<p style="text-align: justify;">Weed competition becomes a major problem in low land rice. Weeds can reduce rice production up to 60-70%. Mixing herbicides is expected to obtain a broader spectrum of control of the weeds. Inappropriate mixing herbicides may cause antagonism effect which can reduce the effectiveness on the target weed. The objective of the research was to study the antagonism activity of two active ingredients herbicide mixture, cyhalofop-butyl and penoxulam. The treatment was consisted of three types of herbicide with five level of doses, i.e. a single herbicide cyhalofop-butyl (0, 375, 750, 1500, and 3000 g ai ha^-1), penoxulam (0, 50, 100, 200, and 400 g ai ha^-1), and the mixture of cyhalofop- butyl 50 g L^-1+ penoxulam 10 g L^-1(0, 225, 450, 900, and 1800 g ai ha^-1). The target weeds were Echinochloa cruss-galliand Monochoria vaginalis. Dry weight of biomass and percent of damage would further determine wheather the herbicide mixture were synergistic, antagonistic, or additive. Since cyhalofop-butyl and penoxulam had a different mode of action, analysis of the data used MSM (Multiplicative Survival Model) method to determine the LD50 of each herbicide treatment and mixture component. The result showed that an active ingredient mixture of cyhalofop-butyl 50 g L^-1+ penoxulam 10 g L^-1 was not antagonist, with LD50-expectation values of 253.231 g ai ha^-1and the LD50-treatment of 211.91 g ai ha^-1. The co-toxicity value was 1.19 (&gt;1).</p><p>Key words:  rice field weeds, cyhalofop-butyl, penoxulam, herbicide mixture, MSM (Multiplicative Survival Model), LD50</p>

The study aims to analyze the land-use changes from paddy fields to non-paddy fields, examine the future sustainability of the paddy fields, and analyze the impact of the paddy fields’ conversion on the socio-economic and environmental aspects. The study was carried out at Ciampea Sub-district, Bogor Regency, West Java Province. Conversion of paddy fields was analyzed through visual interpretation of Ciampea Sub-district 2016 and 2019 imageries using GIS software of ArcGIS 10.5. and later was used to measure the average annual conversion rate and predict the future sustainability of the paddy field, and to measure the impact of the land conversion using the economic valuation method (financial analysis and replacement cost approach). The results showed that, first, during the year of 2016 to 2019, the paddy fields in Ciampea Sub-district transformations were dominated by settlements. Second, the conversion rate was relatively high, by 51.45 hectares per annum. Third, the impact of reduction of paddy field area was relatively high: a potential loss of 3,098.06 tons of food crop production. Meanwhile, the cost for replacing the function of flood, erosion, and sedimentation control reached IDR 257.68 billion.