Residues of vinclozolin and procymidone after treatment of greenhouse grown lettuce,tomato and cucumber

Residues of the fungicides vinclozolin and procymidone, used to control the Botrytis cinerea disease, were studied in greenhouse grown lettuce, tomato and cucumber. Residue concentrations differed between the species of treated vegetables, and depended mostly on time of picking (harvest), size of fruits and mode of chemical application. The differences in concentration between one and two applications became smaller with time after application. The greatest differences occurred in lettuce. The residue contents in cucumber fruits assigned both for industrial and home processing (pickling) were higher than the legal limit (3 mg/kg). As a result of washing cucumbers, 22–24% of the residue was eliminated, and by peeling them 79–85% of the vinclozolin and procymidone residues were eliminated. Therefore it is reasonable that one or two applications of these fungicides should be used, with a time lapse of 14 days, but only with cucumbers intended for salad consumption. Vinclozolin residues, when used as vaporisation tablets, were in all cases 35–65% lower compared with the wettable powder (WP) formulation; however, the rate of of residue decrease was much slower. When applied in the form of vaporable tablets, the vinclozolin residue concentration was lower in all the sampled fruits in comparison with the WP formulation. The concentration of fungicide residues detected in winter tomato fruits was higher than that of the spring crop. Irrespective of vegetable the detected levels of fungicide residues were lower in ripe and bigger fruits than in green and smaller ones.     

Pesticide residue levels in peppers grown in a greenhouse after multiple applications of pyridaben and tralomethrin

Residue levels of pyridaben and tralomethrin were determined in peppers grown in an experimental greenhouse, during a 4 week period in which up to four successive treatments with both pesticides were applied. In all cases, plants were sprayed with a mixture of pyridaben and tralomethrin at application rates of active ingredients of 140 and 36 g/ha, respectively. Sampling was carried out at 1, 3, 7, 8, 10, or 14 days after each multiple application, simulating the typical harvesting practices in greenhouse plantations. Residue levels of pyridaben and tralomethrin were determined by using ethyl acetate extraction and GC-ECD. During the study, residue levels in the plantation ranged between 0.22 and 0.04 mg/kg for pyridaben and between 0.09 and 0.02 mg/kg for tralomethrin, with median values of 0.14 and 0.06 mg/kg, respectively. These values represent 28 and 600%, respectively, of the corresponding maximum reside limits currently established in Spain. The application of an intensive washing process to the pepper samples did not lead to a significant reduction of the residue level of either pesticide. Likewise, no significant differences were found between the residue levels in the "edible" and "inedible" parts of the peppers.     

Decomposition rates of forest residues and soil fertility after clear‐cutting of Eucalyptus grandis stands in response to site management and fertilizer application

Forest residues (i.e. harvest residues and litter) are important nutrient sources for trees because soils of poor fertility are used for eucalypt plantations in Brazil. Understanding the dynamics of decomposition for these residues and their effects on soil fertility are relevant for the management of forest plantations. The objectives with this study were to assess the effects of forest residue management and fertilizer, both applied in the establishment of a Eucalyptus grandis Hill ex Maiden stand, on the decomposition rate (k), nutrient release and soil fertility after harvest of this stand. The treatments were applied to a plantation (R1). After 8 yr, R1 was clear‐cut and all of the treatments were reapplied to a new planting (R2). At the end of R1 (age of 8 yr), there was a reduction of 10% in the wood volume in the treatment with the forest residues removed and 36% reduction with no fertilizer application. At the end of 1 yr for plantation R2, these reductions were 30 and 57%, respectively. Residue decomposition under R2 was assessed by a new approach that involved collecting samples directly on the site without using litter bags. The k of forest residues was 3.6 for leaves, 1.2 for bark and 0.8 for branches. The application of small rates of N and P fertilizer did not influence the k of forest residues. In the first 300 days after clear‐cutting, approximately 50% of N, P, Ca, Mg and S and 80% of K in the forest residues were released. Even so, this did not result in significant changes in soil fertility levels. Only small reductions in soil N and P contents over time and changes in topsoil pH resulted from forest residue removal.     

Investigation on fungicide residues in greenhouse-grown strawberries

Maximum residue limits (MRL's) for different agricultural food products in Norway are harmonized with EU standards. In field-grown strawberries in Norway, tolylfluanid has a 7 day quarantine from last application to harvest, while other approved fungicides have 14 days quarantine. Greenhouse production of strawberries is newly introduced to the country. Residue levels in strawberries of the cultivar Korona grown in a commercial greenhouse were investigated 4, 7, and 14 days after application of eight different fungicides at rates recommended by the manufacturers and at half rates. Iprodione, tolylfluanid, and vinclozolin were tested in two experiments, while chinomethionat, chlorothalonil, imazalil, penconazole, and triadimefon were tested once. For chinomethionat, imazalil, iprodione, penconazole, and vinclozolin, the residue levels were below MRL 2 weeks after application. Application of triadimefon in normal rate gave residues below MRL 14 days after application. However, its metabolite, triadimenol, was above MRL at the same time. Tolylfluanid gave very high residue levels, and except from half concentration in the second experiment, all other residue levels were above MRL. Seven days after application, residues in both experiments were approximately 3 times higher than MRL when normal rate of tolylfluanid was applied. For chlorothalonil at the recommended rate, the residue level was above MRL at any sampling time, while half rate gave residues below MRL 14 days after treatment. In view of the present results, tolylfluanid, chlorothalonil, and triadimefon will need longer time from last application to harvest and/or reduced application rates in greenhouse-grown compared to field-grown strawberries. In addition or as an alternative, recommended rates could be lowered.     

Application and fate of Cyromazine in a closed-cycle hydroponic cultivation of bean (Phaseolus vulgaris L.)

The fate of cyromazine applied via the nutrient solution (20, 40, and 60 mg of active ingredient per plant) in a closed-cycle soilless cultivation of bean with zero discharge of effluents was traced in both the recycled drainage solution and the plant tissues for 99 days. The insecticide was applied once, 15 days after planting (16 days prior to the first harvest). In addition to cyromazine, the residues of melamine, its metabolite, in the drainage solution and plant tissues were also regularly determined during the 99 days. The two higher application doses induced toxicity symptoms on the leaves of the bean plant. The maximum cyromazine levels were measured 8 days after application in the drainage solution (17-46 mg l(-1)), 16 days in the roots (1.1-2.4 mg kg(-1) fresh weight [f. wt.]) and the vegetative shoot (4.5-9.5 mg kg(-1) f. wt.), and 24 days after application in the pods (2.6-4.1 mg kg(-1) f. wt.). However, the cyromazine residues in pods were clearly below the maximum acceptable levels for bean. The half-life of cyromazine in the drainage solution ranged from 16 to 19 days for the three doses. The melamine residues in the drainage solution and in the roots reached a concentration peak 16 days after cyromazine application, whereas in the vegetative shoot and the pods they were constantly increasing over the 99 days after application. Nevertheless, the melamine residues were constantly much lower than those of cyromazine, although on the last sampling day (99) they tended toward convergence. Cyromazine proved to be highly persistent, as indicated by the remarkably high residues measured in both the drainage solution and the plant tissues, even 99 days after application. Nevertheless, the application of cyromazine via the nutrient solution to beans grown in closed-cycle hydroponic systems at doses not exceeding 20 mg per plant seems to be safe with respect to both phytotoxicity and residue levels in the edible pods.     

Determination of fungicide residues in field-grown strawberries following different fungicide strategies against gray mold (Botrytis cinerea)

In a 2 year experiment, residues in field-grown strawberries were investigated from the fungicides fenhexamid, pyrimethanil, tolylfluanid, and kresoxim-methyl resulting from different strategies, as regards the dose, number, and time of fungicide applications. Kresoxim-methyl was only used the first year and in full or no dose to control powdery mildew. In the first year, the highest concentrations analyzed were 0.66 mg kg(-1) for pyrimethanil and 0.63 mg kg(-1) for fenhexamid resulting from the use of recommended dose rates and a preharvest interval (PHI) of 10 days, thus not exceeding the Danish maximum residue limit (MRL) of 1 mg kg(-1). Tolylfluanid was used no later than 21 days before harvest, which left residue contents in the berries of 0.48 mg kg(-1), a value well below the MRL of 5 mg kg(-1). In the second year, fungicide residues found in the samples were generally lower, 0.39 and 0.03 mg kg(-1) for pyrimethanil and fenhexamid, respectively. No residues of kresoxim-methyl were found in any of the samples from the field trials, indicating that kresoxim-methyl residues had declined to a level well below the detection limit within the 28 day period between the last application and the harvest.     

Crop residue position and interference with wheat seedling development

Unweathered crop residues can produce growth-inhibiting substances, stimulate pathogen growth, and immobilize nutrients. The location of seed relative to residue may be an important factor in the early health of a crop. This greenhouse study simulated sowing conditions possible under annual dryland winter wheat (Triticum aestivum L.) production to evaluate the likelihood of inhibitory effects. We placed newly harvested, unweathered winter wheat residue on the soil surface, mixed with the seed, immediately above the seed, or 3 cm below the seed. Treatments using a plastic residue substitute and treatments using pasteurized soil and residue provided comparisons to the natural soil and wheat residue. Residue mixed with or placed above the seed caused a temporary delay in emergence. Since this occurred with both wheat and plastic residue, the delay is explained by the physical impedance of coleoptile growth. Wheat residue 3 cm below the seed reduced the height and rate of wheat plant development, indicating a biological inhibitory effect of the wheat residue. This reduction in height and development rate at 20 days after planting did not occur when the soil and residue were pasteurized. We conclude that winter wheat seedling growth can be inhibited if roots encounter unweathered residues.     

霜霉威吡虫啉腐霉利在结球生菜上的消解动态及相关因子的影响

通过开展结球生菜生产中所用主要农药--霜霉威、吡虫啉、腐霉利的消解规律研究,探讨生菜农药消解与农药种类、浓度及外部因子的关系,为结球生菜生产过程中的安全管理提供参考依据。以目前我国生产上主要使用的结球生菜品种--＂皇帝＂为材料,2007年春季露地种植,按霜霉威、腐霉利、吡虫啉最大推荐用量（计算浓度分别为1203.3、500.0、40.0mg·kg-1）和最大推荐用量的2倍（计算浓度分别为2406.6、1000.0、80.0mg·kg-1）两个农药剂量处理,分别于6月6日施药后当日、2、6、9d取样测定农药残留含量,并记录环境因子温度、光照的变化。结果表明,不论是按最大推荐用量还是最大推荐用量2倍喷施,吡虫啉、霜霉威、腐霉利在生菜上均表现为起始和最后阶段消解快、中间阶段消解平缓的特点;按日本肯定列表制度对生菜吡虫啉、霜霉威和腐霉利最大残留限量（分别为5.0、10.0和5.0mg·kg-1）要求,对于吡虫啉,即使按最大推荐用量2倍喷施,其喷施8h后的残留量仅为1.5mg·kg-1,说明春季露地生菜上喷施吡虫啉的安全性较高;对于霜霉威,按最大推荐用量喷施,施药6d后的残留量为10.7mg·kg-1,接近肯定列表制度的要求,施药9d后的残留量降至8．4mg·kg-1,表明霜霉威自喷药至采收的间隔期应至少在7d以上才可能是安全的;对于腐霉利,到试验结束时,不论何种喷施浓度,其残留量均超过5．0mg·kg-1的要求,其使用安全性需要引起重视。在影响吡虫啉、霜霉威、腐霉利在生菜上消解的因素方面,统计分析表明,外部因子（时间、温度、光照）对3种农药消解具有显著作用（P〈0．05）,农药种类在对其消解率影响方面达到极显著差异（P〈0．01）,其中吡虫啉最易消解,其次为霜霉威,腐霉利消解最慢,但3种农药喷施浓度的高低对各自消解率均无显著影响（P〉0．05）。     

Fungicide residues in strawberry processing.

The fate of three fungicides (dichlofluanid, procymidone, and iprodione) applied under field conditions was studied during strawberry processing to juice, wine, and jam. An untreated control was compared to raw material treated with fungicides according to recommended doses and to a sample with 6-fold higher application rates. The highest residue values were found in the pomace after pressing. Residue values in readily produced juices and fruit wines were very low and did not exceed legally required maximum residue levels. Generally, processing steps such as pressing and clarification diminished fungicide residues from 50 to 100%. If the whole fruit is processed, as in fruit preparations or jam, the residue levels remain higher due to missing processing steps.     

Field-incurred fenitrothion residues in kakis: comparison of individual fruits, composite samples, and peeled and cooked fruits

Field trials have been carried out to determine the variability of residue levels of fenitrothion and its main metabolites fenitrothion-oxon and 3-methyl-4-nitrophenol in individual kaki fruits versus composite samples, in peel versus flesh, and in whole uncooked versus whole cooked fruits. Residue levels have been determined by gas chromatography with thermionic specific detection after extraction with ethyl acetate and without further cleanup. At harvest, residue levels of fenitrothion were below maximum residue levels (MRLs) and the two metabolites 3-methyl-4-nitrophenol and fenitrothion-oxon could be quantified with average amounts of 0.080 and 0.012 mg/kg, respectively. Levels of fenitrothion decreased 88% after peeling, whereas temperature did not result in a high variation. The ratios of the highest residue level in the individual fruits to the corresponding mean of residue levels in the composite samples for fenitrothion were <3. This value is lower than that recommended by the World Health Organization as default value for consumer risk assessment.     

Pesticide residues in grapes, wine, and their processing products

In this review the results obtained in the 1990s from research on the behavior of pesticide residues on grapes, from treatment to harvest, and their fate in drying, wine-making, and alcoholic beverage processing are reported. The fungicide residues on grapes (cyproconazole, hexaconazole, kresoxim-methyl, myclobutanil, penconazole, tetraconazole, and triadimenol), the application rates of which were of a few tens of grams per hectare, were very low after treatment and were not detectable at harvest. Pyrimethanil residues were constant up to harvest, whereas fluazinam, cyprodinil, mepanipyrim, azoxystrobin, and fludioxonil showed different disappearance rates (t(1/2) = 4.3, 12, 12.8, 15.2, and 24 days, respectively). The decay rate of the organophosphorus insecticides was very fast with t(1/2) ranging between 0.97 and 3.84 days. The drying process determined a fruit concentration of 4 times. Despite this, the residue levels of benalaxyl, phosalone, metalaxyl, and procymidone on sun-dried grapes equalled those on the fresh grape, whereas they were higher for iprodione (1.6 times) and lower for vinclozolin and dimethoate (one-third and one-fifth, respectively). In the oven-drying process, benalaxyl, metalaxyl, and vinclozolin showed the same residue value in the fresh and dried fruit, whereas iprodione and procymidone resides were lower in raisins than in the fresh fruit. The wine-making process begins with the pressing of grapes. From this moment onward, because the pesticide on the grape surface comes into contact with the must, it is in a biphasic system, made up of a liquid phase (the must) and a solid phase (cake and lees), and will be apportioned between the two phases. The new fungicides have shown no effect on alcoholic or malolactic fermentation. In some cases the presence of pesticides has also stimulated the yeasts, especially Kloeckera apiculata, to produce more alcohol. After fermentation, pesticide residues in wine were always smaller than those on the grapes and in the must, except for those pesticides that did not have a preferential partition between liquid and solid phase (azoxystrobin, dimethoate, and pyrimethanil) and were present in wine at the same concentration as on the grapes. In some cases (mepanipyrim, fluazinam, and chlorpyrifos) no detectable residues were found in the wines at the end of fermentation. From a comparison of residues in wine obtained by vinification with and without skins, it can be seen that their values were generally not different. Among the clarifying substances commonly used in wine (bentonite, charcoal, gelatin, polyvinylpolypyrrolidone, potassium caseinate, and colloidal silicon dioxide), charcoal allowed the complete elimination of most pesticides, especially at low levels, whereas the other clarifying substances were ineffective. Wine and its byproducts (cake and lees) are used in the industry to produce alcohol and alcoholic beverages. Fenthion, quinalphos, and vinclozolin pass into the distillate from the lees only if present at very high concentrations, but with a very low transfer percantage (2, 1, and 0.1%, respectively). No residue passed from the cake into the distillate, whereas fenthion and vinclozolin pass from the wine, but only at low transfer percentages (13 and 5%, respectively).     

Residue levels of chlorpropham in individual tubers and composite samples of postharvest-treated potatoes

Chlorpropham, a herbicide and sprout suppressant, is used on stored potatoes to prolong the storage period without deterioration of produce quality. Data for residue concentrations on an individual tuber basis are required by WHO for the estimation of the variability factor. In this study, the levels of chlorpropham in individual tubers and in composite samples were determined. The distribution of chlorpropham between the peel and the tuber flesh was examined, and the fate during the cooking process (washing, boiling, frying) was studied. The concentrations in individual tubers ranged from 1.8 to 7.6 mg/kg 10 days postapplication (mean 3.8 mg/kg, RSD 39%), from 0.7 to 4.0 mg/kg 28 days postapplication (mean 2.9 mg/kg, RSD 28%), and from 0.8 to 3.8 mg/kg 65 days postapplication (mean 2.2 mg/kg, RSD 48%). The calculated residues in composite samples 10 days postapplication ranged from 4.3 to 6.1 mg/kg (mean 4.9 mg/kg, RSD 20%). Those in samples taken 28 days postapplication ranged from 3.1 to 4.2 mg/kg (mean 3.8 mg/kg, RSD 15%). The concentrations determined in composite samples of whole tubers 65 days postapplication ranged between 2.6 and 3.2 (mean 2.9 mg/kg, RSD 11%). Peeling removed 91-98% of the total residue; washing reduced residues by 33-47%. Detectable residues were found in boiled potatoes and the boiling water, and in french fries and the frying oil. Monitoring data on commercial prefried frozen french fries are reported.     

Determination and depletion of residues of carbadox, tylosin, and virginiamycin in kidney, liver, and muscle of pigs in feeding experiments

The results of residue determinations of the growth promotors carbadox, tylosin, and virginiamycin in kidney, liver, and muscle from pigs in feeding experiments are described as well as the analytical methods used. Residues of the carbadox metabolite quinoxaline-2-carboxylic acid were found in liver from pigs fed 20 mg/kg in the diet with a withdrawal time of 30 days. No residues were detected in muscle with zero withdrawal time. The limit of determination was 0.01 mg/kg for both tissues. No residues of virginiamycin and tylosin were found in pigs fed 50 and 40 mg/kg, respectively, in the diet, even with zero withdrawal time. Residues of tylosin of 0.06 mg/kg and below were detected in liver and kidney from pigs fed 200 or 400 mg/kg and slaughtered within 3 h after the last feeding.     

The dissipation of tebuconazole and propiconazole in boronia (Boronia megastigma Nees)

The broad spectrum, systemic fungicides tebuconazole and propiconazole are used to control rust in boronia (Boronia megastigma Nees). Gas chromatography combined with either a benchtop quadrupole mass spectrometer or a high-resolution mass spectrometer allowed for the monitoring of both pesticides in boronia leaves, flowers, and concrete. Field trials were established at two sites to determine the rate of dissipation of tebuconazole and propiconazole in boronia. At site 1, two application rates of 125 and 250 g active ingredient/hectare (ai/ha) tebuconazole were employed. Treatments were repeated 17 days later. At harvest, 286 days after the final application, tebuconazole was detected at levels of 0.06 +/- 0.05 and 0.5 +/- 0.1 [mg/kg +/- standard error, on a dry matter basis (DMB)] in the leaves collected from plots treated with 125 and 250 g ai/ha of tebuconazole, respectively. The oil produced from the flowers collected at the final harvest had residues of tebuconazole at levels of 0.06 +/- 0.03 and 0.10 +/- 0.08 mg/kg for the 125 and 250 g ai/ha application rates, respectively. Two repeat applications of 125 g ai/ha propiconazole were also used at site 1. Residues of propiconazole were detected at 0.09 +/- 0.03 mg/kg (DMB) 286 days after the final application. At site 2, treatments of 125 g ai/ha of tebuconazole were applied twice. At harvest, 279 days after the final application of tebuconazole, residues were recorded at 0.30 +/- 0.09 mg/kg in the leaves (DMB) while the oil produced had 0.20 +/- 0.07 mg/kg.     

Dissipation of teflubenzuron and triflumuron residues in field-sprayed and cold-stored pears.

Dissipation of residues of benzoylurea insecticides teflubenzuron (TFB) and triflumuron (TFM) under field conditions was evaluated on a pear orchard in Greece. Residues were determined by UV-HPLC analysis, with a detection limit of 0.030 mg/kg for both pesticides. TFB residues in pears were found to persist for 2 weeks and decline thereafter with 48% of the initial deposit remaining 42 days after the last application. TFM residues were found to decline following first-order kinetics and with a half-life of 39(+/-7) days. Residues of both pesticides found in pears collected at harvest maturity were lower than the maximum residue limits (MRLs) set by individual countries. Dissipation of TFB and TFM in cold-stored pears was also evaluated. TFB residues were very persistent for the whole storage period, whereas TFM residues did not dissipate for 6 weeks and then showed a constant decline; 7% of the initial concentration remained at the end of the storage period of 29 weeks.     

Fate of quinoxyfen residues in grapes, wine, and their processing products

Quinoxyfen is a new fungicide that belongs to the family of the quinolines, recently introduced to control powdery mildew (Uncinula necator). In this paper the fate of quinoxyfen residues from vine to wine and in their processing products was studied. After the last of four applications at the recommended rate, 0.38 mg/kg of residue was found on the grapes, which is under the legal limit fixed in Italy (0.5 mg/kg). The degradation rate was according to a pseudo-first-order kinetics (r = 0.964) and the half-life was 7.24 days. Vinification was carried out with and without maceration. During the vinifications without maceration <50% of the residues passed from the grapes to the musts. Separation of the lees (8%) from the must by centrifugation caused no detectable residues in centrifuged must. At the end of fermentation with and without maceration no quinoxyfen residues were determinable in the wine. No effect on the alcoholic or malolactic fermentation was observed even in the presence of higher quinoxyfen concentrations than those found in the grapes at harvest time. During fermentation, the yeasts partially degraded the pesticides and completly adsorbed them. Bacteria, on the other hand, do not have any degradative effect on the pesticides. The raisins obtained by sun-drying did not contain any residues, whereas those obtained by oven-drying show the same amount of residues as in the fresh grapes. During the sun-drying process the fruit weight decreased by a factor of 4; the decrease in the oven-drying was equivalent. Samples of dregs and liquid lees, fortified with high levels of quinoxyfen. were double-distilled. The first dregs distillate, with an alcohol content of 32.1%, did not show any residues, whereas the first lees distillate, with an alcohol content of 34.5%, showed 7% of the initial residues. After the second lees distillation, the obtained product showed an alcoholic content of 81.2% and no residues of quinoxyfen (<0.01 mg/kg).     

Bioaccumulation of melamine in catfish muscle following continuous, low-dose, oral administration

In this study, catfish muscle was analyzed for melamine (MEL) and cyanuric acid (CYA) residues following experimental feeding with low doses of MEL and MEL and CYA (MEL+CYA) and with the insoluble melamine-cyanurate complex (MEL=CYA). Catfish were daily fed 0.1 mg/kg BW of MEL for 15, 28, or 42 days, 0.1 mg/kg BW of MEL+CYA for 28 days, 2.5 mg/kg BW of MEL+CYA for 14 days, or 400 mg/kg BW of MEL=CYA for 3 days. Residues in the tissue were determined by LC-MS/MS. MEL was extracted with acidic acetonitrile, followed by defatting with dichloromethane, and isolated with cation exchange solid phase extraction (SPE). For CYA analysis, fish were extracted with dilute acetic acid, defatted with hexane, and cleaned up with a graphitic carbon SPE. Catfish fed 0.1 mg/kg BW of MEL reached a maximum muscle residue concentration of 0.33 ± 0.04 mg/kg (ppm) after 28 days of continuous feeding. The same concentration was found for MEL+CYA feeding at the 0.1 mg/kg BW level for 28 days. Feeding at 2.5 mg/kg BW of MEL+CYA yielded muscle concentrations above the 2.5 mg/kg level of concern for most of the study fish. Finally, catfish fed high levels of the MEL=CYA complex (400 mg/kg BW) accumulated relatively little MEL in the muscle (0.14 ± 0.07 mg/kg) and, unlike treatment with MEL+CYA, did not form renal melamine-cyanurate crystals. Appreciable concentrations of CYA were not detected in any of the muscles tested. These studies provide data to model the bioaccumulation of triazine residues into edible fish tissue as a result of the continuous consumption of adulterated feed.     

经济作物替代薯稻三熟制早稻对肥料利用、土壤养分和经济效益的影响

为缩短“薯-稻-稻”三熟制作物早稻的生育期,促进“薯-稻-稻”茬口顺畅衔接,提高整体经济效益,本研究以不同经济作物替代早稻,分别在2016年惠东县和2017年白云区试点进行田间试验,共设置5个处理:休耕T₀(空白对照,不种任何作物)、常规处理T_CK(早稻)、T₁(黄瓜)、T₂(豆角)、T₃(甜玉米),探究不同春播经济作物生育期、产量、种植效益和肥料效率及土壤酶活的差异。结果表明,种植黄瓜、豆角和甜玉米替代早稻均可明显增加经济效益和缩短生育期。其中,T₃效果最优,与T_CK相比,单位面积种植效益增加了1.32~3.72 元·m^-2,生育期缩短了37~43 d,收获指数提高了18.6%~20.1%;同时,增加了土壤有效磷和速效钾含量,增强了土壤脲酶、磷酸酶和过氧化氢酶的活性。综上,甜玉米等经济作物代替早稻形成的“经济作物-中晚稻-冬种马铃薯”三熟轮作模式可以使作物茬口衔接更加顺畅,提升三季作物的整体经济效益,对农民增收具有积极作用。本研究为优化广东乃至华南“薯-稻-稻”三熟区的种植模式提供了理论基础和实践依据。     

噻嗪酮在茶园环境中的残留行为研究

参照《农药残留试验准则》,采用田间试验方法,研究在不同地域、不同气候带、不同施药季节条件下杀虫剂噻嗪酮在南京、南宁地区茶园环境中的残留行为,并进行环境影响因素（降水、温度）分析,药剂的作物适用性及区域适用性分析,探讨了不同种植地域MRL值制定的依据。结果表明,噻嗪酮在不同环境条件下的残留行为不同。同季节施药后在两地茶叶上的消解规律相近,统计分析表明两地区的残留消解行为无显著性差异,半衰期为3.97～4.69 d;不同施药季节的降水及气温均可显著影响噻嗪酮在茶叶上的残留状态,降水可明显减少其残留量,而低温则可延长其残留半衰期;在土壤中的残留消解受土壤性质的影响较大,在南京、南宁地区的半衰期相近,但消解过程差异显著,半衰期为10.34～29.96 d。除2008年南京地区外,其他地区与年份不同处理剂量的噻嗪酮药后7 d在茶叶上的残留量均小于10 mg.kg-1,据此并参考国内外噻嗪酮MRL值的制定情况,建议延用国标（GB/T8321.6—2000）的MRL值10 mg.kg-1,建议噻嗪酮在茶叶上使用的安全间隔期为7 d。     

Evaluation of the fertilizer value and nutrient release from corn and soybean residues under laboratory and greenhouse conditions

Abstract

Laboratory and greenhouse studies were conducted on a moderately fertile Taloka (fine, mixed, thermic mollic Albaqualf) silt loam and a low fertility Leadvale (fine‐silty, siliceous, thermic typic Fragiudult) silt loam to evaluate nutrient release and fertilizer value of soybean [Glycine max (L.) Herr.] and corn (Zea mays L.) residues as compared to the inorganic fertilizer 13–13–13–13 (N‐P₂O₅‐K₂O‐S). Residues and the inorganic fertilizer were applied at 50 mg N/kg in a incubation study and at 25 and 50 mg N/kg in a greenhouse study. The incubation study indicted that carbon dioxide (CO₂) evolution and nitrogen (N) mineralization followed a identical sequence: soybean > corn residues, similar to residue N concentration and carbon/nitrogen (C/N) ratio sequence. Application of corn residues produced N immobilization in both soils (‐20 mg N/kg soil), whereas soybean increased inorganic soil N in the Leadvale soil (3 mg N/kg soil) and particularly in the Taloka soil (17 mg N/kg soil). The greenhouse study showed the superiority of the inorganic fertilizer over corn and soybean residues for sorghum‐sudan yield, and N, phosphorus (P), potassium (K), and sulfur (S) total uptake. No significant differences were found among the residues and between residues and the control with the exception of the higher soybean rate for total N uptake in the Taloka soil, and the higher corn and soybean residue rate in the Leadvale soil for total K uptake. It also appeared that soybean residues provided a substantial amount of N and S to sorghum‐sudan. Higher rates of both soybean and corn residues constituted a prime source of K, particularly in the Landvale soil which had a low exchangeable soil K level.