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Organic and Inorganic Nitrogen Fertilizer Sources on Soybean Growth, Seed Yield, Germinability, and Storability
Thesis Abstract:
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 nitrogen (N) sources during the wet season atthe Universiy of the Philippines Los Banos (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, P205 and Kp) 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 oflarvae. 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), aboveground and root biomass, number of nodules, and plant moisture content (MC) were studied. Biomass produced, N concentration and N content in plant parts, total plant 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 (NUEb, g biomass g·1 plant N), grain utilization efficiency (NUEGN), g grain dry weight (g-1 grain N), seed yield, and seed quality (germ inability and storability) were compared. Number of pests and beneficial insects, scale leaf damage, and soil N status were also examined.
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 toN 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, when plants given inorganic N were taller. For subsequent stages, growth response in terms of plant height, LAI, CGR, and aboveground and root biomass were similar for all treatments. Inorganic N fertilizer tended to suppress nodulation, especially at an early stage but this did not affect accumulation of plant N.
No differences among N sources were found for soil N status. Plant biomass, N concentration, and N content in plant parts, HI, NHI, as well as N utilization efficiency in terms of NUE8, NUEG and NUEGN were also not affected by N sources. This apparent lack of differences may be partly due to the relatively high native N of the soil and the short experimental duration (one season).
Despite a generally higher plant MC observed for inorganic N, the level of pest infestation was similar to organic N sources. The infestation level was generally low though there was no pesticide application. Seed yield and quality did not differ with N sources. Also, carabao manure and gliricidia leaves had similar effect on all parameters measured except that the former increased plant MC at seed filling stage in PSB-Sy2. Results indicated that organic N sources were comparable to inorganic N sources for soybean seed production, at least in the short-term.