SUMMARY

The thesis entiled “Survey on rice production situations and experiment to determine nitrogen doses and seeding rates for rice variety – VND99-3 in winter – spring season in Dak Nong”, had done in Nam Da commune, Krong No district, Dak Nong province, from October 1^st, 2010 to April 25^th, 2011. Its objectives aimed to increase the production effectiveness of rice, and to improve income for growers. The first content of thesis is to implement the survey on rice production situations at Nam Da and Duc Minh communes, and the second content is experiment to determine nitrogen doses and seeding rates for rice in Dak Nong province. The survey was practiced by PRA method (Participatory Rural Appraisal), with modified questionnaires. The experiment was carried out by split plot design, with three replications, nitrogen doses laid out in main plots and seeding rates in subplots. Results of survey were showed that most of cultivated soil of rice in two areas is loamy clay of basalt, rice fields in Nam Da and Duc Minh is rather flat. Percentage of flat fields occupied in two communes as 80% and 42% that is suitable condition to supply water in dry and wet season. However, Nam Da and Duc Minh have some constraints such as slight to medium acidy soils, almost mean rice cultivated area of household is under 0.5 ha in these communes as 85% and 92.8% respectively. Consequently it was problem for rice production in large scale as application of mechanism in small fields, and low investment effectiveness in these areas. Farmers used to apply nitrogen doses about 118 – 165 kgN/ha, phosphorus around 28 – 44 kg P₂O₅/ha, and potassium 41 – 50 kg K₂O/ha. The survey was found in practices of farmers that doses of applied fertilize in Duc Minh was more suitable than Nam Da’s ones. But seeding rates in two communes was too higher than the recommendation as about 179 – 181 kg/ha (Nam Da) and 125 – 152 kg/ha (Duc Minh). Furthermore, almost farmers have exchange of rice seeds each other. Some of them were used to food grains for next cultivation leading to degrading of rice varieties. The yields of rice in Nam Da and Duc Minh were about 5.40 and 5.23 ton/ha, respectively. Therefore the investments efficiency was too low and their net profit margins were 0.072 and 0.049 in dry season, and 0.048 and – 0.062 in wet season. The data of the experiment has showed that nitrogen doses and seeding rates affected significantly in interaction to plant height of rice that was the more seeding rates and higher N doses leading to the direction of higher increase in plants height of rice plants. However, both factor of seed rates and N doses affected singly on growth duration of rice, but they was not interact each other in this character. Average of growth duration of rice in this experiment was about 92 – 100 days. Although yield components were affected both factors of seed rates nitrogen doses, but two factors of seed rates and nitrogen doses not interact to each other on them. However, interaction between seeding rates and nitrogen doses were occurred with grain yield. The highest yield in this experiment were 6.47 ton/ha (theoretical yield) and 6.19 ton/ha (true yield). The data showed that in dry crop at Krong No, Dak Nong province, the optimum applications that seeding rate and nitrogen dose were 90 kg/ha and 120 kg/ha, respectively.