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1.
Summary The rhizosphere microarthropod fauna of a woody, deep-rooted legume, Prosopis glandulosa, was sampled at four sites in the northern Chihuahuan Desert and compared with the rhizosphere microarthropod fauna of a co-dominant shrub, Larrea tridentata. Prostigmatid mites (Speleorchestes sp.,Neognathus sp., Rhagidia sp., Tydaeolus sp., Steneotarsonemus sp., Tarsonemus sp., Nanorchestes sp., Gordialycus sp.), the cryptostigmatid mites (Bankisonoma ovata and Passalozetes neomexicanus), the mesostigmatid (Protogamasellus mica), and the collembolan (Brachystomella arida) characterized the fauna at depths greater than 1 m. Microarthropods were recovered from soils at a depth of 13 m at the edge of a dry lake and at depths of 7 m in a dry wash which were pre-European man P. glandulosa habitats. In habitats where P. glandulosa is a recent invader, root depth and microarthropods were less than 3 m. In most habitats, population densites of microarthropods at depths 0.5 m were more than 100 times those at depths 0.5 m. Population densities of microarthropods associated with P. glandulosa growing at the edge of a dry wash were not significantly smaller at 0.5–1.0 m depth than at 0–0.5 m. The deep-rhizosphere microarthropod fauna is a reduced subset of the fauna of surficial soils, suggesting that this fauna plays a role in decomposition and mineralization processes functionally similar to that of microarthropods in surficial soils.  相似文献   

2.
Abstract

Field experiments were conducted in 1992 on soils which have been classified as Alfisols ranging from Paleustalf to Oxic Paleustalf which represent three different ecological zones of West Africa. This research was conducted to determine the effect of density of planting on yield and yield components at 53,333, 66,666, and 79,999 plants‐ha‐1 and time of nitrogen (N) fertilizer application [50% at planting and 50% at four weeks after planting (4WAP), entire N application at two weeks after planting (2WAP), and 50% at planting and 50% at anthesis]. The experiment was a factorial arrangement fitted to randomized complete block design and replicated three times. The maize (Zea mays L.) varieties used in this study gave increased yields at population density up to 53,333 plants‐ha‐1 in Ikenne and Mokwa, while a response of 79,999 plants‐ha‐1 was obtained at Kaduna. The results also showed that a split application of N at planting and 4 WAP appeared to be the best for Ikenne, while the entire application at 2WAP appeared to be the best in savanna ecologies. The results indicate increase yield with increasing latitude suggesting that the higher solar radiation in the savanna ecologies increase the photosynthetic capacity of the maize plants used in the study. Maize genotypes used in this study did not respond to density beyond 53,333 plants‐ha‐1 at Ikenne and Mokwa, though a response was obtained up to 79,999 plants‐ha‐1 at Kaduna. Thus, it can be concluded that density response is location dependent and that farmers should plant maize at highest optimum plant population density as determined by experimental results in each ecological zone of West Africa. The results also showed that a split application of N at planting and 4WAP appeared to be the best for Ikenne, while the entire N application at 2WAP appeared to be the best for the savanna ecologies.  相似文献   

3.
频率及电压对高压脉冲电场提高陈年棉种活力的影响   总被引：2，自引：2，他引：0  
为研究不同频率脉冲电场对陈年棉种活力的影响,该文利用高压脉冲电源和弧形电极-平板组成的电场系统在极间距离为50 mm、电压分别为16和20 kV条件下对陈年棉种在不同频率(1、5、10、20、50 Hz)下进行了电场处理,处理时间为40 s。结果发现,频率为10 Hz时,陈年棉种的发芽势、发芽率、发芽指数、活力指数等指标与不做电场处理对照相比都有明显提高,且都达到极显著差异(P0.01),16比20 kV条件下的处理效果更好,达到显著性差异(P0.05)。试验结果表明,电场频率对棉种活力指标的影响是存在的,且对各指标的影响趋势是一致的,即在一定处理条件下(电场强度与处理时间)可以找到一个较优频率范围,对种子活力提高达到最大,且该试验研究结果能够为后续种子电场处理提供参考。  相似文献   

4.
The pH of precipitation, and the concentrations in precipitation and depositions by precipitation of H+, major cations, N, S, and chloride were measured in bulk collectors at three sites in Eastern England. The Rothamsted site is 100 km from the coast in a semi-urban environment. The Saxmundham site is 13 km and the Woburn site 120 km from the coast; both are in rural environments. Precipitation is acidic at all three sites, with a pH of 4.3 at Rothamsted and 5.0 at Saxmundham and Woburn at present, but the pH has been increasing. Precipitation chemistry is chiefly controlled by sea-salts (Na, Mg, Cl) and earth salts (K, Ca, Mg, NH4, N03). Sea-salts dominate near the coast at Saxmundham, but earth salts become much more important inland at Rothamsted and at Woburn. The concentration and deposition of non-sea Cl are increasing at Rothamsted and Saxmundham, those of non-sea SO4-S are increasing at Woburn, and those of NO3-N are increasing at all of the sites. Precipitation acidity is associated chiefly with non-sea SO4, and only a little with NO3 and non-sea Cl, at Rothamsted and Woburn. At Saxmundham, no correlation between acidity and anions is observed, presumably because of the overwhelming effect of sea-salts.  相似文献   

5.
Applications of a commercial formulation of carbofuran, a carbamate insecticide, at rates of 2kg and 12kg active ingredient ha–1 to flooded fields planted to rice led to significant inhibition of methane emission. Likewise, laboratory incubation studies showed that carbofuran applied at low rates (5 and 10μgg–1soil) inhibited the net methane production relative to that of the control, but stimulated it when applied at a rate of 100μgg–1soil. Interestingly, carbofuran increased the oxidation of methane when applied at low rates and inhibited it when applied at a rate of 100μgg–1soil. Received: 5 May 1997  相似文献   

6.
Continuous culture methods were used to isolate bacteria from sediment from Lake Ontario. These mixed cultures were grown in chemostats at different dilution rates and the glucose concentration in the culture vessel, the optical density, the biomass of cells, and the number and types of bacteria present were monitored for at least 80 generations. Two bacterial types, bothPseudomonas spp., were present at all dilution rates in significant quantities. The mixed cultures exhibited a reciprocal relationship between dilution rate and biomass (and number of bacteria). When Hg was added to the growth medium at a concentration of 5 mg 1?1, the bacteria tolerated that concentration at a dilution rate of 0.117 h?1 substantial changes in the population were noted at a concentration of 10 mg 1?1 Hg. One of the isolates from the mixed culture would not grow at 5 or 10 mg 1?1 of Hg in continuous culture at a dilution rate of 0.066 h?1. In the mixed continuous culture the same isolate showed only minimal response to a Hg concentration of 10 mg 1?1.  相似文献   

7.
Samples of two Andisols and two Ultisols from southern Chile were incubated with acid or with lime for up to 60 d at 25°C or for 1 day at 40°C or at 60°C. The changes in positive and negative charge were measured. The Andisols reacted slowly at 25°C. They lost protons to the solution at high pH, thus increasing the negative charge on the soils and decreasing the pH of the solution. They gained protons at low pH, thus increasing the positive charge on the soils and increasing the pH of the solution. The Ultisols reacted more quickly but again charge and pH changed through time. For all samples, the rate of reaction was increased by incubating at 60°C. Brief incubation at 60°C produces a similar relation to that obtained after longer incubation at 25°C. This provides a convenient means by which measurements can be made more quickly.  相似文献   

8.
Information about the mineralization rate of compost at various temperatures is a precondition to optimize mineral N fertilization and to minimize N losses in compost‐amended soils. Objectives were to quantify the influence of the temperature on the mineralization rate and leaching of dissolved organic carbon (DOC) and nitrogen (DON), NO3—, and NH4+ from a fresh (C : N = 15.4) and a mature (C : N = 9.2) organic household waste compost. Compost samples were mixed with quartz sand to ensure aerobic conditions, incubated at 5, 10, 15, 20, and 25°C and irrigated weekly for 112 days. For the fresh compost, cumulative CO2 evolution after 112 days ranged from 36% of the initial C content at 5°C to 54% at 25°C. The CO2 evolution was only small in the experiments with mature compost (1 to 6% of the initial C content). The data were described satisfactorily by a combined first‐order (fresh compost) or a first‐order kinetic model (mature compost). For the fresh compost, cumulative DOC production was negatively related to the temperature, probably due to leaching of some of the partly metabolized easily degradable fractions at lower temperatures. The production ratios of DOC : CO2‐C decreased with increasing temperature from 0.094 at 5°C to 0.038 at 25°C for the fresh and from 1.55 at 5°C to 0.26 at 25°C for the mature compost. In the experiments with fresh compost, net release of NO3— occurred after a time lag which depended on the temperature. Cumulative net release of NO3— after 112 days ranged from 1.8% of the initial N content at 5°C to 14.3% at 25°C. Approximately 10% of the initial N content of the mature compost was released as NO3— after 14 days at all temperatures. The DOC : DON ratios in the experiments using fresh compost ranged from 11.5 to 15.7 and no temperature dependency was observed. For the mature compost, DOC : DON ratios were slightly smaller (7.4 to 8.9). The DON : (NH4+ + NO3—) ratio decreased with increasing temperature from 0.91 at 5°C to 0.19 at 25°C for the fresh compost and from 0.21 at 5°C to 0.12 at 25°C for the mature compost. The results of the dynamics of C and N mineralization of fresh and mature compost can be used to assess the appropriate application (timing and amount) of compost to soils.  相似文献   

9.
Abstract

Nitrogen use efficiency and response of sunflower (Helianthus annuus L.) to timing and rate of surface banded N was characterized in a split‐plot 4x2 factorial experiment. Nitrogen rates (main plots) were 0, 34, 67, and 134 kg ha‐1 at Mississippi State and 0, 45, 90 and 180 kg ha‐1 at Brooksville, MS. Nitrogen, applied as NH4NO3, was surface banded either at planting or at the four leaf stage (subplot). Seed yield was significantly influenced by rate of N application at both locations. Seed yield showed a quadratic response at Mississippi State and a Mitscherlich‐type response at Brooksville. Maximum seed yields of 2606 and 2380 kg ha‐1 were obtained at the respective sites. Sunflower responded to N fertilizer application when inorganic N content of the soil to 60 cm depth at planting was less than 50 kg ha‐1. Nitrogen efficiency was influenced by rate and timing of application, exhibiting exponential declines with increasing N rates. Fertilizer losses at the highest rates of applied N were 19 and 52% at Mississippi State and Brooksville, respectively. Clay‐fixed NH^+ accounted for 26% of the applied N fertilizer loss at Brooksville. Nitrogen fertilizer efficiency and recommendations for sunflower could be improved if initial soil inorganic N is taken into account.  相似文献   

10.
Although eggs of the gypsy moth Lymantria dispar (L.) supercool, a steady and substantial portion freezes and dies at a steady temperature below ?26°C. The rate of freezing at steady temperature is about 1% per min at ?27°C and changes about tenfold per degree. The freezing of the eggs at varying temperature is predicted by integration of the rates observed at steady temperature.  相似文献   

11.
Increasing nitrogen deposition due to human activity might have a serious impact on ecosystem functions such as the nitrogen transformations conducted by microbes. We therefore focused on nitrous oxide (N2O) production as an indicator of soil microbial activity. The rates of N2O emission from the forest floor were measured every two weeks in two forest stands in the central part of Japan: a red pine stand at Kannondai and a deciduous stand at Yasato. Nitrogen deposition rates by throughfall were 30.6 kg N ha?1 y?1 at Kannondai and 15.7 at Yasato. The rates of N2O emission ranged from 0.5 to 14.2 µg N m?2 h?1 (mean 4.5) at Kannondai and from 0.2 to 7.0 µg N m?2 h?1 (mean 2.3) at Yasato. The N2O emission rate showed significant positive relationships with soil temperature and nitrogen deposition during the preceding two weeks. The annual emission rates of N2O were 0.38 kg N ha?1 y?1 at Kannondai and 0.20 at Yasato. As a the annual nitrogen deposition, these rates were 1.23% at Kannondai and 1.27% at Yasato.  相似文献   

12.
The inorganic phosphorus (P.) and total P (PT) concentrations of leaf tissue were measured for 9 genotypes from each of 4 white clover lines—Grasslands Sustain, Grasslands Prestige, a low‐P site ecotype, and a high‐P site ecotype— grown at 50 and 400 ug added P g‐1 soil, in a glasshouse. The cultivars/ ecotypes varied significantly for Pi/PT ratio at the high level of P supply, but not at the lower level. The two ecotypes were not significantly different from each other for Pi/PT ratio at either P supply level. Among the 36 genotypes, P/ PT ratio varied 2‐fold at the high P level and 2.5‐fold at the low P level. Broad sense heritabilities for Pi/PT ratio were, however, low, particularly at the high level of P supply.  相似文献   

13.
Abstract

Conventional (CT) and no‐tillage (NT) effects on soil physical properties and bromide (Br) movement were studied at two locations in North Carolina. The soils were a Norfolk sandy loam (fine‐loamy, siliceous, thermic Typic Paleudult) at a North American eastern Coastal Plain location and a Pacolet sandy clay loam (clayey, kaolinitic, thermic Typic Kanhapludult) at a Piedmont location. Bulk density (Db), macroporosity (Mp), and saturated hydraulic conductivity (Ks) were measured in the plant row (R) and trafficked (T) or untrafficked (N) interrow positions. Simulated rain was applied at two intensities to 1?m2 plots after KBr was surface applied. The first simulated rain (30 min) consisted of a low (1.27 cm h?1) or a high (5.08 cm h?1) intensity applied 24 h after Br application. One week later, the high rainfall rate was repeated on all plots. Soil samples for Br determinations were taken 2 days after each rain simulation event to a depth of 40 cm and at the end of the growing season to 120 cm. Soil physical properties were affected by both tillage and position. Bulk density was greater for NT than for CT and in the T compared with R and N row positions. Mp was significantly greater in NT than CT at Coastal Plain location, but the results were opposite at the Piedmont location. Saturated hydraulic conductivity was highly variable ranging from 0.36 cm h?1 to 14.4 cm h?1 at the Coastal Plain location and from 0.06 cm h?1 to 7.12 cm h?1 at the Piedmont location. Saturated hydraulic conductivity at T position was about 100% lower than Ks at N and R positions, but the effect of tillage system was not significant on Ks. The surface 10 cm of soil contained the greatest Br concentration for both tillage systems. For the first and second sampling dates, greater Br movement occurred under NT vs. CT. However, no significant differences were observed in Br movement in the end of season sampling. Because of the coarser soil texture, greater Ks and Mp at the Coastal Plain location, Br moved, to a greater depth at this site than at the Piedmont site.  相似文献   

14.
This study focuses on spatial heterogeneity in the soil microbial biomass (SMB) of typical climax beech (Fagus crenata) at the stand scale in forest ecosystems of the cold-temperate mountain zones of Japan. Three beech-dominated sites were selected along an altitudinal gradient and grid sampling was used to collect soil samples at each site. The highest average SMB density was observed at the site 1500 m a.s.l. (44.9 gC m−2), the lowest was recorded at the site 700 m a.s.l. (18.9 gC m−2); the average SMB density at the 550 m site (36.5 gC m−2) was close to the overall median of all three sites. Geostatistics, which is specifically designed to take spatial autocorrelation into account, was then used to analyze the data collected. All sites generally exhibited stand-scale spatial autocorrelation at a lag distance of 10-18 m in addition to the small-scale spatial dependence noted at <3.5 m at the 550 m site. Correlation analysis with an emphasis on spatial dependency showed SMB to be significantly correlated with bulk density at the 550 and 1500 m sites, dissolved organic carbon (DOC) at the 700 and 1500 m sites, and nitrogen (N) at the 550 and 700 m sites. However, no soil parameter showed a significant correlation with SMB at every site, and some variables were also differently correlated (negative or positive) with SMB at different sites. This suggests that the factors controlling the spatial distribution of SMB are very complex and responsive to local in situ conditions. SMB regression models were generated from both the ordinary least-squares (OLS) and generalized least-squares (GLS) models. GLS performance was only superior to OLS when cross-variograms were accurately fitted. Geostatistics is preferable, however, since these techniques take the spatial non-stationarity of samples into account. In addition, the sampling numbers for given minimum detectable differences (MDDs) are provided for each site for future SMB monitoring.  相似文献   

15.
Bacillus subtilis spread readily along water films beside hyphae of killed colonies of Pythium ultimum on membrane filters at a matric potential of —50 cm of water, but movement was restricted at — 150 cm potential. Similar rates of spread occurred when the bacteria were inoculated at a point on the surface of a layer of artificial soil, placed over the killed fungal colony and equilibrated at either of the two matric potentials. This suggests that dead fungal mycelia do not aid bacterial spread to any extent at a matric potential of —150 cm of water.When live colonies of P. ultimum were grown in the artificial soil held at the two matric potentials, the rate of bacterial movement was comparable to that in killed colonies at ?50 cm potential, but was erratic at the lower potential. The accumulation of inhibitory fungal metabolites in the thin water films beside the actively-respiring hyphae probably restricted bacterial spread at some points in the soil. It appears that dead fungal mycelia may aid in the local spread of bacteria at matric potentials higher than —150 cm of water, but live mycelia may not. The ability of bacteria to spread along dead fungal hyphae was explained by a consideration of the thickness of water films imposed by the prevailing matric potential.  相似文献   

16.
Surface wash erosion was measured at runoff plots on low to moderate slopes in clayey and sandy silts underlain by continuous permafrost on the Fosheim Peninsula, Ellesmere Island. Due to snow redistribution in winter, total precipitation on the plots varied from 34 to 150 mm, with corresponding surface runoff values of 0 to 102 mm. Where runoff occurred, at least 80% of it was derived from snowmelt. Suspended sediment removal was <75 g m−2 a−1 at relatively well-vegetated sites but averaged more than 1200 g m−2 a−1 at a plot where the vegetation had been removed by landsliding. Niveo-aeolian deposition was greater than suspended sediment removal at some plots, indicating net accumulation. Solute removal ranged up to 80 g m−2 a−1 and exceeded clastic sediment transport at one vegetated site. Elevated rates of erosion at the sites of detachment slides that pre-date 1950 demonstrated that terrain disturbance in permafrost environments can affect slopewash processes for at least several decades.Plot data (precipitation, vegetation and surface grain-size) from the Fosheim Peninsula and Banks Island were used to develop a statistical model of suspended sediment removal by surface wash on undisturbed slopes. For any given grain-size, the model predicts a rise in erosion from zero precipitation (because of an absence of runoff) to a peak at about 50 mm, a decline as precipitation increases to 300 mm and a further increase in erosion beyond this inflection point. This non-linear response is due to the complex interaction of moisture (primarily snow) and vegetation cover. Erosion at any given precipitation value varies through three orders of magnitude depending on surface grain-size. The maximum erosion predicted is 1 kg m−2 a−1 for a runoff plot with 1100 mm of precipitation, a corresponding vegetation cover of 77% and a median surface grain-size of 7 φ.  相似文献   

17.
Spatial variability of greenhouse gas (GHG) emissions from agricultural lands is not well known although it has a great impact on the accuracy of GHG budget.The objectives of this study were to assess the spatial variability of CO2 emission fluxes (CO2-flux) and correlate these emissions with soil physico-chemical properties at two spatial scales and at different depths using a new geostatistical approach (coregionalization analysis with a drift, CRAD) that performs multiscale spatial analysis.Two agricultural sites with sandy and loamy soils were instrumented at 108 geo-referred sampling points and at two depths during spring 2007 where soil surface CO2-flux and soil physico-chemical parameters were measured. The CO2-flux presented spatial patterns characterized by different scales (i.e., non-spatial, small spatial and large spatial scale components), each describing a different fraction of its variability. About a quarter of CO2-flux variability at the first site and one fifth at the other site was attributed to the non-spatial component. Strongest correlations were obtained between CO2-flux and soil temperature, water saturation (Sw), elevation, electrical conductivity, soil bulk density, and the C/N ratio, but with differences between sites. Correlations were much stronger at large scale. Analyzing correlations between CO2-flux and soil properties without discriminating for scales can miss important scale-dependent processes controlling soil gas emissions. Scales at which these processes vary should therefore be taken into account.  相似文献   

18.
From 1986–1989, a team of scientists measured atmospheric concentrations and fluxes in precipitation and throughfall, and modeled dry and cloudwater deposition in a spruce-fir forest of the Great Smoky Mountains National Park which is located in the Southern Appalachian Region of the United States. The work was part of the Integrated Forest Study (IFS) conducted at 12 forests in N. America and Europe. The spruce-fir forest at 1740 m consistently received the highest total deposition rates (～2200, 1200, and 700 eq ha?1 yr?1 for SO4 2?, NO3 ?, and NH4 +). During the summers of 1989 and 1990 we used multiple samplers to measure hydrologie, SO4 2?, and NO3 ? fluxes in rain and throughfall events beneath spruce forests above (1940 m) and below (1720 m) cloud base. Throughfall was used to estimate total deposition using relationships determined during the IFS. Although the SO4 2? fluxes increased with elevation by a factor of ～2 due to higher cloudwater interception at 1940 m, the NO3 ? fluxes decreased with elevation by ～30%. To investigate further, we began year round measurements of fluxes of all major ions in throughfall below spruce-fir forests at 1740 m and at 1920 m in 1993–1994. The fluxes of most ions showed a 10–50% increase with elevation due to the ～70 cm yr?1 cloudwater input at 1920 m. However, total inorganic nitrogen exhibited a 40% lower flux in throughfall at 1920 m than at 1740 m suggesting either higher dry deposition to trees at 1740 m or much higher canopy uptake of nitrogen by trees at 1920 m. Differential canopy absorption of N by trees at different elevations would have significant consequences for the use of throughfall N fluxes to estimate deposition. We used artificial trees to understand the foliar interactions of N.  相似文献   

19.
The contribution of rock fragments to the soil available water content (SAWC) of stony soil has been quantified by measurements of bulk density and gravimetric water content at different water potentials on rock fragments of different lithologies: flints, cherts, chalks, gaizes and limestones. More than 1000 pebbles (2 cm < equivalent diameter of the rock fragment < 5 cm) have been sampled in stony soils developed from each of the five lithologies. We demonstrated that the water content at saturation of the studied pebbles was equal to the water content at −100 hPa and to the water content at field capacity. A linear relationship between the water content at −100 hPa and at −15,840 hPa enabled to derive a simple pedotransfer function to determine the available water content of the rock fragments. We also proposed a second simple pedotransfer function, which expresses the available water content from the dry bulk density of the rock fragments only. A simulation at the horizon scale for a loamy-clay stony horizon showed that the SAWC could be strongly misjudged when the rock fragments were not taken into account: for a stony horizon containing 30% of pebbles, the SAWC is underestimated by 5% for chert pebbles and by 33% for chalk pebbles.  相似文献   

20.
J. O. AZEEZ 《土壤圈》2009,19(5):654-662
Low soil nitrogen (N) and weed infestations are some of the major constraints to maize production in Nigeria.A split-split plot experiment in a randomized complete block design with three replicates was established at two sites with different agroecological zones,Ikenne (Typic Paleudalf) and Shika (Typic Tropaquept),in Nigeria in 2002 and 2003 rainy seasons to investigate the responses of four maize genotypes (Oba super II,Low N pool C2,TZB-SR,and ACR 8328 BN C7) to N fertilizer applied at four rates,0,30,60,and 90 kg N ha-1,and three weed pressure treatments,no weed pressure (weekly weeding),low weed pressure (inter-row weekly weeding),and high weed pressure (no weeding throughout the growing season).Growth and yield parameters of maize and weeds were taken at flwering and harvest.The results indicated that there was a significant reduction in maize leaf area,leaf area index,and photosynthetically active radiation due to weed interference at both sites.The application of nitrogen at 90 kg N ha-1 significantly increased maize leaf area.Reductions in maize growth and yield at flowering and harvest were significant due to weed interference at both Ikenne and Shika,thus showing that the reductions in maize growth and yield due to weed interference were not ecological zone specific even though weed species and their seed banks may differ.Ameliorative management options could thus be the same in the two agroecological zones.Application of 90 kg N ha-1 led to a significant increase in maize grain yield at Shika while there was no fertilizer effect at Ikenne on grain yield.There was no significant difference between 60 and 90 kg N ha-1,suggesting that 60 kg N ha-1 could be a possible replacement for the higher fertilizer rate at least for the identified maize genotypes.Low weed pressure treatment led to 26% and 35% reductions in maize grain yield at Ikenne and Shika,respectively,while 22% and 51 % reductions,respectively,were observed due to high weed pressure.Generally,maize grain yield was higher at Ikenne than Shika.The maize genotypes Low N pool C2 and ACR 8328 BN C7 performed better than the other genotypes at Ikenne while the maize genotype Oba super II had the best performance at harvest at Shika.Application of nitrogen increased weed biomass at flowering at Ikenne.The maize grain yield was highest in the N-efficient genotypes,Oba super II and Low N pool C2;the susceptible genotype TZB-SR had the least yield at Shika.There existed a negative and significant correlation between maize grain yield and weed biomass at both sites.  相似文献   

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