FACTORS AFFECTING THE LOSS OF TRI-ALLATE FROM SOILS

Summary. Electron-capture gas chromatography was used to detect tri-allate residues in persistence studies with two soils. At rates equivalent to 0–75, 15 and 3 Ib/ac, 50% of the amount applied was degraded in 8–11 weeks at 25°C in moist Regina heavy clay and Weyburn loam. No loss occurred in sterile soils, indicating that microbial degradation may be a, major factor contributing to tri-allate breakdown.
When aqueous solutions buffered at pH 4–8 were held at 25° G, only 10–15% of the tri-allate was chemically degraded during 24 weeks.
At the normal field rate of 1·25 Ib/ac, tri-allate was not readily leached. From soil columns of Weyburn loam, 5–7% was eluted by 9 in. of water; with clay the corresponding value was 12–13% of the amount applied. When field plots were sprayed with 125 lb/ac in April, tri-allate could still be detected until the soil froze in November.
Facteurs agissant sur la perte de tri-allate dans les sots     

Tests of soil fertility following repeated applications of MCPA, tri-allate, simazine and linuron

The following herbicides were applied annually from 1963 to experimental plots of appropriate crops grown in monoculture: MCPA 1.7 kg ha^?1, triallate 1.7 kg ha^?1, simazine 1.7 kg ha^?1 and linuron 0.84 kg ha^?1 (applied twice per year). Before the eighth treatment in 1970, nutrient status, pH and growth in greenhouse tests of a range of plants were similar in soils from treated and control plots. There were no significant differences in yield when several test crops were grown in the field plots in 1977. In a similar experiment which ran for 6 years, the same herbicides were applied twice per year at twice the above rates on each occasion (three times a year at 1.7 kg ha^?1 in the case of linuron) to uncropped plots. Three years after the last treatment, there were no differences in extractable nutrients, pH, soil structure and crop yield on treated or control plots. These results support the conclusion from the main monitoring of the experiments reported elsewhere that annual treatments with these herbicides have had no adverse affect on the soil.     

Determination of extractable and non-extractable radioactivity from prairie soils treated with carboxyl- and ring-labelled [14C]2,4-D

Ring- and carboxyl-labelled [¹⁴C]2,4-D were incubated under laboratory conditions, at the 2 g/g level, in a heavy clay, sandy loam, and clay loam at 85% of field capacity and 20 1C. The soils were extracted at regular intervals for 35 days with aqaeous acidic acetonitrile, and analysed for [¹⁴C]2,4-D and possible radioactive degradation products. Following solvent extraction, a portion of the soil residues were combusted in oxygen to determine unextracted radioactivity as [¹⁴C]carbon dioxide. The remaining soil residues were then treated with aqueous sodium hydroxide, and the radioactivity associated with the fulvic and humic soil components determined. In all soils there was a rapid decrease in the amounts of extractable radioacitivity, with only 5% of that applied being recoverable after 35 days. All recoverable radioactivity was attributable to [¹⁴C]2,4-D, and no [¹⁴C]-containing degradation products were observed. This loss of extractable radioactivity was accompanied by an increase in non-extractable radioactivity. Approximately 15% of the applied radioactivity, derived from carboxyl-labelled [¹⁴C]2,4-D, and 30% from the ring-labelled [¹⁴C]2,4-D was associated with the soil in a non-extractable form, after 35 days of incubation. After 35 days, less than 5% of the radioactivity from the carboxyl-labelled herbicide, and less than 10% of the ringlabelled material, was associated with the fulvic components derived from the three soils. Less than 5% of the applied radioactivities were identifiable with any of the humic acid components. It was considered that during the incubation [¹⁴C]2,4-D did not become bound or conjugated to soil components, and that non-extractable radioactivity associated with the three soil types resulted from incorporation of radioactive degradation products, such as [¹⁴C]carbon dioxide, into soil organic matter.     

Field experiments to investigate long-term effects of repeated applications of MCPA, tri-allate, simazine and linuron: II. Crop performance and residues 1969–78

In four field experiments begun in 1963, each of four herbicides was applied to plots planted wilh the same crop each year. The annual treatments were: MCPA at 17 kg/ha to barley (Hordeum sativa Jess) and wheat (Triticum aestivum L.) at growth stage 15. tri-allate at 17 kg/ha pre-emergcnce to barley and wheat, simazine at l7kg/ha pre-emergence to maize (Zea mays L.) and linuron in two applications of 084 kg/ha pre- and post-emergence to carrots (Daucus carota L.). MCPA did not affect growth or yield of either barley or wheat. In general tri-allate also did not aftect the crops although wheat yield was depressed in 1978, wheat 1000 grain weight was reduced in 1972 and barley germination percentage was increased in 1973. Simazine did not influence the height, yield or appearance of maize. Linuron normally produced no effect on carrot yield, density and size. However, in 2 years when the post-emergence application was late, density but not yield was lower than in control plots. There was no accumulation of residues of any of these compounds in the soil. Rates of loss were similar to those predicted on ihe basis of laboratory experiments. In a fifth experiment these herbicides were applied twice per year (3 times in the case of linuron) at double the rales above on each occasion to bare plots. These applications ceased in 1968 (1969 for MCPA) but residues were monitored until 1972 except in the case of MCPA. Disappearance rates were similar to those in the cropped plots and residues were largely confined to the top 10 cm. The plots treated with MCPA had developed an enhanced ability lo degrade il prior to 1968. This persisted for 5 years after the final application.     

Relative persistence of di-and tri-chlorophenoxyalkanoic acid herbicides in Saskatchewan soils

The persistence of 2,4-D, 2,4-DB, dichlorprop, 2,4,5-T, and fenoprop at the 2 ppm level was studied in the laboratory on three prairie soils at 85% of field capacity and 20°C. Following extraction of the soils with aqueous acetonitrile containing acetic acid, the herbicidal acids remaining were analysed gas chromatographically. Breakdown was rapid on all soils and the average half-lives for 2,4-D, 2,4-DB, dichloroprop, 2,4,5-T, and fenoprop were < 7, < 7, 10, 12, and 12 days respectively. Degradation on air-dried soils (15% of field capacity) was negligible with over 85% of the applied herbicides being recoverable after incubation periods during which the herbicides remaining in the moist soils accounted for less than 30% of the original treatments. Persistance relative des acides di et tri-chlorophénoxy-alkanoï-ques herbicides dans des sols du Saskatchewan. La persistance du 2,4-D, du 2,4-DB, du dichlorprop, du 2,4,5-T et du fénoprop, à la concentration de 2 ppm, a étéétudiée au laboratorire, sur trois sols de prairie, a 85% de la capacité au champ et a 20°C. Après leur extraction des sols par l'acétonitrile aqueux contenant de l'acide acétique, les acides herbicides restants ont été analysés par chromatographie en phase gaseuse. La dégradation a été rapide pour tous les sols et les demi-vies moyennes du 2,4-D, du 2,4-DB, du dichlorprop, du 2,4,5-T, et du fénoprop ont été respectivement de <7, <7, 10, 12 et 12 jours. La dégradation sur des sols séchés a l'air (15% de la capacité au champ), a été négligeable, plus de 85% des quantités d'herbicides appliquées étant récupérables après des périodes d'incubation durant lesquelles les herbicides restant dans les sols humides ne représentaient plus que moins de 30% des quantités apportées à l'origine. Relative Persistenz von Di-und Trichlorphenoxyalkansäure-Her-biziden in Böden Saskatchewan In Laborversuchen wurde die Persistenz von 2,4-D, 2,4-DB, Dichlorprop, 2,4,5-T und Fenoprop in drei Prärieböden festgestellt. Die Versuche wurden bei 20°C, 85 % der Feldkapazität und einem anfänglichen Herbizidgehalt der Böden von 2 ppm durchgeführt. Die Extraktion der Böden erfolgte mit wässerigem Acetonitril mit einem geringen Anteil an Essigsäure. Die Herbizide wurden gaschromatographisch nachgewiesen. In allen Böden wurde ein schneller Abbau festgestellt. Die Halbwertszeiten betrugen für 2,4-D, 2,4-DB, Dichlorprop, 2,4,5-T und Fenoprop < 7, < 7,10, 12 bzw. 12Tage. Der Abbau im lufttrockenen Boden (15% der Feldkapazität) war zu vernachlässigen. Hier waren noch mehr als 85% der ausgebrachten Herbizidmenge vorhanden, wenn in den feuchten Böden die Konzentration bereits weniger als 30% betrug.     

Analytical models of weed biocontrol with sterilizing fungi: the consequences of differences in weed and pathogen life-histories

A model of the population dynamics of healthy weed plants, weed seeds in the soil, pathogen-infected weed plants and pathogen spores in the soil, was devised to investigate interactions that are important for the success of biocontrol with pathogens that prevent seed set. Three particular features of the host-pathogen interaction were examined in detail: the form of the density dependent relationship which determined seed and spore production, the host life stage at which infection could occur, and the relative competitive abilities of healthy and infected host plants. It was found that, when both weed and pathogen coexist, the equilibrium abundance of the weed in the presence of the pathogen was independent of the form of the relationship between plant density and seed or spore production. However, the form of this relationship did affect estimated equilibrium densities in the absence of biocontrol, and also affected the parametrizations under which both host and pathogen could coexist. Parameters derived from experiments with isolated host plants may therefore be sufficient to assess the biocontrol potential of new pathogens along with knowledge of densities achievable when the weed is uncontrolled. The form of the relationship used to control seed and spore production also had a marked influence on the range of parameter values over which the pathogen could persist. Other control measures were represented by changes to appropriate parameter values, e.g. weeding was represented by a change in weed death rate. With one exception, the use of additional control measures was not antagonistic to biocontrol. Often, however, the combined effect was less than additive, and the existence of synergy (where the combined effects are more than additive) was critically dependent on the form of the relationship of the rate of seed production per plant with density and the efficiency of the other control measures.     

Policy options for Agriculture Green Development by farmers in China

Farmers are the key agents who manage land and water. Agriculture Green Development (AGD) requires a transformation in farming from high resource consumption and environmental cost to sustainable intensification with high productivity, high resource use efficiency and low environmental risk. This paper analyzes the public policy challenge of AGD and makes the case for a location-sensitive policy mix made up of regulation, advice provision, voluntarism and targeted incentives. The public agricultural extension service in China is a key resource, but one that requires reorientation and reform with the aim of better balancing high farm productivity with environmental protection.     

Movements and behaviors of swordfish in the Atlantic and Pacific Oceans examined using pop‐up satellite archival tags

Swordfish are highly specialized top‐level predators that have been challenging to study. In this paper, data from 31 pop‐up satellite archival tags attached to swordfish from (i) the eastern Pacific, (ii) central Pacific, and (iii) western North Atlantic‐Caribbean were analyzed. Common across locations was a pronounced diel vertical pattern with daytime hours spent primarily below the thermocline and nighttime hours spent in warmer waters, close to the surface. One exception to this pattern was periodic daytime basking events which were most common in cooler waters off California. Maximum daytime depths were significantly correlated with light penetration as measured by the diffuse attenuation coefficient at 490 nm. Temperature did not appear to influence daytime depths, and swordfish tolerated both extremely low temperatures (4°C) and rapid and dramatic temperature changes (>20°C). Temperature did appear to influence the nighttime depths in the Pacific where fish typically remained in the surface mixed layer. In contrast, in the warm tropical Atlantic this was not the case, and nighttime depths were much deeper. In all areas, nighttime depth increased around the full moon. Given the parallels between the vertical movement patterns of swordfish and those of the deep sound scattering layer we suggest that swordfish vertical distribution patterns, especially during daytime, are influenced largely by resource availability. At night, when swordfish are typically targeted by fisheries, both ambient light and temperature influence movements. Understanding vertical movement patterns of swordfish can help evaluate gear vulnerability, improve population assessments, and potentially reduce fisheries bycatch.     

Hatchery production of Florida red tilapia seed in brackishwater tanks: the influence of broodstock age

Abstract. Production of Florida red tilapia seed (eggs, sacfry and fry) in 34-m² above-ground tanks using recirculated brackishwater (12 ppt) was studied over a 5-month period on Lee Stocking Island (Exuma Cays, Bahamas). Four tanks were stocked with year class 1 (YCI) breeders, while 2 tanks were stocked with year class 2 (YCII) breeders at densities of 200 and 240/tank (5·9 and 7·1/m²), respectively, and at a sex ratio of 3 females to 1 male, beginning in November 1988. Seed production was measured by removing free-swimming fry from tanks and eggs and sacfry from the mouths of brooding females, and assessing the number of each at 15 to 16-day intervals from February to June 1989. Average seed production (seed/m²/day) was significantly higher in YCI (52·3) than in YCII (36·0) broodstock, indicating the advantages of replacing broodstock with yearling breeders each year.