| In order to study the characteristic of weed occurrence and its effects on growth,yield and quality of indica rice in direct-seeded field,this study were set up with different direct seeding methods and weeds control treatments in early and late rice experiments,which were carried out to ascertain the weed control period and the appropriate selection of chemical herbicide in direct seeding field.Early trials set up with three sowing methods（dry direct seeding DDS,wet direct seeding WDS and flooding direct seeding FDS）and four manual weeding periods[(from sowing to three leaves（C1）,from three leaves to four leaves（C2）,weeding for the whole growth period（C3）and no weeding over the entire growth period（CK）]for pot experiments;In the late rice experiment,Meixiangzhan 2 and Taiyou 871 were planted in field with two weeding methods of chemical herbicide（36%Bensulfuron propionate,25g/L Penoxsulam and 10%Cyhalofop-butyl+10%Bispyribac-sodium）weeding（CW）and non-weeding（NW）,conducted to study the effects of different direct seeding methods and weed control periods on weed occurrence and grain yield of direct-seeded rice,and the effects of herbicide spraying on rice growth period,plant type,photosynthetic characteristics,yield and quality of rice.The main results were as follows::1.Effects of different direct seeding methods and weed control timing on weed occurrence and grain yield of early Indica riceWeeds such as Echinochloa crusgalli,Euphorbia lathyris,Juncellus serotinus and Monochoria vaginalis occurred seriously in the soil of direct seeding early rice,and their population density accounts for more than 95%of the weed community.Compared with FDS and WDS,weeds such as Echinochloa crusgalli and Euphorbia lathyris were occurred relatively seriously in DDS,while aquatic weeds including Juncellus serotinus and Monochoria vaginalis were relatively serious in FDS and WDS.The weed occurrence in the DDS treatment was serious in early crop development（3-29 days after rice sowing）,but was significantly lower than that of FDS and WDS after 43 days.For the whole rice growing period,the weeds density and biomass in DDS was decreased than that of FDS and WDS.Correlation analysis showed that the weed biomass was negatively correlated with the grain yield and its components for DDS,in which the influence of weeds on 15-22days after sowing significantl.Compared with CK,the grain yield of early indica rice was significantly increased by all weed control treatments,with the ranking for yield being C3>C1>C2>CK,and the average yield increase being 17.91%～31.21%.The best among the weed control treatments was C1;while the effect of DDS yield was the highest,mainly due to the increase of effective panicle number.DDS has potential to reduce the occurrence of weeds in direct seeded paddy fields,and weeding from sowing to the three leaf stage is the critical period for weed control.2.Effects of herbicide spraying on weeds occurrence and the formation of late indica rice yield in direct seeding rice fields.There are various kinds of weeds in the direct seeding late rice field,and the weed population characteristics varied at each growth stage.The weed community density was the largest at the tillering stage of rice,and it was dominated by Monochoria vaginali+Echinochloa crusgalli+Euphorbia lathyris,which accounted for 62.15%～85.21%of the weeds in the field.It was found that 36%Bensulfuron propionate had the highest efficiency on weeds control in the field,up to 95.30%～97.45%,while increase by14.04%～20.54%than 25g/L Penoxsulam and 10%Cyhalofop-butyl+10%Bispyribac-sodium.The competition between weeds and rice result in a significant decline in late rice yield,of which decreased by 40.40%～45.96%,mainly related to the decrease of effective panicles and grains per panicle.In addition,under the symbiosis of weeds and rice,the sowing-heading time and whole growth period of rice were prolonged by 2.0 days and 5.5 days respectively,the plant height and the length of basal internode,the length of the flag leaf leaves,the base and opening angles of the upper three leaves were all significantly increased,while the chlorophyll content,net photosynthetic rate and dry matter accumulation were significantly decreased,meanwhile,the decline of rice processing quality and cooking taste quality was not conducive to the improvement of rice taste quality;It showed that the competition of weeds s in direct seeding late rice field resulted in the changes of rice growth period,plant leaf shape,photosynthetic characteristics and dry matter production,which affected rice yield and quality,and was not conducive to high quality and high yield of rice. |
