difference in either root or shoot phosphorus content. This suggests an improved ability in the semi-dwarf wheat to explore the soil system. In both experiments the rate of uptake of phosphorus, when calculated per unit root fresh weight, was highest with Israel M68. Root measurements in a later experiment (Experiment 2a) indicated similar total fresh weights for both cultivars, but on a unit fresh weight basis, the semi-dwarf cultivar had a greater root number, root area and lateral root volume. Although further studies to clarify the situation are necessary, these differences may be associated with the enhanced grain yield response to superphosphate of some semi-dwarf wheats when compared to standard height cultivars. re]19751104     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley（Hordeum vulgare L. cv. Rum） and two durum wheat Mediterranean cultivars（Triticum turgidum L. var durum cvs Hourani and Karim） were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley（47%） than durum wheat（30%, Hourani）. Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density（RLD） and root volume density（RVD） for 90% available water capture for wheat were similar to（cv. Hourani） or lower than（cv. Karim） for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.     

Genotype and fungicide effects on late-season root growth of winter wheat

The aim of this work was to investigate differences among genotypes in post-anthesis root growth and distribution of modern UK winter wheat cultivars, and the effects of fungicide applications. Post-anthesis root growth of up to six cultivars of winter wheat (Triticum aestivum L.), given either one or three applications of fungicide, was studied in field experiments during two seasons. Total root mass remained unchanged between GS63 (anthesis) and GS85, but root length increased significantly from 14.7 to 31.4 km m⁻² in one season. Overall, there was no evidence for a decline in either root mass or length during grain filling. Root mass as a proportion of total plant mass was about 0.05 at GS85. There were significant differences among cultivars in root length and mass especially below 30 cm. Malacca had the smallest root length and Savannah the largest, and Shamrock had a significantly larger root system below 40 cm in both seasons. Fungicide applied at ear emergence had no significant effect on root mass in either season but increased root length (P<0.01) in the more disease-prone season. By maintaining a green canopy for longer, fungicide applied at flag leaf emergence may have resulted in delayed senescence of the root system and contributed to the post-anthesis maintenance of root mass and length. Section Editor: R. W. Bell     

Phosphorus absorption and utilization efficiency of pigeon pea (Cajanus cajan (L) Millsp.) in relation to dry matter production and dinitrogen fixation

The effect of P supply on absorption and utilization efficiency of P in relation to dry matter production and dinitrogen fixation was examined in 8 pigeon pea cultivars with different growth duration and a soybean cultivar under field conditions. In all the pigeon pea cultivars, the maximum whole plant dry weight was obtained in a P-deficient soil at 100 kg P ha⁻¹ application. The short duration cultivars had smaller whole plant dry weights at low P rates (5 and 25 kg P ha⁻¹) and poor response to P application compared with the medium and long duration cultivars. Increasing the P application rate significantly increased dinitrogen fixation in all the cultivars. At the low P rates, the total nodule activity (TNA) was lower in the short than in the medium and the long duration cultivars. However, at 200 kg P ha⁻¹ application, dinitrogen fixation did not vary among these cultivars except for one short duration cultivar whichregistered very low values. Dry matter production and dinitrogen fixation are strongly controlled by P absorption ability rather than P utilization efficiency. The low absorption ability of the short duration cultivars is mainly due to poor root development. The high P concentrations in the nodules of all the cultivars suggest that nodules have advantage over host plant interms of P distribution under P deficient conditions. Our results suggest that P plays an important role in dinitrogen fixation through an effective translocation of P to the leaf. Thus when P supply is limited, efficient cultivars obtained reasonably high yield through an effective translocation of the absorbed P to the leaf.