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1.
Herbicides atrazine and metolachlor have been detected in water bodies across the world. The objective of this study was to assess the efficiency of 0‐m, 3‐m, 6‐m and 9‐m grass filter strips to reduce masses of dissolved metolachlor, atrazine and deethylatrazine (a degradation product of atrazine) exported in runoff. For that purpose, 16 uncultivated plots (3‐m wide × 65‐m long) with 0‐m‐, 3‐m‐, 6‐m‐ and 9‐m‐long grass filter strips were setup in a completely randomized block design. During four seasons, masses of dissolved atrazine, metolachlor and deethylatrazine were determined for the first four to five rain events, under natural rain conditions, after atrazine and metolachlor application. Generally, grass filter strips reduced exported herbicide masses by more than 90% and influenced atrazine and metolachlor dissipation kinetics in the field. The 3‐m grass filter strip (area ratio source/strip of 22:1) usually provided a reduction in exported herbicide masses similar to the 6‐ or 9‐m grass filter strips. Therefore, under the present experimental soil and climate conditions, a grass filter strip of 3 m would be a good compromise between environmental protection of surface waters against atrazine and metolachlor contamination and conservation of agricultural land use. Such an approach contributes to the acceptability by producers to implement optimized best management practices such as vegetated filter strips for the preservation of the quality of water resources.  相似文献   

2.
The effectiveness of tropical grass species in strips of different length in trapping sediment from cropland was assessed, and the influence of filter length was determined. The assessment was made under natural rainfall which induced sheet and rill erosion in run‐off plots and then using simulated run‐off which caused concentrated erosion. The evaluated grasses were elephant grass, lemon grass, paspalum and sugarcane. Run‐off plots were on a 10% slope in a randomized complete block design replicated three times. Filter lengths were 2.5, 5 and 10 m against a 10‐m‐long sediment source area planted with maize on a clay loam soil. The results show that sediment trapping effectiveness (TE) increases nonlinearly with increasing filter length for all grasses. Under natural rainfall, more than 70% of sediment was trapped in the first 5 m, and lengthening the strip to 10 m only resulted in a marginal increase in TE. With concentrated run‐off, more than 70% of sediment was trapped in the first 5 m and lengthening the strip to 10 m resulted in a significant increase in TE. Paspalum and lemon grass performed significantly better than other grasses (P < 0.05), owing to their spreading growth pattern over the soil surface. Paspalum also has the highest root density in the upper 0.3‐m layer of the soil followed by lemon grass, hence offering the greatest resistance to erosion from concentrated flow. The results demonstrate that tropical grass filter strips provide a viable means for reducing the sediment flux from cropland.  相似文献   

3.
Mobility, extractability, and disappearance of the herbicides diuron, terbuthylazine, metolachlor, and pendimethalin were examined in incubation experiments with two topsoil samples of different natural microbial activity and after sterilization. Soil moisture was held constant at 10, 40, and 60 % WHC. In other variants, the soil water content was changed during the incubation. The four herbicides reveal a fairly different extent of microbial and chemical degradation and immobilization. The herbicide mobility – expressed by coefficients of partition between adsorbed and dissolved herbicide amounts – decreases at a lower rate and extent, when the microbial activity is low or the soil is sterile. With increasing initial soil moisture, also herbicide mobility and extractability increase; but in the course of time, abiotic immobilization occurs to a higher extent. When soil moisture changes during the incubation, formerly non‐extractable herbicide fractions (up to 40 % of the applied amounts) become extractable. Kinetics of herbicide immobilization follow an empirical sigmoidal function, which describes three periods of immobilization. The three‐period shape of the curve and its possible reasons are discussed for the data of the incubation experiments as well as for the results of a long‐term field trial with diuron.  相似文献   

4.
Vegetation strips (VS) along with conservation tillage, application of organic amendments and weed mulching improve crop yields by reducing run‐off and topsoil erosion. To investigate these issues, an experiment was conducted under rainfed conditions using grass VS for four and a half years (June 2007 to October 2011) at Dehradun, Uttarakhand, in the Indian Himalayan region. VS were incorporated in the experimental plots (Entisols) in a randomized complete block design in permanent 100 × 20 m (2000 m2) plots with a 2% slope to evaluate the effects of vegetation strips on run‐off, soil loss and crop yield. Three treatments were evaluated: (i) without VS with recommended NPK under conventional tillage, (ii) panicum as VS with recommended NPK under conventional tillage and (iii) palmarosa+ that consists of palmarosa as VS along with organic amendments (farmyard manure, vermicompost and poultry manure) and weed mulch under minimum tillage. The results show that soil loss and run‐off were significantly lower (P < 0.05) in plots under palmarosa+ than without VS treatment. Mean soil loss of 3.4, 5.2 and 7.1 t/ha was recorded from palmarosa+, panicum and without VS treated plots, respectively. Mean run‐off was 234, 356 and 428 mm from plots under palmarosa+, panicum and without VS, respectively. Maize yield was lower on the plots under palmarosa+ compared with panicum, but significantly higher (P < 0.05) than without a strip. The succeeding rainfed wheat yield was significantly greater in plots under palmarosa+ than in the initial years. The wheat yield equivalent was significantly higher in plots under palmarosa+ followed by panicum and without VS. Thus, vegetation strips are recommended for wider adoption to reduce run‐off and soil loss and to increase crop yield. The long‐term goal is to achieve a palmarosa+ system (palmarosa as a vegetation strip along with organic amendments, farmyard manure, vermicompost and poultry manure) and weed mulch under minimum tillage.  相似文献   

5.
Pasture tillage and reseeding is part of the normal rotation cycle of grassland systems in the UK and a process that could increase the rate of phosphorus (P) transfer to water, thus potentially contributing to eutrophication. The effect of tillage and reseeding on P transfer was investigated at two scales: from drained and undrained 1 ha hydrologically isolated pasture plots within the Rowden Drainage Experiment in Devon, during a 6‐month winter drainage period in 1998–1999, and in replicated soil box experiments during simulated rainfall ‘events’. At the plot scale, total P exports of 3.75 kg P ha?1 were determined over a 16‐day period, indicating that soil and P were most vulnerable to detachment and mobilization during rainfall and run‐off in this period. Once the sward had developed, and the vulnerability to soil detachment reduced, reseeded swards with pipe drainage transferred less P (approx. 0.3 kg P ha?1 yr?1) to water than is commonly measured on permanent grassland (approx. 1 kg P ha?1 yr?1). Soil box experiments showed that tilled soil transferred more P > 0.45 μm but P < 0.45 μm was retained. Sward cover is critical to reducing detachment and resulting P transfer from surface soil, and therefore careful consideration should be taken for the need to reseed. The effects of tillage and reseeding on phosphorus transfers from grassland can be potentially significant and ought to be mitigated against using low‐till practices to reduce potential contribution to water quality.  相似文献   

6.
The presence of clopyralid, a selective broadleaf herbicide, in compost near Spokane, Washington in 2000 was attributed to grass clippings collected from area lawns and subsequently used as compost feedstock. A field study was conducted in 2001 to evaluate the effects of herbicide formulation and mowing practice on the clopyralid content of grass clippings. The objective was to develop guidelines that would limit the concentration of clopyralid in clippings, thereby reducing the amount of clopyralid entering the compost production stream. Clopyralid was applied to turfgrass as either a sprayable (S) or granular (G) formulation. Grass clippings were either collected in a bagging lawn mower and removed from the plots or returned into the plant canopy using a mulching mower designed to finely chop and disperse the leaf blades. Clippings were sampled for a period of ten weeks after application, and again in the summer of 2002, and analyzed for clopyralid content. Mowing treatment had no significant effect on clopyralid content of grass clippings. The S formulation resulted in higher concentration than the G at 4 hours after treatment (193 mg kg?1 and 53 mg kg?1, respectively). At 10 weeks after treatment (WAT), clopyralid concentration averaged 0.9 mg kg?1, and cumulative recovery of clopyralid in grass clippings was 35% and 29% of the amount applied for the S and G formulations, respectively. By 56 and 98 WAT, clopyralid concentration in clippings was 0.06 and 0.02 mg kg?1, respectively. Based on these results, and depending on feedstock dilution and composting conditions, a waiting period of up to one year after application of clopyralid could be necessary for treated grass clippings to be safely used as compost feedstock.  相似文献   

7.
Hydrological pathways of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] transport from a 5.5 ha?1 corn field in southern Ontario were examined. Metolachlor was applied as an early post-emergence surface broadcast treatment at a rate of 334.1 mg active ingredient m?2. Persistence in soils decreased exponentially following application, with slower dissipation in footslope areas. Metolachlor concentrations in runoff from experimental plots also decreased exponentially with time, and were strongly associated with herbicide levels in surrounding soils. Differences between concentrations and yields in saturation overland flow and Horton overland flow during the monitoring period were controlled by near-stream water table conditions. Total herbicide losses in runoff from the plots were in the order of 1% of applied a.i. Metolachlor was rapidly leached to depths of 1 m, such that peak concentrations and instantaneous metolachlor loads in tile drainage were observed within 14 days following application. Peak concentration in streamflow (125 µg L-1) occurred during the first major runoff event 13 days following application; peak concentrations in succeeding events followed an exponential decay during the growing season. Export of metolachlor from the field was in the order of 1% of applied a.i., with overland flow serving as the dominant transport mechanism from site of application. Near-stream hydrologic conditions may determine whether field exports of herbicide enter receiving water courses.  相似文献   

8.
More and more cultivated coastal territories of Syria are being affected by increasing land degradation processes, specifically, by soil erosion due to non‐sustainable soil management. The use of cover crops can be considered an ideal solution to reduce the negative impacts of extreme rainfall events on soil erosion. However, there is no enough information about the main cultivated areas of Syria due to the current conflicts and the very few types of research conducted there. Therefore, the main aim of this research was to assess soil erosion (soil loss and sediment concentration) and hydrological response (run‐off and infiltration) considering the impact of different types of cropping systems on soil organic matter. To achieve this goal, using erosion plots, five grouped natural rainfall events and soil samples were collected, and infiltration measurements were performed between November 2012 and April 2013 (rainy season) on three different cropping systems (wheat, vetch, bean and control) with different sloping gradients (8% and 20%) in Tartous governorate (W Syria). Our results showed a cumulative rainfall amount from 68.8 to 201 mm during the study period. The highest sediment yield was generated in the control and wheat plots, registering 0.468 and 0.368 kg m?2, respectively, with an inclination of 8%. For an inclination of 20%, the control and wheat plots registered 1.145 and 0.967 kg m?2, respectively. In comparison with the control plots, there was a decrease in the total eroded organic matter, which ranged from 0.0579 (control) to 0.0289 (bean) kg m?2 year?1 in the plots with 20% inclination, and from 0.0233 (control) to 0.0069 (bean) kg m?2 year?1 with 8% inclination. To sum up, bean and vetch play an effective role to mitigate soil erosion, delay run‐off and reduce sediment yield. The output of this research provides first insights into the impact of different land uses on soil loss. Also, it could help rural inhabitants and farmers to correctly manage their soils against soil erosion processes.  相似文献   

9.
Revegetation of road cuts and fills is intended to stabilize those drastically disturbed areas so that sediment is not transported to adjacent waterways. Sediment has resulted in water quality degradation, an extremely critical issue in the Lake Tahoe Basin. Many revegetation efforts in this semiarid, subalpine environment have resulted in low levels of plant cover, thus failing to meet project goals. Further, no adequate physical method of assessing project effectiveness has been developed, relative to runoff or sediment movement. This paper describes the use of a portable rainfall simulator (RS) to conduct a preliminary assessment of the effectiveness of a variety of erosion‐control treatments and treatment effects on hydrologic parameters and erosion. The particular goal of this paper is to determine whether the RS method can measure revegetation treatment effects on infiltration and erosion. The RS‐plot studies were used to determine slope, cover (mulch and vegetation) and surface roughness effects on infiltration, runoff and erosion rates at several roadcuts across the basin. A rainfall rate of ≈60 mm h−1, approximating the 100‐yr, 15‐min design storm, was applied over replicated 0·64 m2 plots in each treatment type and over bare‐soil plots for comparison. Simulated rainfall had a mean drop size of ≈2·1 mm and approximately 70% of ‘natural’ kinetic energy. Measured parameters included time to runoff, infiltration, runoff/infiltration rate, sediment discharge rate and average sediment concentration as well as analysis of total Kjeldahl nitrogen (TKN) and dissolved phosphorus (TDP) from filtered (0·45 μm) runoff samples. Runoff rates, sediment concentrations and yields were greater from volcanic soils as compared to that from granitic soils for nearly all cover conditions. For example, bare soil sediment yields from volcanic soils ranged from 2–12 as compared to 0·3–3 g m−2 mm−1 for granitic soils. Pine‐needle mulch cover treatments substantially reduced sediment yields from all plots. Plot microtopography or roughness and cross‐slope had no effect on sediment concentrations in runoff or sediment yield. RS measurements showed discernible differences in runoff, infiltration, and sediment yields between treatments. Runoff nutrient concentrations were not distinguishable from that in the rainwater used. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

10.
Leaching of the broadleaf herbicides 2,4-D and dicamba from home lawns was monitored with ceramic extraction plates placed at a 0.2 m depth beneath undisturbed sod. The site was located on a Merrimac sandy loam. Four treatments, consisting of two rates of herbicide applications coupled with two irrigation regimes. were evaluated on 12 plots. The low herbicide rate consisted of 1.1 and 0.1 kg ha?1 yr?1 of 2,4-D and dicamba, respectively. The high rate used was 3.3 and 0.33 kg ha?1 yr?1 of 2,4-D and dicamba applied in three equal applications. Irrigation treatments were (1) minimal irrigation to avoid drought stress and percolation from the root zone and (2) overwatering at 37.5 mm week?1. Geometric mean concentra tions of 2,4-D ranged from 0.55 to 0.87 μg L?1 compared to 0.26 to 0.55 μg L?1 for dicamba. The low application-minimum irrigation treatment generated significantly higher concentrations than the other treatments for both herbicides. The low concentrations observed for both herbicides suggest that excellent degradation conditions exist in the root zone of turfgrass during the summer months when application occurs.  相似文献   

11.
The environmental behaviour of metolachlor and diuron was studied in the Central-western region of Brazil, by means of a field study where six experimental plots were installed. The soil was classified as a Latosol, and the soil horizons were characterized. Sorption of metolachlor and diuron was evaluated in laboratory batch experiments. Metolachlor and diuron were applied to the experimental plots on uncultivated soil in October 2003. From this date to March 2004, the following processes were studied: leaching, runoff and dissipation in top soil. K oc of metolachlor varied from 179 to 264 mL g?1 in the soil horizons. K oc of diuron in the Ap horizon was 917 mL g?1, decreasing significantly in the deeper horizons. Field dissipation half-lives of metolachlor and diuron were 18 and 15 days, respectively. In percolated water, metolachlor was detected in concentrations ranging from 0.02 to 2.84 μg L?1. In runoff water and sediment, metolachlor was detected in decreasing concentrations throughout the period of study. Losses of 0.02% and 0.54% of the applied amount by leaching and runoff, respectively, were observed confirming the high mobility of this herbicide in the environment. In percolated water, diuron was detected with low frequency but in relatively high concentrations (up to 6.29 μg L?1). In runoff water and soil, diuron was detected in decreasing concentrations until 70 days after application, totalizing 13.9% during the whole sampling period. These results show the importance of practices to reduce runoff avoiding surface water contamination by these pesticides, particularly diuron.  相似文献   

12.
The side effects of fluazifop-butyl on soil fungal populations and oxygen uptake were studied by incubating soil samples with a range of fluazifop-butyl concentrations (0, 0.6, 3 and 6 μg g?1) over 8 weeks. Cellulose decomposition in soil was also studied in laboratory experiments with the herbicide which was either incorporated in soil or sprayed onto calico squares which were buried in soil. The mycelial dry weight of six fungal species under the effect of the herbicide was also examined. Fluazifop-butyl had no significant effect on total fungal propagule populations at 0.6 μg g?1. At 3 and 6 μg g?1, it caused temporary reduction in fungal populations observed after 1 and 2-wk of incubation. The herbicide had no significant effect on OZ uptake. The decay of calico buried in herbicide-treated soil was generally stimulated, while the decomposition of herbicide-treated calico, buried in untreated soil, was temporary delayed. The mycelial dry weight yields of Aspergillus favus (at 2 and 12 μg mL?1 of fluazifop-butyl) and Cunninghamella echinulata (at 12 μg mL?1) were significantly increased. At 24 μg mL?1 the mycelial dry weight of A. flavus and Alternaria alternata was significantly reduced.  相似文献   

13.
Landuse can alter soil organic carbon (SOC) fractions by affecting carbon inflows and outflows. This study evaluated changes in SOC fractions in response to different landuses under variable rainfalls. We compared cropland, grassland and forest soils in high rainfall (Islamabad ~1142 mm) and low rainfall (Chakwal ~667 mm) areas of Pothwar dryland, Pakistan. Forest soils in both rainfall areas had highest SOC (11.32 g kg?1), particulate organic carbon (POC, 1.70 g kg?1), mineral-associated organic carbon (MOC, 7.17 g kg?1) and aggregate-associated organic carbon (AOC, 7.86 g kg?1). However, in rangeland and cropland soils, these varied with rainfall. Under high rainfall, SOC and MOC were 12% and 17% higher in rangeland than in cropland while POC and AOC were equal. Under low rainfall, SOC and MOC were higher in rangeland than in cropland by 7.21 and 1.79 g kg?1 at 0–15 cm and equal at 15–30 cm depth. POC and AOC were higher in rangeland than in cropland, in both depths. Averagely, SOC, POC, MOC and AOC were 26%, 68%, 76% and 30% higher in high rainfall than in low rainfall soils. Sensitivity of SOC fractions to landuses observed under different rainfalls could provide useful information for soil management in subtropical drylands.  相似文献   

14.
Field study on colloid transport using fluorescent microspheres   总被引：1，自引：1，他引：0  
Understanding colloid movement through the vadose zone is important, because colloids may facilitate transport of some less mobile contaminants. Experimental evidence of colloid transport in the vadose zone, especially at the field scale, is rare. We developed and tested a method to detect and quantify local concentrations of fluorescent microspheres (MS) with a diameter of 1 μm in unsaturated soil based on fluorescent microscopy. The detection limit was 400 × 106 MS kg?1 field‐moist soil for an automated counting method, and 20 × 103 MS kg?1 for manual counting. To test the method in the field, we applied a 40‐mm pulse with an input concentration of 14.6 × 109 MS litre?1 on two plots during 6 hours, together with bromide (Br?) and the food dye Brilliant Blue (BB). The concentrations of MS were determined on horizontal cross‐sections by a randomly distributed sampling scheme, either directly after application or 90 days after application and a rainfall of 100 mm. Mass recoveries for the MS of 85 and 65% were acceptable in view of the field conditions. Even after infiltration of particle‐free water, the largest MS concentrations were measured at the soil’s surface, which pointed at physical retention mechanisms. An additional selective sampling of hydrologically active preferential flow pathways, guided by the dye infiltration patterns, revealed that the MS were transported to similar depths as BB, that is 0.80 m directly after irrigation and 1.7 m after 90 days. This implies that also a small fraction of the particulate tracers was rapidly transported to larger depths, regardless of their physico‐chemical properties.  相似文献   

15.
Uptake, deposition and wash off of fluoride and aluminium in/on plant foliage were studied in two experiments near an Al smelter by growing different plant species under cover with free wind-flow underneath, and in the open, and by washing the leaves. With an average ambient air concentration of 2.2 μg F m3, the F and Al contents in leaves varied between species from 138 to 665 mg F kg?1 and from 150 to 1025 mg Al kg?1when grown under cover. An average of about 60% of the F and nearly 70% of the Al could be washed off covered plants. Uncovered plants had 33–51% lower F content, indicating a considerable precipitation wash off. Precipitation wash off varied with species, probably due to different leaf surface properties. The strong effect of precipitation on plant foliage F has to be taken into consideration when comparing differences in F content between years, localities and species. On average about 40–50% of the F and 55% of the Al could be washed off the leaves of uncovered plants. Washed leaves of plants exposed to precipitation had about 20% lower F content, compared to washed leaves of covered plants, thus indicating leaching of F from leaves exposed to rain. In contrast to fluoride, the Al contents in washed leaves of uncovered plants were about 50–80% higher than in covered washed leaves, thus indicating a significant uptake of Al solved in rainwater through the leaf cuticle.  相似文献   

16.
V.O. Polyakov  R. Lal 《Geoderma》2008,143(1-2):216-222
Soil organic carbon (SOC) is an important component of the global carbon cycle. Its dynamics depends upon various natural and anthropogenic factors including soil erosion. A study on Miamian silty clay loam soil in central Ohio was conducted to investigate the effect of soil erosion on SOC transport and mineralization. Runoff plots 10, 20 and 30 m long on a 7% slope under natural rainfall were used. Total soil loss, evolution of CO2 from the displaced aggregates of various fractions, and total SOC concentrations were determined. It was shown that the primary ways of SOC loss resulted from two processes: 1) mechanical preferential removal of SOC by overland flow and 2) erosion-induced mineralization. Significant amounts of SOC mobilized by erosion at the upper part of the slope during the season (358 kg ha? 1) could be lost to the atmosphere within 100 days (15%) and transported off site (44%). Breakup of initial soil aggregates by erosive forces was responsible for increased CO2 emission. During the initial 20 days of incubation the amount of CO2 released from coarse size sediment fractions (0.282 g C kg? 1 soil d? 1) was 9 times greater than that in fine fractions (0.032 g C kg? 1 soil d? 1) due to the greater initial amount of SOC and its exposure to the environment. Sediment size distribution as well as its residence time on the site was the primary controllers of CO2 loss from eroded soil.  相似文献   

17.
草地植被过滤带对高含沙坡面流泥沙的拦截效应研究   总被引：1，自引：0，他引：1  
To evaluate the effect of vegetative filter strips on sediment trapping, the spatial distribution of deposited sediment, and the size distribution of deposited particles from hyperconcentrated flows, a simulated grass filter strip experiment was conducted with plastic grass using an adjustable slope steel flume. The simulated vegetation cover was 36%, and the inflow sediment concentrations applied were 147, 238, 320, and 429 kg m-3. The sediment concentration in the outflow, and the sediment particle size were determined. The results showed that the grass filter strips trapped most of the sediment from inflow at low sediment concentration. The deposition efficiency decreased with increasing sediment concentration, being 55.2% and 15.7% in the 147 and 429 kg m-3sediment treatments, respectively. Most of the deposited sediments were distributed in the upper flume. In addition, the grass filter strips mainly trapped the coarse sediment （particle size>10 μm）.  相似文献   

18.
The aim of the present study was to investigate the uptake of 16 PAHs by willow (Salix viminalis) from soil amended with contaminated sewage sludge. Uptake experiments were conducted on field plots using sludge applications of 0, 30, 75, 150, 300, and 600 Mg ha?1. The total PAH content of control soil and sludge were 49.6 μg kg?1 and 5713 μ g kg?1, respectively. The concentrations for the 16 PAHs listed as priority pollutants were measured for soil and plant tissue samples obtained at 0.5, 1.5, 2.5, and 3.5 years. Soil total PAH content decreased significantly within the first half year, followed by minimal changes over the subsequent three years of treatment. PAH analysis was carried out on a HPLC-UV. Total PAH content in control plants was 3.6–7.3 μ g kg?1 for shoots and 13–27 μ g kg?1 for leaves. Treated plant tissue content was higher with shoots and leaves containing ～5.5–17.6 and 13.5–33.8 μg kg?1, respectively. Plant total PAH content did not show a significant trend relative to controls with respect to time. However, uptake did increase in relation to an increased sludge application. Bioconcentration factors (BCF), adjusted by control values, were calculated for total PAH content. BCF values were highest for the initial sampling (6 months) and did not show a significant temporal relationship. BCF values did decrease with increasing sludge application. With respect to individual PAHs, elevated plant tissue concentrations were measured for “light” PAH (e.g. naphthalene, phenanthrene, acenaphthalene) with leaf BCF values correlated with solubility and organic partitioning coefficients.  相似文献   

19.
Abstract

The effects of pre‐emergent (PRE) application of methabenzthiazuron (MBT), terbutryn, and linuron on plant vigor, number of nodules formed, nitrogenase activity (NA), chlorophyll contents, nitrogen (N) uptake, and seed yield were assessed in inoculated chickpeas, grown in sandy clay loam soil, in a controlled environment. The PRE application of MBT, terbutryn, and linuron at 2.5, 1.25 and 2 g a.i. kg?1, respectively, had no significant adverse effect on plant vitality, yield, and NA of excised nodules in inoculated chickpea plants, but reduced these parameters at 7.5, 3.75, and 6 g a.i. kg?1 of soil. Among the herbicides tested, linuron at each dose rates significantly (P≤0.05) decreased the grain yield, whereas terbutryn at 1.25 and 2.5 g a.i. kg?1 improved the grain yield by 19.4% and 11%, respectively, relative to the nonherbicide control. While comparing the sum of mean values of toxicity of all dose rates of each herbicide on grain yield, the toxicity increased in the following order: control=linuron>methabenzthiazuron>terbutryn. Nodulation (nodule number per plant and their dry mass) and chlorophyll contents per plant decreased consistently with increased herbicide rates, except linuron, which at 2 g a.i. kg?1 improved nodulation at both 45 and 90 days after seeding and corresponded with Mesorhizobium activity. The N content in grain and straw significantly decreased at the highest tested rates of each herbicide. Linuron at 2 and 4 g a.i. kg?1 improved N content in straw, whereas at 4 g a.i. kg?1 it significantly reduced N content in grain.  相似文献   

20.
Abstract

Soil organic carbon (SOC) and nutrient stocks in the soil profile (0–80 cm) in four dominant land uses [forest, upland maize and millet (Bari), irrigated rice (Khet), and grazed systems)] and 0–15 cm depth along elevation gradient 1000 to 3000 m, and aspects in the Mardi watershed were measured. Soil properties at 0–15 cm depth were also measured in undisturbed forest, forest with free grazed system, managed forest, and grassland to compare the soil quality index (SQI) of topsoils. The SOC and nutrient concentration decreased with increasing profile depth. The SOC and N contents in the 0–15 cm depth of forest soils were significantly greater than the corresponding depth in upland maize and millet, irrigated rice, and grazed systems. On the other hand, available P and K concentrations at the same depth were significantly greater in upland maize and millet compared to irrigated rice, grazed system, and forest land uses. The SOC and N stocks (0–15 cm) increased from agricultural land at the valley bottom at about 1000 m above mean sea level (a.s.l.) (24 and 3 Mg ha?1) compared to undisturbed forest (74 and 5.9 Mg ha?1) at 2600 m a.s.l, demonstrating the effects of cover and elevation. Both SOC and N stocks decreased sharply in grassland (54 and 4.5 Mg ha?1) at elevations of 2600 to 2800 m a.s.l. compared with undisturbed forest. Above 2800 m a.s.l. the cover type changed from grass to coniferous forest, and the SOC and N stocks steadily increased at the summit level (3200 m a.s.l.) to 65 and 6.9 Mg ha?1, respectively. Slope and aspect significantly affected SOC with the northwest aspect having significantly higher concentrations (46 g kg?1) than other aspects. Similarly, SOC concentration at the lowest slope position (39 g kg?1) was significantly higher than the middle or upper positions (25 and 13 g kg?1). Integrated soil quality index (SQI) values varied from 0.17 to 0.69 for different land uses, being highest for undisturbed forest and lowest for irrigated rice. The SQI demonstrated the degradation status of land uses in the following ascending order: irrigated rice?>?grazed system?>?forest with free grazing?>?upland maize and millet?>?managed forest?>?grass land?>?undisturbed forest. The irrigated rice, grazed system, upland maize and millet, and freely grazed forestlands need immediate attention to minimize further deterioration of soil quality in these land uses.  相似文献   

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