Effects of repeated applications of ten soil-active herbicides on weed population,residue accumulation and nitrification*

Ten herbicides, bromacil, chlorthal-dimethyl, diphenamid, diuron, fluometuron, neburon, prometryne, pyrazon, simazine and trifluralin at two doses were repeatedly sprayed, in autumn and in spring, for 4 consecutive years on non-cultivated, sprinkler-irrigated field plots. Herbicidal effect was assessed at 1–2 month intervals on the natural weed population and after each observation a paraquat + diquat spray destroyed emerged weeds. The response of various weed species to herbicides varied markedly but a herbicide-induced shift in the composition of weed population did not occur, presumably because of the paraquat treatment. The overall phytotoxicity to weeds present was, in decreasing order: diuron, bromacil, simazine, trifluralin, prometryne, neburon, fluometuron, pyrazon, diphenamid, chlorthal-dimethyl. Persistence of herbicides was in decreasing order: diuron = bromacil, simazine, neburon (at higher rate), fluometuron, trifluralin, prometryne. Control produced by pyrazon improved with the number of applications, but that of diphenamid and chlorthal-dimethyl remained weak and short. After repeated applications, the activity of these herbicides increased or remained at similar level, but in no case decreased. Soil samples were taken 5 months after each application and bioassayed. Phytotoxic residues were detected beneath the disturbed top-soil from bromacil, diuron, fluometuron and simazine after the first application, and from neburon after the second application; residues from trifluralin were found in the top soil only after the fifth application. After the seventh spraying, residues of bromacil were found in the 45–60-cm soil layer. Ammonia content in soil samples taken from treated plots after the fourth, sixth and seventh application was generally similar to the untreated control. In these samples, nitrate content appeared to be correlated negatively with remaining weed number; the control thus contained less nitrate than efficient herbicidal treatments. Soil samples taken after the seventh application of bromacil, diuron, fluometuron, neburon and simazine, which contained appreciable residual concentrations, did not show significant differences from control, in an in vitro nitrification test.     

甘肃中部干旱区柠条生物量特征及利用途径

通过对甘肃省中部干旱区47个柠条样地生物量结构特征分析,选以丛生物量为因变量,丛高、冠幅为自变量的二元线性回归方程W=-1.7537+0.9637H+1.7144C 为估算该区丛生物量的有效模型,并依该模型编制生物量表。为保护柠条资源及提高其生产力,提出了合理的平茬技术措施。     

Behaviour and persistence of trifluralin in soil

The growth response of sorghum to trifluralin, on various soils and soil mixtures, was significantly correlated with organic matter (ranging from <0–1% to 20–4%) but not with clay content (ranging from 3% to 63%). However, in soils with a similar, low organic matter content, the activity of trifluralin increased with increasing clay content. No correlation was found between phytotoxicity of trifluralin and lime content of soils. The persistence of trifluralin incorporated in soil was examined by repeated reseedings of sorghum. Phytotoxicity lasted longer in soil dried and mixed at each interval between seedings than in soil left undisturbed; after 2 months about 50% of the original 4 ppm trifluralin remained in undisturbed soil vs 60 % in repeatedly mixed soil. The rate of degradation, after 2 months of incubation at 50% field capacity, increased with temperatures from 10°to40° the concentration of trifluralin required for a given growth reduction was approximately eight times greater after incubation at 40° than at 10°C. Comportement et persistattce de la trifluraline dans le sol Les effets de Ia trifluraline sur la croissance du sorgho cultivé dans divers sols ou mélanges de sol se sont révlés être en corrélation significative avec la matiere organique (entre < 0,1 % et 20,4 %) mais pas avec la teneur en argile (de 3 % A 63 %). Toutefois dans les sols contenant un taux analogue et faible de matiére organique, l'activité de la trifluraline s'est accrue en même temps que Ia leneur en argile. Aucune corrélation n'a été constatée entre la phytotoxicité de la trifluraline et la teneur en calcaire des sols. La persistance de la trifluraline incorporée dans le sol a été examinée au moyen de ressemis répétés de sorgho. La phytotoxicité dura plus longtemps dans le sol séché et remuéà chaque intervalle entre les semis que dans le sol non travaillé; au bout de 2 mois, 50% environ des 4 ppm de trifluraline apportés à. I'origine restaient dans le sol non remué contre 60% dans le sol plusieurs fois remué. Le taux de degradation, aprés deux mois d'inciibation à 50% de la capacityé au champ, augmenta avec la température de 10°à 40°C; la concentration de trifturaline nécessaire pour obtenir une réduction de croissance donnée fut approximativement huit fois plus grande aprés incubation. à 40° qu'aprés incubation à 10°C. Verhalten und Perststenz von Trifluralin im Boden Die Wachstumsreaktion von Hirse gegenubcr Trifluralin in verschiedenen Böden und Bodenmischungen war signifikant mit dem Gehalt an organischer Substanz (<0–1 %–20–4%) korreliert, nicht aber mit dem Tongehalt (von 3%-63%). Jedoch nahm in Böden mit annähernd gleich niedrigen Gehalten an organischer Substanz die Wirksamkeit von Trifluralin mit steigendeni Tongehalt zu. Zwischen der Phytotoxizität von Trifluralin und dem Kalkgehalt der Böden wurde keine Korrelation gefunden. Die Persistenz von in den Boden eingearbeitetem Trifluralin wurde durch wiederholte Einsaat von Hirse untersucht. Die Phytotoxizität dauerte im Boden, der jeweils zwischen den Einsaaten getrocknet und gemischt worden war, langer an als im nicht derartig behandelten Boden. Nach 2 Monaten waren im letzteren Boden ungefähr 50% der ursprüinglichen 4 ppm Trifluralin verblicben gegenüber 60% im wiederholt durchmischten Boden. Nach 2 Monatlen Inkubation bei 50% Feldkapazität stieg die Abbaurate, wenn die Temperatur von 10° auf 40°C stieg; die für eine gegebene Wachstumsreduktion benötigte Trifluralinkonzentration war bei 40° annShernd achtfach grösser als bei 10°C.     

Conversion of soil particle size distribution and texture classification from ISSS system to FAO/USDA system in Japanese paddy soils

ABSTRACT

The conversion between the two different systems, ISSS and FAO/USDA, of particle size distribution and soil texture classification is useful to characterize soil physical properties and usage of each published. The objective of this study is to test some functions that have been published for conversion from ISSS to FAO/USDA system for Japanese paddy soils and to select the best method. We tested the topsoils of 267 Japanese paddy fields using the log-linear method, log-normal method, multiple regression method, Skaggs et al.’s method, and Minasny and McBratney’s method. The least AIC was obtained using multiple regression method, and the equation derived was given as follows:

si_FAO/USDA = 1.305si_ISSS + 0.396fs_ISSS?0.100cs_ISSS ? 12.323

where si, fs, and cs are the percentage of silt, fine sand, and coarse sand respectively; ISSS and FAO/USDA is the fractionation system; and its RMSE was 3.1%. For the case that only the total sand content (s) is available instead of fine sand and coarse sand, the following equation was obtained:

si_FAO/USDA = 0.314si_ISSS + 1.533s_ISSS ? 20.903 (RMSE = 3.7%)

Among the non-empirical methods, the best estimation method was Skaggs et al.’s method, and its RMSE was 3.3%. The soil texture classification by FAO/USDA system using estimated particle size fractions by the above equation can be classified to correct categories. The accuracy ratio of the classification was 93-97%.