Rice is one of the most important food crops globally. One third of the global population depends on rice for their daily sustenance. In India, rice is the most important food crop in terms of production and consumption. The yield losses due to weed infestation in rice may be as high as16 -90 per cent (Zoschke, 1990). Aerobic rice is one of the methods of cultivation of rice, in which the seeds are seeded directly in non-puddled, non-flooded fields. Aerobic rice requires less water and labour than flooded rice established through transplanting, but is usually subject to much higher weed pressure (Balasubramanian and Hill, 2002), because direct seeded rice weeds and crop seeds germinates simultaneously. Weeds are the greatest yield limiting constraint to aerobic rice, contributing about 50 per cent to yield gaps. Hand weeding is complicated due to morphological similarity Abstract A field study was conducted at ZARS, V.C. Farm Mandya to determine bio efficacy and persistence of oxyfluorfen residue in soil and aerobic rice crop. Oxyfluorfen (23.5% EC) was applied (100 g a.i ha -1 and 200 g a.i ha -1 ) to crop (Var MAS 946 -1 ). Soil samples were collected at 0, 5, 10, 20, 30, 45, 60, 90 days after sowing and at harvest. Plant samples were collected at 60, 90 days after sowing and at harvest. Both the samples were analyzed for oxyfluorfen residues by a validated high-performance liquid chromatography method with an accepted recovery of 82.6% for soil and 92.6% for plant samples at the minimum detectable concentration of 0.05 µg g -1 . Higher persistence of oxyfluorfen was noticed in treatment which received oxyfluorfen at 200 g a.i ha -1 + FYM @ 10 t ha -1 ranging between 0.61 µg g -1 and 0.08 µg g -1 at 0 and 60 days after treatment whereas oxyfluorfen did not persist in rice at any growth stages. A higher half life of 7.0 days and lower rate constant of 9.8 × 10-3 day -1 were also recorded in the same treatment. Highlights •Application of oxyfluorfen @ 200 g a.i ha -1 + FYM @ 10 t ha -1 recorded higher persistence of oxyfluorfen 0.61 µg g -1 and 0.08 µg g -1 at 0 and 60 days after treatment .• Higher half life of 7.0 days and lower rate constant of 9.8 × 10 -3 day -1 was recorded in the treatment receiving oxyfluorfen @ 200 g a.i ha -1 + FYM @ 10 t ha -1 .

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Soil nutrients are essential for crop growth. Spatial variability of nutrients can occur in various scales, between regions, between fields or within the field. RS and GIS techniques enables farm management based on small-scale spatial variability of soil and crop parameters in the field. The present study was carried out in Nagenahalli microwatershed, Doddaballapur taluk, Bangalore rural district with the objective to determine and map the macronutrient status of soils in the watershed using GIS technique. The NPK was analyzed and mapped using Arc GIS to quantify the level of spatial nutrients availability. Results indicated that NPK ranged from 31.36 to 376.32 kg ha -1 (N), 21.29 to 390.62 kg ha -1 (P 2 O 5 ) and 55.10 to 521.47 kg ha -1 (K 2 O) respectively in the surface soils. Nutrient map showed that the soils were poor in available nitrogen and available potassium whereas sufficient in available phosphorous content. Furthermore NPK map can be used to identify deficient or sufficient areas for efficient fertilizer management.

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