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Special Seminar: CESD

Tuesday, June 28, 2016, 10:30am - 11:30am

 

Spatial variability in soil N supply as affected by bulk density and soil water in non-puddled soil
by:
Setia Sari Girsang
Research Affiliate Scholar
Soil Science Group

Abstract:
Spatial variations in soil type, soil water, and topography could have even greater effects on optimal fertilizer management and rice productivity in non-puddled than puddled soils. Site-specific nutrient management is needed to reduce production costs and enable more environmentally friendly agriculture. The study area was located in Los Baños, Laguna, Philippines (14.15º N and 121.246º E) on non-puddled soil in the Experiment Station of the International Rice Research Institute (IRRI). The objectives were to (1) measure spatial variation in bulk density, soil water, indigenous N supply, rice response to N, and infiltration rate across 36 locations in a 3.3-hectare rice field with non-puddled soil; and (2) assess whether indigenous N supply — as determined from soil inorganic N and yield in minus N plots —, bulk density, soil water, and soil infiltration rate could serve as predictive indicators of plant accumulation of N, grain yield with N fertilization, and N fertilizer requirements. Among soil properties, bulk density and anaerobic N mineralization (ANM) were most related to indigenous N supply and grain yield with N fertilizer. Low bulk density and high ANM were associated with high grain yield, plant N, and N use efficiency (NUE). Lower water-filled pore space and volumetric water were associated with accumulation of soil nitrate-N. Saturated hydraulic conductivity was inversely related to ANM, grain yield, and plant N across a 3.3-hectare rice field with non-puddled soil. Based on rice response in rice to N and an assumed target agronomic efficiency for N fertilizer of 12 kg ha-1, the optimal fertilizer N requirement ranged from 81 to 290 kg ha-1 with a mean 174 kg N ha-1 across 36 locations. The response of rice to N and hence the estimated optimal fertilizer N requirement were not correlated with inorganic soil N, bulk density, or anaerobic N mineralization at the start of the season. The results cast doubts on the likelihood of developing a robust soil measure at the start of a season for predicting N fertilizer requirements across variable soils.

Location 

CESD Conference Room 1, DL Umali Bldg

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