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- Growth yield and grain quality of selected soybean (Glycine max (L....
Growth yield and grain quality of selected soybean (Glycine max (L.) Merr) genotypes applied with different nitrogen and phosphorus fertilizer treatments in Ratanakiri, Cambodia
Dissertation Abstract:
Soybean genotypes that can effectively take up nitrogen (N) and phosphorus (P) from the soil, as well as fix N could represent a key step in improving soybean productivity in Cambodia. In this dissertation, three studies, a survey, screenhouse experiment and field trial were carried out to examine the growth, yield, and grain quality of selected soybean genotypes applied with different N and P fertilizer treatments in Ratanakiri, Cambodia. The survey, involving 130 farmer respondents, assessed farmers' perceptions on soybean production and described the profile of soybean farmers in Ratanakiri, their production to marketing practices, and identified key factors influencing farmers' decisions and constraints on soybean production. The average soybean farmer is male, age ranging from 30 to 40 years old, and has primary education. Soybean farmers have < 5 ha production area, and the major soybean production constraints in the province include high production cost, low price of soybean, and low yields. Among these, soybean price, which relates to profitability, determines farmers' decision to grow soybean. Use of traditional production practices which include use of poor quality seeds, lack of fertilization, and high cost of inputs and labor (particularly of weeding) are the major limitations to increasing soybean production. Use of improved variety and fertilization are interventions that could potentially increase soybean yield, while high and increasing cost of inorganic fertilizer can be a major constraint for farmers to adopt the practice. Use of biofertilizer and rhizobium inoculants have the potential to complement and reduce the cost of fertilization for soybean. For the second study, two screenhouse experiments were conducted using different N and P fertilizer sources and five soybean genotypes, specifically, two traditional (Sbung and Hongry) and three improved genotypes (98C81, ACSI and Kaiabi). Sbung produced the highest seed yields and seed protein content in both N and P studies. In the third study, Sbung was used in two field experiments with the following treatments: with and without NitroPlus™) inoculation under different N and P fertilizer rates. More and heavier root nodules, and higher seed yields, better seed quality and higher nitrogen biological fixation (BNF) were obtained in treatments with NitroPlus™ inoculation and half of the recommended rates of urea and Nano-N (45 kg N ha-1) and inorganic P (50 kg P2O5 ha-1). The path analysis identified the following genotypic characteristics that are associated with high seed yield in NitroPlus™ with N and P treatments: high biomass accumulation, higher number and volume of root nodules, high number of pods and high seed protein. The information generated from this study can be used in developing improved soybean varieties and in crafting N and P fertilizer management strategies for cultivated soybean genotypes in Cambodia.