Yield and dry matter response of traditional high-yielding upland rice to nitrogen fertilization

Upland rice (Oryza sativa L.) remains an important crop in the upland agro-ecosystems. This provides opportunity in attaining rice sufficiency and in alleviating upland farmers' income in the country. However, upland rice is mostly cultivated in extremely diverse agro-ecosystems with highly degraded and nutrient deficient soils. Cultivation of upland rice on nutrient deficient soils lead to poor and lower productivity. Among the nutrients, nitrogen is the most important input needed to increase yield of upland rice. Moreover, input-responsive varieties are likewise needed in improving yield of upland rice. The response of traditional upland rice 'Speaker' to different levels of nitrogen fertilization (no fertilization; recommended rate of 120-90-60 kg/ha NPK; 180-90-60 kg/ha NPK; 240-90-60 kg/ha NPK; 300-90-60 kg/ha NPK) was evaluated at the Misamis Oriental State College of Agriculture and Technology research area in 2015. The study was laid out in a randomized complete block design with three replications. The yield of traditional upland rice 'Speaker' plateaued at the application of twice the recommended rate of nitrogen fertilizer. The yield tended to decrease with further increased in nitrogen application. The yield increased by 172% against no fertilization and 60% against the recommended rate when the recommended nitrogen application was doubled. There was a positive correlation between the yield and total dry matter weight at harvest. Moreover, a positive correlation was also observed between the yield and the increased dry matter weight from heading to harvest. A positive correlation was also observed between the dry matter weight at harvest and the relative chlorophyll content at one week after heading. The significant increased in yield of traditional upland rice 'Speaker' from 1 t/ha to 4 t/ha indicates its potential to respond positively under the intensive nutrient upland rice production.