Author : Kraisri Pisithkul

Summary : Modern seed production is highly chemical based and alternatives are currently being sought. The study was conducted to compare the performance of soybean varieties in terms of growth and seed production using inorganic and organic N sources during the wet season at the UPLB experiment station. Two soybean varieties (PSB-Sy2 and BPI-Sy4) were fertilized with organic N (carabao manure and gliricidia leaves) at 24 kg N/ha and inorganic N (24-30-30 kg N, P (subscript 2)O (subscript 5) and K (subscript 2)O sources. A control (without N fertilizer) was included and all treatments were inoculated with rhizobium since no pesticide was applied, infestation was controlled by manual picking of larvae. The study was conducted in a split plot design with varieties as main-plot and N sources as sub-plot, with three replications. Parameters such as plant height, leaf area index (LAI), crop growth rate (CGR), above-ground and root biomass, number of nodules, and plant moisture content (MC) were studied. Biomass produced, N concentration and N content in plant parts, total N content, partitioning of biomass and N in terms of harvest index (HI) and N harvest index (NHI), N use efficiency in terms of conversion to biomass (NUE (subscript b), g biomass g (superscript -1) plant N), grain utilization efficiency (NUE (subscript GN), g grain dry weight g (superscript -1) grain N), seed yield, and seed quality (germinability and storability) were compared. Number of pests and beneficial insects, scale leaf damage, and soil N status were also examined. Both PSB-Sy2 and BPI-Sy4 varieties differed in the parameters mentioned but growth rates, total plant N content, and pest infestation level were similar. Varietal response to N sources was consistent except during pod filling stage for LAI and plant MC but such differences did not relate to other growth parameters, pest infestation level, and seed yield. Differences in plant height due to N sources were not observed except at three weeks after planting where plants given inorganic