Organic Recycling for Soil Quality Conservation in a Sub-tropical Plateau Region

The long-term effect of organic recycling on some aspects of quality in a lowland rice soil of an Indian plateau region was studied. The experiment was set up at the agricultural experimental farm of the Indian Statistical Institute, Giridih, Bihar, India. Two rice cultivars, and treatments with four organic supplements (cowdung manure, Leuceana leaves, decomposed farm residue and Sesbania ), chemical fertilizers (urea, superphosphate and muriate of potash) and no input were arranged in a factorial randomized block design. Organic supplements improved soil quality parameters such as water holding capacity, total organic C, microbial biomass C, urease and acid phosphatase activities of soils in comparison to chemical fertilizers and no input. Among the organic supplements, cowdung manure gave significantly higher organic C (1.39%), microbial biomass C (276.46 μg g⁻¹ dry soil), urease activity (32.79 and 21.22 μg urea hydrolized g⁻¹ dry soil h⁻¹ at 37 °C by the buffer and non-buffer method, respectively) and acid phosphatase activity (1.99 μmol p-nitrophenol released g⁻¹ dry soil h⁻¹ at 37 °C) than the others. The conversion of organic C into biomass C (2.46%) was highest in Leuceana -treated soil.     

Effects of Salinity and Mixed Ammonium and Nitrate Nutrition on the Growth and Nitrogen Utilization of Barley

The absorption and utilization of nitrogen (N) by plants are affected by salinity and the form of N in the root medium. A hydroponic study was conducted under controlled conditions to investigate growth and N uptake by barley ( Hordeum vulgare L.) supplied with five different NH₄⁺-N/NO₃⁻-N ratios at electrical conductivity of 0 and 8 dS m⁻¹. The five NH₄⁺-N/NO₃-N ratios were 0/100, 25/75, 50/50, 75/25 and 100/0, each giving a total N supply of 100 mg N l⁻¹ in the root medium. A mixed N supply of NH₄⁺ and NO₃⁻ resulted in greater accumulation of N in plants than either NO₃⁻ or NH₄⁺ as the sole N source. Plants produced a significantly higher dry matter yield when grown with mixed N nutrition than with NH₄⁺ or NO₃⁻ alone. Total dry matter production and root and shoot N contents decreased with increasing salinity in the root medium. The interaction between salinity and N nutrition was found to be significant for all the variables. A significant positive correlation (r=0.97) was found between nitrogen level in the plant shoot and its dry matter yield.     

Einfluß des Lichtangebotes auf das Wachstum und die biologische Stickstoff-Fixierung von Weißklee (Trifolium repens L.)

Influence of light quantity on growth and biological nitrogen fixation of white clover ( Trifolium repens L.)
The influence of photon irradiance (E_p; 100 to 500 μmol m⁻² s⁻¹) and of the photoperiod (16 or 11 h) on growth and nitrogenase activity of nodulated white clover plants was studied in growth chambers at two nitrate levels (1.0 and 7.5 mM NO₃⁻).
Total dry mass production, the root proportion and nitrogenase activity increased with increasing E_p and photoperiod. Nitrogenase activity generally increased proportionally to root mass. Only at low E_p (100 μmol m⁻² s⁻¹) and under a short photoperiod (11 h) was the specific nitrogenase activity per unit root mass reduced. An abrupt change in E_p led to a rapid and parallel change in nitrogenase activity and relative growth rate.
A higher NO₃⁻ concentration in the nutrient solution (7.5 mM) led to a marked decrease in specific nitrogenase activity, but increased growth between 200 and 500 μmol m⁻² s⁻¹ during early development only. At 100 μmol m⁻² s⁻¹, there was no growth response to nitrate, although its effect on nitrogenase activity was more marked than at a higher E_p.
The results show that with changing light quantity, biological nitrogen fixation of white clover adapts to the existing demand for nitrogen and does not limit growth except during early development, even when light supply is low.     

Nitrogen Nutrition of Potato Cultivars Differing in Maturity

In potato, dry matter (DM) production and partitioning between plant organs and N accumulation are affected by N application; however, since cultivars differ in these processes, N fertilization must be adjusted to each cultivar. This paper studies the response of potato cultivars differing in maturity to N fertilization in the south-east of the Buenos Aires Province (37°45'S, 58°18'W) in two growing seasons. Treatments combined four N doses (0–180 kg ha⁻¹) and four cultivars: Jaerla (early), Spunta (mid-early), Mailén INTA (medium late) and Huinkul MAG (late). DM and N content were measured in leaves, stems and tubers throughout the growing season and intercepted photosynthetically active radiation was regularly assessed. There was an increase in tuber yield up to intermediate N doses (60 kg ha⁻¹ in 1990 and 120 kg ha⁻¹ in 1991). Tuber yield was similar for Spunta and Huinkul MAG. There was no interaction between cultivar and N fertilization for tuber dry matter yield. DM partitioning to leaves and tubers during the growing season differed among cultivars, but N availability affected partitioning similarly for all cultivars. Jaerla had a high and Huinkul MAG had a low radiation use efficiency between plant emergence and the beginning of tuber formation. Jaerla, Spunta and Mailén INTA reached maximum N content in foliage at ≈60 days after emergence and Huinkul MAG 20 days later. Total N content at maturity varied between 120 and 250 kg ha⁻¹ and was affected by cultivar and N dose. The results will help to improve N fertilization recommendations and management practices as related to each cultivar under the environmental conditions of this region.     

Influence of Solar Radiation and Vapour Pressure Deficit on Transpiration Efficiency of Rainfed Sorghum

Besides assimilation, plant water relations are important aspects of physiological basis of productivity of crops in water limited environment. The relationships of photosynthesis rate, transpiration rate, leaf water potential and stomatal conductance with photosynthetically active radiation (PAR) and vapour pressure deficit (VPD) during pre-flowering (panicle initiation to ear emergence) and grain filling (from anthesis to maturity) stages of a sorghum hybrid (cv. CSH-6 ) grown under rainfed conditions were studied. Photosynthesis rate declined when PAR was above 1300 μmol m⁻² s⁻¹. during both the growth stages. Higher transpiration rate during grain filling stage at higher PAR caused the transpiration efficiency to be lower than during pre-flowering stage when PAR was above 1200 μmol m⁻²s⁻¹.Leaf water potential and stomatal conductance decreased with increase in PAR. Leaf water potential was higher during pre-flowering than during grain filling stage but maximum photosynthesis rate was similar during both the growth stages. Changes in VPD did not qualitatively alter the relationships of the physiological variables with PAR.
Decreasing photosynthesis rate and LWP at high PAR suggest that photosynthesis rate was limited by low leaf water potential when PAR was optimal, and by low PAR even when leaf water potential was high in rainfed sorghum during rainy season.     

Differences between Maize Cultivars in Yield Formation, Nitrogen Uptake and associated Depletion of Soil Nitrate

In a 3-year field experiment conducted on a Gleyic Luvisol in Stuttgart-Hohenheim, ten maize cultivars (nine commercial and one experimental hybrid) were compared in their ability to utilize a high soil nitrogen (N) supply. Total N content of the shoots at about silage maturity ranged from 213 to 328 kg N ha⁻¹ (1986), from 177 to 223 kg N ha⁻¹ (1987) and from 185 to 226 kg N ha⁻¹ (1988). In all three experimental years, total shoot N uptake was significantly positively correlated to stover yield, and also to N concentrations in the ears and in the total plant dry matter. In contrast, a negative correlation between ear yields of the cultivars and total N uptake was indicated. Differences between the cultivars in N uptake were reflected in a corresponding soil nitrate depletion. At harvest, residual nitrate-N in the 0–90 cm soil layer ranged from 34–63 kg N ha⁻¹ m 1987 and 32–71 kg N ha⁻¹ in 1988. The results indicate, that growing of cultivars selected for high N uptake-capactiy of the shoots may contribute to an increased utilization of a high soil N supply and thus to a reduction of nitrate leaching.     

Untersuchungen zum Wurzelwachstum von Jungpflanzen alter und neuer Winterweizensorten sowie eines Spelzweizens bei variierter N-Versorgung

Root growth of seedlings of old and new winter wheat cultivars and a spelt wheat at varying levels of nitrogen
Root growth of five old (time period 1882–1920) and five new (time period 1975–1982) winter wheal cultivars and a spelt winter wheat cultivar was investigated in two greenhouse trials. Nitrogen (NH₄NO₃) was supplied at six (Exp. I) and two (Exp. II) levels (sub- to supraoptimal for shoot growth). The seedlings were grown in sand-filled polyethylene tubes of 4.5 cm diameter and 50 cm length at 20 ^oC. The plants were harvested 11 (Exp. I) and 12 (Exp. II) days after emergence. At this early stage of development root growth o: old and new cultivars differed only slightly. The old T. aestivum cultivars had more seminal roots. The longest roots of the modern cultivars penetrated into deeper layers of the substrate. For some traits, cultivar: seemed to respond specifically to the varying N-supply. However, there were no significant difference: between old and new cultivars. Neither were old cultivars better adapted to low N-fertilization nor were modern cultivars superior in tolerating toxic concentrations of NH₄NO₃. Increasing N supply changes root growth as follows: decline in root dry matter, increase in shoot/root ratio of dry weight, decrease in number of seminal roots, shortening of axes and more laterals, increase in diameter of the laterals and less significantly of the main roots, increase in density of laterals, decline in root surface area. The number of apices was affected only to a very small degree.     

Plant Emergence of PEG-osmoprimed Seeds under Suboptimal Temperatures in Two Cultivars of Sweet Sorghum Differing in Seed Tannin Content

The effect of polyethylene glycol (PEG) osmopriming on plant emergence in laboratory at optimal (25 °C) and suboptimal (18 and 14 °C) temperatures was assessed in two cultivars of sweet sorghum differing in kernel colour: Brandes, light-coloured, and Roce, dark-coloured. Sterilized sand or non-sterilized soil were used as substrates. PEG osmopriming enhanced seedling emergence in sand. In soil, the light-seeded cultivar produced seedlings only at optimum temperature, whereas the unprimed dark-seeded cultivar performed well as in sand at all temperatures and reduced dramatically its germination capacity at suboptimal temperatures following priming treatment. These results might be related to the presence of tannins in the seed coat. Seed tannin contents of 80 and 590 mg 100 g⁻¹ seed fresh weight (FW) were determined in Brandes and Roce respectively. These amounts consistently reduced after PEG osmopriming, especially in Roce (217.5 mg 100 g⁻¹ seed FW). The decline in tannin content in Roce, because of osmopriming, might explain the poor emergence of this cultivar in soil. These results suggest the opportunity of using high-tannin cultivars of sweet sorghum in the field, which may better growth in this environment when early sowings are required.     

Light Interception, Leaf Area Index and Dry Matter Yield in Fodder Sorghum at Different Plant Populations

Fodder sorghum (M. P. Chari) was grown at varying populations to examine its influence on light interception, leaf area index and biomass production. DMY, CGR and IPAR depending on LAI reached maximum at LAI 5 of 150 000 plants ha⁻¹ stand and thus yielded higher biomass. Therefore, physiological potential of fodder sorghum crop was found to be maximum at a population density of 150 000 plants ha⁻¹. Further increases in population developed mutual shading and adversely affected the crop growth rate and dry matter accumulation. Significant linear relationships of dry matter yield with IPAR, plant population densities, LAI and CGR clearly indicate the interdependence of these characters.     

Comparative Responses of Wheat (Triticum aestivum L.) Cultivars to Salinity at the Seedling Stage

Seedling growth and ion content of Pakistani bread wheat cultivars was assessed in solution culture in the absence and presence of NaCl (100 and 200 mol m⁻³) to determine whether seedling traits could be used in breeding programs for salt-tolerance. Growth was recorded as seedling fresh weight, and the shoot and leaves analysed for major inorganic ions. Plants subjected to salt stress excluded Na⁺ and Cl⁻ ions from the shoot to varying extents. Exclusion preferentially maintained lower Na⁺ and Cl⁻ levels in the apical tissue, as the leaf to leaf gradient in Na⁺ and Cl⁻ became steeper as the external salinity increased, although there were significant differences between cultivars. Correlation analysis on individual plants indicated that excluding Na⁺ at low salinity, and Na⁺ and Cl⁻ at high salinity, were correlated significantly with growth performance, although it was clear that other factors were also involved. The relationship of tolerance to ion exclusion was stronger when the data were examined on an individual plant basis than when related to pooled cultivar data or to the cultivar rank order derived from field trials, probably due to large variations in Na⁺, and to a lesser extent, Cl⁻ transport in supposedly homozygous cultivars.     

A Rapid Method for Measuring Freezing Resistance in Crop Plants

The objective of this study was to develop a technique based on chlorophyll fluorescence to assess freezing injury and resistance of leaves. Optimization was done with faba bean leaves and applicability to other crops was examined at winter and spring with types of barley, oats, rape and faba beans. Selected leaves from young hardened beans were subjected to standardized freezing tests with different minimum temperatures ( T _min) and fluorescence was monitored. After a dark period basic fluorescence ( F _O was induced by 0.2 μmol m⁻² s⁻¹ pulsed red light and maximum fluorescence ( F _m) was assayed at different light intensities. 1500 μmol m⁻² s⁻¹ rendered to give the maximum possible output of Fm and best differentiation of differently damaged leaves by F _n= F _m - F _O. Leaf temperature during measurement and during a short storage (± 2 h) should be kept at about 0°C to avoid biases between differently damaged leaves. The measuring spot on the leaf must be standardized since fluorescence response differed at the tip and base of a leaflet, but not between the two leaflets of a faba bean leaf. The applicability of F _rr (ratio of F _r of stressed to unstressed leaves) as a measure of resistance was demonstrated by comparison of winter hardiness of cultivars with freezing resistance calculated from the relationship of F _vr and the T _min used in freezing tests.     

Analysis of Wheat Cultivar Differences in Grain Yield, Grain Nitrogen Yield and Nitrogen Utilization Efficiency.

More detailed information on the causes of yield variability among wheat cultivars is needed to further increase wheat yield. Field studies were conducted in Northern Greece over the two cropping seasons of 1985—1986 and 1986—1987 to assess the effects of nitrogen fertilizer and application timing of the various component traits that determine grain yield, grain nitrogen yield and nitrogen utilization efficiency of two bread ( Triticum aestivum L.) and two durum ( Triticum durum Desf.) wheat cultivars, using yield and yield component analysis. Nitrogen at a rate of 150 kg ha^-1 was applied before planting or 100 N kg ha^-1 before planting and then 50 N kg ha^-1 top dressed at early boot stage. Nitrogen and cultivars affected all traits examined, while split nitrogen application affected only some of the traits. Grain yields in the most cases were correlated with number of grains per unit area and grain weight and grain nitrogen yields in all cases with grain number per unit area. The contribution of the number of grains per spike to total variation in grain yield among cultivars was almost consistent (37 to 55 %), while the contribution of grain weight was more significant (up to 55 %) in high yields (>6.500kg ha^-1) and number of spikes per unit area (>500). The number of grains per spike contributed from 60 to 83 % to the total variation in grain nitrogen per spike. Increased grain nitrogen concentration resulted in a reduction of its contribution in grain nitrogen yield variation. Nitrogen utilization efficiency was higher during grain filling than during vegetative biomass accumulation. The contribution of nitrogen harvest index to the variation of utilization efficiency for grain yield was higher in plants receiving nitrogen application.     

Effects of NaCl Salinity on Growth and Production of Young Cladodes of Opuntia ficus-indica

The effects of salinity on the growth and production of `nopalitos' (young cladode sprouts) of Opuntia ficus-indica (L.) Mill. cv. Copena V-1 were investigated. Salinity (NaCl) irrigation levels with electrical conductivities of 2, 5, 10, 13, 18 and 21 dS m^–1 were used. In general, all cladode variables (stem area, number of young cladodes, length and width of cladodes, and fresh and dry weights) decreased with increasing salinity. The root-to-stem ratio and young cladode water content decreased significantly as salinity increased. Other variables that decreased with increasing salinity included harvest index, relative growth rate, stem area ratio, dry mass accumulation, and Na⁺ and Cl^– concentrations. For rooted cladodes, increased salinity decreased fresh weight, succulence, and root fresh weight, dry weight and length. Our conclusions suggest that this species is salt sensitive; however, there is some indication that it could be effectively managed in saline environments. Further studies and evaluation of different cultivars are needed to identify the mechanism of adaptation of salt tolerance in this species.     

氮肥用量对两种不同类型玉米杂交种物质生产及氮素利用的影响

旨在探明东北春玉米不同类型杂交种物质生产及氮素利用特征及其与产量的关系。本文以不同类型杂交种代表性品种郑单958(ZD958,Reid×唐四平头模式)和先玉335(XY335,Reid×Lancaster模式)为试验材料,2014年和2015年设置5个氮肥水平[0 kg hm–2(N0)、100 kg hm–2(N1)、200 kg hm–2(N2)、300 kg hm–2(N3)和400 kg hm–2(N4)]和2个种植密度(67 500株hm–2和90 000株hm–2)试验,比较研究了不同类型玉米杂交种干物质与氮素积累、运转及氮素利用的差异规律。结果表明,两年XY335品种的最高籽粒产量均高于ZD958,最优氮肥施用量明显降低4.8%~10.6%;相比ZD958,不施氮处理,两种种植密度下XY335品种干物质积累能力及物质运转效率都明显降低,而施氮条件下XY335品种的干物质积累量、花后干物质量及干物质运转效率均增加,同时增幅随着施氮量增加逐步提高,且在高密度条件下优势更为明显。开花期XY335叶片与茎鞘氮素含量显著高于ZD958(P0.05),而成熟期由于其较高物质的运转效率表现出明显较低的数值,籽粒氮素含量在高密度下差异较小,而低密度条件下相对ZD958显著提高(P0.05)。施氮条件下XY335品种花前、花后氮素积累量和氮素积累总量均高于ZD958,其中叶片中氮素的转运对籽粒的贡献率显著较高(P0.05)。两种种植密度处理最优施氮条件下XY335氮素利用效率和氮素吸收效率均显著高于ZD958(P0.05),而氮农学利用率和氮肥偏生产力差异不显著。可见,高密度条件下XY335类型品种表现出明显较高的物质积累能力以及花后物质运转对籽粒的贡献率,获得较高的氮素利用效率,表现出明显高氮高效的品种特征,因此生产上建议,东北春玉米区高密度种植条件下该类型品种在较高氮肥施用量时易获得高产高效。     

谷子芽期耐盐碱综合鉴定及评价

以全国主推的53个谷子品种为材料,在100 mmol L^-1混合盐碱(NaCl∶NaHCO₃=4∶1)胁迫下研究了不同谷子品种的耐盐碱性。结果表明,在盐碱胁迫下, 53个谷子品种的发芽势、发芽率、根长、芽长、根鲜重和芽鲜重均受到不同程度的抑制,以对根长的影响最大;相对发芽势与相对发芽率、相对根长与相对芽长及相对根鲜重与相对芽鲜重均呈显著或极显著正相关。通过主成分分析将14个单项性状指标转化为4个主成分,累积贡献率为90.4%;以4个主成分的得分值通过隶属函数分析获得不同品种耐盐碱的综合得分值,并通过聚类分析将53个谷子品种划分为6种耐盐碱类型,其中强耐盐碱品种2个,耐盐碱品种16个,中间型品种17个,盐碱敏感品种6个,不耐盐碱品种9个和极不耐盐碱的品种3个。同时利用回归分析建立了可用于评价谷子耐盐碱性的回归方程D’=0.298+0.037X₂+0.144X₃+0.018X₆+0.209X₇-0.183X₉+0.115X_11<...     

Timing of Nitrogen Application to Enhance Corn (Zea mays, L.) Yields in a Desert Climate

Experiments were conducted in two consecutive years to investigate the response of two corn (Zea mays, L.) cultivars, Eperon and Challenger, to timing of N fertilizer in a desert climate. Fertilizer was applied three times (at planting, 6 weeks after sowing (6WAS) and at 9WAS) to give a seasonal total of 180 kg N ha^-1 The N treatments were N_ooo (control), N_LOH (60 kg N ha^-1 at planting, none at 6WAS and 120 kg N ha^-1 at 9WAS), N_LLL (60 kg N ha^-1 at sowing, 6WAS and at 9WAS) and N_LOH, (60 kgN ha^-1 at planting, 120 kg N ha^-1 at 6WAS and none at 9WAS). Generally, N ha^-1 was associated with the highest grain and dry matter yields. Plants in N treated plots had significantly larger number of leaves and ear leaf N contents than the control at mid-silk. High ear leaf N was associated with high leaf area index and dry matter yield. Based on these results, it would appear that the application of 60 kg N ha^-1 at planting, followed by 120 kg N ha at 6WAS (N_LHO) is the most suitable for enhancing corn yields in the desert climate.     

Phosphorus Accumulation and Translocation in Wheat as Affected by Cultivar and Nitrogen Fertilization

To improve nutrient management strategies in wheat more information is needed about the interaction effects among nutrients in their uptake and redistribution in the plants, in relation to different genotypes. Therefore, two bread ( T. aestivum L.) and two durum ( T. durum Desf.) winter wheat cultivars were grown in the field for 2 years (1986, 1987) in a silty-clay soil under different nitrogen (N) levels, in Northern Greece. Nitrogen at a rate of 150 kg ha⁻¹ was applied before planting or 100 kg ha⁻¹ before planting and then 50 kg ha⁻¹ at early boot stage. Cultivar differences in phosphorus (p) concentration were observed only in vegetative parts but not in the grain. Maximum p accumulation was observed either at anthesis or at maturity. During grain filling dry matter and p accumulation in the grain followed almost the same pattern. Phosphorus translocation efficiency of the cultivars at the 2 years ranged from 70.7 to 84.3 % and the amount of p in the grain derived from translocation 52 to 100 %. Phosphorus translocation efficiency was weakly correlated with p content in grain only in 1986, while phosphorus harvest index (PHI) was positively correlated with harvest indst (HI) both years (r = 0.82** in 1986 and 0.75** in 1987). Nitrogen application mainly affected p accumulation of the cultivars via its effect on biomass production. The split N application promoted slightly the p uptake in 1987 and this resulted in the reduction of both the contribution of the translocated p to the grain and the efficiency of p utilization for total biomass. Results indicated that p accumulation and translocation and the efficiency of p utilization in wheat were mainly determined by the genotype in relation to environmental condition of growth.     

The Influence of Johnsongrass Infestation and Nitrogen Rates on Grain Sorghum

Gram sorghum [ Sorghum bicolor (L.) Moench] is grown on marginal land and johnsongrass [Sorghum haiepense (L.) Pers] is the most common and hard to control weed in this crop. The agronomic performance of gram sorghum at different nitrogen (N) and johnsongrass infestation levels in the field has not been adequately investigated. Therefore, research was conducted on a Decatur silty clay loam soil (Rhodic Paleudult) to determine the influence of N rates (0, 40, 80 and 120 kg ha^-1) and johnsongrass infestation levels (0, 2, 4, 6 and 8 plants per 5 m crop row) on the growth and yield of grain sorghum (cv. GK522G) and johnsongrass. Increase in N rates increased seed weight, seed yield and percent protein in grain sorghum as well as dry matter and percent protein of johnsongrass. The increase in johnsongrass infestation (from 0 to 8 plants per 5 m crop row) significantly decreased the performance of grain sorghum and johnsongrass at all the N rates. The results suggest that 40 kg N ha^-1 with up to 2 johnsongrass plants per 5 m crop row or 80 kg N ha^-1 with up to 4 johnsongrass plants per 5 m crop row produced grain sorghum yields equivalent to absence of johnsongrass in the crop.     

Intraspecific Variation in Nitrogen Uptake and Nitrogen Utilization Efficiency in Wheat (Triticum aestivum L.)

Twenty wheat ( Triticum aestivum L.) varieties differing in plant height were grown in soil culture and evaluated for differences in nitrogen uptake and nitrogen utilization efficiency (NUE) at limited (40 kg N ha⁻¹) and normal (120 kg N ha⁻¹) nitrogen supply. Nitrogen uptake showed 1.4- and 1.5-fold varietal variation at harvest for limited and normal N supply, respectively. NUE for dry matter production (NE1) exhibited 1.28- and 1.38-fold genotypic variation while NUE for grain production (NE2) varied by 1.25- and 1.21-fold at limited and normal N supply, respectively. Tall varieties were found to have higher N uptake and NUE for dry matter production, while dwarf cultivars had greater NUE for grain production. Nitrogen uptake was found to be strongly positively associated with dry matter production (r=0.85 and r =0.77 at limited and normal N supply, respectively), indicating an important effect of growth rate on N uptake. NUE for biomass production, as well as for grain production, was reduced as the supply of nitrogen was increased.     

Response of Rainfed Sunflower (Helianthus annuus L.) to Nitrogen Rates and Plant Population in the Semi-arid Savanna Region of Nigeria

Field experiments were conducted during the wet seasons of 1991,1992 and 1993 at the Abubakar Tafawa Balewa University Farm, Bauchi (10 ° 22'N, 09 ° 47'E) to study the response of sunflower ( Helianthus annaus L.) to N rates and plant population under rainfed conditions. Four N rates (0, 50, 100 and 150 kg N ha ^-1) and four plant populations (40000,80000,120000 and 160000 plants ha^-1) were factorially combined in a randomized complete block design with three replications. Leaf area index, shoot dry weight and seed yield (kg ha^-1) increased significantly with increasing N rates from 0 to 100 kg N ha^-1. The growth and yield parameters per plant decreased significantly with increasing plant populations from 40000 to 160000 plants ha^-1, but the seed yield (kg ha^-1) obtained at 80000 plants ha^-1 was significantly higher than all the other plant populations. The interactions of N x plant population confounded the main effect of each factor on the growth and yield of sunflower. The seed yield (3425 kg ha^-1) obtained from the use of 100 kg N ha^-1 at 80000 plants ha^-1 was significantly higher than those obtained from all other combinations of N x population and out-yielded the main effects of 100 kg N ha^-1 and 80000 plants ha^-1 by 18 % and 25 %, respectively. The use of 100 kg N ha^-1 at 80000 plants ha^-1 is therefore recommended for maximum yield of sunflower in Bauchi.