Composition shift and other characteristics of weeds and yield of sweet corn on Andisols with nitrogen fertilization and weeding at critical period of the crop

A research on weed and crop in a sweet corn field and weed in a fallow agricultural field was conducted at the Experimental Station Lembang for Vegetables Crops (1250 m above sea level) on Andisols from December 1995 to April 1996. Effect of N fertilization and weeding at various times during critical period of crop growth were studied in two experiment, set up in a Randomized Block Design. Thirty five complete bifactorial combinations of nitrogen fertilization (0, 100, 200, 300, and 400 kg N/ha) and weeding (weeds removed at 20, 30, 40, and 50 days after planting (dap), at 20, 35, and 50 dap and, at 20 and 50 dap, removed only at 20 dap or at 50 dap, since planting of seeds until harvest with weeding interval of 10 days, and no weeding at all since planting of seeds up to harvest of sweet corn were replicated three times. The differences among weed composition shifting which were represented by the different number of SDR of weeds caused by weeding conducted at different time depend on N application with increasing dosage which were calculated at certain different plant ages to be observed. At early age (20 dap) of sweet corn plants which weed composition based on the dominant weeds, it was revealed that Galinsoga parviflora Cav., Drymaria villosa Cs., Cyperus rotundus L., Borreria alata (Aubl). DC., Oxalis coniculata L., Eleusine indica (L.) Gaertn, Murdania nudiflora (L.) Brenan, Cynodon dactylon (L.) Pers, and Panicum repens L., which appeared only on the bare soil, all of them were the dominant weeds. By harvest of sweet corn, weed composition based on the SDR values which appeared both on sweet corn plantation and on bare soil were as follows; Galinsoga parviflora, Eleusine indica, Drymaria villosa, Polygonum nepalense, Borreria alata, and Cynodon dactylon appeared on bare soil only. Population of all kind of weeds for mentioned above by harvest of sweet corn differ at different time of weeding and they depend on N dosage at a certain level set up. Variation index of weeds of all kind of weeds for mentioned by harvest of sweet corn not differ at different time of weeding and N dosage at all, except at soil without sweet corn. The longer the growing period of weeds, the higher the weed biomass and its N constituent, both which appeared on sweet corn plantation and on bare soil. However, the biomass and N constituent of weeds from bare soil was higher than that of from sweet corn plantation. Equally, yield component significantly affected sweet corn yield at different times of weeding which depend on N dosage at a certain level applied. The maximum yield of sweet corn gained from weeding treatments conducted two, three, and four times, repectively; and from weeding treatments for the entire of sweet corn growth and development, viz 12.8 ton/ha gained from optimum dosage of 300 kg N/ha. Percentage of yield lost of sweet corn grains from weeding treatment of different time were not significantly different compared to N fertilization treatments at several dosage applied in these experiments. Average yield lost was the highest, viz 45.47 percent was gained from no weeding at all while the lowest yield lost was from weeding treatment at 20, 30, 40, and 50 dap and repeated for four times, respectively, viz 1.98 percent. The values of competition indexes among sweet corn plant and weeds which appeared in these experiments, generally did not figure out the capability of sweet corn plants to compete with weeds, and it could not predict yield lost of sweet corn, all well