Abstract
To quantify the effect of weeds on the nitrogen (N) use, growth and yield of wet season paddy rice in the central and northern regions of Laos, we surveyed the paddy fields in these regions in October 1999 and November 2000. We found 13 weed species in total, but there were few major weeds abundant at the survey sites. In the infertile soils under rainfed conditions, weed growth was poor. Rough rice yield, the number of panicles, the number of seeds per square meter, the above‐ground biomass of paddy rice and the amount of N accumulated in the above‐ground biomass of paddy rice (amount of N in rice) were suppressed by competition with weeds. However, harvest index (HI) and nitrogen use efficiency (NUE) of paddy rice were not suppressed by competition with weeds. The amount of N in rice was suppressed by competition with weeds, the number of panicles decreased as the amount of N in rice decreased, and the number of seeds per square meter decreased as the number of panicles decreased. As a result, rough rice yield was suppressed by competition with weeds. The weeds competed with paddy rice for N uptake during the productive tillering stage. However, the ability of paddy rice to compete for N uptake with weeds was not reduced under rainfed lowland conditions. When the weeds were completely removed, the amount of N in rice increased. Rough rice yield may be increased by 10% under rainfed lowland conditions and by 17–19% under irrigated conditions.
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Claims 12
Claim · model-written summary
Thirteen weed species were found, with few major weeds abundant.
Verbatim
e0“We found 13 weed species in total, but there were few major weeds abundant at the survey sites”
t0“paddy rice”
Claim · model-written summary
Weed growth was poor in infertile rainfed soils.
Verbatim
e0“In the infertile soils under rainfed conditions, weed growth was poor”
t0“paddy rice”
Claim · model-written summary
Weed competition suppressed rice rough yield, panicles and seeds per square meter.
Verbatim
e0“Rough rice yield, the number of panicles, the number of seeds per square meter, the above‐ground biomass of paddy rice and the amount of N accumulated in the above‐ground biomass of paddy rice (amount of N in rice) were suppressed by competition with weeds”
t0“paddy rice”
Claim · model-written summary
Weed competition suppressed rice aboveground biomass and its accumulated nitrogen.
Verbatim
e0“the above‐ground biomass of paddy rice and the amount of N accumulated in the above‐ground biomass of paddy rice (amount of N in rice) were suppressed by competition with weeds”
t0“paddy rice”
Claim · model-written summary
Weed competition did not suppress harvest index and nitrogen use efficiency.
Verbatim
e0“harvest index (HI) and nitrogen use efficiency (NUE) of paddy rice were not suppressed by competition with weeds”
t0“paddy rice”
Claim · model-written summary
Panicle number fell as rice nitrogen accumulation fell.
Verbatim
e0“the number of panicles decreased as the amount of N in rice decreased”
t0“paddy rice”
Claim · model-written summary
Seeds per square meter fell as panicle number fell.
Verbatim
e0“the number of seeds per square meter decreased as the number of panicles decreased”
t0“paddy rice”
Claim · model-written summary
Weeds competed with rice for nitrogen during productive tillering.
Verbatim
e0“The weeds competed with paddy rice for N uptake during the productive tillering stage”
t0“paddy rice”
Claim · model-written summary
Rice ability to compete for nitrogen with weeds was not reduced under rainfed lowland conditions.
Verbatim
e0“the ability of paddy rice to compete for N uptake with weeds was not reduced under rainfed lowland conditions”
t0“paddy rice”
Claim · model-written summary
Complete weed removal increased nitrogen accumulated in rice.
Verbatim
e0“When the weeds were completely removed, the amount of N in rice increased”
t0“paddy rice”
Claim · model-written summary
Weed removal may raise rough rice yield by 10% in rainfed lowlands.
Verbatim
e0“Rough rice yield may be increased by 10% under rainfed lowland conditions and by 17–19% under irrigated conditions”
t0“paddy rice”
e1“When the weeds were completely removed, the amount of N in rice increased”
Claim · model-written summary
Weed removal may raise rough rice yield by 17–19% under irrigation.
Verbatim
e0“Rough rice yield may be increased by 10% under rainfed lowland conditions and by 17–19% under irrigated conditions”
t0“paddy rice”
e1“When the weeds were completely removed, the amount of N in rice increased”